The global high-temperature on-axis hydrothermal fluid and element flux to the modern ocean

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With a fluid flux orders of magnitudes lower than circulation of mildly-tempered hydrothermal fluids in ridge-flanks, or the riverine runoff, the high temperature fluid flux at oceanic plate boundaries can supply element fluxes that exceed the ones in (c)old lithosphere or river waters. Despite our knowledge on the diversity of hydrothermal vent fluid compositions, estimates of the on-axis fluid and element fluxes were carried out with basalt‑hosted mid‑ocean ridge black-smoker-type fluids imposed to be responsible for the global hydrothermal cooling at ridge axes. In this study, we consider current knowledge on vent fluid diversity and estimate global on-axis element fluxes. Our investigation suggests the global fluid- and corresponding element-fluxes were grossly underestimated, due to ignorance of hydrothermal venting in volcanic arcs and omission of different substrate types associated to oceanic plate boundaries. Geochemistry Planetary Science Planetary Geology Geophysics marine geology hydrothermal venting global element budgets mid-ocean ridges volcanic arcs Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction After nearly fifty years of hydrothermal vent research the element fluxes between the ocean crust and the ocean have not been accurately constrained. The fundamental lack of knowledge on these fluxes is based on the absence of data driven approaches towards fluid compositions and hampers our understanding of the ocean floor as interface between the ocean and the ocean crust. Our knowledge on hydrothermal cooling has majorly improved by heat flow measurements 1 , 2 , thermal models of conductive cooling 3 – 5 , and petrological investigations via drilling of in-situ ocean crust 6 – 9 or studies of rocks exposed in ophiolites 10 – 14 . In contrast estimation of hydrothermal element fluxes have only somewhat improved during nearly fifty years of hydrothermal research with many questions unanswered 15 . There are two common approaches to assess hydrothermal element fluxes: (1) The use of rock chemical data 13 , 16 – 19 to deduce the integrated element transfer from the crustal perspective, and (2) the use of vent fluid compositions and heat balances 16 , 17 , 20 , 21 to assess global fluid and element fluxes. The problem of the first approach is the inhomogeneous character of the ocean crust and the spatial and temporal complexity of alteration patterns 8 , 19 , 22 , 23 . Specificially, it is not trivial to overcome latestage or off-axis low-temperature overprinting of high-temperature on-axis alteration assemblages in a dynamically changing ateration regime 8 , 23 . For this reason the results of these studies are hard to upscale to assess global fluxes, with element fluxes often being underestimated 19 . For the hydrothermal vent fluid-based approach, existing estimates relied on assumptions concerning one archetype basalt-hosted mid-ocean ridge black smoker fluid of constant composition and temperature (350°C) to be responsible for the global hydrothermal cooling. These estimates do not address the now well-established compositional and thermophysical diversity of hydrothermal fluids 24 , 25 , with the mentioned archetype fluid being responsible for only 50% of global hydrothermal on-axis cooling. This simplification is majorly based on a lack of easily accessible compositional data of hydrothermal vent fluids. Here we utilize MARHYS database 26 in its current Version 3.0 27 to recalculate global on-axis hydrothermal element fluxes. We consider the global partitioning of oceanic plate boundaries (mid-ocean ridges; MOR, back-arc spreading centers; BASC, volcanic arcs; VA) with their substrate types (igneous rocks, mantle rocks, sediments) and their effects on the global on-axis hydrothermal element budget in the modern ocean. By considering different vent fluid types involved in the global hydrothermal on-axis cooling, our calculations suggest that fluid and element fluxes along the oceanic plate boundaries are significantly larger than prior estimates suggested. Our results improve our understanding of the on-axis hydrothermal element budget and provide a means to resolve significant spatial variation of hydrothermal fluxes across the ocean and the underlying plate boundary types. This paves the road to constraining the evolution of ocean chemistry by considering variable hydrothermal on-axis element fluxes with changing plate tectonic configurations over Earth's history. 2. Results The powers of ocean crust formation and on-axis ventilation High-temperature hydrothermal circulation at oceanic plate boundaries is ultimately driven by heat from the generation of new ocean crust. The amount of thermal energy supplied by crustal production can be calculated from latent heat released by crystallization of magma below the seafloor and thermal energy provided by cooling rocks from magmatic to hydrothermal temperatures 16,20,21 . The total amount of heat supplied by crustal rocks represents an upper limit for the thermal energy potentially available to drive hydrothermal circulation. We calculated the power of oceanic crust generation to be 4.5 TW with a volume production rate of 25.5 km 3 yr -1 (mass production rate: 72.5 GT yr -1 ) for the modern ocean’s plate boundary configuration (Methods 9.1). A significant part of this crustal heat is not carried by hydrothermal circulation. Firstly, the vent fluid temperature (here assumed at 300°C) constitutes a cut-off to cooling and a corresponding amount of heat remains in the ocean crust that is not advectively removed. We integrated a cumulated power equivalent of 0.48 TW that remains stored in 300°C warm ocean crust for the global ocean crust production rate and the penetration depth of hydrothermal fluids. Secondly, a fraction of the total heat is advected to the seafloor by volcanic processes. Basaltic lava flows extruding on the ocean floor are rapidly cooled and release their thermal energy in event plumes and/or rapid thermal conduction to the ocean with minimal chemical exchange 28-30 . Event plumes are characterized by lower He/heat ratios 31 combined with lower Mn/He ratios 32 than chronic plumes from hydrothermal vent sources and suggest lower chemical fluxes to the oceans. Apart from being significantly lower than in chronic plumes, the magnitude of chemical fluxes associated with such megaplume events is largely unknown for most elements. Consequently, we consider a power equivalent of 0.33 TW associated to the production of extrusives to be not available for extensive hydrothermal circulation with significant chemical exchange. Thirdly, a significant amount of crustal energy is lost to the oceans conductively. Heat flow studies have shown that the conductive heat transfer is being responsible for only about 10% of the heat escaping from the young oceancrust within 0–1 Ma after crust formation 33 . We have integrated the effective surface heat flow estimate of Hasterok, et al. 2 over the global oceanic plate boundaries and calculated the conductive power for 0–1 Ma crust to be 0.72 TW (16% of the total 4.5 TW available). With this combined 1.5 TW of power unavailable for hydrothermal circulation, our upper bound for on-axis hydrothermal circulation is 3.0 TW. From petrological perspective it appears that most of the heat in the sheeted-dyke complex is removed hydrothermally. This is based on observations in ophiolites and in-situ ocean crust where the high-temperature reaction zone and its mineralization products are found overlying gabbroic rocks as legacy of extensive hydrothermal cooling 6,22,23 . The gabbroic lower crust is also affected by significant hydrothermal alteration, but uncertainties remain as to the extent and timing of hydrothermal cooling 8,10,12,13 . To account for incomplete hydrothermal cooling of the lower crust, we estimated the global hydrothermal power for oceanic plate boundaries as 2.6 ± 0.4 TW, assuming that 90±10% of the oceanic crust is hydrothermally cooled. For the thicker crust in VA, we assume the fraction of hydrothermal cooling to be 80±20%. With lower proportions of hydrothermal cooling, the calculated fluxes would decrease linearly. Here, we focus on the influence of variable vent fluid compositions and their partitioning among the plate boundaries. Vent fluid types and their partitioning in the modern ocean We have defined different vent fluid classes according to a combination of substrate types, geological settings and reports of fluid characteristics in existing vent fluid publications to find a proper representation of global hydrothermal on-axis processes (Methods 9.2–9.3). We weighted and distributed these fluid classes according to the modern configuration of oceanic plate boundaries (Methods 9.4) and calculated the fluid and element-fluxes according to an heat balance with their share of cooling (Methods 9.5). Based on these constraints, we computed a global on-axis fluid mass flux of 6.3•10 13 kg yr -1 (Figure 1). The total fluid mass flux partitions into circulation of 44% of basalt-hosted MOR hydrothermal fluids, 13% peridotite-related MOR fluids, 11% sediment-related fluids in MOR and BASC, and 32% of non-sediment-related arc- and back‑arc fluids (Figure 1). The global high temperature hydrothermal flux is greater than the 8•10 12 –3.7•10 13 kg yr -1 proposed earlier 16,17,20 . This discrepancy is due to two differences between our and previous estimates: (1) we included hydrothermal venting in arcs and back arcs, while earlier estimates were intended to represent fluxes at MOR, and (2) we used measured temperatures and corresponding thermophysical properties of fluids, while previous workers assumed a uniform venting temperature of 350 °C. Besides their different chemical characteristics, these fluid types involve significantly different thermophysical properties (Table 1). MOR basalt-hosted fluids with a median temperature of 341°C carry 1514 kJ kg -1 . Peridotite-related fluids contain a somewhat higher amount of thermal energy (1549–1623 kJ kg -1 ) and median temperatures between 350 and 360 °C, likely due to somewhat greater reaction zone depths. In contrast sediment-related fluids are found to vent slightly shallower, significantly cooler (276–315°C) and carry ~10–30 % less thermal energy (1173–1373 kJ kg -1 ) compared to MORB-hosted fluids. Arc- and back-arc-related seawater-derived fluids are shallower (1616–2400 mbsl) and cooler with median vent fluid temperatures between 296–300 °C. They carry between 1270 and 1289 kJ kg -1 , which is about 15% less than MOR basalt-hosted fluids. A fundamentally different type of fluid venting in arcs is acid-sulfate fluids that are affected by magmatic degassing. These fluids have a low median temperature of 82 °C and hence a lower median content of thermal energy of 345 kJ kg -1 . They are known to be mostly acidic, very rich in sulfur and carbon, and vent at low temperatures typically below 120°C 34 . The lower temperatures of sediment-hosted and arc-backarc acid-sulfate hydrothermal fluids push their associated fraction of global vent fluid fluxes significantly higher (4% and 10%, respectively), than their share of hydrothermal power (3% and 2%, respectively; cf. Figure 1 and Supplementary Figure 4). In contrast, the higher temperatures of MOR fluids (both, basalt-hosted and peridotite-related) cause lower fluid fluxes (57%) in relation to their share of hydrothermal power (65%). Table 1. Median thermophysical properties of hydrothermal fluid types, hydrothermal power and resulting fluid mass fluxes. Note: Mg concentrations represent average values (see text). Fluid Type n Obs d (mbsl); p (bar) T [°C] Mg mmol kg -1 S (wt.%); Cl (mmol kg -1 ) H (kJ kg -1 ) P (TW) M (kg yr -1 ) Global - - - - - - 2.6 6.3•10 13 MORB-hosted 981 2521; 254 341 4.2 2.86; 456 1514 1.3 2.8•10 13 Peridotite-hosted 105 2307; 233 350 4.6 4.28; 702 1549 0.32 6.7•10 12 Peridotite-influenced 42 2450; 248 360 3.2 3.54; 573 1623 0.08 1.6•10 12 Sediment-hosted 94 2000; 202 276 5.5 3.65; 592 1173 0.09 2.5•10 12 Sediment-influenced 239 2200; 222 315 3.9 2.90; 462 1373 0.18 4.2•10 12 ArcBackarc-mafic 264 2400; 242 300 4.0 3.47; 562 1289 0.32 7.9•10 12 ArcBackarc-felsic 253 1616; 163 296 5.9 3.69; 600 1270 0.25 6.4•10 12 ArcBackarc-acidsulfate 130 1222; 123 82 46.5 3.19; 513 345 0.06 6.4•10 12 Seawater 64 2382; 241 2 52.4 3.35; 540 35.3 - - Compositional diversity of hydrothermal vent fluids in different settings Besides different thermophysical properties (pressures, temperatures, salinities and enthalpies) the fluid types defined in this study involve significantly different median compositions (Table 2, Figure 2). The fluid compositions calculated here are not normalized to seawater chlorine concentration and the median Cl concentrations of peridotite-hosted (701 mmol kg -1 ), sediment‑hosted (592 mmol kg -1 ) and felsic arc-backarc fluids (600 mmol kg -1 ) are significantly higher than seawater chlorinity (540 mmol kg -1 ), whereas MOR basalt‑hosted (456 mmol kg -1 ), sediment‑influenced (462 mmol kg -1 ) and acid-sulfate arc and back-arc fluids (513 mmol kg -1 ) are chloride-depleted. The median compositions for Mg were calculated as zero for some fluid classes where end member Mg compositions dominated the fluid classes. To prevent this bias we use mean values for Mg concentrations instead of median values. The average Mg concentrations are between 3.2 and 5.9 mmol kg -1 for seawater-derived fluids. These Mg concentrations can be an artifact of seawater entrainment during sampling or point to a typical entrainment of ~6-11% of seawater into focused hydrothermal fluids. Acid-sulfate fluids are known to not be represented by zero-Mg endmembers and the average Mg concentration is calculated as 46.5 mmol kg -1 for these arc- and back-arc-related fluids. Table 2. Median chemical composition of some components in the different fluid types. Note that all concentrations are given as mmol kg -1 . No H 2 S concentrations are reported for seawater. Thus the value is set to zero. Fluid Type CO 2 H 2 S K Ca H 2 CH 4 Fe Mn MORB-hosted 25.7 6.2 16.1 16.0 0.201 0.107 2.0 0.475 Peridotite-hosted 16.6 1.4 19.2 55.0 14.2 1.9 17.6 1.5 Peridotite-influenced 7.6 4.0 15.1 28.7 3.6 0.171 4.6 0.836 Sediment-hosted 26.4 4.5 39.2 32.4 1.8 36.1 0.039 0.128 Sediment-influenced 31.7 3.9 34.5 22.4 0.223 2.5 0.305 0.258 ArcBackarc- mafic 12.5 5.0 28.4 34.3 0.044 0.029 0.937 0.544 ArcBackarc- felsic 38.3 3.2 55.3 25.2 0.023 0.023 3.4 0.735 ArcBackarc- acidsulfate 59.4 4.3 10.4 9.1 0.0021 5.9E-4 0.04 0.184 Seawater 2.3 0 10.0 10.2 3.5E-7 4E-7 3.7E-6 2E-6 The extreme compositional differences become apparent for transition metals. Although individual samples of each fluid class span a broad range of compositions, the median compositions of the classes are distinctly different. Median concentrations of Fe and Mn are one to two orders of magnitude lower in sediment-associated and arc- to backarc acid-sulfate hydrothermal vent fluids (Figure 2A). In contrast, peridotite-related hydrothermal fluids can contain up to one order of magnitude higher concentrations of Fe and Mn compared to MORB-hosted vent fluids. Systematic differences also exist in the alkali and alkaliearth metals (Figure 2B). For instance, peridotite-related vent fluids have high Ca and low K concentrations, while systems affected by sediments or hosted in arc/backarc setting can have high K/Ca ratios. Acid-sulfate fluids in arcs, by contrast, are depleted in both elements relative to MOR basalt-hosted systems. The distinct nature of the fluid types becomes particularly apparent in the concentrations of dissolved gases, the median concentrations of which range by up to two orders of magnitudes between vent fluids from different settings. Carbon dioxide is low in concentration in peridotite-associated fluids but high in sediment- and most arc to backarc-related fluids (Figure 2C). By comparison, H 2 S concentrations for all fluid types are not as variable. H 2 and CH 4 concentrations in sediment- and peridotite-related fluids are one to two orders of magnitude higher than in basalt‑hosted MOR fluids (Figure 2D). H 2 contents are highest in peridotite‑related systems, whereas CH 4 is most enriched in sediment‑related systems. Supplementary File S5 summarizes the median values for all elements and compounds in the database. Element per energy flux When estimating hydrothermal fluxes, it is important to not only consider the composition of hydrothermal fluids but also the concentration/energy ratio. This ratio is presented in Equations 2 and 4 (Methods 9.5) by the term (the difference quotient from compositions and specific enthalpies of hydrothermal fluid and seawater). This term provides a normalized view on the element transport ability of hydrothermal fluids in relation to the amount of heat they transport upon cooling of the ocean crust. Figure 3 shows the different fluid types to have different abilities of carrying dissolved compounds. Considering statistical aspects (median values and interquartile ranges), the transport ability of sediment-related hydrothermal fluids for transition metals (Fe, Mn, Zn, Cu) are one (sediment-influenced) to two (sediment-hosted) orders of magnitude lower than for basalt-hosted MOR fluids. This shows the trapping ability for metals in these sediment‑related hydrothermal fluids. In contrast, peridotite-related MOR fluids have a transport ability for these metals that is up to one order of magnitude higher than MOR basalt-hosted hydrothermal fluids. As consequence of this strong substrate-control, the variability of regional hydrothermal element fluxes is very high. This is perhaps most clearly seen in the case of dissolved gases: The concentration/energy ratio for CH 4 and H 2 in sediment‑ and peridotite‑related hydrothermal vent fluids is significantly higher than for MOR basalt‑hosted fluids, as well as, significantly lower for arc- and back-arc-related vent fluids. A striking example is the H 2 flux in peridotite-hosted vent fluids with a concentration/energy ratio that is almost 100 times higher than for basalt‑hosted MOR fluids. With ~50% of the global hydrothermal power being mined by basalt‑hosted MOR vent fluids and ~11% of the global hydrothermal power mined by perdidotite-hosted MOR vent fluids, this means that the actual H 2 delivery from peridotite-hosted fluids is roughly 20 times larger than the one from basalt‑hosted fluids. This example demonstrates that it is imperative to take full account of the influence of different fluid types in the global element budget. Supplementary File 5 contains all concentration/energy ratios calculated from median fluid temperatures and their compositions. The global on-axis hydrothermal element flux Utilizing our different fluid types and their partitioning we derive the global hydrothermal on-axis element fluxes and compare these with previously published estimates (Figure 4) 16,17,20 . For the majority of elements/compounds the element fluxes we calculated exceed previous estimates. These large differences have several reasons: (1) We consider hydrothermal circulation in volcanic arcs (adding another 0.4 TW to the global hydrothermal power), (2) we distinguish between mafic- and ultramafic-hosted sites, (3) we consider significantly lower temperatures for sediment- and arc to backarc-related hydrothermal fluids; and (4) we calculate median compositions from a mixture of endmembers and hydrothermal fluids with their measured temperatures that are lower than theoretical end-member temperatures (overall leading to higher fluid mass fluxes). Our results show that element fluxes for many compounds have been considerably underestimated when assuming that average MOR basalt-hosted vent fluids are representative of global axial hydrothermal fluxes. The largest positive global element flux is calculated for CO 2 as 1.6•10 12 mol yr -1 . This value is two to threefold higher than existing estimates from vent fluid compositions and energy balances 16,20 . Our calculated CO 2 flux for mid-ocean ridges (excluding arcs and backarcs) is 9•10 11 mol yr -1 and is in good agreement with recent estimates of CO 2 fluxes by magma degassing at MOR which was determined as 1.32•10 12 mol yr -1 35 . However, the combined MOR-flux of CO 2 constitutes only 55% of the global CO 2 flux from crust to ocean despite a fraction of 68% of global hydrothermal power. Arc and backarc systems release almost as much CO 2 (7•10 11 mol yr -1 ), although the hydrothermal power is ~3 times lower. The calculated global H 2 and CH 4 fluxes are 1.1•10 11 and 1.2•10 11 mol yr -1 , respectively. Again, these fluxes are significantly higher than previous flux estimates based on fluid compositions and energy balances and are about tenfold increased compared to the mean values of existing estimates 16,17,20 . Our H 2 flux estimate is low compared to flux estimates of 7•10 11 mol/yr derived from serpentinization of rocks 36-38 but suggests that the role of on-axis circulation with regards to serpentinization is more pronounced than expected. However, our flux estimate for CH 4 is in agreement with 0.7–1.2•10 11 mol yr -1 derived from a serpentinization-based hydrogen flux estimate and assuming a hydrogen to methane ratio between 1:1 and 10:1 36 . The median fluid compositions here show higher H 2 /CH 4 ratios for peridotite-related fluids (peridotite-influenced: 10, peridotite-hosted: 20). However, the low H 2 /CH 4 ratios for sediment‑related systems (sediment-influenced: 1/11, sediment-hosted: 1/20) counteract that effect and lead to a global H 2 /CH 4 flux ratio of unity. We calculated Fe and Mn fluxes of 2.1•10 11 and 3.6•10 10 mol yr -1 , respectively that are also higher than previous estimates, although sediment‑related systems (which make up 11% of the global fluid mass flux) have very low metal/energy ratios. The higher metal/energy ratios in peridotite-related and arc- to back-arc‑related fluids counteract and even exceed this effect. From biogeochemical models a much lower global Fe hydrothermal input of 4•10 9 mol/yr was estimated 39 . Our calculation suggest that the actual Fe delivery by hydrothermal circulation is much larger than expected by these biogeochemical models. The discrepancy might be explained by near-field plume precipitation and rapid removal of the majority of hydrothermal Fe before being dispersed in the far-field. Geochemical models estimate a modern MOR Li flux of 1.37•10 10 mol yr -1 40 . Here we calculate the MOR Li flux as 1.5•10 10 mol yr -1 but a total hydrothermal on-axis Li flux of 2.5•10 11 mol yr -1 . This Li flux exceeds by far the reported riverine input of Li (8•10 9 mol yr -1 41 ) to the ocean. Our flux estimates for other trace metals (Pb, Cs, Co, Cd, Ag) are all nearly one order of magnitude higher than in the previous fluid-based estimates 16,17,20 (Figure 4). Our results suggest that MORB-hosted vent fluids are not representative of global hydrothermal venting for these elements, because these elements are enriched in arc/backarc hydrothermal vent fluids. The role of arc and back-arc hydrothermal systems is amplified by higher concentration/energy ratios of their fluids. Hydrothermal systems are not only sources for elements to the ocean but can also act as sinks. We calculated negative fluxes for U, Br, Alkalinity, Cl, SO 4 , Na and Mg. The highest negative flux was calculated for Mg (‑2.8•10 12 mol yr -1 ). Mg and SO 4 (‑1.5•10 12 mol yr -1 ) are known to be quantitatively removed due to high-T fluid rock interactions 42,43 and our estimated sink fluxes of Mg and SO 4 are both increased compared to previous fluid-based flux estimates due to our higher global fluid mass flux. The Cl flux estimate of 1.0•10 12 mol yr -1 should be treated with caution. The strong deviations from seawater chlorinity in the MOR basalt-hosted fluids is due to phase separation and predominant venting of vapor-rich fluids after volcanic eruptions at MOR. It could also reflect fluid-rock interactions in the subsurface during which Cl may be taken up by secondary minerals. Lower-than-seawater Cl concentrations for many arc/backarc systems could be likely due to influx of magmatic vapor that decreases the chlorinity when mixing with seawater-derived solutions. Our calculated Na flux is -2.4•10 12 mol yr -1 and exceeds the Cl sink flux by 1.4•10 12 mol yr -1 . This value may represent the global albitization rate in the deeper part of hydrothermal convection systems. The Na sink flux is almost twice as large as the effective Ca source flux of 8.8•10 11 mol yr -1 , which is consistent with albitization reactions that balance the loss of 2 moles of Na with the release of 1 mole of Ca . Partitioning of element fluxes by fluid types We calculated the relative contributions of the different vent fluid types to the global on-axis fluxes for a large range of elements. These contributions differ due to variations in fluid mass fluxes (resulting from heat flux and thermophysical properties) between the different vent types (top bar in Figure 5). The fluxes for most elements, however, show relative contribution patterns that are succinctly different from those of the fluid mass fluxes. These in part extreme discrepancies between fluid mass flux and element flux reflect strong contrasts in the composition of fluids venting in the different settings. MOR basalt-hosted vents account for a relative fluid mass flux of 44% but make up 57% of the H 2 S and 50% of the Si fluxes indicating that the contributions of this vent type for the global fluxes of these compounds is somewhat higher than expected from the fluid mass flux. In contrast, the global flux contribution of MOR basalt-hosted vents for K (19 %), Ca (18 %), B(7 %), H 2 (5 %), CH 4 (3 %) is much smaller than 44%. MORB-hosted systems play only a subordinate role in determining the on-axis element cycles of these compounds, despite their importance in terms of energy- and mass fluxes. In contrast, we find that peridotite-related hydrothermal vents, which represent large parts of the slow to ultra-slow spreading MORs, dominate the fluxes of numerous substances. For instance, peridotite-related hydrothermal vents deliver 90% of the global hydrothermal H 2 , 59% of Fe, 42% of Cu, 37% of Ca, 32% Mn, 29% Co and 24% Zn, although they account for only 13% of the global vent fluid mass flux. For other substances, the flux contributions are smaller than suggested by the fluid mass flux (Al: 2%, Pb: 3%, Cd: 5%, H 2 S: 5%, CO 2 : 6%). In addition, peridotite-hosted and peridotite-influenced systems are the only ones that act as sinks of B (-7%). Sediment-related hydrothermal vents contribute 11% to the global hydrothermal fluid mass flux but deliver 99% of the global on-axis hydrothermal NH 3 , 86% of CH 4 , 48% of B, 20% of K, 18% of Sr, 17% of Rb and 17% of Cs. Sediment-hosted systems are the only source of alkalinity among the fluid types defined in this study, while all other represent sinks to the ocean. On the other hand, the global element fluxes for metals in sediment-related systems are extremely low at 0.65 % Fe, 2.0 % Cu, 2.2 % Ag, 3.5 % Co, 3.8 % Mn and 4.9 % Zn. This shows that upwelling hydrothermal fluids effectively loose these elements during cooling/seawater mixing, as they pass through sediments. Arc and back-arc hydrothermal fluids play a major role for the global element fluxes by (1) host rock compositions and (2) influence of magmatic volatiles. Arc and back-arc mafic-hosted hydrothermal fluids comprise 12% of the global fluid mass flux and show slightly higher flux contributions for Ca (21%), Li (18%) and K (17%), while the flux contributions for other substances are significantly lower (H 2 : 0.3%, CH 4 : 0.2%, Co: 1%, Ag: 2%, Cu: 3%, Fe: 4%, and Al: 5%). This is not surprising as basalt-fluid interactions govern element solubilities and lower pressures and temperatures in arc/backarcs come with a lower release of metals and H 2 . In contrast, the group of felsic arc/backarc hydrothermal system , which carry 10% of the vent water flux supply a much greater proportion of many elements. For instance, these systems contribute 49% of hydrothermal Pb, 46% of Cs, 34% of K, 34% of Ag, 33% of Cd, 33% of Cu, 28% of B and 24% of Rb. The fluxes of metals are significantly increased in felsic-hosted hydrothermal vent fluids over their mafic-hosted counterparts, because basement composition or intensity of magmatic influx matter. Acid-sulfate fluids, despite accounting for only 2% of the global hydrothermal power, make up 10 % of the global hydrothermal fluid mass flux. In addition, the often highly acidic nature of these fluids allows them to dissolve large amounts of Al and REE. As a consequence, this type of vents dominates the global hydrothermal discharge of high field strength elements such as Al (67%) and REE (Sm :66%, Nd: 61%) that are virtually insoluble in most natural waters. They also contribute disproportionately to the fluxes of other components, such as Co (29%), CO 2 (23%), Pb (21%). In contrast, the proportions provided are low for other elements, inluding K, Si, Fe, Mn, Li, Cu, and Ag. Unique to this vent type are negative fluxes of Ca and Sr and a positive flux of SO 4 . As generally, the negative flux of SO 4 exceeds the flux of H 2 S by roughly a factor of five, all seawater-derived hydrothermal systems act as sinks of S to the oceans. This is different for acid-sulfate vents that act as source of sulfur to the ocean. 3. Discussion We calculated a global high-temperature hydrothermal power of 2.6 ± 0.4 TW from the global submarine formation of crust, along oceanic spreading centers and volcanic arcs. Submarine volcanic arcs contribute 0.4 ± 0.1 TW, leaving a heat flux of 2.2 ± 0.3 TW along the global spreading ridges. This power estimate is somewhat lower than what Mottl 21 had estimated for oceanic spreading centers (2.8 ± 0.4 TW). Our estimate, however, agrees well with the oceanic spreading-related heat flux suggested by Elderfield & Schultz 20 of 2 ± 1 TW. These authors calculated the annual fluid flow associated with this heat flux to 3.0 ± 1.5•10 13 kg yr - 1 by assuming a uniform venting temperature of 350°C. Alt (2003) 16 suggested a vent fluid flux of 3.7•10 13 kg yr - 1 using refined thermal properties of hydrothermal fluids and a lower axial hydrothermal power of 1.8 ± 0.3 TW, which corresponds to the hydrothermal heat flux estimated for crust < 0.1Ma 21 . Our analyses yields a higher global vent fluid mass flux of 6.3•10 13 kg yr - 1 . Our calculated fluid flux for oceanic spreading centers (BASC and MOR) is 5.0•10 13 kg yr - 1 . The remaining 1.3•10 13 kg yr - 1 are attributed by hydrothermalism associated to volcanic arcs. The reason for the higher fluid fluxes in our estimate is that we used actual fluid temperatures from the MARHYS database and did not assumed a uniformly high venting temperatue of 350°C. Because many vents (in particular those in sediment-related MOR and acid-sulfate type inarcs) issue fluids with much lower temperatures, our global fluid flux estimate is much greater than earlier suggested, although our heat flux estimate is only 10–20% higher. We considered different hydrothermal vent fluid types according to geological setting and basement type and mined a hydrothermal vent fluid database to calculate chemical fluxes. The higher fluid flux results in overall higher element fluxes than in previous estimates, but the differences also reflect distinct fluid compositions in different settings and their share in the global heat budget. Peridotite-related systems provide the majority of hydrothermal H 2 and Fe and comparably large amounts of Cu, Ca, Ba, Mn, Co and Zn. We find that sediment-related systems provide nearly the entire supply of NH 3 and CH 4 with significant contributions of B, K, Sr, Rb, Cs. The delivery of Fe, Cu, Ag, Co, Mn and Zn from these systems to the ocean is strongly diminished. Felsic-hosted arc and back-arc hydrothermal fluids provide a large fraction of Pb, Cs, K, Ag, Cd, Cu, B, Rb. Acid-sulfate vents in arc/back-arc settings carry the majority of Al and REE and significant CO 2 to the ocean but only minimum amounts of other elements (K, Si, Fe, CH 4 , H 2 , Mn, Li, Cu, Rb, Ba, Cs, Ag). Notably, the fluxes we calculated are valid for the assumption that the entire hydrothermal power is used to generate high temperature fluids. Much of the heat, however, is carried by low-temperature diffuse fluids 44 , which can have concentration/heat ratios different from those of high-temprature focused vent fluids. Transition metals (Fe, Cu, Zn) and dissolved gases (H 2 S, H 2 ) have been shown to be systematically depleted in low-temperature diffuse fluids 45 – 47 . The element fluxes provided for these compounds should hence be considered maximum values. More geochemical analyses of diffuse fluids and data on the partitioning of high and low temperature fluids is required to further improve our global flux estimates for non-conservative compounds. Another source of uncertainty revolves around the question of whether or not the sampled vent fluids are representative of global hydrothermal vent fluid compositions. After all, of the estimated 1430 vent sites 48 , 49 only 142 were sampled. The intensity of sampling of those 142 sites is highly variable, which introduces a certain amount of bias. A good illustration for this issue is the Rainbow vent field as a prominent representative of the “peridotite-hosted” fluid category. Of the 104 fluid samples within this category, more than half (55 samples) originate from vents in the Rainbow vent field. Hence, the compositions of the Fe-rich Rainbow vent fluids strongly affect the median fluid compositions, and the large Fe-fluxes calculated for peridotite-hosted vents could reflect a sampling bias. If the available data were weighted by vent field instead of samples, the median value would be significantly lower. But equally weighting by vent field does not consider the vast range in field-scale hydrothermal heat fluxes among vent sites (16-3800 MW) and Rainbow has an exceptionally large field-scale heat flux 50 . Continued vent fluid sampling will ultimately improve the data situation in this regard. Rainbow fluids may currently seem to have anomalously high Fe-centrations, but fluids from only four high-T peridotite-hosted systems are represented in the data base, and there are indications of additional extremely Fe-rich hydrothermal sites, such as the Fåvne vent field on the Mohns Ridge 51 . Our results provide important information on the regional availability of nutrients and dissolved compounds to the ocean. The different fluid classes do not only have implications for the global on-axis element fluxes, but also for the occurence of ecosystems in the different plate boundaries. Our results suggest a highly variable input of elements for different settings in the modern ocean. These insights are important for earth system models: On-axis hydrothermal circulation of seawater is one of the main sources and sinks of chemicals in the ocean. The highly variable input of the different fluid classes reveals that variations in the plate tectonic configuration on our planet may strongly influence hydrothermal element fluxes. These changes can be related to changes in the global crustal volume production but changing the (geographical) distribution of plate boundaries can also have a profound impact on these element fluxes. For instance, an increased strike length of mid-ocean ridges or back-arc spreading centers near continent shelves would boost the CH 4 and NH 3 emmisions and reduce the delivery of metals like Fe, Cu and Zn. Changes in the relative crustal production rates of arcs, backarcs and mid ocean ridges (maintaining the global crustal production rate) would have a huge impact on the fluxes of REE, Al, S, CO 2 . Changing the partitioning between ultra-slow to slow and fast to super-fast spreading over the mid ocean ridges strike length (again preserving the global crustal production rate) would massively influence H 2 and Fe delivery to ocean. Coupling a spatially resolved and setting-specific flux estimate such as presented here with plate tectonic reconstruction of the past will facilitate the calculation of the temporal variability of on-axis hydrothermal circulation and its effects on the composition of past oceans. Methods Configuration of oceanic plate boundaries The total length of global oceanic plate boundaries is 92,984 km, including 60,139 km of Mid-Ocean Ridge spreading centers (MOR), of which 22,723 km spread at intermediate to fast rates of > 5mm yr - 1 , while 37,416 km are slow to ultra-slow spreading ridges with a full spreading rate of < 5mm yr -1 49, 52 . Back-arc spreading centers (BASC) make up 11,145 km 49 , 52 and volcanic arcs (VA) comprise 21,700 km of plate boundary length 34 (Supplementary Fig. 1a). We considered the length-weighted average spreading rates and their average crustal thicknesses and deduced the global crustal production rate (Supplementary Fig. 1b, Supplementary File S1). For VA the calculation of crustal production rates is complicated by processes of crustal growth (increase in thickness), delamination and/or subduction erosion, with magma production rates potentially being larger than the crustal production rate 53 . We inferred that magma emplaced within a VA provides thermal energy for hydrothermal circulation, regardless of whether or not it is removed from the arc at a later stage. We chose to follow published magma production rates 53 and calculated the global arc magma production rate as the lengthweighted average of the major intraoceanic arcs (Aleutians, Izu-Bonin, Mariana, Lesser Antilles, Tonga-Kermadec). We accounted for different crustal thicknesses of fast spreading MOR (5.8 km) 54 , slow spreading MOR (8 km), BASC (6 km) and VA (15 km). The crustal thickness of slow spreading MOR is meant to be an average that represents ultra-slow spreading rates with crustal thicknesses of up to 10 km 55 and intermediate spreading rates with crustal thickness as low as 6 km 56 . The crustal thickness of VA also represents an average, as VA crust can be between 10 and 30 km thick 53 . We additionally accounted for different thicknesses of extrusives (between 350 and 750 m) following different geophysical surveys of ultraslow to slow and fast spreading MOR 54 , 56 . The power of crust generation (Supplementary Fig. 1c, Supplementary S1) was calculated by an energy balance that accounts for heat of crystallization 57 and cooling of rocks from the magmatic to hydrothermal temperatures according to their heat capacities 58 . We considered that MOR with basaltic crust have slightly higher magmatic temperatures (1250°C) than more evolved BASC (1200°C) or VA (1100°C). At all plate boundaries, except slow to ultra-slow MOR, crust is exclusively made up of igneous rocks that release heat of crystallization. For slow to ultra-slow spread crust we assume that half of the “crustal” thickness is made up by mantle peridotites that are either exposed at the seafloor or are buried under a thin carapace of basalt. The mantle section is denser and provides more thermal energy by cooling per volume of crust but lacks latent heat of crystallization. The proportions of magmatic versus mantle rocks are hard to estimate on a global scale, but the 50:50 proportion assumed here may be representative of ultra-slow to slow spreading MOR with variable extents of magmatic vs amagmatic accretion which is not exclusively controlled by spreading rate 59 , 60 . We integrated the predicted conductive surface heat flow 2 for 0–1 Ma over the global plate boundaries. The conductive power was calculated as 0.72 TW and is not utilized to drive hydothermal fluid flow. Our estimate of the likely hydrothermal power (Supplementary Fig. 1d, Supplementary File S1) is impaired by the absence of knowledge whether the entire lower crust or only parts are cooled by hydrothermal ventilation. We infer that 80–100% (60–100% for thicker VA) of hydrothermal cooling is a plausible range for the depth extent of hydrothermal circulation with our favorable estimate of 90% (80% for VA). Our estimate of the global hydrothermal power does not include heat from extrusives that is released in event plumes with only minimal chemical exchange (0.33 TW). Heat stored in 300°C hot crust remains in the crust and is not hydrothermally removed (0.48 TW). The global on-axis hydrothermal power estimated this way is 2.6 ± 0.4 TW. Analysis of vent fluid compositions In its current version 3.0 MARHYS database contains 4221 entries of fluid samples, 1458 hydrothermal vent fluid end member compositions and 314 seawater samples. The hydrothermal fluid and end member data originate from more than 881 individual vents in more than 330 “vent sites” (“vent sites” may be distingt discharge sites within “vent areas”) from 142 “vent areas”. For the definition of these terms the reader is conferred to Diehl and Bach 26 . According to an extrapolation of the relationship between spreading rate and vent field incidence along well explored parts of MOR and BASC 48 , 49 , we expect about 1300 vent areas in these setting, with another 130 vent areas estimated to be situated along VA. With 142 vent areas embodied in the database, 10% of the vent areas expected to be found in the modern oceans are represented, which is a robust basis for upscaling to calculate global fluxes. This representation enables us to quantify the amount and uncertainties of hydrothermal fluid and element-fluxes for different geological settings and substrate types. We analysed the metadata in MARHYS database (“geologic setting”, “rock type primary”, “rock type secondary”) and grouped vent fluids into eight classes that are either defined by their host-rock types, and/or their geologic setting, or by chemical signature as reported by vent fluid chemists. The first fluid type we define is called “mid-ocean ridge basalthosted” (”MORB-hosted”). This fluid type comprises all fluids venting in areas for which only basaltic substrate is reported in the database (“rock type primary” & “rock type secondary”). This group resembles the archetype hydrothermal fluid that had been considered to account for all hydrothermal cooling in previous flux estimates 16 , 17 , 20 . The “sediment-hosted” group contains fluids that are hosted in sediments (“rock type primary”=”sediment”). The third group is “sediment-influenced”; it entails fluids venting from basalt, but the fluids are reported in publications of chemical vent fluid data to be influenced by sediments in the subseafloor. For this group we scanned existing literature for reports of sediment influence on hydrothermal systems that are hosted in igneous substrate. This search revealed the Endeavour Vent Field 61 & Loki’s Castle 62 at MOR and Minami-Ensei 63 , Hatoma 64 , Iheya North 63 , Hakurei 65 & Sakai 65 at BASC to be of this kind. The fourth type is named “peridotitehosted” and comprises vent fluids venting in areas where peridotites occur as prevailing basement type. The fifth type is “peridotite-influenced” and (analogous to “sediment-influenced”) the fluids share chemical characterisics with the ones from group 4, although igneous crust has been recognized to dominate in the vent areas. It is assumed that peridotites (or other ultramafic rocks) are present in the root zones of these systems and influence their vent fluid compositions. This type of fluid is reported for the Kairei 66 , Nibelungen 67 , Pelagia 68 and Daxi 69 vent areas. The next three types (5, 6, and 7) are related to VA and BASC hydrothermal convection systems. The fifth type “arc-backarc mafic” represents all fluids from vents hosted in basement of basalt or basaltic-andesite composition. The sixth class “arc-backarc felsic” comprises fluids venting from andesitic to rhyoilitic basement in VA and BASC. The seventh group “arc-backarc acid-sulfate” includes all fluids that are reported to be heavily influenced by magmatic degassing. These fluids span a broad range of chemical properties, but were clearly classified as influenced by magma degassing in the original publications. Vent areas where this class of fluids vent are: Onsen Site 70 , North Su 71 , Kasuga Vent sites 72 , NW Rota-1 73 , NW Eifuku 73 , Nikko 73 , Volcano-1 73 , Brothers Upper Cone 74 – 76 , Brothers Lower Cone 74 – 76 , Macauley Cone 75 , 76 , West Mata 77 , Niua North 77 , and Kemp Caldera Cone 78 . Note that for the sake of convenience in the following evaluation we will regularly use terms like sediment-associated or sediment-related: these terms encompass both sediment-hosted and sediment-influenced hydrothermal fluids. Likewise, other classes will occasionally be grouped in peridotite-related or arc-backarc-related fluids. Filtering of fluid compositions The variability in the chemical compositions and thermophysical properties of hydrothermal fluids complicates the calculation of element fluxes along oceanic plate boundaries. This variability can be considered a result of five major processes in the reaction- and upflow-zones of hydrothermal circulation cells. The extent of fluid-rock interaction and the rock types present in the reaction- and upflow-zone produce different compositions of endmember fluids. Influx of magmatic volatiles (CO 2 , SO 2 , H 2 O, HCl) that are released by magmatic degassing may directly affect fluid compositions or influence the pathways of fluid-rock interaction. In the reaction zone or during upflow, fluids commonly undergo phase separation, which is typically followed by phase segregation. Chlorine concentrations in vent fluids 26 and salinities in fluid inclusion in hydrothermal precipitates 11 , 79 provide evidence for the common occurrence of phase separation and segregation. Elements that are primarily chloro-complexed in high-temperature hydrothermal fluids become enriched in the Cl-rich brine phase and are depleted in the Cl-poor vapor phase. Dissolved gases show the opposite partitioing behavior. Most element flux estimates use a Cl-normalized fluid composition (seawater chlorinity) and assume that the shifts in element contributions of vapors and brines cancel out each other, as ultimately all fluids reach the seafloor. Here we use fluid compositions “as is” to test if this hypothesis is actually supported by the extensive data from MARHYS database. Entrainment of seawater occurs during upflow or outflow of hydrothermal fluids. Entrainment of cold seawater influences the thermal budget, due to lower-than-endmember temperatures, but in the same manner decreases/increases concentrations of chemical compounds if they behave conservatively during mixing. The concentration/energy flux ratio during the process of mixing will be maintained, but the fluid mass flux will consequently increase. For nonconservative compounds this assumption cannot be made and the computation of element fluxes based on fixed concentration/energy ratios is problematic. Conductive cooling/heating influences the thermal budget of hydrothermal fluids and concentration/energy flux ratios. As fluids conductively cool/heat they will redistribute thermal energy in the crust that is available for other fluids to heat/cool and compensate this effect. If globally thermal heating and cooling of fluids compensate each other, thermal conduction does not influence flux estimates but solely their uncertainties. To minimize the compositional and energetic variability due to thermal conduction we analyzed magnesium concentrations along with their temperatures for seawater derived-hydrothermal fluids (excluding acid-sulfate fluids) in the global dataset (Supplementary Fig. 2a-b). The relationship of these parameters reveals not only entrainment of seawater, but also conductive cooling/heating of rising hydrothermal fluids. Cooled/heated hydrothermal vent fluid samples would impose variability to the concentration/energy ratios. We applied a filter procedure to minimize the effects of conductive cooling/heating by relating the chemical dilution due to Mg concentration, to the expected temperature of the diluted fluid. We assumed that the temperature of the zero-Mg endmember is determined by the position of the two-phase curve of seawater in the pressure-temperature plane (calculated after 80 ) at depth and the temperature change is solely determined by mixing of hot hydrothermal fluid and cold seawater. To address the entrainment of cold seawater we analyzed the distribution of Mg concentrations and temperatures in the dataset. Both parameter show a bimodal distribution, suggesting that two groups of hydrothermal fluids are responsible for the majority of the global hydrothermal fluid flow at plate boundaries (Supplementary Fig. 2c-d). The first group is nearly pure endmember fluids with temperatures > > 150°C and Mg concentrations of less than ~ 10mmol kg - 1 . These samples represent hydrothermal fluids from focused vents where fluids issue vigorously. The second group is moderate temperature-fluids 40 mmol kg - 1 that mostly represent highly diluted shimmering waters. Few samples fall in between these two groups, which suggests that these intermediately diluted fluids can be neglected in the calculation of hydrothermal element fluxes. We applied a lowtemperature cut-off (Supplementary Fig. 2b) and calculated element fluxes with hightemperature focused hydrothermal fluids only. Excerpts of MARHYS database that contain the individual fluid compositions used to derive the median compositions for the eight individual fluid classes (after application of the Mg-T filter) are given in Supplementary File S2. Configuration of oceanic plate boundaries and rock types To determine the distribution of rock types along the different plate boundaries, we considered reports in publications and used global datasets of sediment thickness and lithospheric age 81 . We combined a dataset of global lithospheric ages of MOR and BASC and the global oceanic sediment thickness to deduce the fraction of sedimented ridge axes. We investigated the globally cumulated surface area (of 0–1 Ma crust) with regards to sediment thickness (Supplementary Fig. 3a). 82% of the surface area along MOR and BASC is covered by less than 100 m of sediments, with 98% of the on-axis surface area (0–1 Ma) covered by less than 300 m of sediment. We have developed three gaussian functions that relate the probability of occurrence of sediment-free, sediment-influenced and sediment-hosted hydrothermal vents areas to the (large scale) onaxis sediment thickness (Supplementary Fig. 3b, Supplementary File S3). These probability functions reflect that sediments are less permeable than igneous rocks and that for low (large scale) sediment thicknesses (< 250 m) the probability for sediment-free or sediment-influenced hydrothermal systems is higher than for sedimenthosted systems. This low probability of sediment-hosted systems is reflected by the fact that, if the sediment coverage is lower than the average roughness of volcanic ridges, these ridges will stick out of the sediment cover and provide likely pathways for hydrothermal fluids instead of circulating through impermeable sediments. Using these probability functions results in our estimate of 90% of hydrothermal systems being sediment-free, 7% being sediment-influenced and 3% being sediment-hosted (area-wise and power-wise). After we deduced the share of sediment-related hydrothermal fluids we estimated the relative proportions of different substrate types for non-sedimented MOR. For fast to ultra-fast MOR we assume all hydrothermal systems to be basalt-hosted. For slow-ultraslow MOR we assume that 50% of hydrothermal systems is hosted in basalt, whereas 40% are hosted in peridotite. The remaining 10% of vent systems along slow-ultraslow MOR is assumed to be basalt-hosted, but influenced by peridotite in the reaction zone. This partitioning is consistent with surveys of the ultraslow spreading southwest Indian ridge after Cannat, et al. 82 . For hydrothermal fluxes in convergent margin settings, we did not distinguish between BASC and VA, but instead grouped vents from both settings according to basement compositions and intensity of magmatic degassing. Most of the vent sites in these settings are hosted in basement with a pronounced geochemical arc-affinity, although BASC show varying contributions of hydrous, slab-derived or decompressional mantle melts 83 . Arc affinities are common in BASC, and a prominent example are volcanic 84 and hydrothermal 70 , 71 , 85 systems associated with the South Eastern Rift of the Manus basin. In terms of the relative contributions of the three categories that were discerned we assumed that,50% of hydrothermal venting is from mafic crust (basalt-basaltic andesite), 40% from felsic rocks (andesite-rhyolite) and 10% is of the acid-sulfate type (magmatic degassing dominated, irrespective of rock type). This partitioning is based on reports of 70% of arc hydrothermal fluids to represent acid-sulfate venting 34 . This estimate is based on surveys of plume properties along the Mariana arc 86 and Tonga-Kermadec arc 87 . The global hydrothermal power of acid-sulfate fluids is lower than expected from their vent field incidence considering that 70% of vent sites in arcs have been suggested to be of this type. This is due to the lower venting temperatures of acid-sulfate fluids and the corresponding low enthalpy calculated from the median temperature (345 kJ kg - 1 , cf. Table 1 ). Arcs show a bimodal distribution of basement rocks that are either mafic or more felsic in nature. In arcs we find a bimodal distribution of differentiated rocks being either mafic in origin or rather felsic. For the Kermadec and Tonga arc 11 out of 30 volcanoes are identified to be predominantly felsic in composition 88 , but some volcanoes are mentioned to be mafic stratovolcanoes that host felsic calderas. In the South Kermadec arc at least 11 edifices are reported to be of this type 89 . This shows that it is hard to estimate the occurrence of these rock types on a global scale. We analyzed the PETDB ( www.earthchem.org/petdb ; downloaded on 15th, March 2024, using the following parameters: Tectonic setting = Volcanic_Arc, Rock Types = Igneous_Rocks) and counted samples according to their rock names (Supplementary File S4). Rocks named “basalt, basaltic andesite, gabbro, picrite or trachybasalt” were counted as “mafic” and rocks named “andesite, dacite, rhyodacite or rhyolite“ were counted as “felsic”. Additionally, we checked for the silica content of samples named “tephra” and classified samples below or above 56 wt.% SiO 2 , the boundary between basaltic andesite and andesite 90 , which divides our classification into mafic and felsic rocks. Of 3267 rock samples considered, 1913 (59%) have mafic and 1354 (41%) have felsic compositions. This provides a first approximation for the occurrence of mafic to felsic rocks in volcanic arcs which occur in relative proportions between 2:1 and 1:1. After considering the partitioning of sedimented and non-sedimented hydrothermal circulation and the distribution of rock types among the plate boundaries, we infer the hydrothermal power to partition into 50% MOR basalt-hosted, 15% MOR peridotite-related, 10% sediment-related and 25% arc- and backarc-related cooling (Supplementary Fig. 4). Calculation of fluid and element fluxes We calculated global fluid mass fluxes by estimating the global hydrothermal power and involving the energy content of hydrothermal fluids. These mass fluxes were then combined with the composition of hydrothermal fluids to compute element fluxes 16 , 20 , 91 . We calculated the fluid mass flux (M hyd ) according to Eq. 1 using Q Hyd ,the global hydrothermal power, and ΔH, the difference between specific enthalpies of seawater and the hydrothermal fluid. Associated hydrothermal element fluxes were calculated by Eq. 2, where c SW and c HF are the concentrations of elements in seawater and hydrothermal fluids, and H HF and H SW are the specific enthalpies of the respective fluids. The fluxes were calculated for each class of venting, and the different contributions were added up to derive global fluxes (Eq. 3–4). $$\:Eq.1\:\:\:\:\:\:{M}_{hyd}=\frac{{Q}_{Hyd}}{{\varDelta\:}_{H}}$$ $$\:Eq.2\:\:\:\:\:\:{F}_{El}=\frac{{\varDelta\:}_{C}}{{\varDelta\:}_{H}}*{Q}_{Hyd}=\frac{{c}_{Hf}-{c}_{SW}}{{H}_{Hf}-{H}_{SW}}*{Q}_{Hyd}$$ $$\:Eq.3\:\:\:\:\:{M}_{hyd}={\sum\:}_{i=1}^{n}(\frac{{Q}_{Hyd,i}}{{\varDelta\:}_{H,i}})$$ $$\:Eq.4\:\:\:\:\:\:{F}_{El}={\sum\:}_{i=1}^{n}(\frac{{\varDelta\:}_{C,i}}{{\varDelta\:}_{H,i}}*{Q}_{Hyd,i})={\sum\:}_{i=1}^{n}(\frac{{c}_{Hf,i}-{c}_{SW}}{{H}_{Hf,i}-{H}_{SW}}*{Q}_{Hyd,i})$$ The specific enthalpies of the fluids were calculated as f(T,p,X NaCl ) from the thermodynamic properties of pure water 92 and an empirical relationship that relates these properties to the properties of NaCl-H 2 O solutions 93 . The most influencial term for this enthalpy calculation is temperature, as the most substantial parameter influencing the solutions specific enthalpy. Supplementary Fig. 5 shows the enthalpy differences to cold seawater for the fluid classes defined in this study. Declarations Acknowledgments This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2077. We thank all scientist who published data of vent fluid chemistry that is incorporated in MARHYS database 3.0. Their work provides the basis for this article. Author contributions A.D. and W.B. aquired funding and designed the research. A.D. did all data compilation and analyses and wrote the manuscript draft.W.B. edited the manuscript and assisted in revisions led by A.D. Conflict of interests The authors declare no competing interests. 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Geofluids 1–22 (2020). https://doi.org/10.1155/2020/8868259 Driesner T, Heinrich CA (2007) The system H2O–NaCl. Part I: Correlation formulae for phase relations in temperature–pressure–composition space from 0 to 1000°C, 0 to 5000bar, and 0 to 1 XNaCl. Geochim Cosmochim Acta 71:4880–4901. https://doi.org/10.1016/j.gca.2006.01.033 Straume EO et al (2019) GlobSed: Updated Total Sediment Thickness in the World's Oceans. Geochem Geophys Geosyst 20:1756–1772. https://doi.org/10.1029/2018gc008115 Cannat M et al (2006) Modes of seafloor generation at a melt-poor ultraslow-spreading ridge. Geology 34. https://doi.org/10.1130/g22486.1 Pearce JA, Stern RJ (2006) in Back-Arc Spreading Systems: Geological, Biological, Chemical, and Physical Interactions Geophysical Monograph Series 63–86 Park S-H, Lee S-M, Kamenov GD, Kwon S-T, Lee K-Y (2010) Tracing the origin of subduction components beneath the South East rift in the Manus Basin, Papua New Guinea. Chem Geol 269:339–349. https://doi.org/10.1016/j.chemgeo.2009.10.008 Reeves EP et al (2011) Geochemistry of hydrothermal fluids from the PACMANUS, Northeast Pual and Vienna Woods hydrothermal fields, Manus Basin, Papua New Guinea. Geochim Cosmochim Acta 75:1088–1123. https://doi.org/10.1016/j.gca.2010.11.008 Baker ET et al (2008) Hydrothermal activity and volcano distribution along the Mariana arc. J Geophys Research: Solid Earth 113. https://doi.org/10.1029/2007jb005423 de Ronde CEJ et al (2001) Intra-oceanic subduction-related hydrothermal venting, Kermadec volcanic arc, New Zealand. Earth Planet Sci Lett 193:359–369. https://doi.org/Doi 10.1016/S0012-821x(01)00534-9 Smith IEM, Worthington TJ, Stewart RB, Price RC, Gamble JA (2003) Felsic volcanism in the Kermadec arc, SW Pacific: crustal recycling in an oceanic setting. Geol Soc Lond Special Publications 219:99–118. https://doi.org/10.1144/gsl.Sp.2003.219.01.05 Wright IC et al (2002) Towed-camera investigations of shallow-intermediate water-depth submarine stratovolcanoes of the southern Kermadec arc, New Zealand. Mar Geol 185:207–218. https://doi.org/10.1016/S0025-3227(01)00285-7 Le Bas MJ, Maitre L, R. W., Woolley AR (1992) The construction of the Total Alkali-Silica chemical classification of volcanic rocks. Min Petrol 46:1–22. https://doi.org/10.1007/bf01160698 Schultz A, Elderfield H (1997) Controls on the physics and chemistry of seafloor hydrothermal circulation. Philosophical Trans Royal Soc Lond Ser A: Math Phys Eng Sci 355:387–425. https://doi.org/10.1098/rsta.1997.0014 Haar L, Gallagher JS, Kell GS (1984) NBS/NRC Steam Tables: Thermodynamic and Transport Properties and Computer Programs for Vapor and Liquid States of Water in SI Units. Hemisphere Publishing Corporation Driesner T (2007) The system H2O–NaCl. Part II: Correlations for molar volume, enthalpy, and isobaric heat capacity from 0 to 1000°C, 1 to 5000bar, and 0 to 1 XNaCl. Geochim Cosmochim Acta 71:4902–4919. https://doi.org/10.1016/j.gca.2007.05.026 Additional Declarations The authors declare no competing interests. Supplementary Files DiehlandBach2025HydrothermalFluxesPreprintSupplementaryFigures.docx Supplementary Figures DiehlandBach2025S1EnergyCalc.xlsx S1_Thermal Budget Calculation DiehlandBach2025S2FilteredFluids.xlsx S2_FilteredFluids DiehlandBach2025S3ProbabilitySediment.xlsx S3_Probability Sediments DiehlandBach2025S4ArcRocks.xlsx S4_Arc Rocks Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6352431","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":436843499,"identity":"260afa88-3d9e-41ab-87ab-438f4cde29b2","order_by":0,"name":"Alexander Diehl","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYDCCwwxsDA8qGIAkD0wogQgtCWdI0nIAqDixDcQiVgvfceZjDxLnHc7jY+A99uFjjk0eA3vyAbxaJA+zpRskbjtczMbAlzxz5ra0YgaeZ/itMTjMYyYB1JLYJv/GmJkXyGiQyDEgoIX/m0TiHKAWBh5j5r/b/gO15H8gZAubRGIDVAvjtgMgW/DqAPnFTCLhWDpQC18yY++25MQ2nmf4HcZ3/vAziQ811onzG3gPM/zcZpfYz578AL81GICNRPWjYBSMglEwCrAAAMtPRM5WOx6SAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-8875-8796","institution":"MARUM - Zentrum für Marine Umweltwissenschaften","correspondingAuthor":true,"prefix":"","firstName":"Alexander","middleName":"","lastName":"Diehl","suffix":""},{"id":436843856,"identity":"9151ed27-0a17-41f8-b571-4f3a13c50be3","order_by":1,"name":"Wolfgang Bach","email":"","orcid":"https://orcid.org/0000-0002-3099-7142","institution":"MARUM - Zentrum für Marine Umweltwissenschaften","correspondingAuthor":false,"prefix":"","firstName":"Wolfgang","middleName":"","lastName":"Bach","suffix":""}],"badges":[],"createdAt":"2025-04-01 11:02:59","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6352431/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6352431/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":79732770,"identity":"39d76ca9-9a66-4468-aae1-1bdcca12976e","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":42872,"visible":true,"origin":"","legend":"\u003cp\u003eGlobal hydrothermal fluid fluxes of different types of hydrothermal fluids. Note that MORB-hosted fluids represent less than 50% of the global fluid flux.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/5b5faf0717fff03ae62e6b15.png"},{"id":79733463,"identity":"7dbfc13b-fc70-457a-87c1-5877014b4a2b","added_by":"auto","created_at":"2025-04-02 06:24:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":196414,"visible":true,"origin":"","legend":"\u003cp\u003eSingle values and median compositions of a:Mn vs Fe, b:Ca vs K, c:H\u003csub\u003e2\u003c/sub\u003eS vs CO\u003csub\u003e2\u003c/sub\u003e, d:CH\u003csub\u003e4\u003c/sub\u003e vs H\u003csub\u003e2\u003c/sub\u003e in vent fluids. Note: Crosshairs represent interquartile ranges.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/b4a8dd789d4087a531c35fb3.png"},{"id":79732780,"identity":"e14ede98-abdf-4e04-86dc-50712985cf28","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":118282,"visible":true,"origin":"","legend":"\u003cp\u003eConcentration-to-energy flux ratio for assorted elements/compounds. The whiskers represent the interquartile ranges due to the natural temperature‑ and compositional variability within each group. Note that the Ca flux for acid-sulfate fluids is negative and not represented in the figure.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/4fc2b266f0dce691dd719156.png"},{"id":79733462,"identity":"814641ef-25fd-4926-a5f0-b94485c3c6de","added_by":"auto","created_at":"2025-04-02 06:24:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":141174,"visible":true,"origin":"","legend":"\u003cp\u003eGlobal hydrothermal on-axis fluxes for all elements/compounds where data for each fluid type is available. The elements/compounds are sorted in descending order so that highest positive fluxes are found on the left hand side and highest negative fluxes on the right hand side.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/e050a7d155111d98b95a98b7.png"},{"id":79733465,"identity":"25abc46f-c8d7-4518-aef0-752e0b2e7751","added_by":"auto","created_at":"2025-04-02 06:24:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":106726,"visible":true,"origin":"","legend":"\u003cp\u003ePartitioning of the global on-axis hydrothermal element fluxes among different plate boundary types. The top bar represents the distribution of global fluid mass fluxes along these plate boundaries and is projected in mirror image onto positive and negative fluxes.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/2ded690575310269f537841e.png"},{"id":79734382,"identity":"acc8cf45-6a4f-46c7-8ce5-4046ae39d892","added_by":"auto","created_at":"2025-04-02 06:40:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1348033,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/91cf6994-9f40-444c-a6b9-ad97ef115d56.pdf"},{"id":79732772,"identity":"02cff1f5-a6d4-4d6c-958e-2596c5e73b28","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1556486,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Figures\u003c/p\u003e","description":"","filename":"DiehlandBach2025HydrothermalFluxesPreprintSupplementaryFigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/71d77f2364200d1a45af7103.docx"},{"id":79733461,"identity":"2750b8c0-92e1-4d01-9bdb-2bd8c4f5bb07","added_by":"auto","created_at":"2025-04-02 06:24:23","extension":"xlsx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":137442,"visible":true,"origin":"","legend":"\u003cp\u003eS1_Thermal Budget Calculation\u003c/p\u003e","description":"","filename":"DiehlandBach2025S1EnergyCalc.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/e98e2995ac32707e60c41557.xlsx"},{"id":79732784,"identity":"1813bb3f-01c0-43bd-b8c3-af816aa2bcf8","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"xlsx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":2323358,"visible":true,"origin":"","legend":"\u003cp\u003eS2_FilteredFluids\u003c/p\u003e","description":"","filename":"DiehlandBach2025S2FilteredFluids.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/5f5740c93d1eb4b785ce3973.xlsx"},{"id":79732777,"identity":"e526bd15-d207-4b22-a046-fff735714cae","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"xlsx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":88793,"visible":true,"origin":"","legend":"\u003cp\u003eS3_Probability Sediments\u003c/p\u003e","description":"","filename":"DiehlandBach2025S3ProbabilitySediment.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/d3b694e168586409c3af36e2.xlsx"},{"id":79732790,"identity":"be22f3db-9bbf-4487-a082-4d04de61dbcf","added_by":"auto","created_at":"2025-04-02 06:16:23","extension":"xlsx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":685911,"visible":true,"origin":"","legend":"\u003cp\u003eS4_Arc Rocks\u003c/p\u003e","description":"","filename":"DiehlandBach2025S4ArcRocks.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6352431/v1/408d008b2df5a14a1aa5c90f.xlsx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eThe global high-temperature on-axis hydrothermal fluid and element flux to the modern ocean\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAfter nearly fifty years of hydrothermal vent research the element fluxes between the ocean crust and the ocean have not been accurately constrained. The fundamental lack of knowledge on these fluxes is based on the absence of data driven approaches towards fluid compositions and hampers our understanding of the ocean floor as interface between the ocean and the ocean crust. Our knowledge on hydrothermal cooling has majorly improved by heat flow measurements \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, thermal models of conductive cooling \u003csup\u003e\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, and petrological investigations via drilling of in-situ ocean crust \u003csup\u003e\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e or studies of rocks exposed in ophiolites \u003csup\u003e\u003cspan additionalcitationids=\"CR11 CR12 CR13\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. In contrast estimation of hydrothermal element fluxes have only somewhat improved during nearly fifty years of hydrothermal research with many questions unanswered \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThere are two common approaches to assess hydrothermal element fluxes: (1) The use of rock chemical data \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan additionalcitationids=\"CR17 CR18\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e to deduce the integrated element transfer from the crustal perspective, and (2) the use of vent fluid compositions and heat balances \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e to assess global fluid and element fluxes. The problem of the first approach is the inhomogeneous character of the ocean crust and the spatial and temporal complexity of alteration patterns \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Specificially, it is not trivial to overcome latestage or off-axis low-temperature overprinting of high-temperature on-axis alteration assemblages in a dynamically changing ateration regime \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. For this reason the results of these studies are hard to upscale to assess global fluxes, with element fluxes often being underestimated \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFor the hydrothermal vent fluid-based approach, existing estimates relied on assumptions concerning one archetype basalt-hosted mid-ocean ridge black smoker fluid of constant composition and temperature (350\u0026deg;C) to be responsible for the global hydrothermal cooling. These estimates do not address the now well-established compositional and thermophysical diversity of hydrothermal fluids \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, with the mentioned archetype fluid being responsible for only 50% of global hydrothermal on-axis cooling. This simplification is majorly based on a lack of easily accessible compositional data of hydrothermal vent fluids. Here we utilize MARHYS database \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e in its current Version 3.0 \u003csup\u003e27\u003c/sup\u003e to recalculate global on-axis hydrothermal element fluxes. We consider the global partitioning of oceanic plate boundaries (mid-ocean ridges; MOR, back-arc spreading centers; BASC, volcanic arcs; VA) with their substrate types (igneous rocks, mantle rocks, sediments) and their effects on the global on-axis hydrothermal element budget in the modern ocean.\u003c/p\u003e \u003cp\u003eBy considering different vent fluid types involved in the global hydrothermal on-axis cooling, our calculations suggest that fluid and element fluxes along the oceanic plate boundaries are significantly larger than prior estimates suggested. Our results improve our understanding of the on-axis hydrothermal element budget and provide a means to resolve significant spatial variation of hydrothermal fluxes across the ocean and the underlying plate boundary types. This paves the road to constraining the evolution of ocean chemistry by considering variable hydrothermal on-axis element fluxes with changing plate tectonic configurations over Earth's history.\u003c/p\u003e"},{"header":"2. Results","content":"\u003cp\u003eThe powers of ocean crust formation and on-axis ventilation\u003c/p\u003e\n\u003cp\u003eHigh-temperature hydrothermal circulation at oceanic plate boundaries is ultimately driven by heat from the generation of new ocean crust. The amount of thermal energy supplied by crustal production can be calculated from latent heat released by crystallization of magma below the seafloor and thermal energy provided by cooling rocks from magmatic to hydrothermal temperatures \u003csup\u003e16,20,21\u003c/sup\u003e. The total amount of heat supplied by crustal rocks represents an upper limit for the thermal energy potentially available to drive hydrothermal circulation. We calculated the power of oceanic crust generation to be 4.5 TW with a volume production rate of 25.5 km\u003csup\u003e3\u003c/sup\u003e yr\u003csup\u003e-1\u003c/sup\u003e (mass production rate: 72.5 GT yr\u003csup\u003e-1\u003c/sup\u003e) for the modern ocean\u0026rsquo;s plate boundary configuration (Methods 9.1).\u003c/p\u003e\n\u003cp\u003eA significant part of this crustal heat is not carried by hydrothermal circulation. Firstly, the vent fluid temperature (here assumed at 300\u0026deg;C) constitutes a cut-off to cooling and a corresponding amount of heat remains in the ocean crust that is not advectively removed. We integrated a cumulated power equivalent of 0.48 TW that remains stored in 300\u0026deg;C warm ocean crust for the global ocean crust production rate and the penetration depth of hydrothermal fluids. Secondly, a fraction of the total heat is advected to the seafloor by volcanic processes. Basaltic lava flows extruding on the ocean floor are rapidly cooled and release their thermal energy in event plumes and/or rapid thermal conduction to the ocean with minimal chemical exchange \u003csup\u003e28-30\u003c/sup\u003e. Event plumes are characterized by lower He/heat ratios \u003csup\u003e31\u003c/sup\u003e combined with lower Mn/He ratios \u003csup\u003e32\u003c/sup\u003e than chronic plumes from hydrothermal vent sources and suggest lower chemical fluxes to the oceans. Apart from being significantly lower than in chronic plumes, the magnitude of chemical fluxes associated with such megaplume events is largely unknown for most elements. Consequently, we consider a power equivalent of 0.33 TW associated to the production of extrusives to be not available for extensive hydrothermal circulation with significant chemical exchange. Thirdly, a significant amount of crustal energy is lost to the oceans conductively. Heat flow studies have shown that the conductive heat transfer is being responsible for only about 10% of the heat escaping from the young oceancrust within 0\u0026ndash;1 Ma after crust formation \u003csup\u003e33\u003c/sup\u003e. We have integrated the effective surface heat flow estimate of Hasterok, et al. \u003csup\u003e2\u003c/sup\u003e over the global oceanic plate boundaries and calculated the conductive power for 0\u0026ndash;1 Ma crust to be 0.72 TW (16% of the total 4.5 TW available). With this combined 1.5 TW of power unavailable for hydrothermal circulation, our upper bound for on-axis hydrothermal circulation is 3.0 TW.\u003c/p\u003e\n\u003cp\u003eFrom petrological perspective it appears that most of the heat in the sheeted-dyke complex is removed hydrothermally. This is based on observations in ophiolites and in-situ ocean crust where the high-temperature reaction zone and its mineralization products are found overlying gabbroic rocks as legacy of extensive hydrothermal cooling \u003csup\u003e6,22,23\u003c/sup\u003e. The gabbroic lower crust is also affected by significant hydrothermal alteration, but uncertainties remain as to the extent and timing of hydrothermal cooling \u003csup\u003e8,10,12,13\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTo account for incomplete hydrothermal cooling of the lower crust, we estimated the global hydrothermal power for oceanic plate boundaries as 2.6\u0026nbsp;\u0026plusmn;\u0026nbsp;0.4\u0026nbsp;TW, assuming that 90\u0026plusmn;10% of the oceanic crust is hydrothermally cooled. For the thicker crust in VA, we assume the fraction of hydrothermal cooling to be 80\u0026plusmn;20%. With lower proportions of hydrothermal cooling, the calculated fluxes would decrease linearly. Here, we focus on the influence of variable vent fluid compositions and their partitioning among the plate boundaries.\u003c/p\u003e\n\u003cp\u003eVent fluid types and their partitioning in the modern ocean\u003c/p\u003e\n\u003cp\u003eWe have defined different vent fluid classes according to a combination of substrate types, geological settings and reports of fluid characteristics in existing vent fluid publications to find a proper representation of global hydrothermal on-axis processes (Methods 9.2\u0026ndash;9.3). We weighted and distributed these fluid classes according to the modern configuration of oceanic plate boundaries (Methods 9.4) and calculated the fluid and element-fluxes according to an heat balance with their share of cooling (Methods 9.5).\u003c/p\u003e\n\u003cp\u003eBased on these constraints, we computed a global on-axis fluid mass flux of 6.3\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-1\u003c/sup\u003e (Figure 1). The total fluid mass flux partitions into circulation of 44% of basalt-hosted MOR hydrothermal fluids, 13% peridotite-related MOR fluids, 11% sediment-related fluids in MOR and BASC, \u0026nbsp;and 32% of non-sediment-related arc- and back‑arc fluids (Figure 1). The global high temperature hydrothermal flux is greater than the 8\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u0026ndash;3.7\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-1\u003c/sup\u003e proposed earlier \u003csup\u003e16,17,20\u003c/sup\u003e. This discrepancy is due to two differences between our and previous estimates: (1) we included hydrothermal venting in arcs and back arcs, while earlier estimates were intended to represent fluxes at MOR, and (2) we used measured temperatures and corresponding thermophysical properties of fluids, while previous workers assumed a uniform venting temperature of 350 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eBesides their different chemical characteristics, these fluid types involve significantly different thermophysical properties (Table 1). MOR basalt-hosted fluids with a median temperature of 341\u0026deg;C carry 1514\u0026nbsp;kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e. Peridotite-related fluids contain a somewhat higher amount of thermal energy (1549\u0026ndash;1623\u0026nbsp;kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) and median temperatures between 350 and 360\u0026nbsp;\u0026deg;C, likely due to somewhat greater reaction zone depths. In contrast sediment-related fluids are found to vent slightly shallower, significantly cooler (276\u0026ndash;315\u0026deg;C) and carry ~10\u0026ndash;30\u0026nbsp;% less thermal energy (1173\u0026ndash;1373\u0026nbsp;kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) compared to MORB-hosted fluids.\u003c/p\u003e\n\u003cp\u003eArc- and back-arc-related seawater-derived fluids are shallower (1616\u0026ndash;2400\u0026nbsp;mbsl) and cooler with median vent fluid temperatures between 296\u0026ndash;300\u0026nbsp;\u0026deg;C. They carry between 1270 and 1289\u0026nbsp;kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e, which is about 15% less than MOR basalt-hosted fluids. A fundamentally different type of fluid venting in arcs is acid-sulfate fluids that are affected by magmatic degassing. These fluids have a low median temperature of 82\u0026nbsp;\u0026deg;C and hence a lower median content of thermal energy of 345\u0026nbsp;kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e. They are known to be mostly acidic, very rich in sulfur and carbon, and vent at low temperatures typically below 120\u0026deg;C \u003csup\u003e34\u003c/sup\u003e. The lower temperatures of sediment-hosted and arc-backarc acid-sulfate hydrothermal fluids push their associated fraction of global vent fluid fluxes significantly higher (4% and 10%, respectively), than their share of hydrothermal power (3% and 2%, respectively; cf. Figure 1 and Supplementary Figure 4). In contrast, the higher temperatures of MOR fluids (both, basalt-hosted and peridotite-related) cause lower fluid fluxes (57%) in relation to their share of hydrothermal power (65%).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Median thermophysical properties of hydrothermal fluid types, hydrothermal power and resulting fluid mass fluxes. Note: Mg concentrations represent average values (see text).\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"623\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFluid Type\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e\u003cstrong\u003en\u003csub\u003eObs\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e\u003cstrong\u003ed (mbsl); p (bar)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT [\u0026deg;C]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMg mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eS (wt.%); Cl (mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eH (kJ\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eP (TW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eM (kg\u0026nbsp;yr\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eGlobal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e2.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e6.3\u0026bull;10\u003csup\u003e13\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eMORB-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e981\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2521; 254\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e341\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e2.86; 456\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1514\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e2.8\u0026bull;10\u003csup\u003e13\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003ePeridotite-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e105\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2307; 233\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e350\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e4.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e4.28; 702\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1549\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e6.7\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003ePeridotite-influenced\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2450; 248\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e360\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.54; 573\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1623\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e1.6\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eSediment-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2000; 202\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e276\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.65; 592\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1173\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e2.5\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eSediment-influenced\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e239\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2200; 222\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e2.90; 462\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1373\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e4.2\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eArcBackarc-mafic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e264\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2400; 242\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.47; 562\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1289\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e7.9\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eArcBackarc-felsic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e253\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1616; 163\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e296\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.69; 600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1270\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e6.4\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eArcBackarc-acidsulfate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e1222; 123\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e46.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.19; 513\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e345\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e6.4\u0026bull;10\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 29.374%;\"\u003e\n \u003cp\u003eSeawater\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.38363%;\"\u003e\n \u003cp\u003e64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e2382; 241\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.82825%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.0754%;\"\u003e\n \u003cp\u003e52.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.63082%;\"\u003e\n \u003cp\u003e3.35; 540\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.98876%;\"\u003e\n \u003cp\u003e35.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.54414%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.1862%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eCompositional diversity of hydrothermal vent fluids in different settings\u003c/p\u003e\n\u003cp\u003eBesides different thermophysical properties (pressures, temperatures, salinities and enthalpies) the fluid types defined in this study involve significantly different median compositions (Table\u0026nbsp;2, Figure\u0026nbsp;2). The fluid compositions calculated here are not normalized to seawater chlorine concentration and the median Cl concentrations of peridotite-hosted (701\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e), sediment‑hosted (592\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) and felsic arc-backarc fluids (600\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) are significantly higher than seawater chlorinity (540\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e), whereas MOR basalt‑hosted (456\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e), sediment‑influenced (462\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) and acid-sulfate arc and back-arc fluids (513\u0026nbsp;mmol\u0026nbsp;kg\u003csup\u003e-1\u003c/sup\u003e) are chloride-depleted.\u003c/p\u003e\n\u003cp\u003eThe median compositions for Mg were calculated as zero for some fluid classes where end member Mg compositions dominated the fluid classes. To prevent this bias we use mean values for Mg concentrations instead of median values. The average Mg concentrations are between 3.2 \u0026nbsp;and 5.9 mmol kg\u003csup\u003e-1\u003c/sup\u003e for seawater-derived fluids. These Mg concentrations can be an artifact of seawater entrainment during sampling or point to a typical entrainment of ~6-11% of seawater into focused hydrothermal fluids. Acid-sulfate fluids are known to not be represented by zero-Mg endmembers and the average Mg concentration is calculated as 46.5 mmol kg\u003csup\u003e-1\u003c/sup\u003e for these arc- and back-arc-related fluids.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Median chemical composition of some components in the different fluid types. Note that all concentrations are given as mmol kg\u003csup\u003e-1\u003c/sup\u003e. No H\u003csub\u003e2\u003c/sub\u003eS concentrations are reported for seawater. Thus the value is set to zero.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"627\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eFluid Type\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003eCH\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eMORB-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e25.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e16.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e16.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e0.201\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e0.107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.475\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003ePeridotite-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e16.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e19.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e55.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e14.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e17.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003ePeridotite-influenced\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e7.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e15.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e28.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e0.171\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e4.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.836\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eSediment-hosted\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e26.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e39.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e32.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e36.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.039\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.128\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eSediment-influenced\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e31.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e34.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e22.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e0.223\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.305\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.258\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eArcBackarc- mafic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e12.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e5.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e28.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e34.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e0.044\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e0.029\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.937\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.544\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eArcBackarc- felsic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e38.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e55.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e25.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e0.023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e0.023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.735\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eArcBackarc- acidsulfate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e59.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e10.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e9.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e0.0021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e5.9E-4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e0.184\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13.2588%;\"\u003e\n \u003cp\u003eSeawater\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.8211%;\"\u003e\n \u003cp\u003e10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 11.3419%;\"\u003e\n \u003cp\u003e10.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11.0224%;\"\u003e\n \u003cp\u003e3.5E-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.7029%;\"\u003e\n \u003cp\u003e4E-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e3.7E-6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 9.10543%;\"\u003e\n \u003cp\u003e2E-6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe extreme compositional differences become apparent for transition metals. Although individual samples of each fluid class span a broad range of compositions, the median compositions of the classes are distinctly different. Median concentrations of Fe and Mn are one to two orders of magnitude lower in sediment-associated and arc- to backarc acid-sulfate hydrothermal vent fluids (Figure 2A). In contrast, peridotite-related hydrothermal fluids can contain up to one order of magnitude higher concentrations of Fe and Mn compared to MORB-hosted vent fluids. Systematic differences also exist in the alkali and alkaliearth metals (Figure 2B). For instance, peridotite-related vent fluids have high Ca and low K concentrations, while systems affected by sediments or hosted in arc/backarc setting can have high K/Ca ratios. Acid-sulfate fluids in arcs, by contrast, are depleted in both elements relative to MOR basalt-hosted systems.\u003c/p\u003e\n\u003cp\u003eThe distinct nature of the fluid types becomes particularly apparent in the concentrations of dissolved gases, the median concentrations of which range by up to two orders of magnitudes between vent fluids from different settings. Carbon dioxide is low in concentration in peridotite-associated fluids but high in sediment- and most arc to backarc-related fluids (Figure 2C). By comparison, H\u003csub\u003e2\u003c/sub\u003eS concentrations for all fluid types are not as variable. H\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e concentrations in sediment- and peridotite-related fluids are one to two orders of magnitude higher than in basalt‑hosted MOR fluids (Figure 2D). H\u003csub\u003e2\u003c/sub\u003e contents are highest in peridotite‑related systems, whereas CH\u003csub\u003e4\u003c/sub\u003e is most enriched in sediment‑related systems. Supplementary File S5 summarizes the median values for all elements and compounds in the database.\u003c/p\u003e\n\u003cp\u003eElement per energy flux\u003c/p\u003e\n\u003cp\u003eWhen estimating hydrothermal fluxes, it is important to not only consider the composition of hydrothermal fluids but also the concentration/energy ratio. This ratio is presented in Equations 2 and 4 (Methods 9.5) by the term \u0026nbsp; \u0026nbsp;(the difference quotient from compositions and specific enthalpies of hydrothermal fluid and seawater). This term provides a normalized view on the element transport ability of hydrothermal fluids in relation to the amount of heat they transport upon cooling of the ocean crust. Figure 3 shows the different fluid types to have different abilities of carrying dissolved compounds. Considering statistical aspects (median values and interquartile ranges), the transport ability of sediment-related hydrothermal fluids for transition metals (Fe, Mn, Zn, Cu) are one (sediment-influenced) to two (sediment-hosted) orders of magnitude lower than for basalt-hosted MOR fluids. This shows the trapping ability for metals in these sediment‑related hydrothermal fluids. In contrast, peridotite-related MOR fluids have a transport ability for these metals that is up to one order of magnitude higher \u0026nbsp;than MOR basalt-hosted hydrothermal fluids. As consequence of this strong substrate-control, the variability of regional hydrothermal element fluxes is very high. This is perhaps most clearly seen in the case of dissolved gases: The concentration/energy ratio for CH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e in sediment‑ and peridotite‑related hydrothermal vent fluids is significantly higher than for MOR basalt‑hosted fluids, as well as, significantly lower for arc- and back-arc-related vent fluids. A striking example is the H\u003csub\u003e2\u003c/sub\u003e flux in peridotite-hosted vent fluids with a concentration/energy ratio that is almost 100 times higher than for basalt‑hosted MOR fluids. With ~50% of the global hydrothermal power being mined by basalt‑hosted MOR vent fluids and ~11% of the global hydrothermal power mined by perdidotite-hosted MOR vent fluids, this means that the actual H\u003csub\u003e2\u003c/sub\u003e delivery from peridotite-hosted fluids is roughly 20 times larger than the one from basalt‑hosted fluids. This example demonstrates that it is imperative to take full account of the influence of different fluid types in the global element budget. Supplementary File 5 contains all concentration/energy ratios calculated from median fluid temperatures and their compositions.\u003c/p\u003e\n\u003cp\u003eThe global on-axis hydrothermal element flux\u003c/p\u003e\n\u003cp\u003eUtilizing\u0026nbsp;our different fluid types and their partitioning we derive the global hydrothermal on-axis element fluxes and compare these with previously published estimates (Figure 4)\u003csup\u003e16,17,20\u003c/sup\u003e. For the majority of elements/compounds the element fluxes we calculated exceed previous estimates. These large differences have several reasons: (1) We consider hydrothermal circulation in volcanic arcs (adding another 0.4 TW to the global hydrothermal power), (2) we distinguish between mafic- and ultramafic-hosted sites, (3) we consider significantly lower temperatures for sediment- and arc to backarc-related hydrothermal fluids; and (4) we calculate median compositions from a mixture of endmembers and hydrothermal fluids with their measured temperatures that are lower than theoretical end-member temperatures (overall leading to higher fluid mass fluxes).\u003c/p\u003e\n\u003cp\u003eOur results show that element fluxes for many compounds have been considerably underestimated when assuming that average MOR basalt-hosted vent fluids are representative of global axial hydrothermal fluxes. The largest positive global element flux is calculated for CO\u003csub\u003e2\u003c/sub\u003e as 1.6\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e. This value is two to threefold higher than existing estimates from vent fluid compositions and energy balances \u003csup\u003e16,20\u003c/sup\u003e. Our calculated CO\u003csub\u003e2\u003c/sub\u003e flux for mid-ocean ridges (excluding arcs and backarcs) is 9\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e and is in good agreement with recent estimates of CO\u003csub\u003e2\u003c/sub\u003e fluxes by magma degassing at MOR which was determined as 1.32\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e \u003csup\u003e35\u003c/sup\u003e. However, the combined MOR-flux of CO\u003csub\u003e2\u003c/sub\u003e constitutes only 55% of the global CO\u003csub\u003e2\u003c/sub\u003e flux from crust to ocean despite a fraction of 68% of global hydrothermal power. Arc and backarc systems release almost as much CO\u003csub\u003e2\u003c/sub\u003e (7\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e), although the hydrothermal power is ~3 times lower.\u003c/p\u003e\n\u003cp\u003eThe calculated global H\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e fluxes are 1.1\u0026bull;10\u003csup\u003e11\u003c/sup\u003e and 1.2\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e, respectively. Again, these fluxes are significantly higher than previous flux estimates based on fluid compositions and energy balances and are about tenfold increased compared to the mean values of existing estimates\u003csup\u003e16,17,20\u003c/sup\u003e. Our H\u003csub\u003e2\u003c/sub\u003e flux estimate is low compared to flux estimates of 7\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol/yr derived from serpentinization of rocks \u003csup\u003e36-38\u003c/sup\u003e but suggests that the role of on-axis circulation with regards to serpentinization is more pronounced than expected. However, our flux estimate for CH\u003csub\u003e4\u003c/sub\u003e is in agreement with 0.7\u0026ndash;1.2\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e derived from a serpentinization-based hydrogen flux estimate and assuming a hydrogen to methane ratio between 1:1 and 10:1\u003csup\u003e36\u003c/sup\u003e. The median fluid compositions here show higher H\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e ratios for peridotite-related fluids (peridotite-influenced: 10, peridotite-hosted: 20). However, the low H\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e ratios for sediment‑related systems (sediment-influenced: 1/11, sediment-hosted: 1/20) counteract that effect and lead to a global H\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e flux ratio of unity.\u003c/p\u003e\n\u003cp\u003eWe calculated Fe and Mn fluxes of 2.1\u0026bull;10\u003csup\u003e11\u003c/sup\u003e and 3.6\u0026bull;10\u003csup\u003e10\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e, respectively that are also higher than previous estimates, although sediment‑related systems (which make up 11% of the global fluid mass flux) have very low metal/energy ratios. The higher metal/energy ratios in peridotite-related and arc- to back-arc‑related fluids counteract and even exceed this effect. From biogeochemical models a much lower global Fe hydrothermal input of 4\u0026bull;10\u003csup\u003e9\u003c/sup\u003e mol/yr was estimated \u003csup\u003e39\u003c/sup\u003e. Our calculation suggest that the actual Fe delivery by hydrothermal circulation is much larger than expected by these biogeochemical models. The discrepancy might be explained by near-field plume precipitation and rapid removal of the majority of hydrothermal Fe before being dispersed in the far-field.\u003c/p\u003e\n\u003cp\u003eGeochemical models estimate a modern MOR Li flux of 1.37\u0026bull;10\u003csup\u003e10\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e \u003csup\u003e40\u003c/sup\u003e. Here we calculate the MOR Li flux as 1.5\u0026bull;10\u003csup\u003e10\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e but a total hydrothermal on-axis Li flux of 2.5\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e. This Li flux exceeds by far the reported riverine input of Li (8\u0026bull;10\u003csup\u003e9\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e \u003csup\u003e41\u003c/sup\u003e) to the ocean.\u003c/p\u003e\n\u003cp\u003eOur flux estimates for other trace metals (Pb, Cs, Co, Cd, Ag) are all nearly one order of magnitude higher than in the previous fluid-based estimates \u003csup\u003e16,17,20\u003c/sup\u003e (Figure 4). Our results suggest that MORB-hosted vent fluids are not representative of global hydrothermal venting for these elements, because these elements are enriched in arc/backarc hydrothermal vent fluids. The role of arc and back-arc hydrothermal systems is amplified by higher concentration/energy ratios of their fluids.\u003c/p\u003e\n\u003cp\u003eHydrothermal systems are not only sources for elements to the ocean but can also act as sinks. We calculated negative fluxes for U, Br, Alkalinity, Cl, SO\u003csub\u003e4\u003c/sub\u003e, Na and Mg. The highest negative flux was calculated for Mg (‑2.8\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e). Mg and SO\u003csub\u003e4\u003c/sub\u003e (‑1.5\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e) are known to be quantitatively removed due to high-T fluid rock interactions\u003csup\u003e42,43\u003c/sup\u003e and our estimated sink fluxes of Mg and SO\u003csub\u003e4\u003c/sub\u003e are both increased compared to previous fluid-based flux estimates due to our higher global fluid mass flux.\u003c/p\u003e\n\u003cp\u003eThe Cl flux estimate of \u0026nbsp;1.0\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e should be treated with caution. The strong deviations from seawater chlorinity in the MOR basalt-hosted fluids is due to phase separation and predominant venting of vapor-rich fluids after volcanic eruptions at MOR. It could also reflect fluid-rock interactions in the subsurface during which Cl may be taken up by secondary minerals. Lower-than-seawater Cl concentrations for many arc/backarc systems could be likely due to influx of magmatic vapor that decreases the chlorinity when mixing with seawater-derived solutions.\u003c/p\u003e\n\u003cp\u003eOur calculated Na flux is -2.4\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e and exceeds the Cl sink flux by 1.4\u0026bull;10\u003csup\u003e12\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e. This value may represent the global albitization rate in the deeper part of hydrothermal convection systems. The Na sink flux is almost twice as large as the effective Ca source flux of 8.8\u0026bull;10\u003csup\u003e11\u003c/sup\u003e mol yr\u003csup\u003e-1\u003c/sup\u003e, which is consistent with albitization reactions that balance the loss of 2 moles of Na with the release of 1 mole of Ca .\u003c/p\u003e\n\u003cp\u003ePartitioning of element fluxes by fluid types\u003c/p\u003e\n\u003cp\u003eWe calculated the relative contributions of the different vent fluid types to the global on-axis fluxes for a large range of elements. These contributions differ due to variations in fluid mass fluxes (resulting from heat flux and thermophysical properties) between the different vent types (top bar in Figure 5). The fluxes for most elements, however, show relative contribution patterns that are succinctly different from those of the fluid mass fluxes. These in part extreme discrepancies between fluid mass flux and element flux reflect strong contrasts in the composition of fluids venting in the different settings.\u003c/p\u003e\n\u003cp\u003eMOR basalt-hosted vents account for a relative fluid mass flux of 44% but make up 57% of the H\u003csub\u003e2\u003c/sub\u003eS and 50% of the Si fluxes indicating that the contributions of this vent type for the global fluxes of these compounds is somewhat higher than expected from the fluid mass flux. In contrast, the global flux contribution of MOR basalt-hosted vents for K (19\u0026nbsp;%), Ca (18\u0026nbsp;%), B(7\u0026nbsp;%), H\u003csub\u003e2\u003c/sub\u003e (5 %), CH\u003csub\u003e4\u003c/sub\u003e (3 %) is much smaller than 44%. MORB-hosted systems play only a subordinate role in determining the on-axis element cycles of these compounds, despite their importance in terms of energy- and mass fluxes.\u003c/p\u003e\n\u003cp\u003eIn contrast, we find that peridotite-related hydrothermal vents, which represent large parts of the slow to ultra-slow spreading MORs, dominate the fluxes of numerous substances. For instance, \u0026nbsp;peridotite-related hydrothermal vents deliver 90% of the global hydrothermal H\u003csub\u003e2\u003c/sub\u003e, 59% of Fe, 42% of Cu, 37% of Ca, 32% Mn, 29% Co and 24% Zn, although they account for only 13% of the global vent fluid mass flux. For other substances, the flux contributions are smaller than suggested by the fluid mass flux (Al: 2%, Pb: 3%, Cd: 5%, H\u003csub\u003e2\u003c/sub\u003eS: 5%, CO\u003csub\u003e2\u003c/sub\u003e: 6%). In addition, peridotite-hosted and peridotite-influenced systems are the only ones that act as sinks of B (-7%).\u003c/p\u003e\n\u003cp\u003eSediment-related hydrothermal vents contribute 11% to the global hydrothermal fluid mass flux but deliver 99% of the global on-axis hydrothermal NH\u003csub\u003e3\u003c/sub\u003e, 86% of CH\u003csub\u003e4\u003c/sub\u003e, 48% of B, 20% of K, 18% of Sr, 17% of Rb and 17% of Cs. Sediment-hosted systems are the only source of alkalinity among the fluid types defined in this study, while all other represent sinks to the ocean. On the other hand, the global element fluxes for metals in sediment-related systems are extremely low at 0.65 % Fe, 2.0 % Cu, 2.2 % Ag, 3.5 % Co, 3.8 % Mn and 4.9 % Zn. This shows that upwelling hydrothermal fluids effectively loose these elements during cooling/seawater mixing, as they pass through sediments.\u003c/p\u003e\n\u003cp\u003eArc and back-arc hydrothermal fluids play a major role for the global element fluxes by (1) host rock compositions and (2) influence of magmatic volatiles. Arc and back-arc mafic-hosted hydrothermal fluids comprise 12% of the global fluid mass flux and show slightly higher flux contributions for Ca (21%), Li (18%) and K (17%), while the flux contributions for other substances are significantly lower (H\u003csub\u003e2\u003c/sub\u003e: 0.3%, CH\u003csub\u003e4\u003c/sub\u003e: 0.2%, Co: 1%, Ag: 2%, Cu: 3%, Fe: 4%, and Al: 5%). This is not surprising as basalt-fluid interactions govern element solubilities and lower pressures and temperatures in arc/backarcs come with a lower release of metals and H\u003csub\u003e2\u003c/sub\u003e. In contrast, the group of felsic arc/backarc hydrothermal system , which carry 10% of the vent water flux supply a much greater proportion of many elements. For instance, these systems contribute 49% of hydrothermal Pb, 46% of Cs, 34% of K, 34% of Ag, 33% of Cd, 33% of Cu, 28% of B and 24% of Rb. The fluxes of metals are significantly increased in felsic-hosted hydrothermal vent fluids over their mafic-hosted counterparts, because basement composition or intensity of magmatic influx matter. Acid-sulfate fluids, despite accounting for only 2% of the global hydrothermal power, make up 10 % of the global hydrothermal fluid mass flux. In addition, the often highly acidic nature of these fluids allows them to dissolve large amounts of Al and REE. As a consequence, this type of vents dominates the global hydrothermal discharge of high field strength elements such as Al (67%) and REE (Sm :66%, Nd: 61%) that are virtually insoluble in most natural waters. They also contribute disproportionately to the fluxes of other components, such as Co (29%), CO\u003csub\u003e2\u003c/sub\u003e (23%), Pb (21%). In contrast, the proportions provided are low for other elements, inluding K, Si, Fe, Mn, Li, Cu, and Ag. Unique to this vent type are negative fluxes of Ca and Sr and a positive flux of SO\u003csub\u003e4\u003c/sub\u003e. As generally, the negative flux of SO\u003csub\u003e4\u003c/sub\u003e exceeds the flux of H\u003csub\u003e2\u003c/sub\u003eS by roughly a factor of five, all seawater-derived hydrothermal systems act as sinks of S to the oceans. This is different for acid-sulfate vents that act as source of sulfur to the ocean.\u003c/p\u003e"},{"header":"3. Discussion","content":"\u003cp\u003eWe calculated a global high-temperature hydrothermal power of 2.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 TW from the global submarine formation of crust, along oceanic spreading centers and volcanic arcs. Submarine volcanic arcs contribute 0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 TW, leaving a heat flux of 2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 TW along the global spreading ridges. This power estimate is somewhat lower than what Mottl \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e had estimated for oceanic spreading centers (2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 TW). Our estimate, however, agrees well with the oceanic spreading-related heat flux suggested by Elderfield \u0026amp; Schultz \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e of 2\u0026thinsp;\u0026plusmn;\u0026thinsp;1 TW. These authors calculated the annual fluid flow associated with this heat flux to 3.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eby assuming a uniform venting temperature of 350\u0026deg;C. Alt (2003) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e suggested a vent fluid flux of 3.7\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e using refined thermal properties of hydrothermal fluids and a lower axial hydrothermal power of 1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 TW, which corresponds to the hydrothermal heat flux estimated for crust\u0026thinsp;\u0026lt;\u0026thinsp;0.1Ma \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Our analyses yields a higher global vent fluid mass flux of 6.3\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Our calculated fluid flux for oceanic spreading centers (BASC and MOR) is 5.0\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The remaining 1.3\u0026bull;10\u003csup\u003e13\u003c/sup\u003e kg yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e are attributed by hydrothermalism associated to volcanic arcs. The reason for the higher fluid fluxes in our estimate is that we used actual fluid temperatures from the MARHYS database and did not assumed a uniformly high venting temperatue of 350\u0026deg;C. Because many vents (in particular those in sediment-related MOR and acid-sulfate type inarcs) issue fluids with much lower temperatures, our global fluid flux estimate is much greater than earlier suggested, although our heat flux estimate is only 10\u0026ndash;20% higher.\u003c/p\u003e\n\u003cp\u003eWe considered different hydrothermal vent fluid types according to geological setting and basement type and mined a hydrothermal vent fluid database to calculate chemical fluxes. The higher fluid flux results in overall higher element fluxes than in previous estimates, but the differences also reflect distinct fluid compositions in different settings and their share in the global heat budget. Peridotite-related systems provide the majority of hydrothermal H\u003csub\u003e2\u003c/sub\u003e and Fe and comparably large amounts of Cu, Ca, Ba, Mn, Co and Zn. We find that sediment-related systems provide nearly the entire supply of NH\u003csub\u003e3\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e with significant contributions of B, K, Sr, Rb, Cs. The delivery of Fe, Cu, Ag, Co, Mn and Zn from these systems to the ocean is strongly diminished. Felsic-hosted arc and back-arc hydrothermal fluids provide a large fraction of Pb, Cs, K, Ag, Cd, Cu, B, Rb. Acid-sulfate vents in arc/back-arc settings carry the majority of Al and REE and significant CO\u003csub\u003e2\u003c/sub\u003e to the ocean but only minimum amounts of other elements (K, Si, Fe, CH\u003csub\u003e4\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003e, Mn, Li, Cu, Rb, Ba, Cs, Ag).\u003c/p\u003e\n\u003cp\u003eNotably, the fluxes we calculated are valid for the assumption that the entire hydrothermal power is used to generate high temperature fluids. Much of the heat, however, is carried by low-temperature diffuse fluids \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e, which can have concentration/heat ratios different from those of high-temprature focused vent fluids. Transition metals (Fe, Cu, Zn) and dissolved gases (H\u003csub\u003e2\u003c/sub\u003eS, H\u003csub\u003e2\u003c/sub\u003e) have been shown to be systematically depleted in low-temperature diffuse fluids \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. The element fluxes provided for these compounds should hence be considered maximum values. More geochemical analyses of diffuse fluids and data on the partitioning of high and low temperature fluids is required to further improve our global flux estimates for non-conservative compounds.\u003c/p\u003e\n\u003cp\u003eAnother source of uncertainty revolves around the question of whether or not the sampled vent fluids are representative of global hydrothermal vent fluid compositions. After all, of the estimated 1430 vent sites \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e only 142 were sampled. The intensity of sampling of those 142 sites is highly variable, which introduces a certain amount of bias. A good illustration for this issue is the Rainbow vent field as a prominent representative of the \u0026ldquo;peridotite-hosted\u0026rdquo; fluid category. Of the 104 fluid samples within this category, more than half (55 samples) originate from vents in the Rainbow vent field. Hence, the compositions of the Fe-rich Rainbow vent fluids strongly affect the median fluid compositions, and the large Fe-fluxes calculated for peridotite-hosted vents could reflect a sampling bias. If the available data were weighted by vent field instead of samples, the median value would be significantly lower. But equally weighting by vent field does not consider the vast range in field-scale hydrothermal heat fluxes among vent sites (16-3800 MW) and Rainbow has an exceptionally large field-scale heat flux \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. Continued vent fluid sampling will ultimately improve the data situation in this regard. Rainbow fluids may currently seem to have anomalously high Fe-centrations, but fluids from only four high-T peridotite-hosted systems are represented in the data base, and there are indications of additional extremely Fe-rich hydrothermal sites, such as the F\u0026aring;vne vent field on the Mohns Ridge \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eOur results provide important information on the regional availability of nutrients and dissolved compounds to the ocean. The different fluid classes do not only have implications for the global on-axis element fluxes, but also for the occurence of ecosystems in the different plate boundaries. Our results suggest a highly variable input of elements for different settings in the modern ocean. These insights are important for earth system models: On-axis hydrothermal circulation of seawater is one of the main sources and sinks of chemicals in the ocean. The highly variable input of the different fluid classes reveals that variations in the plate tectonic configuration on our planet may strongly influence hydrothermal element fluxes. These changes can be related to changes in the global crustal volume production but changing the (geographical) distribution of plate boundaries can also have a profound impact on these element fluxes. For instance, an increased strike length of mid-ocean ridges or back-arc spreading centers near continent shelves would boost the CH\u003csub\u003e4\u003c/sub\u003e and NH\u003csub\u003e3\u003c/sub\u003e emmisions and reduce the delivery of metals like Fe, Cu and Zn. Changes in the relative crustal production rates of arcs, backarcs and mid ocean ridges (maintaining the global crustal production rate) would have a huge impact on the fluxes of REE, Al, S, CO\u003csub\u003e2\u003c/sub\u003e. Changing the partitioning between ultra-slow to slow and fast to super-fast spreading over the mid ocean ridges strike length (again preserving the global crustal production rate) would massively influence H\u003csub\u003e2\u003c/sub\u003e and Fe delivery to ocean. Coupling a spatially resolved and setting-specific flux estimate such as presented here with plate tectonic reconstruction of the past will facilitate the calculation of the temporal variability of on-axis hydrothermal circulation and its effects on the composition of past oceans.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eConfiguration of oceanic plate boundaries\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe total length of global oceanic plate boundaries is 92,984 km, including 60,139 km of Mid-Ocean Ridge spreading centers (MOR), of which 22,723 km spread at intermediate to fast rates of \u0026gt;\u0026thinsp;5mm yr\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, while 37,416 km are slow to ultra-slow spreading ridges with a full spreading rate of \u0026lt;\u0026thinsp;5mm yr\u003csup\u003e-1 49,\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. Back-arc spreading centers (BASC) make up 11,145 km \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e and volcanic arcs (VA) comprise 21,700 km of plate boundary length \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;1a). We considered the length-weighted average spreading rates and their average crustal thicknesses and deduced the global crustal production rate (Supplementary Fig.\u0026nbsp;1b, Supplementary File S1). For VA the calculation of crustal production rates is complicated by processes of crustal growth (increase in thickness), delamination and/or subduction erosion, with magma production rates potentially being larger than the crustal production rate \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e. We inferred that magma emplaced within a VA provides thermal energy for hydrothermal circulation, regardless of whether or not it is removed from the arc at a later stage. We chose to follow published magma production rates \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e and calculated the global arc magma production rate as the lengthweighted average of the major intraoceanic arcs (Aleutians, Izu-Bonin, Mariana, Lesser Antilles, Tonga-Kermadec). We accounted for different crustal thicknesses of fast spreading MOR (5.8 km) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e, slow spreading MOR (8 km), BASC (6 km) and VA (15 km). The crustal thickness of slow spreading MOR is meant to be an average that represents ultra-slow spreading rates with crustal thicknesses of up to 10 km \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e and intermediate spreading rates with crustal thickness as low as 6 km \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e. The crustal thickness of VA also represents an average, as VA crust can be between 10 and 30 km thick \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e. We additionally accounted for different thicknesses of extrusives (between 350 and 750 m) following different geophysical surveys of ultraslow to slow and fast spreading MOR \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe power of crust generation (Supplementary Fig.\u0026nbsp;1c, Supplementary S1) was calculated by an energy balance that accounts for heat of crystallization\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e and cooling of rocks from the magmatic to hydrothermal temperatures according to their heat capacities\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. We considered that MOR with basaltic crust have slightly higher magmatic temperatures (1250\u0026deg;C) than more evolved BASC (1200\u0026deg;C) or VA (1100\u0026deg;C). At all plate boundaries, except slow to ultra-slow MOR, crust is exclusively made up of igneous rocks that release heat of crystallization. For slow to ultra-slow spread crust we assume that half of the \u0026ldquo;crustal\u0026rdquo; thickness is made up by mantle peridotites that are either exposed at the seafloor or are buried under a thin carapace of basalt. The mantle section is denser and provides more thermal energy by cooling per volume of crust but lacks latent heat of crystallization. The proportions of magmatic versus mantle rocks are hard to estimate on a global scale, but the 50:50 proportion assumed here may be representative of ultra-slow to slow spreading MOR with variable extents of magmatic vs amagmatic accretion which is not exclusively controlled by spreading rate \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eWe integrated the predicted conductive surface heat flow \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e for 0\u0026ndash;1 Ma over the global plate boundaries. The conductive power was calculated as 0.72 TW and is not utilized to drive hydothermal fluid flow. Our estimate of the likely hydrothermal power (Supplementary Fig.\u0026nbsp;1d, Supplementary File S1) is impaired by the absence of knowledge whether the entire lower crust or only parts are cooled by hydrothermal ventilation. We infer that 80\u0026ndash;100% (60\u0026ndash;100% for thicker VA) of hydrothermal cooling is a plausible range for the depth extent of hydrothermal circulation with our favorable estimate of 90% (80% for VA). Our estimate of the global hydrothermal power does not include heat from extrusives that is released in event plumes with only minimal chemical exchange (0.33 TW). Heat stored in 300\u0026deg;C hot crust remains in the crust and is not hydrothermally removed (0.48 TW). The global on-axis hydrothermal power estimated this way is 2.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 TW.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis of vent fluid compositions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn its current version 3.0 MARHYS database contains 4221 entries of fluid samples, 1458 hydrothermal vent fluid end member compositions and 314 seawater samples. The hydrothermal fluid and end member data originate from more than 881 individual vents in more than 330 \u0026ldquo;vent sites\u0026rdquo; (\u0026ldquo;vent sites\u0026rdquo; may be distingt discharge sites within \u0026ldquo;vent areas\u0026rdquo;) from 142 \u0026ldquo;vent areas\u0026rdquo;. For the definition of these terms the reader is conferred to Diehl and Bach \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. According to an extrapolation of the relationship between spreading rate and vent field incidence along well explored parts of MOR and BASC \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e, we expect about 1300 vent areas in these setting, with another 130 vent areas estimated to be situated along VA. With 142 vent areas embodied in the database, 10% of the vent areas expected to be found in the modern oceans are represented, which is a robust basis for upscaling to calculate global fluxes. This representation enables us to quantify the amount and uncertainties of hydrothermal fluid and element-fluxes for different geological settings and substrate types.\u003c/p\u003e\n\u003cp\u003eWe analysed the metadata in MARHYS database (\u0026ldquo;geologic setting\u0026rdquo;, \u0026ldquo;rock type primary\u0026rdquo;, \u0026ldquo;rock type secondary\u0026rdquo;) and grouped vent fluids into eight classes that are either defined by their host-rock types, and/or their geologic setting, or by chemical signature as reported by vent fluid chemists. The first fluid type we define is called \u0026ldquo;mid-ocean ridge basalthosted\u0026rdquo; (\u0026rdquo;MORB-hosted\u0026rdquo;). This fluid type comprises all fluids venting in areas for which only basaltic substrate is reported in the database (\u0026ldquo;rock type primary\u0026rdquo; \u0026amp; \u0026ldquo;rock type secondary\u0026rdquo;). This group resembles the archetype hydrothermal fluid that had been considered to account for all hydrothermal cooling in previous flux estimates \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. The \u0026ldquo;sediment-hosted\u0026rdquo; group contains fluids that are hosted in sediments (\u0026ldquo;rock type primary\u0026rdquo;=\u0026rdquo;sediment\u0026rdquo;). The third group is \u0026ldquo;sediment-influenced\u0026rdquo;; it entails fluids venting from basalt, but the fluids are reported in publications of chemical vent fluid data to be influenced by sediments in the subseafloor. For this group we scanned existing literature for reports of sediment influence on hydrothermal systems that are hosted in igneous substrate. This search revealed the Endeavour Vent Field\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e \u0026amp; Loki\u0026rsquo;s Castle\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e at MOR and Minami-Ensei\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e, Hatoma\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e, Iheya North\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e, Hakurei\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e \u0026amp; Sakai\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e at BASC to be of this kind. The fourth type is named \u0026ldquo;peridotitehosted\u0026rdquo; and comprises vent fluids venting in areas where peridotites occur as prevailing basement type. The fifth type is \u0026ldquo;peridotite-influenced\u0026rdquo; and (analogous to \u0026ldquo;sediment-influenced\u0026rdquo;) the fluids share chemical characterisics with the ones from group 4, although igneous crust has been recognized to dominate in the vent areas. It is assumed that peridotites (or other ultramafic rocks) are present in the root zones of these systems and influence their vent fluid compositions. This type of fluid is reported for the Kairei\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e, Nibelungen\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e, Pelagia\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e and Daxi\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e vent areas. The next three types (5, 6, and 7) are related to VA and BASC hydrothermal convection systems. The fifth type \u0026ldquo;arc-backarc mafic\u0026rdquo; represents all fluids from vents hosted in basement of basalt or basaltic-andesite composition. The sixth class \u0026ldquo;arc-backarc felsic\u0026rdquo; comprises fluids venting from andesitic to rhyoilitic basement in VA and BASC. The seventh group \u0026ldquo;arc-backarc acid-sulfate\u0026rdquo; includes all fluids that are reported to be heavily influenced by magmatic degassing. These fluids span a broad range of chemical properties, but were clearly classified as influenced by magma degassing in the original publications. Vent areas where this class of fluids vent are: Onsen Site\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e70\u003c/span\u003e\u003c/sup\u003e, North Su\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e71\u003c/span\u003e\u003c/sup\u003e, Kasuga Vent sites\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e, NW Rota-1\u003csup\u003e73\u003c/sup\u003e, NW Eifuku\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e73\u003c/span\u003e\u003c/sup\u003e, Nikko\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e73\u003c/span\u003e\u003c/sup\u003e, Volcano-1\u003csup\u003e73\u003c/sup\u003e, Brothers Upper Cone \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e74\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e, Brothers Lower Cone \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e74\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e, Macauley Cone \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e75\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e, West Mata\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e77\u003c/span\u003e\u003c/sup\u003e, Niua North\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e77\u003c/span\u003e\u003c/sup\u003e, and Kemp Caldera Cone\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e78\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eNote that for the sake of convenience in the following evaluation we will regularly use terms like sediment-associated or sediment-related: these terms encompass both sediment-hosted and sediment-influenced hydrothermal fluids. Likewise, other classes will occasionally be grouped in peridotite-related or arc-backarc-related fluids.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFiltering of fluid compositions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variability in the chemical compositions and thermophysical properties of hydrothermal fluids complicates the calculation of element fluxes along oceanic plate boundaries. This variability can be considered a result of five major processes in the reaction- and upflow-zones of hydrothermal circulation cells.\u003c/p\u003e\n\u003cp\u003eThe extent of fluid-rock interaction and the rock types present in the reaction- and upflow-zone produce different compositions of endmember fluids. Influx of magmatic volatiles (CO\u003csub\u003e2\u003c/sub\u003e, SO\u003csub\u003e2\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003eO, HCl) that are released by magmatic degassing may directly affect fluid compositions or influence the pathways of fluid-rock interaction.\u003c/p\u003e\n\u003cp\u003eIn the reaction zone or during upflow, fluids commonly undergo phase separation, which is typically followed by phase segregation. Chlorine concentrations in vent fluids\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e and salinities in fluid inclusion in hydrothermal precipitates\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e79\u003c/span\u003e\u003c/sup\u003e provide evidence for the common occurrence of phase separation and segregation. Elements that are primarily chloro-complexed in high-temperature hydrothermal fluids become enriched in the Cl-rich brine phase and are depleted in the Cl-poor vapor phase. Dissolved gases show the opposite partitioing behavior. Most element flux estimates use a Cl-normalized fluid composition (seawater chlorinity) and assume that the shifts in element contributions of vapors and brines cancel out each other, as ultimately all fluids reach the seafloor. Here we use fluid compositions \u0026ldquo;as is\u0026rdquo; to test if this hypothesis is actually supported by the extensive data from MARHYS database.\u003c/p\u003e\n\u003cp\u003eEntrainment of seawater occurs during upflow or outflow of hydrothermal fluids. Entrainment of cold seawater influences the thermal budget, due to lower-than-endmember temperatures, but in the same manner decreases/increases concentrations of chemical compounds if they behave conservatively during mixing. The concentration/energy flux ratio during the process of mixing will be maintained, but the fluid mass flux will consequently increase. For nonconservative compounds this assumption cannot be made and the computation of element fluxes based on fixed concentration/energy ratios is problematic.\u003c/p\u003e\n\u003cp\u003eConductive cooling/heating influences the thermal budget of hydrothermal fluids and concentration/energy flux ratios. As fluids conductively cool/heat they will redistribute thermal energy in the crust that is available for other fluids to heat/cool and compensate this effect. If globally thermal heating and cooling of fluids compensate each other, thermal conduction does not influence flux estimates but solely their uncertainties.\u003c/p\u003e\n\u003cp\u003eTo minimize the compositional and energetic variability due to thermal conduction we analyzed magnesium concentrations along with their temperatures for seawater derived-hydrothermal fluids (excluding acid-sulfate fluids) in the global dataset (Supplementary Fig.\u0026nbsp;2a-b). The relationship of these parameters reveals not only entrainment of seawater, but also conductive cooling/heating of rising hydrothermal fluids. Cooled/heated hydrothermal vent fluid samples would impose variability to the concentration/energy ratios. We applied a filter procedure to minimize the effects of conductive cooling/heating by relating the chemical dilution due to Mg concentration, to the expected temperature of the diluted fluid. We assumed that the temperature of the zero-Mg endmember is determined by the position of the two-phase curve of seawater in the pressure-temperature plane (calculated after \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e80\u003c/span\u003e\u003c/sup\u003e) at depth and the temperature change is solely determined by mixing of hot hydrothermal fluid and cold seawater. To address the entrainment of cold seawater we analyzed the distribution of Mg concentrations and temperatures in the dataset. Both parameter show a bimodal distribution, suggesting that two groups of hydrothermal fluids are responsible for the majority of the global hydrothermal fluid flow at plate boundaries (Supplementary Fig.\u0026nbsp;2c-d). The first group is nearly pure endmember fluids with temperatures\u0026thinsp;\u0026gt;\u0026thinsp;\u0026gt;\u0026thinsp;150\u0026deg;C and Mg concentrations of less than ~\u0026thinsp;10mmol kg\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. These samples represent hydrothermal fluids from focused vents where fluids issue vigorously. The second group is moderate temperature-fluids\u0026thinsp;\u0026lt;\u0026thinsp;50\u0026deg;C with Mg concentrations of \u0026gt;\u0026thinsp;40 mmol kg\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e that mostly represent highly diluted shimmering waters. Few samples fall in between these two groups, which suggests that these intermediately diluted fluids can be neglected in the calculation of hydrothermal element fluxes. We applied a lowtemperature cut-off (Supplementary Fig.\u0026nbsp;2b) and calculated element fluxes with hightemperature focused hydrothermal fluids only. Excerpts of MARHYS database that contain the individual fluid compositions used to derive the median compositions for the eight individual fluid classes (after application of the Mg-T filter) are given in Supplementary File S2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConfiguration of oceanic plate boundaries and rock types\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo determine the distribution of rock types along the different plate boundaries, we considered reports in publications and used global datasets of sediment thickness and lithospheric age \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e81\u003c/span\u003e\u003c/sup\u003e. We combined a dataset of global lithospheric ages of MOR and BASC and the global oceanic sediment thickness to deduce the fraction of sedimented ridge axes. We investigated the globally cumulated surface area (of 0\u0026ndash;1 Ma crust) with regards to sediment thickness (Supplementary Fig.\u0026nbsp;3a). 82% of the surface area along MOR and BASC is covered by less than 100 m of sediments, with 98% of the on-axis surface area (0\u0026ndash;1 Ma) covered by less than 300 m of sediment. We have developed three gaussian functions that relate the probability of occurrence of sediment-free, sediment-influenced and sediment-hosted hydrothermal vents areas to the (large scale) onaxis sediment thickness (Supplementary Fig.\u0026nbsp;3b, Supplementary File S3). These probability functions reflect that sediments are less permeable than igneous rocks and that for low (large scale) sediment thicknesses (\u0026lt;\u0026thinsp;250 m) the probability for sediment-free or sediment-influenced hydrothermal systems is higher than for sedimenthosted systems. This low probability of sediment-hosted systems is reflected by the fact that, if the sediment coverage is lower than the average roughness of volcanic ridges, these ridges will stick out of the sediment cover and provide likely pathways for hydrothermal fluids instead of circulating through impermeable sediments. Using these probability functions results in our estimate of 90% of hydrothermal systems being sediment-free, 7% being sediment-influenced and 3% being sediment-hosted (area-wise and power-wise).\u003c/p\u003e\n\u003cp\u003eAfter we deduced the share of sediment-related hydrothermal fluids we estimated the relative proportions of different substrate types for non-sedimented MOR. For fast to ultra-fast MOR we assume all hydrothermal systems to be basalt-hosted. For slow-ultraslow MOR we assume that 50% of hydrothermal systems is hosted in basalt, whereas 40% are hosted in peridotite. The remaining 10% of vent systems along slow-ultraslow MOR is assumed to be basalt-hosted, but influenced by peridotite in the reaction zone. This partitioning is consistent with surveys of the ultraslow spreading southwest Indian ridge after Cannat, et al. \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e82\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFor hydrothermal fluxes in convergent margin settings, we did not distinguish between BASC and VA, but instead grouped vents from both settings according to basement compositions and intensity of magmatic degassing. Most of the vent sites in these settings are hosted in basement with a pronounced geochemical arc-affinity, although BASC show varying contributions of hydrous, slab-derived or decompressional mantle melts \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e83\u003c/span\u003e\u003c/sup\u003e. Arc affinities are common in BASC, and a prominent example are volcanic \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e and hydrothermal \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e70\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e71\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e85\u003c/span\u003e\u003c/sup\u003e systems associated with the South Eastern Rift of the Manus basin. In terms of the relative contributions of the three categories that were discerned we assumed that,50% of hydrothermal venting is from mafic crust (basalt-basaltic andesite), 40% from felsic rocks (andesite-rhyolite) and 10% is of the acid-sulfate type (magmatic degassing dominated, irrespective of rock type). This partitioning is based on reports of 70% of arc hydrothermal fluids to represent acid-sulfate venting \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. This estimate is based on surveys of plume properties along the Mariana arc \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e86\u003c/span\u003e\u003c/sup\u003e and Tonga-Kermadec arc \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e87\u003c/span\u003e\u003c/sup\u003e. The global hydrothermal power of acid-sulfate fluids is lower than expected from their vent field incidence considering that 70% of vent sites in arcs have been suggested to be of this type. This is due to the lower venting temperatures of acid-sulfate fluids and the corresponding low enthalpy calculated from the median temperature (345 kJ kg\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, cf. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eArcs show a bimodal distribution of basement rocks that are either mafic or more felsic in nature. In arcs we find a bimodal distribution of differentiated rocks being either mafic in origin or rather felsic. For the Kermadec and Tonga arc 11 out of 30 volcanoes are identified to be predominantly felsic in composition \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e88\u003c/span\u003e\u003c/sup\u003e, but some volcanoes are mentioned to be mafic stratovolcanoes that host felsic calderas. In the South Kermadec arc at least 11 edifices are reported to be of this type \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e89\u003c/span\u003e\u003c/sup\u003e. This shows that it is hard to estimate the occurrence of these rock types on a global scale. We analyzed the PETDB (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ewww.earthchem.org/petdb\u003c/span\u003e\u003c/span\u003e; downloaded on 15th, March 2024, using the following parameters: Tectonic setting\u0026thinsp;=\u0026thinsp;Volcanic_Arc, Rock Types\u0026thinsp;=\u0026thinsp;Igneous_Rocks) and counted samples according to their rock names (Supplementary File S4). Rocks named \u0026ldquo;basalt, basaltic andesite, gabbro, picrite or trachybasalt\u0026rdquo; were counted as \u0026ldquo;mafic\u0026rdquo; and rocks named \u0026ldquo;andesite, dacite, rhyodacite or rhyolite\u0026ldquo; were counted as \u0026ldquo;felsic\u0026rdquo;. Additionally, we checked for the silica content of samples named \u0026ldquo;tephra\u0026rdquo; and classified samples below or above 56 wt.% SiO\u003csub\u003e2\u003c/sub\u003e, the boundary between basaltic andesite and andesite \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e90\u003c/span\u003e\u003c/sup\u003e, which divides our classification into mafic and felsic rocks. Of 3267 rock samples considered, 1913 (59%) have mafic and 1354 (41%) have felsic compositions. This provides a first approximation for the occurrence of mafic to felsic rocks in volcanic arcs which occur in relative proportions between 2:1 and 1:1.\u003c/p\u003e\n\u003cp\u003eAfter considering the partitioning of sedimented and non-sedimented hydrothermal circulation and the distribution of rock types among the plate boundaries, we infer the hydrothermal power to partition into 50% MOR basalt-hosted, 15% MOR peridotite-related, 10% sediment-related and 25% arc- and backarc-related cooling (Supplementary Fig.\u0026nbsp;4).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCalculation of fluid and element fluxes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe calculated global fluid mass fluxes by estimating the global hydrothermal power and involving the energy content of hydrothermal fluids. These mass fluxes were then combined with the composition of hydrothermal fluids to compute element fluxes \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e91\u003c/span\u003e\u003c/sup\u003e. We calculated the fluid mass flux (M\u003csub\u003ehyd\u003c/sub\u003e) according to Eq.\u0026nbsp;1 using Q\u003csub\u003eHyd\u003c/sub\u003e,the global hydrothermal power, and \u0026Delta;H, the difference between specific enthalpies of seawater and the hydrothermal fluid. Associated hydrothermal element fluxes were calculated by Eq.\u0026nbsp;2, where c\u003csub\u003eSW\u003c/sub\u003e and c\u003csub\u003eHF\u003c/sub\u003e are the concentrations of elements in seawater and hydrothermal fluids, and H\u003csub\u003eHF\u003c/sub\u003e and H\u003csub\u003eSW\u003c/sub\u003e are the specific enthalpies of the respective fluids. The fluxes were calculated for each class of venting, and the different contributions were added up to derive global fluxes (Eq.\u0026nbsp;3\u0026ndash;4).\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\:Eq.1\\:\\:\\:\\:\\:\\:{M}_{hyd}=\\frac{{Q}_{Hyd}}{{\\varDelta\\:}_{H}}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e$$\\:Eq.2\\:\\:\\:\\:\\:\\:{F}_{El}=\\frac{{\\varDelta\\:}_{C}}{{\\varDelta\\:}_{H}}*{Q}_{Hyd}=\\frac{{c}_{Hf}-{c}_{SW}}{{H}_{Hf}-{H}_{SW}}*{Q}_{Hyd}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e$$\\:Eq.3\\:\\:\\:\\:\\:{M}_{hyd}={\\sum\\:}_{i=1}^{n}(\\frac{{Q}_{Hyd,i}}{{\\varDelta\\:}_{H,i}})$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e$$\\:Eq.4\\:\\:\\:\\:\\:\\:{F}_{El}={\\sum\\:}_{i=1}^{n}(\\frac{{\\varDelta\\:}_{C,i}}{{\\varDelta\\:}_{H,i}}*{Q}_{Hyd,i})={\\sum\\:}_{i=1}^{n}(\\frac{{c}_{Hf,i}-{c}_{SW}}{{H}_{Hf,i}-{H}_{SW}}*{Q}_{Hyd,i})$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe specific enthalpies of the fluids were calculated as f(T,p,X\u003csub\u003eNaCl\u003c/sub\u003e) from the thermodynamic properties of pure water\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e92\u003c/span\u003e\u003c/sup\u003e and an empirical relationship that relates these properties to the properties of NaCl-H\u003csub\u003e2\u003c/sub\u003eO solutions \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003e. The most influencial term for this enthalpy calculation is temperature, as the most substantial parameter influencing the solutions specific enthalpy. Supplementary Fig.\u0026nbsp;5 shows the enthalpy differences to cold seawater for the fluid classes defined in this study.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgments\u003c/p\u003e\n\u003cp\u003eThis research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany\u0026rsquo;s Excellence Strategy \u0026nbsp;\u0026ndash; EXC-2077. We thank all scientist who published data of vent fluid chemistry that is incorporated in MARHYS database 3.0. Their work provides the basis for this article.\u003c/p\u003e\n\u003cp\u003eAuthor contributions\u003c/p\u003e\n\u003cp\u003eA.D. and W.B. aquired funding and designed the research. A.D. did all data compilation and analyses and wrote the manuscript draft.W.B. edited the manuscript and assisted in revisions led by A.D.\u003c/p\u003e\n\u003cp\u003eConflict of interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eMaterials and correspondence\u003c/p\u003e\n\u003cp\u003eInquiries about the manuscript and materials should be addressed to Alexander Diehl ([email protected]).\u003c/p\u003e\n\u003cp\u003eData availability\u003c/p\u003e\n\u003cp\u003eHydrothermal vent fluid data used in this study is available at the data center PANGAEA (https://www.pangaea.de/) under Creative Commons Attribution 4.0 International (https://doi.org/10.1594/PANGAEA.958978). All remaining methods and data are made available in the methods section and in the supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDavies JH, Davies DR (2010) Earth's surface heat flux. 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Geochim Cosmochim Acta 71:4902\u0026ndash;4919. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.gca.2007.05.026\u003c/span\u003e\u003cspan address=\"10.1016/j.gca.2007.05.026\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"9d4a0c05-b938-4145-8834-76d98ac809b3","identifier":"10.13039/501100001659","name":"Deutsche Forschungsgemeinschaft","awardNumber":" EXC-2077-The Ocean Floor - Earth’s Uncharted Interface – 390741603","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"MARUM - Zentrum für Marine Umweltwissenschaften","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"marine geology, hydrothermal venting, global element budgets, mid-ocean ridges, volcanic arcs","lastPublishedDoi":"10.21203/rs.3.rs-6352431/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6352431/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSeafloor hydrothermal venting is one of the major processes that regulate the composition of the ocean. With a fluid flux orders of magnitudes lower than circulation of mildly-tempered hydrothermal fluids in ridge-flanks, or the riverine runoff, the high temperature fluid flux at oceanic plate boundaries can supply element fluxes that exceed the ones in (c)old lithosphere or river waters. Despite our knowledge on the diversity of hydrothermal vent fluid compositions, estimates of the on-axis fluid and element fluxes were carried out with basalt‑hosted mid‑ocean ridge black-smoker-type fluids imposed to be responsible for the global hydrothermal cooling at ridge axes. In this study, we consider current knowledge on vent fluid diversity and estimate global on-axis element fluxes. Our investigation suggests the global fluid- and corresponding element-fluxes were grossly underestimated, due to ignorance of hydrothermal venting in volcanic arcs and omission of different substrate types associated to oceanic plate boundaries.\u003c/p\u003e","manuscriptTitle":"The global high-temperature on-axis hydrothermal fluid and element flux to the modern ocean","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-02 06:16:18","doi":"10.21203/rs.3.rs-6352431/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2c51c1aa-656a-4131-a423-3976ed33c8e6","owner":[],"postedDate":"April 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":46517907,"name":"Geochemistry"},{"id":46517908,"name":"Planetary Science"},{"id":46517909,"name":"Planetary Geology"},{"id":46517910,"name":"Geophysics"}],"tags":[],"updatedAt":"2025-04-02T06:16:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-02 06:16:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6352431","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6352431","identity":"rs-6352431","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}