Intensified global volcanism during Late Pleistocene glacial strength shift

Intensified global volcanism during Late Pleistocene glacial strength shift | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Intensified global volcanism during Late Pleistocene glacial strength shift Jack Longman, Thomas Gernon, Thea Hincks, Sina Panitz, Martin Palmer This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3954094/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Reduced ice volume during interglacials is thought to amplify volcanic activity because ice-mass removal depressurises magma chambers 1 . While this process has been detected on regional 2 and perhaps semi-global scales 3 , a lack of globally representative tephra production records leaves the global relationship between glacial-interglacial cycles and volcanism uncertain. Here, we interrogate this relationship by using a database of visible tephra layers in marine sediments 4 and applying statistical sampling techniques to develop a globally representative tephra production record spanning the past million years. We find that explosive volcanism intensified globally at about 420 to 400 thousand years ago (ka), coinciding with Marine Isotope Stage (MIS) 11 – the warmest interglacial of the past million years when sea level was approximately 10 m above present 5 , and Greenland was largely ice-free 6 . We propose that positive feedbacks between icesheet ablation and increased volcanic carbon dioxide (CO2) outgassing may explain this warmth, and in turn, the Mid-Brunhes transition which heralded warmer interglacials 7 . Concurrently, we observe a shift to more organised volcanic cycles, characterised by higher intensity peaks, mirroring eccentricity forcing seen in ice volume records. More pronounced ice-volcano feedbacks may explain the stronger interglacials of the past 400,000 years, a crucial period of hominin evolution 8 . Earth and environmental sciences/Climate sciences/Palaeoclimate Earth and environmental sciences/Ocean sciences/Marine chemistry Earth and environmental sciences/Solid Earth sciences/Volcanology Figures Figure 1 Figure 2 Figure 3 Introduction Volcanic eruptions can impact global carbon and climate cycles, largely through the release of greenhouse gases, gaseous sulfate, and lava 9 . On millennial timescales, carbon dioxide (CO 2 ) release can enhance the greenhouse warming effect 10,11 , whilst sulfate release increases atmospheric albedo and reduces global temperatures 12 . On million-year timescales, this CO 2 release can lead to runaway global warming, with extended periods of volcanism linked to global carbon cycle perturbations, climate change and mass extinctions 13,14 . Conversely, the emplacement of large volumes of lava and tephra (i.e., the products of explosive volcanism) can enhance the silicate weathering feedback and biological pump in the oceans, eventually leading to carbon sequestration and global cooling 15 . However, volcanism is not only a forcing mechanism in the Earth climate system, with evidence suggesting that volcanic activity also responds to global climate change 1,16 . For example, studies in Iceland and other glaciated regions suggest removal of ice sheets after the last glacial maximum (LGM) increased volcanic activity 2,16 . This occurs either because of the direct unloading of glaciers on volcanoes 1 , or by sea level change forcing variations in magma production 17 and hydrothermal activity 18 . To investigate the apparent linkage between volcanism and glaciation on longer timescales through the Pleistocene (i.e., last 2.6 million years (Ma)), studies typically use records of tephra deposition in marine sediments 3 . Such work has demonstrated an apparent linkage between volcanism and glaciation, with higher levels of volcanism during interglacial periods 19–21 . Studies also suggest that volcanic activity may be linked to orbital (Milankovitch) cycles of climate forcing, further supporting a glaciation-related control 3 , and that tephra deposits exhibit periodicities matching the 23 kyr precession 22 , 40 kyr obliquity 23 , and 100 kyr eccentricity cycles 24 . Most long-term (million-year) studies have focussed on volcanism encompassing the Pacific Ocean, in particular the ‘Ring of Fire 3,23 , excluding many other locations susceptible to deglaciation-driven variation (e.g., Iceland). A further limitation is that these studies do not typically consider volumes of tephra; rather they extrapolate volcanic intensity from the absolute numbers of eruptions 23,24 , whereas the intensity of volcanic eruptions are best estimated from the thicknesses of the tephra layers they generate. However, this requires consideration of the distance between the location of a tephra layer from its volcanic source, which has not been considered in previous attempts to use marine sedimentary tephra layers for volcanic reconstruction 23,24 . Because the thickness of a tephra deposit is linked to the distance from eruption 25 , larger local eruptions are more likely to be better preserved in the sedimentary record than distal ones 25 . Thus, the bias in marine sedimentary tephra records towards local volcanic signals poses challenges for inferring global trends. Towards a global volcanic record Here we exploit VOLCORE, a database representing all visible tephra layers deposited in marine sedimentary cores recovered by the International Ocean Discovery Program and its predecessors 4 . From this database, we extract a measure of volcanic tephra intensity globally for the last million years , and investigate the relationship between explosive volcanism and climate over this interval. We employ Monte Carlo bootstrap resampling, a method which provides a weighting for each tephra layer in the database that is inversely proportional to the spatiotemporal sampling density. This record attempts to mitigate sampling and preservation biases, and biases relating to the proximity of the core to the volcano, thereby providing a more globally representative record of the intensity of explosive volcanism for the last million years. We find that the period from 1,000 to 500 ka has a corrected average tephra production rate of 0.2 ± 0.4 km 3 /yr (1SD) (Fig. 1), compared to an average production rate of 0.5 ± 0.6 km 3 /yr during 500 ka to present, and a modern production rate of ~1.14 km 3 /yr (ref. 26 ). While the 1,000-500 ka interval contains several discrete pulses of enhanced volcanism (most notably between 960-930 ka; marine isotope stage (MIS) 25), it is nevertheless apparent that the intensity of tephra deposition is lower and less variable, compared to the 500-0 ka interval. This observation is consistent with other reconstructions of the period 1000-500 ka, with low levels of tephra deposition found in a Pacific-wide synthesis of tephra deposition 23 , and from offshore California 19 . A major shift in tephra intensity between 500 and 400 ka Between 500 and 400 ka, we identify a notable shift in tephra intensity, with the appearance of more frequent and higher intensity pulses of tephra deposition (Fig. 1). We perform changepoint analysis (see Methods) to determine where statistically significant shifts in behaviour most likely occur (Fig. 2). The first changepoint, representing an increase in running mean of the dataset (that is, a positive changepoint), occurs at 420 ka followed by two further negative changepoints at 400 and 380 ka. Subsequently, there are no further significant shifts other than at 80 ka (where a brief peak in the modelled mean is observed), with the tephra intensity remaining relatively constant until approximately 18 ka (Fig. 2). The shift to overall greater tephra deposition between 500–400 ka may indicate a change in the forcings controlling volcanism. In the absence of contradictory evidence, and as geography and rift lengths have not changed during this interval, we assume that magma production rates driven by partial melting of the mantle have not changed considerably between 1,000-0 ka. It is therefore notable that the largest positive changepoint at 420 ka occurs during MIS11 (Fig. 2), the warmest interglacial of the past million years when sea level was around 10 m above present 5 and Greenland was largely ice-free 6 . It is feasible that this increase in volcanism was related to the abrupt melting of ice sheets in and near volcanically active terrains. While this hypothesis may suggest that glaciation plays a first-order role in determining volcanic intensity, it does not explain why the intensity of tephra deposition has more than doubled since 500 ka (Fig. 2). The observed shift in volcanism between 500–400 ka coincides with a major change in the intensity of interglacial periods after approximately 450 ka 7,27 . The subsequent interglacial periods, and especially from MIS 11 (424 – 374 ka) onwards, were warmer than those of the preceding 650,000 years, a shift termed the Mid-Brunhes Transition (MBT) 7 . The MBT is manifested in atmospheric CO 2 levels 28 , Antarctic temperatures 33 and deep ocean temperature records 29 , and represents a well-accepted step change in the global climate state 7 . The MBT is thought to have been driven by changes in orbital cyclicity 30 , and marks a switch in the relationship between interglacial and glacial strength 31 , with the arrival of high-amplitude 100 kyr variability. However, the MBT occurs during a period of low insolation and reduced eccentricity, and periods of similar orbital forcing occurred before and after the MBT, without eliciting the same system response 32 . This suggests the MBT is not a feature of orbital configuration change alone. Indeed, other additional mechanisms have been proposed, including changes in Antarctic ice sheet stability 33 and enhanced Southern Ocean carbon upwelling 34 . MIS 13 defines the first phase of the MBT 7 , in which a northward shift in the location of the intertropical convergence zone (ITCZ) drove higher levels of precipitation in the northern hemisphere 35 and an associated increase in atmospheric temperatures 35 . The first prominent peak in the tephra volume record after MIS25 occurs at about 510 ka, during MIS 13 (Fig. 1). The warmer climatic conditions of MIS 13 led to lower ice coverage in the northern polar regions, and when coupled with the high spatial concentration of volcanoes in northern high latitudes 36 , may have stimulated the first peak in tephra deposition (Fig. 1). The subsequent interglacial MIS 11 has the lowest ice volume and is the warmest within the last 1 Myrs 29 , with evidence suggesting Antarctic and Greenland ice sheets began to disintegrate 29 . This ablation of ice sheets is linked to warm conditions spanning the northern hemisphere 37 , and coincides with a pulse in volcanism, and the single large positive changepoint, in our record (Fig. 2). This shift may indicate positive feedbacks between ice sheet ablation and volcanism. The transition between MIS 12 and MIS 11 (also termed Termination 5) led to the greatest deglaciation in terms of land-ice mass of the Quaternary Period 37 , and thus the greatest differential in terms of the pressure exerted by ice sheets on volcanoes and their sub-volcanic magmatic systems. Recent finite element models demonstrate how glacial retreat can perturb the tectonic stress field sufficiently to influence magmatic intrusion regimes and thus physical volcanism 38 . The pulse of volcanism identified from the positive change point in our analysis (Fig. 2b) likely released large amounts of CO 2 , contributing to the warm conditions observed in the MIS 11 interglacial. Post MBT, global ice volumes 39 , atmospheric CO 2 (ref. 40 ), and surface temperatures 41 were consistently lower during interglacials (Fig. 1), especially in the southern hemisphere 41 . In contrast, in the northern hemisphere, perennial sea ice cover and permafrost became more common post MBT 42 , suggesting colder temperatures and indicating hemispheric asymmetry in ice volumes. Thus, the MBT led to considerable reorganisation of the Earth’s ice masses. We propose that this reorganisation paved the way for a new Earth system state in which explosive volcanism was more common than before. Notably, our data do not simply reveal increased volcanism during interglacials and vice versa. We can also identify occasional peaks in volcanism during glacial intervals, such as mid MIS10 and early MIS8 (Fig. 1). These peaks appear to represent isolated pulses of increased activity, more likely related to sea level change than ice sheet growth. It is well-established that when ice sheets grow, hydrostatic pressure on coastal volcanoes is reduced as sea level falls 43 . Thus, the focus of depressurisation shifts, moving from ice sheet removal causing volcanism in interglacials to sea level fall causing volcanism during glacials. Cyclicity in late Pleistocene explosive volcanism? Using wavelet analysis, we next investigate whether orbital forcing is evidenced in the volcanic record (Methods). We find evidence for a 100 kyr cyclicity in the tephra record and a less-well defined 41 kyr cyclicity (Fig. 3), which correspond to Earth’s orbital eccentricity and obliquity cycles, respectively. Notably, both cycles only appear after the change in tephra intensity at approximately 420 ka (Fig. 2). Prior to this, we find no clear evidence of orbital forcing (i.e., cycles greater than 30 kyr) in the volcanic record. Although present, we cannot interpret 100,000-year periodicity after ~200 ka as it falls within the cone of influence where edge effects are important 44 . To further investigate this relationship, we perform wavelet transform coherence (WTC) and cross wavelet transform (XWT) analysis between the tephra dataset and the canonical benthic d 18 O stack 39 (Methods; Fig. 3). These approaches detect a coherence between explosive volcanism and ice volume, both directly and in time-frequency space. The cross-correlation between the two variables is limited to the period between 500 ka to 200 ka, with a dominant cyclicity of 100 kyrs (Fig. 3) indicating that both glaciation and tephra deposition are forced by eccentricity since 500 kyr. The phase narrowing for the period 500–300 ka for both WTC and XWT indicates the two datasets vary in phase at an amplitude of 100 kyr, with changes in ice volume leading tephra deposition (Fig. 3). This relationship, where glaciation (and deglaciation) leads tephra deposition, has been documented before, with an approximately 13 kyr lead observed in the northwest Pacific tephra record 24 , 600 years in Icelandic volcanism 45 , and between 2-3 kyrs in southern Chile 16 . To interrogate the relationship between ice volume and tephra deposition intensity, we use the Lat 32 and LGM+1000 km datasets (see Methods), representing tephra layers at latitudes >32° (Lat 32), and any which are 1,000 km outside the estimated spatial extent of icesheets at the LGM (ref. 46 ; LGM + 1,000km), respectively. In general, we find that the trends are similar to the global dataset, with low tephra deposition for the period from 1000 to 500 ka, and high and variable tephra intensity thereafter (Extended Data Figure 1). This result supports the observed global increase in volcanic intensity concurrent with the MBT (Figs. 1-2), irrespective of site selection, thus supporting an influence of ice sheet volume variations in explaining this increase. However, only weak cyclicities are evident in both datasets (Extended Data Figs. 2 and 3) with no statistically significant cross-correlations or cross-wavelet similarities with the d 18 O stack (Extended Data Figs. 2 and 3). The weak cyclicities in our reduced datasets—which should be representative of volcanoes covered by ice sheets during glacial periods—compared to the global dataset, suggests their activity is insensitive to changes in ice volume. This in turn indicates that eruptions of volcanoes which drive the cyclicity evident in the global dataset are not located at the poles and therefore that low-latitude ice cap removal driven by orbital forcing is more important in controlling global tephra intensities than those at high latitudes. Indeed, many of the largest Andean volcanoes are located well north of 32°S, including those in the Cordillera Occidental and the Altiplano-Puna Volcanic Complex. Glacier extent in the Andes has fluctuated in time with global climate for the last 700 kyr 47 . Other locations where ice caps formed during glacial periods include across southeast Asia such as Borneo 48 , and in Central America 49 . These are some of the locations of most explosive volcanism at present 26,36 . Therefore, their ice coverage (or lack thereof) is expected to be more prominently reflected in changes in global tephra depositional intensity. Our analysis of global tephra intensity for the past million years indicates that at around 420 to 400 ka, the intensity of volcanism increased globally. This event corresponds to the warmest interglacial of the past million years, suggesting a link between volcanic degassing and ice sheet ablation. After MIS 11, interglacials remain warm, and peaks in tephra intensity remain high, with evidence for orbital controls on the timing of pulses of tephra production. This apparent orbital forcing suggests that ice sheet volume after 400 ka exerts a control on volcanism, but our analysis suggests this is unlikely to be associated with polar ice sheet growth and retreat. Rather, cyclicity of tephra production appears to be a result of ice cap growth and removal in the tropics and mid-latitudes. Our analyses suggest that feedbacks between global ice coverage and volcanic activity are important on global scales spanning the past 400,000 years, a period when glacial-interglacial shifts prompted hominin interbreeding episodes that shaped human evolution 8 . Declarations Author Contributions J.L. and T.M.G. conceived the research. Data analysis was completed by T.M.G. and T.K.H. with input from J.L. J.L., T.M.G, S.P. and M.R.P. interpreted the data. J.L. and T.M.G. wrote the paper, with all authors contributing to and approving its contents. Competing Interests The authors declare no competing interests. References Huybers, P. & Langmuir, C. Feedback between deglaciation, volcanism, and atmospheric CO 2 . Earth Planet Sci Lett 286, 479–491 (2009). Maclennan, J., Jull, M., McKenzie, D., Slater, L. & Grönvold, K. The link between volcanism and deglaciation in Iceland. Geochemistry, Geophysics, Geosystems 3, 1–25 (2002). Kutterolf, S., Schindlbeck, J. C., Jegen, M., Freundt, A. & Straub, S. M. Milankovitch frequencies in tephra records at volcanic arcs: The relation of kyr-scale cyclic variations in volcanism to global climate changes. Quat Sci Rev 204, 1–16 (2019). Mahony, S. H., Barnard, N. H., Sparks, R. S. J. & Rougier, J. C. VOLCORE, a global database of visible tephra layers sampled by ocean drilling. Sci Data 7, 330 (2020). Dutton, A. et al. Sea-level rise due to polar ice-sheet mass loss during past warm periods. 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Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years. Science (1979) 317, 793–796 (2007). Vaks, A. et al. Palaeoclimate evidence of vulnerable permafrost during times of low sea ice. Nature 577, 221–225 (2020). Crowley, J. W., Katz, R. F., Huybers, P., Langmuir, C. H. & Park, S.-H. Glacial cycles drive variations in the production of oceanic crust. Science (1979) 347, 1237–1240 (2015). Torrence, C., Compo, G. P., Torrence, C. & Compo, G. P. A Practical Guide to Wavelet Analysis. Bull Am Meteorol Soc 79, 61–78 (1998). Swindles, G. T. et al. Climatic control on Icelandic volcanic activity during the mid-Holocene. Geology 46, 47–50 (2018). Batchelor, C. L. et al. The configuration of Northern Hemisphere ice sheets through the Quaternary. Nat Commun 10, 3713 (2019). Rodbell, D. T. et al. 700,000 years of tropical Andean glaciation. Nature 607, 301–306 (2022). Hope, G. S. Glaciation of Malaysia and Indonesia, excluding New Guinea. in 211–214 (2004). doi:10.1016/S1571-0866(04)80125-8. Lachniet, M. S. & Vazquez-Selem, L. Last Glacial Maximum equilibrium line altitudes in the circum-Caribbean (Mexico, Guatemala, Costa Rica, Colombia, and Venezuela). Quaternary International 138–139, 129–144 (2005). Berger, A. & Loutre, M. F. Insolation values for the climate of the last 10 million years. Quat Sci Rev 10, 297–317 (1991). Ganopolski, A. Toward generalized Milankovitch theory (GMT). Climate of the Past 20, 151–185 (2024). Methods Data In our analysis, we utilize VOLCORE, a comprehensive database of visible tephra layers in Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), Integrated Ocean Drilling Program and International Ocean Discovery Program (IODP) marine sediment cores 4 . The database contains records of nearly 30,000 dated tephra layers and was developed through inspection of visual core description data available for all cores, and we refer the reader to the original publication 4 for more information on the dating of the tephra layers. This method has been shown to successfully identify ~75% of all visible tephra layers recorded in the original database 52 and thus represents the most complete record of global tephra layer frequency available to date. Synthesis and correction From the primary VOLCORE database, we extract all data relating to tephra layers dated between 1000 and 0 ka (thousand years before present). This yields a total of 7,182 layers for the past million years, compared to 430 layers in the only previous global synthesis 23 . Each tephra layer in the record has a thickness and an age, such that this data subset can be used to produce a record of absolute volumes of tephra deposited per thousand years at 1-kyr and 5-kyr resolution over the last million years, with a unit of m/kyr (Fig. 1). As discussed above, locations close to volcanic sites will contain more and thicker tephra layers than those located in the middle of ocean basins, far from volcanic centres. To mitigate this issue, we convert all raw thicknesses to values which consider location density via weighted bootstrap resampling 53 . This approach assigns weights ( W i ) to each tephra layer ( i ) which are inversely dependant on spatiotemporal density (Equation 1), as follows: where n is the total number of tephra layers in our subset. For each layer, z is the spatial location (taken to be a latitude and longitude of the core) and t the age (in years). Subscript i and j indicate the layer of interest and another layer in the dataset, and a and b are normalisation coefficients of 100 km and 500 years, respectively. The net result of this approach is that individual layers located in areas of low spatiotemporal density are weighted more highly than tephra layers in areas of high spatiotemporal density. This weighted, binned record is what we primarily interpret, and we consider it representative of changing tephra deposition intensity (Fig. 1). As this primary dataset considers locations in all oceans except the Arctic, with each layer weighted by relative data density, we consider it to be a global record (Supplementary Data 1). To convert these data into a more meaningful measure, we also present weighted tephra deposition normalised to the average value for the most recent 12,000 years (which we take to represent Holocene tephra deposition – 1.14 km 3 (ref. 26 )). To further investigate the role of glaciation as a control of explosive volcanism, we filter our dataset into two further subsets, ensuring most tephra layers sourced from glacier-covered volcanoes during the study period are considered. The first subset only includes layers located at >32° (hereafter referred to as “Lat 32”; Supplementary Figure 2). North and south of 32° includes all regions previously shown to either have evidence for glacial unloading and eruption (e.g. Iceland and Alaska), or cyclicity in tephra records (e.g. California and Japan). The second subset comprises only samples which would have been covered by ice at the end of the last glacial maximum (c. 23 ka), with ice coverage taken from ref. 46 . As ice distribution in the past is inherently uncertain, we extend the ice by 1000 km to ensure all volcanoes which may have been covered by ice are included (hereafter referred to as “LGM + 1000km”). Statistical Analysis To determine statistically significant changes in our record, we employ changepoint modelling. This approach identifies when abrupt changes occur in a dataset, using Monte Carlo statistics to create many simulated versions of the dataset based on the range of datapoints 54 which are used to derive probability distributions on the number and locations of changepoints (Fig. 2). We investigate cyclicity in the record using a wavelet analysis. Specifically, we identify non-stationary cyclicity using continuous Morlet wavelet transform analysis 44 , performed on the 1000-year binned datasets. To further investigate the interaction between ice coverage and tephra deposition we perform cross wavelet analysis and wavelet coherence analysis 55 , on the weighted tephra datasets and the classic stacked benthic δ 18 O record 39 . For this, both time series are considered on the same timescale of 1000-year intervals, via Gaussian interpolation (3000-year window). All cyclicity analysis was complete during the cross wavelet and wavelet coherence toolbox in MATLAB. Methods References 52. Mahony, S. H., Sparks, R. S. J. & Barnard, N. H. Quantifying uncertainties in marine volcanic ash layer records from ocean drilling cores. Mar Geol 357, 218–224 (2014). 53. Keller, C. B. & Schoene, B. Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5 Gyr ago. Nature 485, 490–493 (2012). 54. Gallagher, K. et al. Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models. Earth Planet Sci Lett 311, 182–194 (2011). 55. Grinsted, A., Moore, J. C. & Jevrejeva, S. Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Process Geophys 11, 561–566 (2004). Supplementary Information Supplementary Information is not available with this version Additional Declarations There is NO Competing Interest. 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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-3954094","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":273104866,"identity":"9a3b05f7-6341-4549-9b44-cd4b004d642c","order_by":0,"name":"Jack Longman","email":"data:image/png;base64,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","orcid":"","institution":"Northumbria University","correspondingAuthor":true,"prefix":"","firstName":"Jack","middleName":"","lastName":"Longman","suffix":""},{"id":273104867,"identity":"723ea572-2ce6-4ce3-8ea6-da98d332e5ed","order_by":1,"name":"Thomas Gernon","email":"","orcid":"https://orcid.org/0000-0002-7717-2092","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"Gernon","suffix":""},{"id":273104868,"identity":"e63e79d4-678c-49cd-a74c-d75b8f95bfa4","order_by":2,"name":"Thea Hincks","email":"","orcid":"https://orcid.org/0000-0003-4537-6194","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Thea","middleName":"","lastName":"Hincks","suffix":""},{"id":273104869,"identity":"f24af0f9-2e30-4124-8ff0-f05d22558e14","order_by":3,"name":"Sina Panitz","email":"","orcid":"","institution":"Teesside University","correspondingAuthor":false,"prefix":"","firstName":"Sina","middleName":"","lastName":"Panitz","suffix":""},{"id":273104870,"identity":"78ed4c12-f377-4d34-b0dd-749dc3f0e0b9","order_by":4,"name":"Martin Palmer","email":"","orcid":"https://orcid.org/0000-0002-3020-0914","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Martin","middleName":"","lastName":"Palmer","suffix":""}],"badges":[],"createdAt":"2024-02-13 17:50:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3954094/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3954094/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52287402,"identity":"1cb79a0f-ae5c-40ac-86ec-d036f5e4ea9a","added_by":"auto","created_at":"2024-03-08 15:56:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":199616,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of weighted global tephra record to paleoclimate records for the past million years.\u003c/strong\u003e (a) Reconstructed values for insolation50, (b) atmospheric CO2 (ref.40); (c) corrected temperature anomaly41, and (d) benthic d18O stack39. (e) Weighted global tephra deposition record (this work), with 1,000-year bin in blue and 5,000-year bin in black. Also highlighted in blue rectangles and denoted by numbers are marine isotope stages, and the timings of the Mid Pleistocene Transition and Mid-Brunhes Event are highlighted with arrows (see text for details).\u0026nbsp;\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-3954094/v1/df3d3f3419de1be1e38f4a1c.png"},{"id":52287406,"identity":"42976b49-d8c5-47d1-9791-2e8b4822f4d6","added_by":"auto","created_at":"2024-03-08 15:56:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":297380,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStatistical analysis of the weighted global tephra deposition dataset. \u003c/strong\u003e(a) Results of wavelet analysis, with amplitude of the cyclicity in thousand years; warm colours signify periodicity. Dashed lines indicate where the orbital cyclicities of precession (P), obliquity (O) and eccentricity (E) would be expected. Colour indicates the magnitude of correlation between wavelet transform and the dataset, with black lines enclosing regions with \u0026gt;95% confidence. White shaded areas indicate the cone of influence where edge effects may become important. (b,c) Output of the changepoint modelling, with the raw data shown by black circles, the mean model by a blue line and the dashed red lines indicating the 5th and 95th percentiles of the models. Changepoint probability is indicated by the black line in (c), with positive changepoints highlighted in purple, and negative in orange. (d) Weighted global tephra deposition dataset, with Marine isotope stages, the Mid-Pleistocene Transition and Mid-Brunhes Event highlighted as in Figure 1.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-3954094/v1/ef7614326ffa79149355aa47.png"},{"id":52287403,"identity":"8fbdb053-8a79-4f1d-9ac6-a58850c149a0","added_by":"auto","created_at":"2024-03-08 15:56:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":656994,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of cyclicity between weighted global tephra dataset and benthic δ18O stack. \u003c/strong\u003e(a) and (b) show wavelet analysis of the weighted global tephra dataset and the benthic δ18O stack39,51, respectively. (c) Wavelet transform coherence (WTC) of the two datasets, demonstrating the cross-correlation of the two signals in frequency and time space (see Methods). (d) Cross wavelet transform (XWT) of the two datasets showing the interaction between the wavelet transform of the two datasets. \u0026nbsp;In a-c colour indicates the magnitude of correlation between wavelet transform and the dataset. In d, colour indicates the transformed magnitude of coherence between the datasets. In c and d, phase arrows indicate lead-lag between datasets, with only those significant at the 95th percentile highlighted in d. In all panels, dark black lines enclose regions with \u0026gt;95% confidence and white shaded areas indicate the cone of influence, where edge effects become important.\u0026nbsp;\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-3954094/v1/2c5380b0996c742eaedff5ba.png"},{"id":52288116,"identity":"6adb0f68-db05-474a-83c3-f2913108a6e9","added_by":"auto","created_at":"2024-03-08 16:04:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1820603,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3954094/v1/a2e9932e-9775-4439-aae1-5e0f5991483c.pdf"},{"id":52287404,"identity":"5d60ea9c-48ac-4aff-904b-954749e653cd","added_by":"auto","created_at":"2024-03-08 15:56:10","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1486755,"visible":true,"origin":"","legend":"Extended Data file","description":"","filename":"Longman1MyrTephra2023SIVFinal.docx","url":"https://assets-eu.researchsquare.com/files/rs-3954094/v1/063a46f39391a409af7d752d.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Intensified global volcanism during Late Pleistocene glacial strength shift","fulltext":[{"header":"Introduction","content":"\u003cp\u003eVolcanic eruptions can impact global carbon and climate cycles, largely through the release of greenhouse gases, gaseous sulfate, and lava\u003csup\u003e9\u003c/sup\u003e. On millennial timescales, carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) release can enhance the greenhouse warming effect\u003csup\u003e10,11\u003c/sup\u003e, whilst sulfate release increases atmospheric albedo and reduces global temperatures\u003csup\u003e12\u003c/sup\u003e. \u0026nbsp; On million-year timescales, this CO\u003csub\u003e2\u003c/sub\u003e release can lead to runaway global warming, with extended periods of volcanism linked to global carbon cycle perturbations, climate change and mass extinctions\u003csup\u003e13,14\u003c/sup\u003e. Conversely, the emplacement of large volumes of lava and tephra (i.e., the products of explosive volcanism) can enhance the silicate weathering feedback and biological pump in the oceans, eventually leading to carbon sequestration and global cooling\u003csup\u003e15\u003c/sup\u003e. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHowever, volcanism is not only a forcing mechanism in the Earth climate system, with evidence suggesting that volcanic activity also responds to global climate change\u003csup\u003e1,16\u003c/sup\u003e. For example, studies in Iceland and other glaciated regions suggest removal of ice sheets after the last glacial maximum (LGM) increased volcanic activity\u003csup\u003e2,16\u003c/sup\u003e. This occurs either because of the direct unloading of glaciers on volcanoes\u003csup\u003e1\u003c/sup\u003e, or by sea level change forcing variations in magma production\u003csup\u003e17\u003c/sup\u003e and hydrothermal activity\u003csup\u003e18\u003c/sup\u003e. \u0026nbsp;To investigate the apparent linkage between volcanism and glaciation on longer timescales through the Pleistocene (i.e., last 2.6 million years (Ma)), studies typically use records of tephra deposition in marine sediments\u003csup\u003e3\u003c/sup\u003e. Such work has demonstrated an apparent linkage between volcanism and glaciation, with higher levels of volcanism during interglacial periods\u003csup\u003e19–21\u003c/sup\u003e. Studies also suggest that volcanic activity may be linked to orbital (Milankovitch) cycles of climate forcing, further supporting a glaciation-related control\u003csup\u003e3\u003c/sup\u003e, and that tephra deposits exhibit periodicities matching the 23 kyr precession\u003csup\u003e22\u003c/sup\u003e, 40 kyr obliquity\u003csup\u003e23\u003c/sup\u003e, and 100 kyr eccentricity cycles\u003csup\u003e24\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMost long-term (million-year) studies have focussed on volcanism encompassing the Pacific Ocean, in particular the ‘Ring of Fire\u003csup\u003e3,23\u003c/sup\u003e, excluding many other locations susceptible to deglaciation-driven variation (e.g., Iceland). A further limitation is that these studies do not typically consider volumes of tephra; rather they extrapolate volcanic intensity from the absolute numbers of eruptions\u003csup\u003e23,24\u003c/sup\u003e, whereas the intensity of volcanic eruptions are best estimated from the thicknesses of the tephra layers they generate. However, this requires consideration of the distance between the location of a tephra layer from its volcanic source, which has not been considered in previous attempts to use marine sedimentary tephra layers for volcanic reconstruction\u003csup\u003e23,24\u003c/sup\u003e. Because the thickness of a tephra deposit is linked to the distance from eruption\u003csup\u003e25\u003c/sup\u003e, larger local eruptions are more likely to be better preserved in the sedimentary record than distal ones\u003csup\u003e25\u003c/sup\u003e. Thus, the bias in marine sedimentary tephra records towards local volcanic signals poses challenges for inferring global trends.\u003cs\u003e\u0026nbsp;\u003c/s\u003e\u003c/p\u003e\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"},{"header":"Towards a global volcanic record","content":"\u003cp\u003eHere we exploit VOLCORE, a database representing all visible tephra layers deposited in marine sedimentary cores recovered by the International Ocean Discovery Program and its predecessors\u003csup\u003e4\u003c/sup\u003e. From this database, we extract a measure\u0026nbsp;of volcanic tephra intensity globally for the last million years\u003cs\u003e,\u003c/s\u003e and investigate the relationship between explosive volcanism and climate over this interval. We employ Monte Carlo bootstrap resampling, a method which provides a weighting for each tephra layer in the database that is inversely proportional to the spatiotemporal sampling density. This record attempts to mitigate sampling and preservation biases, and biases relating to the proximity of the core to the volcano, thereby providing a more globally representative record of the intensity of explosive volcanism for the last million years.\u003c/p\u003e\u003cp\u003eWe find that the period from 1,000 to 500 ka has a corrected average tephra production rate of 0.2 ± 0.4 km\u003csup\u003e3\u003c/sup\u003e/yr (1SD) (Fig. 1), compared to an average production rate of 0.5\u0026nbsp;± 0.6\u0026nbsp;km\u003csup\u003e3\u003c/sup\u003e/yr during 500 ka to present, and a modern production rate of ~1.14 km\u003csup\u003e3\u003c/sup\u003e/yr (ref.\u003csup\u003e26\u003c/sup\u003e). While the 1,000-500 ka interval contains several discrete pulses of enhanced volcanism (most notably between 960-930 ka; marine isotope stage (MIS) 25), it is nevertheless apparent that the intensity of tephra deposition is lower and less variable, compared to the 500-0 ka interval. This observation is consistent with other reconstructions of the period 1000-500 ka, with low levels of tephra deposition found in a Pacific-wide synthesis of tephra deposition\u003csup\u003e23\u003c/sup\u003e, and from offshore California\u003csup\u003e19\u003c/sup\u003e.\u003c/p\u003e"},{"header":"A major shift in tephra intensity between 500 and 400 ka ","content":"\u003cp\u003eBetween 500 and 400 ka, we identify a notable shift in tephra intensity, with the appearance of more frequent and higher intensity pulses of tephra deposition (Fig. 1). We perform changepoint analysis (see Methods) to determine where statistically significant shifts in behaviour most likely occur (Fig. 2). The first changepoint, representing an increase in running mean of the dataset (that is, a positive changepoint), occurs at 420 ka followed by two further negative changepoints at 400 and 380 ka. Subsequently, there are no further significant shifts other than at 80 ka (where a brief peak in the modelled mean is observed), with the tephra intensity remaining relatively constant until approximately 18 ka (Fig. 2).\u003c/p\u003e\u003cp\u003eThe shift to overall greater tephra deposition between 500–400 ka may indicate a change in the forcings controlling volcanism. In the absence of contradictory evidence, and as geography and rift lengths have not changed during this interval, we assume that magma production rates driven by partial melting of the mantle have not changed considerably between 1,000-0 ka. It is therefore notable that the largest positive changepoint at 420 ka occurs during MIS11 (Fig. 2), the warmest interglacial of the past million years when sea level was around 10 m above present\u003csup\u003e5\u003c/sup\u003e and Greenland was largely ice-free\u003csup\u003e6\u003c/sup\u003e.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eIt is feasible that this increase in volcanism was related to the abrupt melting of ice sheets in and near volcanically active terrains. \u0026nbsp;While this hypothesis may suggest that glaciation plays a first-order role in determining volcanic intensity, it does not explain why the intensity of tephra deposition has more than doubled since 500 ka (Fig. 2).\u0026nbsp;\u003c/p\u003e\u003cp\u003eThe observed shift in volcanism between 500–400 ka coincides with a major change in the intensity of interglacial periods after approximately 450 ka\u003csup\u003e7,27\u003c/sup\u003e. The subsequent interglacial periods, and especially from MIS 11 (424 – 374 ka) onwards, were warmer than those of the preceding 650,000 years, a shift termed the Mid-Brunhes Transition (MBT)\u003csup\u003e7\u003c/sup\u003e. The MBT is manifested in atmospheric CO\u003csub\u003e2\u003c/sub\u003e levels\u003csup\u003e28\u003c/sup\u003e, Antarctic temperatures\u003csup\u003e33\u003c/sup\u003e and deep ocean temperature records\u003csup\u003e29\u003c/sup\u003e, and represents a well-accepted step change in the global climate state\u003csup\u003e7\u003c/sup\u003e. The MBT is thought to have been driven by changes in orbital cyclicity\u003csup\u003e30\u003c/sup\u003e, and marks a switch in the relationship between interglacial and glacial strength\u003csup\u003e31\u003c/sup\u003e, with the arrival of high-amplitude 100 kyr variability. However, the MBT occurs during a period of low insolation and reduced eccentricity, and periods of similar orbital forcing occurred before and after the MBT, without eliciting the same system response\u003csup\u003e32\u003c/sup\u003e. This suggests the MBT is not a feature of orbital configuration change alone. Indeed, other additional mechanisms have been proposed, including changes in Antarctic ice sheet stability\u003csup\u003e33\u003c/sup\u003e and enhanced Southern Ocean carbon upwelling\u003csup\u003e34\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\u003cp\u003eMIS 13 defines the first phase of the MBT\u003csup\u003e7\u003c/sup\u003e, in which a northward shift in the location of the intertropical convergence zone (ITCZ) drove higher levels of precipitation in the northern hemisphere\u003csup\u003e35\u003c/sup\u003e and an associated increase in atmospheric temperatures\u003csup\u003e35\u003c/sup\u003e. The first prominent peak in the tephra volume record after MIS25 occurs at about 510 ka, during MIS 13 (Fig. 1). The warmer climatic conditions of MIS 13 led to lower ice coverage in the northern polar regions, and when coupled with the high spatial concentration of volcanoes in northern high latitudes\u003csup\u003e36\u003c/sup\u003e, may have stimulated the first peak in tephra deposition (Fig. 1).\u003c/p\u003e\u003cp\u003eThe subsequent interglacial MIS 11 has the lowest ice volume and is the warmest within the last 1 Myrs\u003csup\u003e29\u003c/sup\u003e, with evidence suggesting Antarctic and Greenland ice sheets began to disintegrate\u003csup\u003e29\u003c/sup\u003e. This ablation of ice sheets is linked to warm conditions spanning the northern hemisphere\u003csup\u003e37\u003c/sup\u003e, and coincides with a pulse in volcanism, and the single large positive changepoint, in our record (Fig. 2). This shift may indicate positive feedbacks between ice sheet ablation and volcanism. The transition between MIS 12 and MIS 11 (also termed Termination 5) led to the greatest deglaciation in terms of land-ice mass of the Quaternary Period\u003csup\u003e37\u003c/sup\u003e, and thus the greatest differential in terms of the pressure exerted by ice sheets on volcanoes and their sub-volcanic magmatic systems. Recent finite element models demonstrate how glacial retreat can perturb the tectonic stress field sufficiently to influence magmatic intrusion regimes\u003csup\u003e\u0026nbsp;\u003c/sup\u003eand thus physical volcanism\u003csup\u003e38\u003c/sup\u003e. The pulse of volcanism identified from the positive change point in our analysis (Fig. 2b) likely released large amounts of CO\u003csub\u003e2\u003c/sub\u003e, contributing to the warm conditions observed in the MIS 11 interglacial.\u0026nbsp;\u003c/p\u003e\u003cp\u003e\u0026nbsp;Post MBT, global ice volumes\u003csup\u003e39\u003c/sup\u003e, atmospheric CO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(ref.\u003csup\u003e40\u003c/sup\u003e), and surface temperatures\u003csup\u003e41\u003c/sup\u003e were consistently lower during interglacials (Fig. 1), especially in the southern hemisphere\u003csup\u003e41\u003c/sup\u003e. In contrast, in the northern hemisphere, perennial sea ice cover and permafrost became more common post MBT\u003csup\u003e42\u003c/sup\u003e, suggesting colder temperatures and indicating hemispheric asymmetry in ice volumes. Thus, the MBT led to considerable reorganisation of the Earth’s ice masses. We propose that this reorganisation paved the way for a new Earth system state in which explosive volcanism was more common than before.\u0026nbsp;\u003c/p\u003e\u003cp\u003eNotably, our data do not simply reveal increased volcanism during interglacials and vice versa. We can also identify occasional peaks in volcanism during glacial intervals, such as mid MIS10 and early MIS8 (Fig. 1). These peaks appear to represent isolated pulses of increased activity, more likely related to sea level change than ice sheet growth. It is well-established that when ice sheets grow, hydrostatic pressure on coastal volcanoes is reduced as sea level falls\u003csup\u003e43\u003c/sup\u003e. Thus, the focus of depressurisation shifts, moving from ice sheet removal causing volcanism in interglacials to sea level fall causing volcanism during glacials.\u003c/p\u003e"},{"header":"Cyclicity in late Pleistocene explosive volcanism?","content":"\u003cp\u003eUsing\u0026nbsp;wavelet analysis, we next investigate whether orbital forcing is evidenced in the volcanic record\u0026nbsp;(Methods). We find evidence for a 100 kyr cyclicity in the tephra record and a less-well defined 41 kyr cyclicity (Fig. 3), which correspond to Earth’s orbital eccentricity and obliquity cycles, respectively. Notably, both cycles only appear after the change in tephra intensity at approximately 420 ka (Fig. 2). Prior to this, we find no clear evidence of orbital forcing (i.e., cycles greater than 30 kyr) in the volcanic record. Although present, we cannot interpret 100,000-year periodicity after ~200 ka as it falls within the cone of influence where edge effects are important\u003csup\u003e44\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eTo further investigate this relationship, we perform wavelet transform coherence (WTC) and cross wavelet transform (XWT) analysis between the tephra dataset and the canonical benthic d\u003csup\u003e18\u003c/sup\u003eO stack\u003csup\u003e39\u003c/sup\u003e (Methods; Fig. 3). These approaches detect a coherence between explosive volcanism and ice volume, both directly and in time-frequency space. The cross-correlation between the two variables is limited to the period between 500 ka to 200 ka, with a dominant cyclicity of 100 kyrs (Fig. 3) indicating that both glaciation and tephra deposition are forced by eccentricity since 500 kyr. \u0026nbsp;The phase narrowing for the period 500–300 ka for both WTC and XWT indicates the two datasets vary in phase at an amplitude of 100 kyr, with changes in ice volume leading tephra deposition (Fig. 3). This relationship, where glaciation (and deglaciation) leads tephra deposition, has been documented before, with an approximately 13 kyr lead observed in the northwest Pacific tephra record\u003csup\u003e24\u003c/sup\u003e, 600 years in Icelandic volcanism\u003csup\u003e45\u003c/sup\u003e, and between 2-3 kyrs in southern Chile\u003csup\u003e16\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\u003cp\u003eTo interrogate the relationship between ice volume and tephra deposition intensity, we use the Lat 32 and LGM+1000 km datasets (see Methods), representing tephra layers at latitudes \u0026gt;32° (Lat 32), and any which are 1,000 km outside the estimated spatial extent of icesheets at the LGM (ref.\u003csup\u003e46\u003c/sup\u003e; LGM + 1,000km), respectively. In general, we find that the trends are similar to the global dataset, with low tephra deposition for the period from 1000 to 500 ka, and high and variable tephra intensity thereafter (Extended Data Figure 1). This result supports the observed global increase in volcanic intensity concurrent with the MBT (Figs. 1-2), irrespective of site selection, thus supporting an influence of ice sheet volume variations in explaining this increase. However, only weak cyclicities are evident in both datasets (Extended Data Figs. 2 and 3) with no statistically significant cross-correlations or cross-wavelet similarities with the\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO stack (Extended Data Figs. 2 and 3).\u0026nbsp;\u003c/p\u003e\u003cp\u003eThe weak cyclicities in our reduced datasets—which should be representative of volcanoes covered by ice sheets during glacial periods—compared to the global dataset, suggests their activity is insensitive to changes in ice volume. This in turn indicates that eruptions of volcanoes which drive the cyclicity evident in the global dataset are not located at the poles and therefore that low-latitude ice cap removal driven by orbital forcing is more important in controlling global tephra intensities than those at high latitudes. Indeed, many of the largest Andean volcanoes are located well north of 32°S, including those in the Cordillera Occidental and the Altiplano-Puna Volcanic Complex. Glacier extent in the Andes has fluctuated in time with global climate for the last 700 kyr\u003csup\u003e47\u003c/sup\u003e. Other locations where ice caps formed during glacial periods include across southeast Asia such as Borneo\u003csup\u003e48\u003c/sup\u003e, and in Central America\u003csup\u003e49\u003c/sup\u003e. \u0026nbsp;These are some of the locations of most explosive volcanism at present\u003csup\u003e26,36\u003c/sup\u003e. Therefore, their ice coverage (or lack thereof) is expected to be more prominently reflected in changes in global tephra depositional intensity.\u0026nbsp;\u003c/p\u003e\u003cp\u003eOur analysis of global tephra intensity for the past million years indicates that at around 420 to 400 ka, the intensity of volcanism increased globally. This event corresponds to the warmest interglacial of the past million years, suggesting a link between volcanic degassing and ice sheet ablation. After MIS 11, interglacials remain warm, and peaks in tephra intensity remain high, with evidence for orbital controls on the timing of pulses of tephra production. This apparent orbital forcing suggests that ice sheet volume after 400 ka exerts a control on volcanism, but our analysis suggests this is unlikely to be associated with polar ice sheet growth and retreat. Rather, cyclicity of tephra production appears to be a result of ice cap growth and removal in the tropics and mid-latitudes. Our analyses suggest that feedbacks between global ice coverage and volcanic activity are important on global scales spanning the past 400,000 years, a period when glacial-interglacial shifts prompted hominin interbreeding episodes that shaped human evolution\u003csup\u003e8\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ.L. and T.M.G. conceived the research. Data analysis was completed by T.M.G. and T.K.H. with input from J.L. J.L., T.M.G, S.P. and M.R.P. interpreted the data. J.L. and T.M.G. wrote the paper, with all authors contributing to and approving its contents.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHuybers, P. \u0026amp; Langmuir, C. 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Glacial cycles drive variations in the production of oceanic crust. Science (1979) 347, 1237\u0026ndash;1240 (2015).\u003c/li\u003e\n\u003cli\u003eTorrence, C., Compo, G. P., Torrence, C. \u0026amp; Compo, G. P. A Practical Guide to Wavelet Analysis. Bull Am Meteorol Soc 79, 61\u0026ndash;78 (1998).\u003c/li\u003e\n\u003cli\u003eSwindles, G. T. et al. Climatic control on Icelandic volcanic activity during the mid-Holocene. Geology 46, 47\u0026ndash;50 (2018).\u003c/li\u003e\n\u003cli\u003eBatchelor, C. L. et al. The configuration of Northern Hemisphere ice sheets through the Quaternary. Nat Commun 10, 3713 (2019).\u003c/li\u003e\n\u003cli\u003eRodbell, D. T. et al. 700,000 years of tropical Andean glaciation. Nature 607, 301\u0026ndash;306 (2022).\u003c/li\u003e\n\u003cli\u003eHope, G. S. Glaciation of Malaysia and Indonesia, excluding New Guinea. in 211\u0026ndash;214 (2004). doi:10.1016/S1571-0866(04)80125-8.\u003c/li\u003e\n\u003cli\u003eLachniet, M. S. \u0026amp; Vazquez-Selem, L. Last Glacial Maximum equilibrium line altitudes in the circum-Caribbean (Mexico, Guatemala, Costa Rica, Colombia, and Venezuela). Quaternary International 138\u0026ndash;139, 129\u0026ndash;144 (2005).\u003c/li\u003e\n\u003cli\u003eBerger, A. \u0026amp; Loutre, M. F. Insolation values for the climate of the last 10 million years. Quat Sci Rev 10, 297\u0026ndash;317 (1991).\u003c/li\u003e\n\u003cli\u003eGanopolski, A. Toward generalized Milankovitch theory (GMT). Climate of the Past 20, 151\u0026ndash;185 (2024).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Methods","content":"\u003ch2\u003eData\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eIn our analysis, we utilize VOLCORE, a comprehensive database of visible tephra layers in Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), Integrated Ocean Drilling Program and International Ocean Discovery Program (IODP) marine sediment cores\u003csup\u003e4\u003c/sup\u003e. The database contains records of nearly 30,000 dated tephra layers and was developed through inspection of visual core description data available for all cores, and we refer the reader to the original publication\u003csup\u003e4\u003c/sup\u003e for more information on the dating of the tephra layers. This method has been shown to successfully identify ~75% of all visible tephra layers recorded in the original database\u003csup\u003e52\u003c/sup\u003e and thus represents the most complete record of global tephra layer frequency available to date.\u003c/p\u003e\n\u003ch2\u003eSynthesis and correction\u003c/h2\u003e\n\u003cp\u003eFrom the primary VOLCORE database, we extract all data relating to tephra layers dated between 1000 and 0 ka (thousand years before present). This yields a total of 7,182 layers for the past million years, compared to 430 layers in the only previous global synthesis\u003csup\u003e23\u003c/sup\u003e. \u0026nbsp;Each tephra layer in the record has a thickness and an age, such that this data subset can be used to produce a record of absolute volumes of tephra deposited per thousand years at 1-kyr and 5-kyr resolution over the last million years, with a unit of m/kyr (Fig. 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAs discussed above, locations close to volcanic sites will contain more and thicker tephra layers than those located in the middle of ocean basins, far from volcanic centres. To mitigate this issue, we convert all raw thicknesses to values which consider location density via weighted bootstrap resampling\u003csup\u003e53\u003c/sup\u003e. This approach assigns weights (\u003cem\u003eW\u003csub\u003ei\u003c/sub\u003e\u003c/em\u003e) to each tephra layer (\u003cem\u003ei\u003c/em\u003e) which are inversely dependant on spatiotemporal density (Equation 1), as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"352\" height=\"74\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003en\u003c/em\u003e is the total number of tephra layers in our subset. For each layer, \u003cem\u003ez\u003c/em\u003e is the spatial location (taken to be a latitude and longitude of the core) and \u003cem\u003et\u003c/em\u003e the age (in years). Subscript \u003cem\u003ei\u003c/em\u003e and \u003cem\u003ej\u0026nbsp;\u003c/em\u003eindicate the layer of interest and another layer in the dataset, and \u003cem\u003ea\u0026nbsp;\u003c/em\u003eand \u003cem\u003eb\u0026nbsp;\u003c/em\u003eare normalisation coefficients of 100 km and 500 years, respectively. The net result of this approach is that individual layers located in areas of low spatiotemporal density are weighted more highly than tephra layers in areas of high spatiotemporal density. This weighted, binned record is what we primarily interpret, and we consider it representative of changing tephra deposition intensity (Fig. 1). As this primary dataset considers locations in all oceans except the Arctic, with each layer weighted by relative data density, we consider it to be a global record (Supplementary Data 1). To convert these data into a more meaningful measure, we also present weighted tephra deposition normalised to the average value for the most recent 12,000 years (which we take to represent Holocene tephra deposition \u0026ndash; 1.14 km\u003csup\u003e3\u003c/sup\u003e (ref.\u003csup\u003e26\u003c/sup\u003e)).\u003c/p\u003e\n\u003cp\u003eTo further investigate the role of glaciation as a control of explosive volcanism, we filter our dataset into two further subsets, ensuring most tephra layers sourced from glacier-covered volcanoes during the study period are considered. The first subset only includes layers located at \u0026gt;32\u0026deg; (hereafter referred to as \u0026ldquo;Lat 32\u0026rdquo;; Supplementary Figure 2). North and south of 32\u0026deg; includes all regions previously shown to either have evidence for glacial unloading and eruption (e.g. Iceland and Alaska), or cyclicity in tephra records (e.g. California and Japan). The second subset comprises only samples which would have been covered by ice at the end of the last glacial maximum (c. 23 ka), with ice coverage taken from ref.\u003csup\u003e46\u003c/sup\u003e. As ice distribution in the past is inherently uncertain, we extend the ice by 1000 km to ensure all volcanoes which may have been covered by ice are included (hereafter referred to as \u0026ldquo;LGM + 1000km\u0026rdquo;). \u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\n\u003cp\u003eTo determine statistically significant changes in our record, we employ changepoint modelling. This approach identifies when abrupt changes occur in a dataset, using Monte Carlo statistics to create many simulated versions of the dataset based on the range of datapoints\u003csup\u003e54\u003c/sup\u003e which are used to derive probability distributions on the number and locations of changepoints (Fig. 2). \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe investigate cyclicity in the record using a wavelet analysis. Specifically, we identify non-stationary cyclicity using continuous Morlet wavelet transform analysis\u003csup\u003e44\u003c/sup\u003e, performed on the 1000-year binned datasets. To further investigate the interaction between ice coverage and tephra deposition we perform cross wavelet analysis and wavelet coherence analysis\u003csup\u003e55\u003c/sup\u003e, on the weighted tephra datasets and the classic stacked benthic \u0026delta;\u003csup\u003e18\u003c/sup\u003eO record\u003csup\u003e39\u003c/sup\u003e. For this, both time series are considered on the same timescale of 1000-year intervals, via Gaussian interpolation (3000-year window). All cyclicity analysis was complete during the cross wavelet and wavelet coherence toolbox in MATLAB.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods References\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e52. \u0026nbsp; \u0026nbsp; \u0026nbsp; Mahony, S. H., Sparks, R. S. J. \u0026amp; Barnard, N. H. Quantifying uncertainties in marine volcanic ash layer records from ocean drilling cores. Mar Geol 357, 218\u0026ndash;224 (2014).\u003c/p\u003e\n\u003cp\u003e53. \u0026nbsp; \u0026nbsp; \u0026nbsp; Keller, C. B. \u0026amp; Schoene, B. Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5\u0026thinsp;Gyr ago. Nature 485, 490\u0026ndash;493 (2012).\u003c/p\u003e\n\u003cp\u003e54. \u0026nbsp; \u0026nbsp; \u0026nbsp; Gallagher, K. et al. Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models. Earth Planet Sci Lett 311, 182\u0026ndash;194 (2011).\u003c/p\u003e\n\u003cp\u003e55. \u0026nbsp; \u0026nbsp; \u0026nbsp; Grinsted, A., Moore, J. C. \u0026amp; Jevrejeva, S. Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Process Geophys 11, 561\u0026ndash;566 (2004).\u003c/p\u003e"},{"header":"Supplementary Information","content":"\u003cp\u003eSupplementary Information is not available with this version\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3954094/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3954094/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eReduced ice volume during interglacials is thought to amplify volcanic activity because ice-mass removal depressurises magma chambers\u003csup\u003e1\u003c/sup\u003e. While this process has been detected on regional\u003csup\u003e2\u003c/sup\u003e and perhaps semi-global scales\u003csup\u003e3\u003c/sup\u003e, a lack of globally representative tephra production records leaves the global relationship between glacial-interglacial cycles and volcanism uncertain. Here, we interrogate this relationship by using a database of visible tephra layers in marine sediments\u003csup\u003e4\u003c/sup\u003e and applying statistical sampling techniques to develop a globally representative tephra production record spanning the past million years. We find that explosive volcanism intensified globally at about 420 to 400 thousand years ago (ka), coinciding with Marine Isotope Stage (MIS) 11 – the warmest interglacial of the past million years when sea level was approximately 10 m above present\u003csup\u003e5\u003c/sup\u003e, and Greenland was largely ice-free\u003csup\u003e6\u003c/sup\u003e. We propose that positive feedbacks between icesheet ablation and increased volcanic carbon dioxide (CO2) outgassing may explain this warmth, and in turn, the Mid-Brunhes transition which heralded warmer interglacials\u003csup\u003e7\u003c/sup\u003e. Concurrently, we observe a shift to more organised volcanic cycles, characterised by higher intensity peaks, mirroring eccentricity forcing seen in ice volume records. More pronounced ice-volcano feedbacks may explain the stronger interglacials of the past 400,000 years, a crucial period of hominin evolution\u003csup\u003e8\u003c/sup\u003e.\u003c/p\u003e","manuscriptTitle":"Intensified global volcanism during Late Pleistocene glacial strength shift","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-08 15:56:05","doi":"10.21203/rs.3.rs-3954094/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"13c5581c-5581-4899-91c4-098a5363b144","owner":[],"postedDate":"March 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":28790746,"name":"Earth and environmental sciences/Climate sciences/Palaeoclimate"},{"id":28790747,"name":"Earth and environmental sciences/Ocean sciences/Marine chemistry"},{"id":28790748,"name":"Earth and environmental sciences/Solid Earth sciences/Volcanology"}],"tags":[],"updatedAt":"2024-03-08T15:56:05+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-08 15:56:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3954094","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3954094","identity":"rs-3954094","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}