Sub-precessional pacing of ice conditions and organic carbon burial in the Ross Sea, Antarctica, during the mid-Pliocene Warm Period

Sub-precessional pacing of ice conditions and organic carbon burial in the Ross Sea, Antarctica, during the mid-Pliocene Warm Period | 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 Article Sub-precessional pacing of ice conditions and organic carbon burial in the Ross Sea, Antarctica, during the mid-Pliocene Warm Period Isabela Sousa, Claude Hillaire-Marcel, Anne de Vernal, Simone Kasemann This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7511634/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 For over 200 ka during the mid-Pliocene Warm Period (mPWP), sustained high atmospheric pCO₂ (> 350 ppm) maintained global temperatures above pre-industrial levels. Nonetheless, as documented here, ice growth pulses occurred during this interval along the margin of the West Antarctic Ice Sheet, impacting the carbon cycle. These events resulted in high amplitude changes in the source and burial rate of organic carbon (Corg) in the Ross Sea. Warm intervals with seasonally open sea-ice conditions were recorded by thick, greenish, diatom-rich sediments containing relatively abundant marine Corg. Cold intervals, assigned to perennial ice cover pulses, were recorded by grayish, decimeter-thick layers with very low Corg content, likely relating to the erosion of sedimentary rocks on land. Although the obliquity forcing is evident in the sequence, the cold pulses occurred at a much higher frequency (~ 16 ka), not matched by any direct precession insolation control, thus involving the interference of complex glaciological, oceanic and atmospheric processes which warrant closer examination. Remarkably, even under the "warm Earth scenario" of the mPWP, these processes have sustained perennial ice cover pulses beyond the continental Ross Sea shelf limit. Earth and environmental sciences/Climate sciences/Palaeoceanography Earth and environmental sciences/Climate sciences/Cryospheric science Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Due to the similarities between the late Pliocene and the present, such as high pCO₂ levels 1 and land-ocean configurations 2 , investigating the carbon cycle during this interval may offer insights into the potential response of the biological carbon pump and carbon storage processes to the ongoing global warming trend. From this viewpoint, the organic carbon (Corg) fate at the margins of the large late Cenozoic ice sheets deserves attention as it has strongly varied between glacial and interglacial stages during the Quaternary 3 – 5 , but also during the late Pliocene 6 – 8 . These large-amplitude fluctuations in the carbon cycle and climate remain " not easily explained as direct consequences of the astronomical forcing ", as mentioned by Paillard (2017) 9 . The specific responses of northern and southern hemisphere ice fluctuations, as well as the relative roles of astronomical and CO 2 forcings 9 – 11 , thus require attention. During the mid-Pliocene Warm Period (mPWP), in particular, ice fluctuations over Greenland were likely driven by a ca. 40 ka obliquity forcing 8 . Naish et al. (2009) 12 suggested a similar orbital forcing for the Antarctica Ice Sheet during this interval, whereas Patterson et al. (2014) 14 suggest a transition toward a combined eccentricity and precession forcing. Later studies either suggested a " transient cyclicity, reproducing unique patterns of glacial cyclicity " 15 or a highly dynamic Antarctica Ice Sheet 16 , 17 with time scales of ice fluctuations of the order of several thousand years. Thus, the linkage between high-frequency 12 Pliocene Antarctica Ice Sheet fluctuations and orbital parameters remains unascertained during the mPWP, an interval marked by dampened fluctuations in the benthic d 18 O stack record 18 , 19 . Here, we aim to document the behaviour of the Western Antarctica Ice Sheet (WAIS) margin during the mPWP interval, before the WAIS expanded closer to its modern configuration during the Pleistocene 20 , with specific attention to its impacts on organic matter (OM) cycling. Our study is based on high-resolution analyses of a sedimentary record from the Hilary Canyon in the Ross Sea, Antarctica (Fig. 1 ). In this area, the Plio-Pleistocene interval has been characterized by a strong climate variability, with an orbital to suborbital pacing 12 , and a highly dynamic ice margin 17 . The Hilary Canyon serves as the primary conduit for Ross Sea Bottom Water, a key component of Antarctic Bottom Water (AABW) 21 . The study site (IODP Site U1524), drilled in 2018, offers a high-recovery Plio-Pleistocene record 22 . A first set of investigations of the ~ 3.1 to ~ 2.5 Ma interval at IODP Site U1524, by Patterson et al. (2024) illustrates a complex combination of orbital parameters governing sedimentation, as recorded in the ≥ 250 mm fraction related to ice-rafted debris. Our primary objective here is to examine specifically the OM properties (Corg, Corg/Ntot, δ 13 Corg), which contribute to documenting the Corg sources and flux variability between warm and cold intervals (Fig. 2 ). In a second step, we examine the potential astronomical forcing governing these parameters. Results The data supporting this study are archived in the PANGAEA database. The 90-m study interval is characterized by olive-green, diatomaceous-rich sediments 22 with interbedded gray beds of variable thickness (10 to 130 cm) as shown in Fig. 2 . The contact at the base of the gray beds is gradational, and the contact at the top is abrupt. The elemental analysis reveals that olive green sediments have a Corg content of 0.63 ± 0.08% (2s, sample standard deviation, n = 34), whereas the gray sediments average 0.22 ± 0.10% (2s, sample standard deviation, n = 24). The δ¹³Corg of the olive-green layers averages 25 ± 0.31‰ (2s, sample standard deviation, n = 34) and − 27.1 ± 1.21‰ (2s, sample standard deviation, n = 24) in the gray sediments. Corg/Ntot ratios of the olive-green sediments range from 9 to 11, whereas they range from 3 to 9 in the gray layers. All OM parameters (Corg, δ¹³Corg, and Corg/Ntot) exhibit a robust bimodal distribution (Fig. 3 ), which is closely associated with the green vs gray sediment colour. A statistical test-t demonstrates that the two populations are significantly different. Detailed results are provided in the Supplementary Material (Fig. S2). We also refer to two elementary ratios obtained through X-ray fluorescence (XRF) measurements. XRF data are available through the Laboratory Information Management System (LIMS) database ( http://web.iodp.tamu.edu/LORE ). The Mn/Al ratio is used as an indicator of Mn-fluxes and redox conditions in the sediment: it correlates with the Corg content and exhibits a bimodal distribution (Fig. 4 ). Gray layers have lower Mn/Al ratios. In contrast, the Zr/Rb ratios exhibit a single mode distribution. Discussion The WAIS during the mPWP The highly dynamic character of the WAIS during the Pliocene has been addressed by several authors, notably Gohl et al. (2021) 17 through seismic data, Naish et al. (2009) 12 through sedimentary facies analyses beneath the northwest part of the Ross ice shelf, and by several other authors through modelling 15 , 23 , 24 . Indirect information about polar ice-volume fluctuations is also provided by paleo-sea level variability estimates of 13 ± 5 m over glacial–interglacial cycles during the middle-to-late Pliocene, according to Grant et al. (2019) 25 . However, Hollyday et al. (2023) suggest a slightly higher mean sea level value for the early Pliocene (17.5 ± 6.4 m). As the WAIS is grounded below sea level at its margins 27 , 28 , it is highly susceptible to collapse under conditions warmer than those of the pre-industrial time. The near-full melting of the WAIS during the mPWP thus seems likely 29 . In this scenario, the WAIS could have contributed up to 3.3 m to the high sea level of the interval, according to estimates from Bamber et al. (2009) 30 . More direct information about the overall status and variability of the WAIS during the mPWP was searched from the sedimentary record on the Ross Sea shelf. The search was challenging due to the presence of several ice erosional surfaces 31 , 32 , and boulder-sized ice-rafted material that hampered drilling at sites close to the ice margin. From this viewpoint, the location of Site U1524 on the Ross Sea slope is better suited for setting a continuous mPWP sedimentary record. The site remained sufficiently distant from glacial erosion during major ice-sheet expansions, preserving a complete record of the targeted mPWP interval 22 . The green sediments recorded a high primary productivity environment during most of the mPWP, while the gray layers record periods of limited primary production. The temporal duration of the interbedded gray layers is unclear. These layers depict gradational bases with traces of bioturbation and sharp tops (Fig. 2 ), thus recording a progressive decline in productivity linked to perennial sea-ice/ice-shelf spreading events, culminating in rapid melt events and resumption of marine productivity. Other depositional mechanisms cannot be ruled out. For example, in the modern Ross Ice Shelf, Horgan et al. (2025) 33 observed occasional subglacial turbid plumes, leading to the deposition of dm-thick, gray sedimentary layers, thus presenting some analogy with the mPWP gray layers. This mechanism would imply the presence of an ice shelf during their deposition. As occasional pebbles are found in these layers (Fig. S1 ), indicating some ice-rafting deposition, the presence of an ice shelf was likely. The circulation of icebergs from a remote origin is unlikely, as the Ross Embayment and the drilling site are sheltered from the major currents transporting icebergs around Antarctica 34 – 36 . Variations in the Mn/Al ratios, thus the relative fluxes of Mn-oxyhydroxides vs terrigenous particles, cannot help to assess relative changes in the sedimentation rate. Nonetheless, these ratios are distinctly higher in the green layers than in the gray layers (Fig. 4 ). In the Ross Sea, high Mn fluxes are essentially linked to high meltwater supplies and high scavenging rates in the water column, thus to high productivity 37 , 38 during the deposition of the green layers. Ultimately, Mn fluxes at the seafloor and Mn diagenetic evolution in the sediment are governed by redox conditions 39 , and may also indicate less oxidizing conditions during the deposition of gray layers. The nearly constant Zr/Rb ratio observed (Fig. 4 ) throughout the study interval suggests minimal variation in the proportion of coarse versus fine material and no significant shifts in provenance. The Ross Sea is fed by ice streams that drain from both West and East Antarctica, with the study site primarily receiving material from West Antarctica channelled through the Glomar Challenger Basin (Fig. 1 ). Time resolution of the mPWP record Before interpreting the pace of ice-spreading events in the record, a proper assessment of the time resolution and potential changes in the sedimentation rate is necessary. The studied interval is anchored by four paleomagnetic reversals (Kaena top, Kaena bottom, Mammoth top and Mammoth bottom 22 ; Fig. 5 ). Most of these reversals were dated with age uncertainties of ~ 15 ka 40 . Unfortunately, establishing an oxygen isotope stratigraphy at Site U1524 is challenging due to the dissolution of foraminifera shells 41 . Furthermore, any tentative correlation of proxy-paleoclimate records from Site U1524 with the LR04 stack 42 is problematic. First, the LR04 δ¹⁸O stack for the Pliocene shows low-amplitude interglacial shifts (≤ 0.3‰ 19 ), second, there is a few thousand years of uncertainty linked to the benthic δ¹⁸O stacking of changes that may be diachronous between ocean basins 19 , 43 , 44 . Both features result in equivocally defined glacial–interglacial stages during the mPWP based on δ¹⁸O records 8 , 45 . Nonetheless, between 3.3 and 3.0 Ma, the LR04 stack exhibits three major peaks in global ice volume, defining the marine isotope stages KM2, KM6, and M2 42,46 . Assuming a similar sedimentation rate of the gray layers from one another, the thickest of these layers could then reflect the longer-duration glacials of LR04. Thus, the two > 1 m-thick gray layers (at ~ 240 m CSF-B and ~ 270 m CSF-B) (Figs. 3 and 5 ) could be associated with the KM6 and M2 glacials, respectively. Not only are these layers thicker than the other ones (Figs. 3 and 5 ), but their chronology is relatively well constrained by the paleomagnetic anchors: the Kaena bottom (~ 3027 ka) 40 is recorded within the gray layer at 240 m CSF-B, and the Mammoth bottom (~ 3330 ka) 47 is immediately below the gray layer at 270 m CSF-B. However, we will continue to assign the gray and green layers to "cold" and "warm" events, respectively, as they depict a higher frequency than the formal “glacials" and “interglacials” of the standard paleoclimatic LR04 stack 42 . High diatom fluxes characterize the green layers 22 . Primary productivity changes from one warm interval to another may have thus impacted their relative sedimentation rate. Estimating a proportionality between layer thicknesses and time seems risky. The thinner gray layers likely recorded shorter intervals, but their relative durations remain speculative, aside from the KM6 and M2 intervals discussed above. Carbon cycling variability As illustrated in Figs. 3 and 4 , the bimodal distributions of the Corg abundance and isotopic composition (δ¹³Corg), as well as of the C/N and Mn/Al ratios (Fig. 4 ), match the colour-banded sedimentary alternation. The OM buried during warm periods (green layers) displays consistent δ¹³Corg values values (-25 ± 0.31‰ ,2s, sample standard deviation, n = 34) throughout the mPWP. Ren et al. (2022) 48 report similar values in Holocene sediments from neighbouring sites. This narrow cluster of δ¹³Corg values differs from the modern particulate OM (δ¹³Corg = ~ -22) in the water column of the Ross Sea 49 , 50 . Arrigo et al. (2003) 51 , who analyzed organic matter in the Ross Sea pack-ice along a transect from ~ 64° to 78°S, observed Corg/Ntot values close to 10 and d 13 Corg values ranging from − 18 to -28‰ in the basal ice. South of ~ 73°, d 13 Corg ranged from − 23 to -28‰, with values close to -25‰ at the latitude of our study core. Munro et al. (2010) 49 analyzed the organic matter from brines in sea ice near our study site, which yielded organic matter with a mean d 13 Corg value of -24.4‰. It is thus unclear if the OM from the green layer represents major supplies from sea-ice or an ice-shelf, or a mixture from marine production and terrestrial supplies. Several mechanisms may explain the 13 C-offset between the water column OM (δ¹³Corg = ~ -22) and the sedimented OM (-25 ± 0.31‰ ,2s, sample standard deviation, n = 34) during warm intervals: (i) a steady mixing of the continental 13 C-depleted aged and refractory OM (~ -27.5‰) 52 with contemporary marine OM; (ii) an early diagenetic 13 C-fractionating decay of the marine OM fraction carrying its δ 13 C signature to ~ -25‰ in the sediment; (iii) a significant contribution of OM from sea-ice or ice-packs, and (iv) supplies from a nearly contemporary terrestrial Corg (terrestrial vegetation, lacustrine OM; see Wei et al., 2016 53 ), with a δ 13 C content close to -25‰ as one cannot neglect the potential development of terrestrial vegetation during Pliocene interglacials in Antarctica 54 . Comparatively, the d 13 Corg of OM during cold spells (gray layers) shows a larger scatter (-28.5 to -26‰; Fig. 4 ) with a mean value of -27.1 ± 1.21‰ (2s, sample standard deviation, n = 24), distinct from that of the warm intervals. As illustrated in Fig. 4 , the d 13 Corg vs Corg/Ntot content of these layers defines a cluster of 13 C-enriched, N-depleted (δ¹³Corg ~ -25‰; C/N ~ 10) samples for sediments deposited under warmer conditions. In contrast, the ¹³C-depleted, N-enriched sediments (δ¹³Corg ~ − 28‰; C/N ≈ 5) display a scattered, but broadly linear trend that does not align with the ~–25‰ cluster endmember. In accordance with Venkatesan's observations (1988) 55 , we assign the gray layer to some residual refractory OM, carried with the terrestrial fraction of the sediment. Here, as suggested by Sackett et al. (1974) 52 , this residual OM would result from glacial erosion of older inland sedimentary rocks. Determining their nature would require deeper investigations into the OM molecular composition. The periodic δ¹³Corg excursions towards low values (-27‰) are likely driven by a drawdown of the primary productivity, suppressing the burial of fresh organic matter and enhancing the concentration of refractory organic matter in the sediments. This mature organic matter, which has undergone varying degrees of diagenetic transformation, may originate from supracrustal rocks eroded by the ice sheet, and/or from ice shelf scouring along the shelf. Upstream of the study site, the Glomar Challenger Trough (Fig. 1 ), a primary channel in the Ross Sea, drains a wide area of West Antarctica, including the Kamb, Whillans, Mercer, and Beardmore ice streams 56 , and potentially delivered organic matter sourced from these areas to Site U1524 (Fig. S3). The trend observed in the Corg (%) vs. δ¹³Corg illustrates the overall partition of the organic matter buried in the Ross Sea: An isotopically heavier organic matter (δ¹³Corg ~ -25 to -22‰) associated with algal blooms thus warm intervals, and an isotopically lighter organic matter (δ¹³Corg ~ -27‰), during intervals of collapse productivity 50 associated with cool conditions. It is also worth mentioning that, although grounded ice could have resulted in the reworking of Miocene sediments from the shelf, the occurrence of redeposited Miocene microfossils in the Pliocene sediments was reported to be negligible by McKay et al. (2019) 22 . Altogether, we do not have robust evidence of the mPWP ice-sheet mean position grounding line. However, we can infer from the above features that during warm intervals, Site U1524 was exposed to open waters, where algal blooms led to the export of fresh organic matter to the seafloor. In contrast, during cold periods, the site was likely situated beneath an ice shelf/perennial sea ice cover, resulting in low primary productivity. Age control & recurring frequency of glacial pulses Precise age tuning of the record is compromised by uncertainties in the age of the paleomagnetic anchors, which are at the order of 15 ka (± 1σ) 40 . Sedimentation rates are thus poorly constrained, leading to difficulties in correlating cooling intervals with either marine isotope stages or specific orbital configurations. Nevertheless, Bergamasco et al. (2002) 21 associated cold intervals with low sedimentation rates, based on the assumption of a reduced water export, thus of particulate matter, through the Hillary Canyon during glacial periods, as dense water formation was suppressed in the absence of seasonal sea-ice development. We tentatively plotted the insolation (at 75°S), obliquity and eccentricity curves anchored on magnetic reversal ages (Fig. 5 ). However, due to the inherent uncertainties associated with these reversal ages, we cannot unequivocally link low insolation values to glacial beds. Even so, the thick glacial bed located at the top of the Mammoth Subchron (Fig. 5 ) is relatively well dated at 3.207 Ma 40,57 and possibly MIS KM6. Insolation values at this time were tuned by moderate precession values, modulated by the lowermost eccentricity values of the Earth’s orbit. Thus, at this very moment, in the Ross Sea, the low eccentricity might have been a key driver of the ice volume. Contrastingly, the single other thick glacial bed at ~ 270 m downcore does not match a consistent low eccentricity interval. This bed is located above the Mammoth bottom (~ 3330 ka) and possibly represents the MIS M2 glacial stage. In contrast to Halberstadt et al. (2024) 15 , whose model did not produce an orbitally driven glaciation, we propose that a low insolation linked to orbital wobbling may have indeed contributed to the M2 glaciation. The M2 glaciation could have been more intense than most other glaciations of the mPWP (as indicated by its thick recording interval), despite the absence of notably low pCO₂ levels at that time. Several sedimentological reconstructions suggest that ice margin advances and retreats around Antarctica were paced by obliquity during the Pleistocene 58 and the Pliocene 12 . Spectral analysis (Fig. 5 ) of δ¹³Corg data the studied interval (~ 3–3.3 Ma), following linear age interpolation between paleomagnetic tie points, reveals a strong imprint of the 41 kyr obliquity cycle, significant at the 99% confidence level. The analysis also identifies a ~ 16 kyr recurrence interval for the gray layers (Fig. 5 ), although the underlying mechanism remains unresolved, this periodicity is unlikely to reflect precession forcing. A sub-precession frequency has already been proposed as a key driver of climate variability during the Miocene 59 . Regardless of the forcing, the occurrence of ~ 16 ka cyclicity suggests that complex processes govern the ice coverage over the Ross Sea during the mPWP. Thus, aside from direct orbital influences, other forcings and complex mechanisms are likely, warranting closer attention to better understand the sub-orbital frequency variability of the West Antarctic Ice Sheet (WAIS). They include: oceanic and atmospheric processes 58 , 60 , 61 , the internal dynamics of ice sheets 62 , 63 , variations in ocean heat transport and atmospheric circulation 62 , 64 , 65 , and solar variability. In conclusion, our study provides evidence for high variability of the Western Antarctic ice margin during the mPWP, complementing the variability already documented by sea level and ocean δ 18 O data 25 . At the Ross Sea scale, these high-frequency fluctuations resulted in significant changes in both the burial rate and the nature of the buried organic carbon. Based on our data, it is not possible to determine with certainty the type of ice cover (i.e., perennial sea ice vs. ice shelf) at the Ross Sea shelf and slope during the cold pulses. Nonetheless, the recurring pulses at ~ 16 ka intervals sustained ice coverage that extended beyond the continental slope and involved mechanisms tuned to a higher frequency than precession. Our findings highlight the dynamic yet resilient behavior of the ice on the Antarctic Western margin under pCO₂ conditions higher than pre-industrial levels, while also shedding light on the implications of ice coverage on the Southern Ocean carbon pump and ecosystem productivity. Materials and Methods The study samples are from the levee deposits of the Hilary Canyon, located on the continental slope of the Ross Sea, Antarctica. Samples are from Site U1524 (74°13.05′S, 173°37.98′W), located at a water depth of 2394 m. The drilling led to the recovery of a continuous record of the mid-Pliocene Warm Period (mPWP) assigned to the 3.264–3.025 Ma interval 66 . The analyzed sedimentary sequence spans the ~ 3.3 to -3.0 Ma interval (~ 200 to 290 m CSF-B). The record consists of 90 meters of diatom-rich muds, predominantly olive-green, intercalating with decimetre-thick gray layers (Fig. 2 ). The alternation of colour in the sediments has been documented by McKay et al. (2019) and Patterson et al. (2024), but the origin of the sediment was not discussed. The sampling resolution for the present study was designed to recover material from all alternating layers of gray and green colour. Total carbon (Ctot), total organic carbon (Corg), δ 13 Corg and total nitrogen (Ntot) analyses were performed in 53 samples with an average sampling resolution of 8 ka. Aluminum, manganese, zirconium, and rubidium measurements are available through the IODP LIMS database. Approximately 0.5 g of each sample was weighed and freeze-dried overnight. Samples were then ground to homogeneity in an agate mortar, which was cleaned with milli-Q water, HCl (1M), and methanol between samples. For total carbon (Ctot) and total nitrogen (Ntot), 10 mg samples were weighed in tin cups and measurements were performed in an Elementar Vario Micro Cube elemental analyzer. For organic carbon (Corg) and δ 13 Corg measurements, carbonate removal was performed using acid fumigation 67 : samples were weighed into silver cups and loaded onto a clean tray, which was placed in a closed glass container with a beaker of concentrated HCl for 24 hours. The air in the glass container rapidly saturates with HCl, which reacts with carbonate minerals in the sample (e.g., Ramnarine et al., 2011 68 ). After carbonate removal and drying, silver cups were closed and put inside tin cups for measurements. For organic carbon measurements, 10 mg of the sample underwent fumigation and was analyzed in the Elementar Vario Micro Cube elemental analyzer. Once the organic carbon content of the samples was determined, different amounts were weighed for δ 13 Corg measurements to ensure the same amount of CO 2 for all samples and reference materials. The samples were then analyzed with a Micromass model Isoprime 100 isotope ratio mass spectrometer coupled to an Elementar Vario MicroCube elemental analyser in continuous flow mode. Two internal reference materials (δ 13 C=-28.74 ± 0.02‰ and − 11.80 ± 0.03‰) were used to normalize the results on the NBS19-LSVEC scale. A third reference material (δ 13 C=-17.06 ± 0.02‰) was analyzed as an unknown to assess the normalization. Results are given in delta unit (δ) vs VPDB. For δ¹³Corg, the uncertainty is 0.1‰. This uncertainty is calculated by propagating the standard deviations of the measured standards and the uncertainties of their accepted values 69 . It is also verified using a control measured during each analytical sequence. For Ctot(%) and Corg(%), the certified value of the control is 1.52 ± 0.02% (1σ). The long-term average of daily control measurements is 1.51 ± 0.04% (1σ). For Ntot(%), the certified value of the control is 0.13 ± 0.02% (1σ). The long-term average of daily control measurements is 0.12 ± 0.01% (1σ). Analyses were performed at the Light stable isotope geochemistry laboratory, in the Geotop (Université du Québec à Montréal), Canada. Elemental analysis by XRF scanning was conducted on Site U1524 cores using a third-generation Avaatech™ core scanner at the IODP Gulf Coast Repository at Texas A&M University. Al and Mn measurements were performed with an accelerating voltage of 10 kV and a current of 0.16 mA, without filtering. The counting time (live time) of each measurement was 6 seconds, and the spot size in the down-core direction was 10 mm. Zr and Rb measurements were performed with an accelerating voltage of 30 kV and a current of 1.25 mA, using a Palladium filter. The counting time (live time) of each measurement was 6 seconds, and the spot size in the down-core direction was 10 mm. The ratios Mn/Al and Zr/Rb (effective concentrations have not been determined) were used to identify relative chemical changes between glacial and interglacial beds. Declarations Acknowledgments The authors thank J.-F. Hélie and A. Adamowicz, both at Geotop, for the provided support in the laboratory. This work has been supported by the Natural Sciences and Engineering Research Council (NSERC) Canada Discovery Grant to CHM. IMCS also acknowledges a post-doctoral fellowship from the Coordination for the Improvement of Higher Education Personnel (CAPES) - - Finance Code 001 (IMCS) and the Humboldt Research Fellowship for Postdoctoral Researchers. References Berends, C. J., De Boer, B., Dolan, A. M., Hill, D. J. & Van De Wal, R. S. W. Modelling ice sheet evolution and atmospheric CO 2 during the Late Pliocene. Clim. Past 15, 1603–1619 (2019). Burke, K. D. et al. Pliocene and Eocene provide best analogs for near-future climates. Proc. Natl. Acad. Sci. 115, 13288–13293 (2018). Bentaleb, I. & Fontugne, M. The role of the southern Indian Ocean in the glacial to interglacial atmospheric CO2 change: organic carbon isotope evidences. Glob. Planet. Change 16–17, 25–36 (1998). Hall, I. R. & McCave, I. N. Glacial-interglacial variation in organic carbon burial on the slope of the N.W. European Continental Margin (48°–50°N). Prog. Oceanogr. 42, 37–60 (1998). Kim, S. et al. Glacial-interglacial environmental changes in the Drake Passage over the past 600 kyrs. Palaeogeogr. Palaeoclimatol. Palaeoecol. 631, 111835 (2023). De Boer, B. et al. Simulating the Antarctic ice sheet in the late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project. The Cryosphere 9, 881–903 (2015). Herbert, T. D. A long marine history of carbon cycle modulation by orbital-climatic changes. Proc. Natl. Acad. Sci. 94, 8362–8369 (1997). Sousa, I. M. C., Hillaire-Marcel, C., De Vernal, A., Montero-Serrano, J.-C. & Aubry, A. M. R. Cold spells over Greenland during the mid-Pliocene Warm Period. Nat. Commun. 16, 1877 (2025). Paillard, D. The Plio-Pleistocene climatic evolution as a consequence of orbital forcing on the carbon cycle. Clim. Past 13, 1259–1267 (2017). Burton, L. E. et al. On the climatic influence of CO 2 forcing in the Pliocene. Clim. Past 19, 747–764 (2023). Dolan, A. M. et al. Sensitivity of Pliocene ice sheets to orbital forcing. Palaeogeogr. Palaeoclimatol. Palaeoecol. 309, 98–110 (2011). Naish, T. et al. Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature 458, 322–328 (2009). Patterson, M. O. et al. Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene. Nat. Geosci. 7, 841–847 (2014). Patterson, M. et al. Spatially variable response of Antarctica’s ice sheets to orbital forcing during the Pliocene. Preprint at https://doi.org/ 10.21203/rs.3.rs-4837964/v1 (2024). Halberstadt, A. R. W., Gasson, E., Pollard, D., Marschalek, J. & DeConto, R. M. Geologically constrained 2-million-year-long simulations of Antarctic Ice Sheet retreat and expansion through the Pliocene. Nat. Commun. 15, 7014 (2024). Cook, C. P. et al. Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. Nat. Geosci. 6, 765–769 (2013). Gohl, K. et al. Evidence for a Highly Dynamic West Antarctic Ice Sheet During the Pliocene. Geophys. Res. Lett. 48, (2021). Lisiecki, Lorraine E. et al. Revisiting the LR04 Pliocene-Pleistocene Benthic δ18O Stack. in AGU Fall Meeting Abstracts (San Francisco, 2023). Raymo, M. E., Kozdon, R., Evans, D., Lisiecki, L. & Ford, H. L. The accuracy of mid-Pliocene δ18O-based ice volume and sea level reconstructions. Earth-Sci. Rev. 177, 291–302 (2018). Rahaman, W., Gutjahr, M. & Prabhat, P. Late Pliocene growth of the West Antarctic Ice Sheet to near-modern configuration. Nat. Commun. 16, (2025). Bergamasco, A., Defendi, V., Zambianchi, E. & Spezie, G. Evidence of dense water overflow on the Ross Sea shelf-break. Antarct. Sci. 14, 271–277 (2002). Ross Sea West Antarctic Ice Sheet History . vol. 374 (International Ocean Discovery Program, 2019). Dolan, A. M., De Boer, B., Bernales, J., Hill, D. J. & Haywood, A. M. High climate model dependency of Pliocene Antarctic ice-sheet predictions. Nat. Commun. 9, 2799 (2018). Mas E Braga, M. et al. A thicker Antarctic ice stream during the mid-Pliocene warm period. Commun. Earth Environ. 4, 321 (2023). Grant, G. R. et al. The amplitude and origin of sea-level variability during the Pliocene epoch. Nature 574, 237–241 (2019). Hollyday, A. et al. A Revised Estimate of Early Pliocene Global Mean Sea Level Using Geodynamic Models of the Patagonian Slab Window. Geochem. Geophys. Geosystems 24, e2022GC010648 (2023). Fretwell, P. et al. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7, 375–393 (2013). Tankersley, M. D., Horgan, H. J., Siddoway, C. S., Caratori Tontini, F. & Tinto, K. J. Basement Topography and Sediment Thickness Beneath Antarctica’s Ross Ice Shelf. Geophys. Res. Lett. 49, e2021GL097371 (2022). Blasco, J. et al. Antarctic tipping points triggered by the mid-Pliocene warm climate. Clim. Past 20, 1919–1938 (2024). Bamber, J. L., Riva, R. E. M., Vermeersen, B. L. A. & LeBrocq, A. M. Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet. Science 324, 901–903 (2009). Conte, R. et al. Bottom current control on sediment deposition between the Iselin Bank and the Hillary Canyon (Antarctica) since the late Miocene: An integrated seismic-oceanographic approach. Deep Sea Res. Part Oceanogr. Res. Pap. 176, 103606 (2021). McKay, R. et al. Antarctic and Southern Ocean influences on Late Pliocene global cooling. Proc. Natl. Acad. Sci. 109, 6423–6428 (2012). Horgan, H. J. et al. A West Antarctic grounding-zone environment shaped by episodic water flow. Nat. Geosci. 18, 389–395 (2025). Lamy, F. et al. Five million years of Antarctic Circumpolar Current strength variability. Nature 627, 789–796 (2024). Roach, C. J. & Speer, K. Exchange of Water Between the Ross Gyre and ACC Assessed by Lagrangian Particle Tracking. J. Geophys. Res. Oceans 124, 4631–4643 (2019). Thompson, A. F., Speer, K. G. & Schulze Chretien, L. M. Genesis of the Antarctic Slope Current in West Antarctica. Geophys. Res. Lett. 47, e2020GL087802 (2020). Gerringa, L. J. A. et al. Dissolved Trace Metals in the Ross Sea. Front. Mar. Sci. 7, 577098 (2020). Sedwick, P. N., DiTullio, G. R. & Mackey, D. J. Iron and manganese in the Ross Sea, Antarctica: Seasonal iron limitation in Antarctic shelf waters. J. Geophys. Res. Oceans 105, 11321–11336 (2000). Anschutz, P., Dedieu, K., Desmazes, F. & Chaillou, G. Speciation, oxidation state, and reactivity of particulate manganese in marine sediments. Chem. Geol. 218, 265–279 (2005). Deino, A. L. et al. Chronostratigraphy of the Baringo-Tugen Hills-Barsemoi (HSPDP-BTB13-1A) core – 40Ar/39Ar dating, magnetostratigraphy, tephrostratigraphy, sequence stratigraphy and Bayesian age modeling. Palaeogeogr. Palaeoclimatol. Palaeoecol. 570, 109519 (2021). Kennett, J. P. Foraminiferal Evidence of a Shallow Calcium Carbonate Solution Boundary, Ross Sea, Antarctica. Science 153, 191–193 (1966). Lisiecki, L. E. & Raymo, M. E. A Pliocene-Pleistocene stack of 57 globally distributed benthic δ 18 O records: PLIOCENE-PLEISTOCENE BENTHIC STACK. Paleoceanography 20, n/a-n/a (2005). Hobart, B., Lisiecki, L. E., Rand, D., Lee, T. & Lawrence, C. E. Late Pleistocene 100-kyr glacial cycles paced by precession forcing of summer insolation. Nat. Geosci. 16, 717–722 (2023). Lisiecki, L. E. & Raymo, M. E. Diachronous benthic δ 18 O responses during late Pleistocene terminations: TERMINATION LAGS. Paleoceanography 24, (2009). Sarnthein, M. et al. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates. Clim. Past 5, 269–283 (2009). De Schepper, S., Gibbard, P. L., Salzmann, U. & Ehlers, J. A global synthesis of the marine and terrestrial evidence for glaciation during the Pliocene Epoch. Earth-Sci. Rev. 135, 83–102 (2014). Hilgen, F. J. Extension of the astronomically calibrated (polarity) time scale to the Miocene/Pliocene boundary. Earth Planet. Sci. Lett. 107, 349–368 (1991). Ren, P. et al. Isotopic Records of Ancient Wildfires in C 4 Grasses Preserved in the Sediment of the Ross Sea, Antarctica. Geophys. Res. Lett. 49, e2022GL098979 (2022). Munro, D. R., Dunbar, R. B., Mucciarone, D. A., Arrigo, K. R. & Long, M. C. Stable isotope composition of dissolved inorganic carbon and particulate organic carbon in sea ice from the Ross Sea, Antarctica. J. Geophys. Res. Oceans 115, 2009JC005661 (2010). Villinski, J. C., Dunbar, R. B. & Mucciarone, D. A. Carbon 13/Carbon 12 ratios of sedimentary organic matter from the Ross Sea, Antarctica: A record of phytoplankton bloom dynamics. J. Geophys. Res. Oceans 105, 14163–14172 (2000). Arrigo, K. R., Robinson, D. H., Dunbar, R. B., Leventer, A. R. & Lizotte, M. P. Physical control of chlorophyll a , POC, and TPN distributions in the pack ice of the Ross Sea, Antarctica. J. Geophys. Res. Oceans 108, 2001JC001138 (2003). Sackett, W. M., Poag, C. W. & Eadie, B. J. Kerogen Recycling in the Ross Sea, Antarctica. Science 185, 1045–1047 (1974). WEI, Yangyang et al. Sources of organic matter and paleo-environmental implications inferred from carbon isotope compositions of lacustrine sediments at Inexpressible Island, Ross Sea, Antarctica. Adv. Polar Sci. 27, 233–244 (2016). Fielding, C. R., Harwood, D. M., Winter, D. M. & Francis, J. E. Neogene stratigraphy of Taylor Valley, Transantarctic Mountains, Antarctica: Evidence for climate dynamism and a vegetated Early Pliocene coastline of McMurdo Sound. Glob. Planet. Change 96–97, 97–104 (2012). Venkatesan, M. I. Organic geochemistry of marine sediments in Antarctic region: Marine lipids in McMurdo Sound. Org. Geochem. 12, 13–27 (1988). Danielson, M. A. & Bart, P. J. The staggered retreat of grounded ice in the Ross Sea, Antarctica, since the Last Glacial Maximum (LGM). The Cryosphere 18, 1125–1138 (2024). Ogg, J. G. Geomagnetic Polarity Time Scale. in Geologic Time Scale 2020 159–192 (Elsevier, 2020). doi: 10.1016/B978-0-12-824360-2.00005-X . Ohneiser, C. et al. West Antarctic ice volume variability paced by obliquity until 400,000 years ago. Nat. Geosci. 16, 44–49 (2023). Sullivan, N. B. et al. Millennial-scale variability of the Antarctic ice sheet during the early Miocene. Proc. Natl. Acad. Sci. 120, e2304152120 (2023). Braaten, A. H. et al. Limited exchange between the deep Pacific and Atlantic oceans during the warm mid-Pliocene and Marine Isotope Stage M2 “glaciation”. Clim. Past 19, 2109–2125 (2023). Smith, B. et al. Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes. Science 368, 1239–1242 (2020). Clark, P. U., Alley, R. B. & Pollard, D. Northern Hemisphere Ice-Sheet Influences on Global Climate Change. Science 286, 1104–1111 (1999). MacAyeal, D. R. Binge/purge oscillations of the Laurentide Ice Sheet as a cause of the North Atlantic’s Heinrich events. Paleoceanography 8, 775–784 (1993). Bond, G. et al. A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates. Science 278, 1257–1266 (1997). Marcott, S. A. et al. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events. Proc. Natl. Acad. Sci. 108, 13415–13419 (2011). Haywood, A. M., Dowsett, H. J. & Dolan, A. M. Integrating geological archives and climate models for the mid-Pliocene warm period. Nat. Commun. 7, 10646 (2016). Hélie, J.-F. Elemental and stable isotopic approaches for studying the organic and inorganic carbon components in natural samples. IOP Conf. Ser. Earth Environ. Sci. 5, 012005 (2009). Ramnarine, R., Voroney, R. P., Wagner-Riddle, C. & Dunfield, K. E. Carbonate removal by acid fumigation for measuring the δ 13 C of soil organic carbon. Can. J. Soil Sci. 91, 247–250 (2011). Hélie, J. & Hillaire-Marcel, C. Designing working standards for stable H, C, and O isotope measurements in CO 2 and H 2 O. Rapid Commun. Mass Spectrom. 35, (2021). Li, M., Hinnov, L. & Kump, L. Acycle: Time-series analysis software for paleoclimate research and education. Comput. Geosci. 127, 12–22 (2019). Tables Table 1 is available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files Table1.xlsx Table 1 SupplementarymaterialSep1.docx Supplementary material Cite Share Download PDF Status: Under Review 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-7511634","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":521057942,"identity":"48360a55-5f95-49d9-9733-ae54a75a040c","order_by":0,"name":"Isabela Sousa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIiWNgGAWjYBACNjAqADETGB8ASR4+4rQYgLUwgygeNuIsgmhhk4By8QM+/sPPHnwwsIvmb09/Vvk1x06GjYH54aMb+KyQSDM3nGGQnDvjzBuz27LbkoEOYzM2zsGrhcFMmseAOXeDRA7bbcltzEAtPGzSeLXwH/8m/cegHqgl/Vmx5LZ6IrQw5JhJMxgcBmpJMGP8uO0wEVokcsoNewyOg/xiLM247TgPGzMBv8j3H9/24EdFdW5/e/rDjz+3Vdvzszc/fIxPCwpg5gGTxCoHAcYfpKgeBaNgFIyCEQMAkTFBdiQ7OWoAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-7285-3633","institution":"MARUM—Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany","correspondingAuthor":true,"prefix":"","firstName":"Isabela","middleName":"","lastName":"Sousa","suffix":""},{"id":521057943,"identity":"5f1a7a9b-fe6e-41b4-9fac-901ebfc1a770","order_by":1,"name":"Claude Hillaire-Marcel","email":"","orcid":"https://orcid.org/0000-0002-3733-4632","institution":"Geotop, UQAM","correspondingAuthor":false,"prefix":"","firstName":"Claude","middleName":"","lastName":"Hillaire-Marcel","suffix":""},{"id":521057944,"identity":"e2093d95-cb5d-48fe-9d6e-d5d7c7ad9f80","order_by":2,"name":"Anne de Vernal","email":"","orcid":"https://orcid.org/0000-0001-5656-724X","institution":"Université du Québec à Montréal","correspondingAuthor":false,"prefix":"","firstName":"Anne","middleName":"","lastName":"de Vernal","suffix":""},{"id":521057945,"identity":"79332976-1f31-4a36-99d4-6db2e9f6369b","order_by":3,"name":"Simone Kasemann","email":"","orcid":"https://orcid.org/0000-0002-6913-7748","institution":"University of Bremen","correspondingAuthor":false,"prefix":"","firstName":"Simone","middleName":"","lastName":"Kasemann","suffix":""}],"badges":[],"createdAt":"2025-09-01 21:45:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7511634/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7511634/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":94478604,"identity":"0524c5e1-a3f3-4c3e-bbd1-0b01f0946929","added_by":"auto","created_at":"2025-10-27 16:03:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1243298,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of Site U1524 and other sites from IODP Expedition 374. Dark blue arrows indicate the export of dense, saline waters formed in the Ross Sea (Ross Sea Bottom Water). White arrows indicate the Antarctic Slope Current. Modified after McKay et al. (2019)\u003csup\u003e22\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/1426952ca03b968aaad969f8.png"},{"id":94479471,"identity":"f16f9368-e101-4b0d-8210-75fbea70582e","added_by":"auto","created_at":"2025-10-27 16:05:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":468521,"visible":true,"origin":"","legend":"\u003cp\u003eGray beds, interpreted as glacial deposits, are identifiable by their distinct color within the 195–290 m CSF-B interval. A. Close-up photography of core 28H, section 1, between 72 cm and 102 cm, from site U1524. \u0026nbsp;The gray layer shown in the photo is located at a depth of 247.11 m (CSF-B) and represents one of the twenty-five gray layers targeted for sampling. Note its gradational contact at the base and the sharp contact at the top. B: Smoothed distribution of Reflectance b* (Kernel Density estimation) for all analyzed samples (twenty-five samples collected from gray layers, and thirty-four from green layers). Color reflectance is represented in the L*a*b*color space system\u003csup\u003e22\u003c/sup\u003e, which expresses color as a function of lightness (L*; grayscale) and color values a* and b*, where a* reflects the balance between red (positive a*) and green (negative a*) and b* reflects the balance between yellow (positive b*) and blue (negative b*). The colour variation in the sediment samples is only noticeable in the b* channel.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/e57b62d9d64aa16b02d49335.png"},{"id":94478767,"identity":"5cb6745b-63fa-4281-8f2a-0e2501946ad8","added_by":"auto","created_at":"2025-10-27 16:03:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61749,"visible":true,"origin":"","legend":"\u003cp\u003eOrganic geochemical signatures of warm (green) and cold (gray) intervals in the studied record. A: Schematic representation of gray sediment layers, interpreted as cold periods, interbedded overall green layers (diatom rich sediments) . Shaded horizontal stripes are extended across the other plots. B, C and D: respectively Corg, d\u003csup\u003e13\u003c/sup\u003eCorg and Corg /Ntot vs. depth (CSF-B, in meters). Gray (cold periods) and green (warm periods) dots correspond to the samples analyzed.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/d47c902b065ebda48ee9b2e6.png"},{"id":94479523,"identity":"02f9011b-eb4e-4cc5-939a-22dd18b62ddb","added_by":"auto","created_at":"2025-10-27 16:06:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":159280,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation matrix between selected parameters. Histograms show the smoothed distributions (Kernel Density Estimation). Sediments deposited under warm conditions (in dark green, n = 34) vs. cold conditions (in gray, n = 25) show clear distinctions in terms of Corg (%), δ¹³Corg, and C/N ratios. The bimodal pattern is less evident in Mn/Al ratios and absent in Zr/Rb.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/c338615e530fb409bc35fef8.png"},{"id":94479003,"identity":"5a1d97a1-cb28-4215-878d-b33951d559c5","added_by":"auto","created_at":"2025-10-27 16:04:37","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":73803,"visible":true,"origin":"","legend":"\u003cp\u003eAge control for the studied interval. A: Magnetic reversals at their respective depths on Site U1524.B: Schematic representation of gray sediment beds, interpreted as cold periods, interbedded with diatom-rich green sediments. Marine isotope stages KM6 and M2 are identified. C: Insolation at 75°S (W/m²). D: Eccentricity (light gray) and obliquity (in radians, dark gray). E: Spectral analysis of d\u003csup\u003e13\u003c/sup\u003eCorg performed using Acycle\u003csup\u003e70\u003c/sup\u003e after linear interpolation of ages between paleomagnetic anchors (Supplementary material). The spectrum shows a prominent ~41 ka cycle above the 99% confidence level and a signal around 16 ka above 90% confidence interval.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/0149e474fae6c775cce42d3e.png"},{"id":94489835,"identity":"e2ff8a3b-7b68-420f-abb1-3af5ba42192d","added_by":"auto","created_at":"2025-10-27 17:06:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3203166,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/f5f51bc8-0a46-4a72-853a-8e8d71036dc7.pdf"},{"id":94479238,"identity":"db74efc7-e856-47ef-969e-192a4f25d81a","added_by":"auto","created_at":"2025-10-27 16:05:19","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":19805,"visible":true,"origin":"","legend":"Table 1","description":"","filename":"Table1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/dd59b952865aec2f52495b09.xlsx"},{"id":94479395,"identity":"2c37236f-6c20-4926-bbea-67cf5cc895c6","added_by":"auto","created_at":"2025-10-27 16:05:36","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":26449654,"visible":true,"origin":"","legend":"Supplementary material","description":"","filename":"SupplementarymaterialSep1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7511634/v1/be37e0a5aa4605034abb4d67.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Sub-precessional pacing of ice conditions and organic carbon burial in the Ross Sea, Antarctica, during the mid-Pliocene Warm Period","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDue to the similarities between the late Pliocene and the present, such as high pCO₂ levels\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e and land-ocean configurations\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, investigating the carbon cycle during this interval may offer insights into the potential response of the biological carbon pump and carbon storage processes to the ongoing global warming trend. From this viewpoint, the organic carbon (Corg) fate at the margins of the large late Cenozoic ice sheets deserves attention as it has strongly varied between glacial and interglacial stages during the Quaternary\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, but also during the late Pliocene\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. These large-amplitude fluctuations in the carbon cycle and climate remain \"\u003cem\u003enot easily explained as direct consequences of the astronomical forcing\u003c/em\u003e\", as mentioned by Paillard (2017)\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. The specific responses of northern and southern hemisphere ice fluctuations, as well as the relative roles of astronomical and CO\u003csub\u003e2\u003c/sub\u003e forcings\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, thus require attention.\u003c/p\u003e\u003cp\u003eDuring the mid-Pliocene Warm Period (mPWP), in particular, ice fluctuations over Greenland were likely driven by a ca. 40 ka obliquity forcing\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Naish et al. (2009)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e suggested a similar orbital forcing for the Antarctica Ice Sheet during this interval, whereas Patterson et al. (2014)\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e suggest a transition toward a combined eccentricity and precession forcing. Later studies either suggested a \"\u003cem\u003etransient cyclicity, reproducing unique patterns of glacial cyclicity\u003c/em\u003e\"\u003csup\u003e15\u003c/sup\u003e or a highly dynamic Antarctica Ice Sheet\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e with time scales of ice fluctuations of the order of several thousand years. Thus, the linkage between high-frequency\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Pliocene Antarctica Ice Sheet fluctuations and orbital parameters remains unascertained during the mPWP, an interval marked by dampened fluctuations in the benthic d\u003csup\u003e18\u003c/sup\u003eO stack record\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eHere, we aim to document the behaviour of the Western Antarctica Ice Sheet (WAIS) margin during the mPWP interval, before the WAIS expanded closer to its modern configuration during the Pleistocene\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, with specific attention to its impacts on organic matter (OM) cycling. Our study is based on high-resolution analyses of a sedimentary record from the Hilary Canyon in the Ross Sea, Antarctica (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In this area, the Plio-Pleistocene interval has been characterized by a strong climate variability, with an orbital to suborbital pacing\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, and a highly dynamic ice margin\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. The Hilary Canyon serves as the primary conduit for Ross Sea Bottom Water, a key component of Antarctic Bottom Water (AABW)\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. The study site (IODP Site U1524), drilled in 2018, offers a high-recovery Plio-Pleistocene record\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. A first set of investigations of the ~\u0026thinsp;3.1 to ~\u0026thinsp;2.5 Ma interval at IODP Site U1524, by Patterson et al. (2024) illustrates a complex combination of orbital parameters governing sedimentation, as recorded in the \u0026ge;\u0026thinsp;250 mm fraction related to ice-rafted debris. Our primary objective here is to examine specifically the OM properties (Corg, Corg/Ntot, δ \u003csup\u003e13\u003c/sup\u003eCorg), which contribute to documenting the Corg sources and flux variability between warm and cold intervals (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In a second step, we examine the potential astronomical forcing governing these parameters.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe data supporting this study are archived in the PANGAEA database. The 90-m study interval is characterized by olive-green, diatomaceous-rich sediments\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e with interbedded gray beds of variable thickness (10 to 130 cm) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The contact at the base of the gray beds is gradational, and the contact at the top is abrupt.\u003c/p\u003e\u003cp\u003eThe elemental analysis reveals that olive green sediments have a Corg content of 0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08% (2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;34), whereas the gray sediments average 0.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10% (2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;24). The δ\u0026sup1;\u0026sup3;Corg of the olive-green layers averages 25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31\u0026permil; (2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;34) and \u0026minus;\u0026thinsp;27.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.21\u0026permil; (2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;24) in the gray sediments. Corg/Ntot ratios of the olive-green sediments range from 9 to 11, whereas they range from 3 to 9 in the gray layers. All OM parameters (Corg, δ\u0026sup1;\u0026sup3;Corg, and Corg/Ntot) exhibit a robust bimodal distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), which is closely associated with the green vs gray sediment colour. A statistical test-t demonstrates that the two populations are significantly different. Detailed results are provided in the Supplementary Material (Fig. S2).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWe also refer to two elementary ratios obtained through X-ray fluorescence (XRF) measurements. XRF data are available through the Laboratory Information Management System (LIMS) database (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://web.iodp.tamu.edu/LORE\u003c/span\u003e\u003cspan address=\"http://web.iodp.tamu.edu/LORE\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The Mn/Al ratio is used as an indicator of Mn-fluxes and redox conditions in the sediment: it correlates with the Corg content and exhibits a bimodal distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Gray layers have lower Mn/Al ratios. In contrast, the Zr/Rb ratios exhibit a single mode distribution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003eThe WAIS during the mPWP\u003c/h2\u003e\u003cp\u003eThe highly dynamic character of the WAIS during the Pliocene has been addressed by several authors, notably Gohl et al. (2021)\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e through seismic data, Naish et al. (2009)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e through sedimentary facies analyses beneath the northwest part of the Ross ice shelf, and by several other authors through modelling\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Indirect information about polar ice-volume fluctuations is also provided by paleo-sea level variability estimates of 13\u0026thinsp;\u0026plusmn;\u0026thinsp;5 m over glacial\u0026ndash;interglacial cycles during the middle-to-late Pliocene, according to Grant et al. (2019)\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. However, Hollyday et al. (2023) suggest a slightly higher mean sea level value for the early Pliocene (17.5\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4 m). As the WAIS is grounded below sea level at its margins\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, it is highly susceptible to collapse under conditions warmer than those of the pre-industrial time. The near-full melting of the WAIS during the mPWP thus seems likely\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. In this scenario, the WAIS could have contributed up to 3.3 m to the high sea level of the interval, according to estimates from Bamber et al. (2009)\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eMore direct information about the overall status and variability of the WAIS during the mPWP was searched from the sedimentary record on the Ross Sea shelf. The search was challenging due to the presence of several ice erosional surfaces\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, and boulder-sized ice-rafted material that hampered drilling at sites close to the ice margin. From this viewpoint, the location of Site U1524 on the Ross Sea slope is better suited for setting a continuous mPWP sedimentary record. The site remained sufficiently distant from glacial erosion during major ice-sheet expansions, preserving a complete record of the targeted mPWP interval\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. The green sediments recorded a high primary productivity environment during most of the mPWP, while the gray layers record periods of limited primary production. The temporal duration of the interbedded gray layers is unclear. These layers depict gradational bases with traces of bioturbation and sharp tops (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), thus recording a progressive decline in productivity linked to perennial sea-ice/ice-shelf spreading events, culminating in rapid melt events and resumption of marine productivity. Other depositional mechanisms cannot be ruled out. For example, in the modern Ross Ice Shelf, Horgan et al. (2025)\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e observed occasional subglacial turbid plumes, leading to the deposition of dm-thick, gray sedimentary layers, thus presenting some analogy with the mPWP gray layers. This mechanism would imply the presence of an ice shelf during their deposition. As occasional pebbles are found in these layers (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), indicating some ice-rafting deposition, the presence of an ice shelf was likely. The circulation of icebergs from a remote origin is unlikely, as the Ross Embayment and the drilling site are sheltered from the major currents transporting icebergs around Antarctica\u003csup\u003e\u003cspan additionalcitationids=\"CR35\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eVariations in the Mn/Al ratios, thus the relative fluxes of Mn-oxyhydroxides vs terrigenous particles, cannot help to assess relative changes in the sedimentation rate. Nonetheless, these ratios are distinctly higher in the green layers than in the gray layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In the Ross Sea, high Mn fluxes are essentially linked to high meltwater supplies and high scavenging rates in the water column, thus to high productivity\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e during the deposition of the green layers. Ultimately, Mn fluxes at the seafloor and Mn diagenetic evolution in the sediment are governed by redox conditions\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, and may also indicate less oxidizing conditions during the deposition of gray layers. The nearly constant Zr/Rb ratio observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) throughout the study interval suggests minimal variation in the proportion of coarse versus fine material and no significant shifts in provenance. The Ross Sea is fed by ice streams that drain from both West and East Antarctica, with the study site primarily receiving material from West Antarctica channelled through the Glomar Challenger Basin (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eTime resolution of the mPWP record\u003c/h3\u003e\n\u003cp\u003eBefore interpreting the pace of ice-spreading events in the record, a proper assessment of the time resolution and potential changes in the sedimentation rate is necessary. The studied interval is anchored by four paleomagnetic reversals (Kaena top, Kaena bottom, Mammoth top and Mammoth bottom\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Most of these reversals were dated with age uncertainties of ~\u0026thinsp;15 ka\u003csup\u003e40\u003c/sup\u003e. Unfortunately, establishing an oxygen isotope stratigraphy at Site U1524 is challenging due to the dissolution of foraminifera shells \u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Furthermore, any tentative correlation of proxy-paleoclimate records from Site U1524 with the LR04 stack\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e is problematic. First, the LR04 δ\u0026sup1;⁸O stack for the Pliocene shows low-amplitude interglacial shifts (\u0026le;\u0026thinsp;0.3\u0026permil;\u003csup\u003e19\u003c/sup\u003e), second, there is a few thousand years of uncertainty linked to the benthic δ\u0026sup1;⁸O stacking of changes that may be diachronous between ocean basins\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Both features result in equivocally defined glacial\u0026ndash;interglacial stages during the mPWP based on δ\u0026sup1;⁸O records\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. Nonetheless, between 3.3 and 3.0 Ma, the LR04 stack exhibits three major peaks in global ice volume, defining the marine isotope stages KM2, KM6, and M2\u003csup\u003e42,46\u003c/sup\u003e. Assuming a similar sedimentation rate of the gray layers from one another, the thickest of these layers could then reflect the longer-duration glacials of LR04. Thus, the two\u0026thinsp;\u0026gt;\u0026thinsp;1 m-thick gray layers (at ~\u0026thinsp;240 m CSF-B and ~\u0026thinsp;270 m CSF-B) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) could be associated with the KM6 and M2 glacials, respectively. Not only are these layers thicker than the other ones (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), but their chronology is relatively well constrained by the paleomagnetic anchors: the Kaena bottom (~\u0026thinsp;3027 ka)\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e is recorded within the gray layer at 240 m CSF-B, and the Mammoth bottom (~\u0026thinsp;3330 ka)\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e is immediately below the gray layer at 270 m CSF-B. However, we will continue to assign the gray and green layers to \"cold\" and \"warm\" events, respectively, as they depict a higher frequency than the formal \u0026ldquo;glacials\" and \u0026ldquo;interglacials\u0026rdquo; of the standard paleoclimatic LR04 stack \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eHigh diatom fluxes characterize the green layers\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Primary productivity changes from one warm interval to another may have thus impacted their relative sedimentation rate. Estimating a proportionality between layer thicknesses and time seems risky. The thinner gray layers likely recorded shorter intervals, but their relative durations remain speculative, aside from the KM6 and M2 intervals discussed above.\u003c/p\u003e\n\u003ch3\u003eCarbon cycling variability\u003c/h3\u003e\n\u003cp\u003eAs illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the bimodal distributions of the Corg abundance and isotopic composition (δ\u0026sup1;\u0026sup3;Corg), as well as of the C/N and Mn/Al ratios (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), match the colour-banded sedimentary alternation. The OM buried during warm periods (green layers) displays consistent δ\u0026sup1;\u0026sup3;Corg values values (-25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31\u0026permil; ,2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;34) throughout the mPWP. Ren et al. (2022)\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e report similar values in Holocene sediments from neighbouring sites. This narrow cluster of δ\u0026sup1;\u0026sup3;Corg values differs from the modern particulate OM (δ\u0026sup1;\u0026sup3;Corg = ~ -22) in the water column of the Ross Sea\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. Arrigo et al. (2003)\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e, who analyzed organic matter in the Ross Sea pack-ice along a transect from ~\u0026thinsp;64\u0026deg; to 78\u0026deg;S, observed Corg/Ntot values close to 10 and d\u003csup\u003e13\u003c/sup\u003eCorg values ranging from \u0026minus;\u0026thinsp;18 to -28\u0026permil; in the basal ice. South of ~\u0026thinsp;73\u0026deg;, d\u003csup\u003e13\u003c/sup\u003eCorg ranged from \u0026minus;\u0026thinsp;23 to -28\u0026permil;, with values close to -25\u0026permil; at the latitude of our study core. Munro et al. (2010)\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e analyzed the organic matter from brines in sea ice near our study site, which yielded organic matter with a mean d\u003csup\u003e13\u003c/sup\u003eCorg value of -24.4\u0026permil;. It is thus unclear if the OM from the green layer represents major supplies from sea-ice or an ice-shelf, or a mixture from marine production and terrestrial supplies.\u003c/p\u003e\u003cp\u003eSeveral mechanisms may explain the \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC-offset between the water column OM (δ\u0026sup1;\u0026sup3;Corg = ~ -22) and the sedimented OM (-25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31\u0026permil; ,2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;34) during warm intervals: (i) a steady mixing of the continental \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC-depleted aged and refractory OM (~ -27.5\u0026permil;)\u003csup\u003e52\u003c/sup\u003e with contemporary marine OM; (ii) an early diagenetic \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC-fractionating decay of the marine OM fraction carrying its δ\u003csup\u003e13\u003c/sup\u003eC signature to ~ -25\u0026permil; in the sediment; (iii) a significant contribution of OM from sea-ice or ice-packs, and (iv) supplies from a nearly contemporary terrestrial Corg (terrestrial vegetation, lacustrine OM; see Wei et al., 2016\u003csup\u003e53\u003c/sup\u003e), with a δ\u003csup\u003e13\u003c/sup\u003eC content close to -25\u0026permil; as one cannot neglect the potential development of terrestrial vegetation during Pliocene interglacials in Antarctica\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eComparatively, the d\u003csup\u003e13\u003c/sup\u003eCorg of OM during cold spells (gray layers) shows a larger scatter (-28.5 to -26\u0026permil;; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) with a mean value of -27.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.21\u0026permil; (2s, sample standard deviation, n\u0026thinsp;=\u0026thinsp;24), distinct from that of the warm intervals. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the d\u003csup\u003e13\u003c/sup\u003eCorg vs Corg/Ntot content of these layers defines a cluster of \u003csup\u003e13\u003c/sup\u003eC-enriched, N-depleted (δ\u0026sup1;\u0026sup3;Corg ~ -25\u0026permil;; C/N\u0026thinsp;~\u0026thinsp;10) samples for sediments deposited under warmer conditions. In contrast, the \u0026sup1;\u0026sup3;C-depleted, N-enriched sediments (δ\u0026sup1;\u0026sup3;Corg ~ \u0026minus;\u0026thinsp;28\u0026permil;; C/N\u0026thinsp;\u0026asymp;\u0026thinsp;5) display a scattered, but broadly linear trend that does not align with the ~\u0026ndash;25\u0026permil; cluster endmember. In accordance with Venkatesan's observations (1988)\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e, we assign the gray layer to some residual refractory OM, carried with the terrestrial fraction of the sediment. Here, as suggested by Sackett et al. (1974)\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, this residual OM would result from glacial erosion of older inland sedimentary rocks. Determining their nature would require deeper investigations into the OM molecular composition.\u003c/p\u003e\u003cp\u003eThe periodic δ\u0026sup1;\u0026sup3;Corg excursions towards low values (-27\u0026permil;) are likely driven by a drawdown of the primary productivity, suppressing the burial of fresh organic matter and enhancing the concentration of refractory organic matter in the sediments. This mature organic matter, which has undergone varying degrees of diagenetic transformation, may originate from supracrustal rocks eroded by the ice sheet, and/or from ice shelf scouring along the shelf. Upstream of the study site, the Glomar Challenger Trough (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), a primary channel in the Ross Sea, drains a wide area of West Antarctica, including the Kamb, Whillans, Mercer, and Beardmore ice streams\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e, and potentially delivered organic matter sourced from these areas to Site U1524 (Fig. S3).\u003c/p\u003e\u003cp\u003eThe trend observed in the Corg (%) vs. δ\u0026sup1;\u0026sup3;Corg illustrates the overall partition of the organic matter buried in the Ross Sea: An isotopically heavier organic matter (δ\u0026sup1;\u0026sup3;Corg ~ -25 to -22\u0026permil;) associated with algal blooms thus warm intervals, and an isotopically lighter organic matter (δ\u0026sup1;\u0026sup3;Corg ~ -27\u0026permil;), during intervals of collapse productivity\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e associated with cool conditions.\u003c/p\u003e\u003cp\u003eIt is also worth mentioning that, although grounded ice could have resulted in the reworking of Miocene sediments from the shelf, the occurrence of redeposited Miocene microfossils in the Pliocene sediments was reported to be negligible by McKay et al. (2019)\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eAltogether, we do not have robust evidence of the mPWP ice-sheet mean position grounding line. However, we can infer from the above features that during warm intervals, Site U1524 was exposed to open waters, where algal blooms led to the export of fresh organic matter to the seafloor. In contrast, during cold periods, the site was likely situated beneath an ice shelf/perennial sea ice cover, resulting in low primary productivity.\u003c/p\u003e\n\u003ch3\u003eAge control \u0026 recurring frequency of glacial pulses\u003c/h3\u003e\n\u003cp\u003ePrecise age tuning of the record is compromised by uncertainties in the age of the paleomagnetic anchors, which are at the order of 15 ka (\u0026plusmn;\u0026thinsp;1σ)\u003csup\u003e40\u003c/sup\u003e. Sedimentation rates are thus poorly constrained, leading to difficulties in correlating cooling intervals with either marine isotope stages or specific orbital configurations. Nevertheless, Bergamasco et al. (2002)\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e associated cold intervals with low sedimentation rates, based on the assumption of a reduced water export, thus of particulate matter, through the Hillary Canyon during glacial periods, as dense water formation was suppressed in the absence of seasonal sea-ice development.\u003c/p\u003e\u003cp\u003eWe tentatively plotted the insolation (at 75\u0026deg;S), obliquity and eccentricity curves anchored on magnetic reversal ages (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). However, due to the inherent uncertainties associated with these reversal ages, we cannot unequivocally link low insolation values to glacial beds. Even so, the thick glacial bed located at the top of the Mammoth Subchron (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) is relatively well dated at 3.207 Ma\u003csup\u003e40,57\u003c/sup\u003e and possibly MIS KM6. Insolation values at this time were tuned by moderate precession values, modulated by the lowermost eccentricity values of the Earth\u0026rsquo;s orbit. Thus, at this very moment, in the Ross Sea, the low eccentricity might have been a key driver of the ice volume.\u003c/p\u003e\u003cp\u003eContrastingly, the single other thick glacial bed at ~\u0026thinsp;270 m downcore does not match a consistent low eccentricity interval. This bed is located above the Mammoth bottom (~\u0026thinsp;3330 ka) and possibly represents the MIS M2 glacial stage. In contrast to Halberstadt et al. (2024)\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, whose model did not produce an orbitally driven glaciation, we propose that a low insolation linked to orbital wobbling may have indeed contributed to the M2 glaciation. The M2 glaciation could have been more intense than most other glaciations of the mPWP (as indicated by its thick recording interval), despite the absence of notably low pCO₂ levels at that time.\u003c/p\u003e\u003cp\u003eSeveral sedimentological reconstructions suggest that ice margin advances and retreats around Antarctica were paced by obliquity during the Pleistocene\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e and the Pliocene\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Spectral analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) of δ\u0026sup1;\u0026sup3;Corg data the studied interval (~\u0026thinsp;3\u0026ndash;3.3 Ma), following linear age interpolation between paleomagnetic tie points, reveals a strong imprint of the 41 kyr obliquity cycle, significant at the 99% confidence level. The analysis also identifies a\u0026thinsp;~\u0026thinsp;16 kyr recurrence interval for the gray layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), although the underlying mechanism remains unresolved, this periodicity is unlikely to reflect precession forcing.\u003c/p\u003e\u003cp\u003eA sub-precession frequency has already been proposed as a key driver of climate variability during the Miocene \u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. Regardless of the forcing, the occurrence of ~\u0026thinsp;16 ka cyclicity suggests that complex processes govern the ice coverage over the Ross Sea during the mPWP. Thus, aside from direct orbital influences, other forcings and complex mechanisms are likely, warranting closer attention to better understand the sub-orbital frequency variability of the West Antarctic Ice Sheet (WAIS). They include: oceanic and atmospheric processes\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e,\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e,\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e, the internal dynamics of ice sheets\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e,\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e, variations in ocean heat transport and atmospheric circulation\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e,\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e,\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e, and solar variability.\u003c/p\u003e\u003cp\u003eIn conclusion, our study provides evidence for high variability of the Western Antarctic ice margin during the mPWP, complementing the variability already documented by sea level and ocean δ\u003csup\u003e18\u003c/sup\u003eO data\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. At the Ross Sea scale, these high-frequency fluctuations resulted in significant changes in both the burial rate and the nature of the buried organic carbon. Based on our data, it is not possible to determine with certainty the type of ice cover (i.e., perennial sea ice vs. ice shelf) at the Ross Sea shelf and slope during the cold pulses. Nonetheless, the recurring pulses at ~\u0026thinsp;16 ka intervals sustained ice coverage that extended beyond the continental slope and involved mechanisms tuned to a higher frequency than precession.\u003c/p\u003e\u003cp\u003eOur findings highlight the dynamic yet resilient behavior of the ice on the Antarctic Western margin under pCO₂ conditions higher than pre-industrial levels, while also shedding light on the implications of ice coverage on the Southern Ocean carbon pump and ecosystem productivity.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eThe study samples are from the levee deposits of the Hilary Canyon, located on the continental slope of the Ross Sea, Antarctica. Samples are from Site U1524 (74\u0026deg;13.05\u0026prime;S, 173\u0026deg;37.98\u0026prime;W), located at a water depth of 2394 m. The drilling led to the recovery of a continuous record of the mid-Pliocene Warm Period (mPWP) assigned to the 3.264\u0026ndash;3.025 Ma interval\u003csup\u003e\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e. The analyzed sedimentary sequence spans the ~\u0026thinsp;3.3 to -3.0 Ma interval (~\u0026thinsp;200 to 290 m CSF-B). The record consists of 90 meters of diatom-rich muds, predominantly olive-green, intercalating with decimetre-thick gray layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The alternation of colour in the sediments has been documented by McKay et al. (2019) and Patterson et al. (2024), but the origin of the sediment was not discussed. The sampling resolution for the present study was designed to recover material from all alternating layers of gray and green colour.\u003c/p\u003e\u003cp\u003eTotal carbon (Ctot), total organic carbon (Corg), δ \u003csup\u003e13\u003c/sup\u003eCorg and total nitrogen (Ntot) analyses were performed in 53 samples with an average sampling resolution of 8 ka. Aluminum, manganese, zirconium, and rubidium measurements are available through the IODP LIMS database.\u003c/p\u003e\u003cp\u003eApproximately 0.5 g of each sample was weighed and freeze-dried overnight. Samples were then ground to homogeneity in an agate mortar, which was cleaned with milli-Q water, HCl (1M), and methanol between samples. For total carbon (Ctot) and total nitrogen (Ntot), 10 mg samples were weighed in tin cups and measurements were performed in an Elementar Vario Micro Cube elemental analyzer. For organic carbon (Corg) and δ \u003csup\u003e13\u003c/sup\u003eCorg measurements, carbonate removal was performed using acid fumigation\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e: samples were weighed into silver cups and loaded onto a clean tray, which was placed in a closed glass container with a beaker of concentrated HCl for 24 hours. The air in the glass container rapidly saturates with HCl, which reacts with carbonate minerals in the sample (e.g., Ramnarine et al., 2011\u003csup\u003e68\u003c/sup\u003e). After carbonate removal and drying, silver cups were closed and put inside tin cups for measurements.\u003c/p\u003e\u003cp\u003eFor organic carbon measurements, 10 mg of the sample underwent fumigation and was analyzed in the Elementar Vario Micro Cube elemental analyzer. Once the organic carbon content of the samples was determined, different amounts were weighed for δ \u003csup\u003e13\u003c/sup\u003eCorg measurements to ensure the same amount of CO\u003csub\u003e2\u003c/sub\u003e for all samples and reference materials. The samples were then analyzed with a Micromass model Isoprime 100 isotope ratio mass spectrometer coupled to an Elementar Vario MicroCube elemental analyser in continuous flow mode. Two internal reference materials (δ\u003csup\u003e13\u003c/sup\u003eC=-28.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u0026permil; and \u0026minus;\u0026thinsp;11.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u0026permil;) were used to normalize the results on the NBS19-LSVEC scale. A third reference material (δ\u003csup\u003e13\u003c/sup\u003eC=-17.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u0026permil;) was analyzed as an unknown to assess the normalization. Results are given in delta unit (δ) vs VPDB. For δ\u0026sup1;\u0026sup3;Corg, the uncertainty is 0.1\u0026permil;. This uncertainty is calculated by propagating the standard deviations of the measured standards and the uncertainties of their accepted values\u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e. It is also verified using a control measured during each analytical sequence. For Ctot(%) and Corg(%), the certified value of the control is 1.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02% (1σ). The long-term average of daily control measurements is 1.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04% (1σ). For Ntot(%), the certified value of the control is 0.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02% (1σ). The long-term average of daily control measurements is 0.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01% (1σ). Analyses were performed at the Light stable isotope geochemistry laboratory, in the Geotop (Universit\u0026eacute; du Qu\u0026eacute;bec \u0026agrave; Montr\u0026eacute;al), Canada.\u003c/p\u003e\u003cp\u003eElemental analysis by XRF scanning was conducted on Site U1524 cores using a third-generation Avaatech\u0026trade; core scanner at the IODP Gulf Coast Repository at Texas A\u0026amp;M University. Al and Mn measurements were performed with an accelerating voltage of 10 kV and a current of 0.16 mA, without filtering. The counting time (live time) of each measurement was 6 seconds, and the spot size in the down-core direction was 10 mm. Zr and Rb measurements were performed with an accelerating voltage of 30 kV and a current of 1.25 mA, using a Palladium filter. The counting time (live time) of each measurement was 6 seconds, and the spot size in the down-core direction was 10 mm. The ratios Mn/Al and Zr/Rb (effective concentrations have not been determined) were used to identify relative chemical changes between glacial and interglacial beds.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe authors thank J.-F. H\u0026eacute;lie and A. Adamowicz, both at Geotop, for the provided support in the laboratory. This work has been supported by the Natural Sciences and Engineering Research Council (NSERC) Canada Discovery Grant to CHM. IMCS also acknowledges a post-doctoral fellowship from the Coordination for the Improvement of Higher Education Personnel (CAPES) - - Finance Code 001 (IMCS) and the Humboldt Research Fellowship for Postdoctoral Researchers.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBerends, C. J., De Boer, B., Dolan, A. M., Hill, D. J. \u0026amp; Van De Wal, R. S. W. Modelling ice sheet evolution and atmospheric CO\u003csub\u003e2\u003c/sub\u003e during the Late Pliocene. \u003cem\u003eClim. Past\u003c/em\u003e 15, 1603\u0026ndash;1619 (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBurke, K. D. \u003cem\u003eet al.\u003c/em\u003e Pliocene and Eocene provide best analogs for near-future climates. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 115, 13288\u0026ndash;13293 (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBentaleb, I. \u0026amp; Fontugne, M. The role of the southern Indian Ocean in the glacial to interglacial atmospheric CO2 change: organic carbon isotope evidences. \u003cem\u003eGlob. Planet. Change\u003c/em\u003e 16\u0026ndash;17, 25\u0026ndash;36 (1998).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHall, I. R. \u0026amp; McCave, I. N. Glacial-interglacial variation in organic carbon burial on the slope of the N.W. European Continental Margin (48\u0026deg;\u0026ndash;50\u0026deg;N). \u003cem\u003eProg. Oceanogr.\u003c/em\u003e 42, 37\u0026ndash;60 (1998).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKim, S. \u003cem\u003eet al.\u003c/em\u003e Glacial-interglacial environmental changes in the Drake Passage over the past 600 kyrs. \u003cem\u003ePalaeogeogr. Palaeoclimatol. Palaeoecol.\u003c/em\u003e 631, 111835 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDe Boer, B. \u003cem\u003eet al.\u003c/em\u003e Simulating the Antarctic ice sheet in the late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project. \u003cem\u003eThe Cryosphere\u003c/em\u003e 9, 881\u0026ndash;903 (2015).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHerbert, T. D. A long marine history of carbon cycle modulation by orbital-climatic changes. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 94, 8362\u0026ndash;8369 (1997).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSousa, I. M. C., Hillaire-Marcel, C., De Vernal, A., Montero-Serrano, J.-C. \u0026amp; Aubry, A. M. R. Cold spells over Greenland during the mid-Pliocene Warm Period. \u003cem\u003eNat. Commun.\u003c/em\u003e 16, 1877 (2025).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePaillard, D. The Plio-Pleistocene climatic evolution as a consequence of orbital forcing on the carbon cycle. \u003cem\u003eClim. Past\u003c/em\u003e 13, 1259\u0026ndash;1267 (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBurton, L. E. \u003cem\u003eet al.\u003c/em\u003e On the climatic influence of CO\u003csub\u003e2\u003c/sub\u003e forcing in the Pliocene. \u003cem\u003eClim. Past\u003c/em\u003e 19, 747\u0026ndash;764 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDolan, A. M. \u003cem\u003eet al.\u003c/em\u003e Sensitivity of Pliocene ice sheets to orbital forcing. \u003cem\u003ePalaeogeogr. Palaeoclimatol. Palaeoecol.\u003c/em\u003e 309, 98\u0026ndash;110 (2011).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNaish, T. \u003cem\u003eet al.\u003c/em\u003e Obliquity-paced Pliocene West Antarctic ice sheet oscillations. \u003cem\u003eNature\u003c/em\u003e 458, 322\u0026ndash;328 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePatterson, M. O. \u003cem\u003eet al.\u003c/em\u003e Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene. \u003cem\u003eNat. Geosci.\u003c/em\u003e 7, 841\u0026ndash;847 (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePatterson, M. \u003cem\u003eet al.\u003c/em\u003e Spatially variable response of Antarctica\u0026rsquo;s ice sheets to orbital forcing during the Pliocene. Preprint at https://doi.org/\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.21203/rs.3.rs-4837964/v1\u003c/span\u003e\u003cspan address=\"10.21203/rs.3.rs-4837964/v1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHalberstadt, A. R. W., Gasson, E., Pollard, D., Marschalek, J. \u0026amp; DeConto, R. M. Geologically constrained 2-million-year-long simulations of Antarctic Ice Sheet retreat and expansion through the Pliocene. \u003cem\u003eNat. Commun.\u003c/em\u003e 15, 7014 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCook, C. P. \u003cem\u003eet al.\u003c/em\u003e Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. \u003cem\u003eNat. Geosci.\u003c/em\u003e 6, 765\u0026ndash;769 (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGohl, K. \u003cem\u003eet al.\u003c/em\u003e Evidence for a Highly Dynamic West Antarctic Ice Sheet During the Pliocene. \u003cem\u003eGeophys. Res. Lett.\u003c/em\u003e 48, (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLisiecki, Lorraine E. \u003cem\u003eet al.\u003c/em\u003e Revisiting the LR04 Pliocene-Pleistocene Benthic δ18O Stack. in \u003cem\u003eAGU Fall Meeting Abstracts\u003c/em\u003e (San Francisco, 2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaymo, M. E., Kozdon, R., Evans, D., Lisiecki, L. \u0026amp; Ford, H. L. The accuracy of mid-Pliocene δ18O-based ice volume and sea level reconstructions. \u003cem\u003eEarth-Sci. Rev.\u003c/em\u003e 177, 291\u0026ndash;302 (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRahaman, W., Gutjahr, M. \u0026amp; Prabhat, P. Late Pliocene growth of the West Antarctic Ice Sheet to near-modern configuration. \u003cem\u003eNat. Commun.\u003c/em\u003e 16, (2025).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBergamasco, A., Defendi, V., Zambianchi, E. \u0026amp; Spezie, G. Evidence of dense water overflow on the Ross Sea shelf-break. \u003cem\u003eAntarct. Sci.\u003c/em\u003e 14, 271\u0026ndash;277 (2002).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e\u003cem\u003eRoss Sea West Antarctic Ice Sheet History\u003c/em\u003e. vol. 374 (International Ocean Discovery Program, 2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDolan, A. M., De Boer, B., Bernales, J., Hill, D. J. \u0026amp; Haywood, A. M. High climate model dependency of Pliocene Antarctic ice-sheet predictions. \u003cem\u003eNat. Commun.\u003c/em\u003e 9, 2799 (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMas E Braga, M. \u003cem\u003eet al.\u003c/em\u003e A thicker Antarctic ice stream during the mid-Pliocene warm period. \u003cem\u003eCommun. Earth Environ.\u003c/em\u003e 4, 321 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrant, G. R. \u003cem\u003eet al.\u003c/em\u003e The amplitude and origin of sea-level variability during the Pliocene epoch. \u003cem\u003eNature\u003c/em\u003e 574, 237\u0026ndash;241 (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHollyday, A. \u003cem\u003eet al.\u003c/em\u003e A Revised Estimate of Early Pliocene Global Mean Sea Level Using Geodynamic Models of the Patagonian Slab Window. \u003cem\u003eGeochem. Geophys. Geosystems\u003c/em\u003e 24, e2022GC010648 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFretwell, P. \u003cem\u003eet al.\u003c/em\u003e Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. \u003cem\u003eThe Cryosphere\u003c/em\u003e 7, 375\u0026ndash;393 (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTankersley, M. D., Horgan, H. J., Siddoway, C. S., Caratori Tontini, F. \u0026amp; Tinto, K. J. Basement Topography and Sediment Thickness Beneath Antarctica\u0026rsquo;s Ross Ice Shelf. \u003cem\u003eGeophys. Res. Lett.\u003c/em\u003e 49, e2021GL097371 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBlasco, J. \u003cem\u003eet al.\u003c/em\u003e Antarctic tipping points triggered by the mid-Pliocene warm climate. \u003cem\u003eClim. Past\u003c/em\u003e 20, 1919\u0026ndash;1938 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBamber, J. L., Riva, R. E. M., Vermeersen, B. L. A. \u0026amp; LeBrocq, A. M. Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet. \u003cem\u003eScience\u003c/em\u003e 324, 901\u0026ndash;903 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eConte, R. \u003cem\u003eet al.\u003c/em\u003e Bottom current control on sediment deposition between the Iselin Bank and the Hillary Canyon (Antarctica) since the late Miocene: An integrated seismic-oceanographic approach. \u003cem\u003eDeep Sea Res. Part Oceanogr. Res. Pap.\u003c/em\u003e 176, 103606 (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMcKay, R. \u003cem\u003eet al.\u003c/em\u003e Antarctic and Southern Ocean influences on Late Pliocene global cooling. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 109, 6423\u0026ndash;6428 (2012).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHorgan, H. J. \u003cem\u003eet al.\u003c/em\u003e A West Antarctic grounding-zone environment shaped by episodic water flow. \u003cem\u003eNat. Geosci.\u003c/em\u003e 18, 389\u0026ndash;395 (2025).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLamy, F. \u003cem\u003eet al.\u003c/em\u003e Five million years of Antarctic Circumpolar Current strength variability. \u003cem\u003eNature\u003c/em\u003e 627, 789\u0026ndash;796 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRoach, C. J. \u0026amp; Speer, K. Exchange of Water Between the Ross Gyre and ACC Assessed by Lagrangian Particle Tracking. \u003cem\u003eJ. Geophys. Res. Oceans\u003c/em\u003e 124, 4631\u0026ndash;4643 (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eThompson, A. F., Speer, K. G. \u0026amp; Schulze Chretien, L. M. Genesis of the Antarctic Slope Current in West Antarctica. \u003cem\u003eGeophys. Res. Lett.\u003c/em\u003e 47, e2020GL087802 (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGerringa, L. J. A. \u003cem\u003eet al.\u003c/em\u003e Dissolved Trace Metals in the Ross Sea. \u003cem\u003eFront. Mar. Sci.\u003c/em\u003e 7, 577098 (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSedwick, P. N., DiTullio, G. R. \u0026amp; Mackey, D. J. Iron and manganese in the Ross Sea, Antarctica: Seasonal iron limitation in Antarctic shelf waters. \u003cem\u003eJ. Geophys. Res. Oceans\u003c/em\u003e 105, 11321\u0026ndash;11336 (2000).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnschutz, P., Dedieu, K., Desmazes, F. \u0026amp; Chaillou, G. Speciation, oxidation state, and reactivity of particulate manganese in marine sediments. \u003cem\u003eChem. Geol.\u003c/em\u003e 218, 265\u0026ndash;279 (2005).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDeino, A. L. \u003cem\u003eet al.\u003c/em\u003e Chronostratigraphy of the Baringo-Tugen Hills-Barsemoi (HSPDP-BTB13-1A) core \u0026ndash; 40Ar/39Ar dating, magnetostratigraphy, tephrostratigraphy, sequence stratigraphy and Bayesian age modeling. \u003cem\u003ePalaeogeogr. Palaeoclimatol. Palaeoecol.\u003c/em\u003e 570, 109519 (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKennett, J. P. Foraminiferal Evidence of a Shallow Calcium Carbonate Solution Boundary, Ross Sea, Antarctica. \u003cem\u003eScience\u003c/em\u003e 153, 191\u0026ndash;193 (1966).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLisiecki, L. E. \u0026amp; Raymo, M. E. A Pliocene-Pleistocene stack of 57 globally distributed benthic δ \u003csup\u003e18\u003c/sup\u003e O records: PLIOCENE-PLEISTOCENE BENTHIC STACK. \u003cem\u003ePaleoceanography\u003c/em\u003e 20, n/a-n/a (2005).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHobart, B., Lisiecki, L. E., Rand, D., Lee, T. \u0026amp; Lawrence, C. E. Late Pleistocene 100-kyr glacial cycles paced by precession forcing of summer insolation. \u003cem\u003eNat. Geosci.\u003c/em\u003e 16, 717\u0026ndash;722 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLisiecki, L. E. \u0026amp; Raymo, M. E. Diachronous benthic δ \u003csup\u003e18\u003c/sup\u003e O responses during late Pleistocene terminations: TERMINATION LAGS. \u003cem\u003ePaleoceanography\u003c/em\u003e 24, (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSarnthein, M. \u003cem\u003eet al.\u003c/em\u003e Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates. \u003cem\u003eClim. Past\u003c/em\u003e 5, 269\u0026ndash;283 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDe Schepper, S., Gibbard, P. L., Salzmann, U. \u0026amp; Ehlers, J. A global synthesis of the marine and terrestrial evidence for glaciation during the Pliocene Epoch. \u003cem\u003eEarth-Sci. Rev.\u003c/em\u003e 135, 83\u0026ndash;102 (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHilgen, F. J. Extension of the astronomically calibrated (polarity) time scale to the Miocene/Pliocene boundary. \u003cem\u003eEarth Planet. Sci. Lett.\u003c/em\u003e 107, 349\u0026ndash;368 (1991).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRen, P. \u003cem\u003eet al.\u003c/em\u003e Isotopic Records of Ancient Wildfires in C\u003csub\u003e4\u003c/sub\u003e Grasses Preserved in the Sediment of the Ross Sea, Antarctica. \u003cem\u003eGeophys. Res. Lett.\u003c/em\u003e 49, e2022GL098979 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMunro, D. R., Dunbar, R. B., Mucciarone, D. A., Arrigo, K. R. \u0026amp; Long, M. C. Stable isotope composition of dissolved inorganic carbon and particulate organic carbon in sea ice from the Ross Sea, Antarctica. \u003cem\u003eJ. Geophys. Res. Oceans\u003c/em\u003e 115, 2009JC005661 (2010).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVillinski, J. C., Dunbar, R. B. \u0026amp; Mucciarone, D. A. Carbon 13/Carbon 12 ratios of sedimentary organic matter from the Ross Sea, Antarctica: A record of phytoplankton bloom dynamics. \u003cem\u003eJ. Geophys. Res. Oceans\u003c/em\u003e 105, 14163\u0026ndash;14172 (2000).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArrigo, K. R., Robinson, D. H., Dunbar, R. B., Leventer, A. R. \u0026amp; Lizotte, M. P. Physical control of chlorophyll \u003cem\u003ea\u003c/em\u003e, POC, and TPN distributions in the pack ice of the Ross Sea, Antarctica. \u003cem\u003eJ. Geophys. Res. Oceans\u003c/em\u003e 108, 2001JC001138 (2003).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSackett, W. M., Poag, C. W. \u0026amp; Eadie, B. J. Kerogen Recycling in the Ross Sea, Antarctica. \u003cem\u003eScience\u003c/em\u003e 185, 1045\u0026ndash;1047 (1974).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWEI, Yangyang \u003cem\u003eet al.\u003c/em\u003e Sources of organic matter and paleo-environmental implications inferred from carbon isotope compositions of lacustrine sediments at Inexpressible Island, Ross Sea, Antarctica. \u003cem\u003eAdv. Polar Sci.\u003c/em\u003e 27, 233\u0026ndash;244 (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFielding, C. R., Harwood, D. M., Winter, D. M. \u0026amp; Francis, J. E. Neogene stratigraphy of Taylor Valley, Transantarctic Mountains, Antarctica: Evidence for climate dynamism and a vegetated Early Pliocene coastline of McMurdo Sound. \u003cem\u003eGlob. Planet. Change\u003c/em\u003e 96\u0026ndash;97, 97\u0026ndash;104 (2012).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVenkatesan, M. I. Organic geochemistry of marine sediments in Antarctic region: Marine lipids in McMurdo Sound. \u003cem\u003eOrg. Geochem.\u003c/em\u003e 12, 13\u0026ndash;27 (1988).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDanielson, M. A. \u0026amp; Bart, P. J. The staggered retreat of grounded ice in the Ross Sea, Antarctica, since the Last Glacial Maximum (LGM). \u003cem\u003eThe Cryosphere\u003c/em\u003e 18, 1125\u0026ndash;1138 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOgg, J. G. Geomagnetic Polarity Time Scale. in \u003cem\u003eGeologic Time Scale 2020\u003c/em\u003e 159\u0026ndash;192 (Elsevier, 2020). doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/B978-0-12-824360-2.00005-X\u003c/span\u003e\u003cspan address=\"10.1016/B978-0-12-824360-2.00005-X\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOhneiser, C. \u003cem\u003eet al.\u003c/em\u003e West Antarctic ice volume variability paced by obliquity until 400,000 years ago. \u003cem\u003eNat. Geosci.\u003c/em\u003e 16, 44\u0026ndash;49 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSullivan, N. B. \u003cem\u003eet al.\u003c/em\u003e Millennial-scale variability of the Antarctic ice sheet during the early Miocene. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 120, e2304152120 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBraaten, A. H. \u003cem\u003eet al.\u003c/em\u003e Limited exchange between the deep Pacific and Atlantic oceans during the warm mid-Pliocene and Marine Isotope Stage M2 \u0026ldquo;glaciation\u0026rdquo;. \u003cem\u003eClim. Past\u003c/em\u003e 19, 2109\u0026ndash;2125 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSmith, B. \u003cem\u003eet al.\u003c/em\u003e Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes. \u003cem\u003eScience\u003c/em\u003e 368, 1239\u0026ndash;1242 (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eClark, P. U., Alley, R. B. \u0026amp; Pollard, D. Northern Hemisphere Ice-Sheet Influences on Global Climate Change. \u003cem\u003eScience\u003c/em\u003e 286, 1104\u0026ndash;1111 (1999).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMacAyeal, D. R. Binge/purge oscillations of the Laurentide Ice Sheet as a cause of the North Atlantic\u0026rsquo;s Heinrich events. \u003cem\u003ePaleoceanography\u003c/em\u003e 8, 775\u0026ndash;784 (1993).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBond, G. \u003cem\u003eet al.\u003c/em\u003e A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates. \u003cem\u003eScience\u003c/em\u003e 278, 1257\u0026ndash;1266 (1997).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarcott, S. A. \u003cem\u003eet al.\u003c/em\u003e Ice-shelf collapse from subsurface warming as a trigger for Heinrich events. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 108, 13415\u0026ndash;13419 (2011).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHaywood, A. M., Dowsett, H. J. \u0026amp; Dolan, A. M. Integrating geological archives and climate models for the mid-Pliocene warm period. \u003cem\u003eNat. Commun.\u003c/em\u003e 7, 10646 (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH\u0026eacute;lie, J.-F. Elemental and stable isotopic approaches for studying the organic and inorganic carbon components in natural samples. \u003cem\u003eIOP Conf. Ser. Earth Environ. Sci.\u003c/em\u003e 5, 012005 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRamnarine, R., Voroney, R. P., Wagner-Riddle, C. \u0026amp; Dunfield, K. E. Carbonate removal by acid fumigation for measuring the δ\u003csup\u003e13\u003c/sup\u003e C of soil organic carbon. \u003cem\u003eCan. J. Soil Sci.\u003c/em\u003e 91, 247\u0026ndash;250 (2011).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH\u0026eacute;lie, J. \u0026amp; Hillaire-Marcel, C. Designing working standards for stable H, C, and O isotope measurements in CO\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO. \u003cem\u003eRapid Commun. Mass Spectrom.\u003c/em\u003e 35, (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, M., Hinnov, L. \u0026amp; Kump, L. Acycle: Time-series analysis software for paleoclimate research and education. \u003cem\u003eComput. Geosci.\u003c/em\u003e 127, 12\u0026ndash;22 (2019).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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-7511634/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7511634/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFor over 200 ka during the mid-Pliocene Warm Period (mPWP), sustained high atmospheric pCO₂ (\u0026gt;\u0026thinsp;350 ppm) maintained global temperatures above pre-industrial levels. Nonetheless, as documented here, ice growth pulses occurred during this interval along the margin of the West Antarctic Ice Sheet, impacting the carbon cycle. These events resulted in high amplitude changes in the source and burial rate of organic carbon (Corg) in the Ross Sea. Warm intervals with seasonally open sea-ice conditions were recorded by thick, greenish, diatom-rich sediments containing relatively abundant marine Corg. Cold intervals, assigned to perennial ice cover pulses, were recorded by grayish, decimeter-thick layers with very low Corg content, likely relating to the erosion of sedimentary rocks on land. Although the obliquity forcing is evident in the sequence, the cold pulses occurred at a much higher frequency (~\u0026thinsp;16 ka), not matched by any direct precession insolation control, thus involving the interference of complex glaciological, oceanic and atmospheric processes which warrant closer examination. Remarkably, even under the \"warm Earth scenario\" of the mPWP, these processes have sustained perennial ice cover pulses beyond the continental Ross Sea shelf limit.\u003c/p\u003e","manuscriptTitle":"Sub-precessional pacing of ice conditions and organic carbon burial in the Ross Sea, Antarctica, during the mid-Pliocene Warm Period","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-27 15:09:16","doi":"10.21203/rs.3.rs-7511634/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"9ba46103-d60c-4d48-af14-56543a2d5a2e","owner":[],"postedDate":"October 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":55388557,"name":"Earth and environmental sciences/Climate sciences/Palaeoceanography"},{"id":55388558,"name":"Earth and environmental sciences/Climate sciences/Cryospheric science"}],"tags":[],"updatedAt":"2025-10-27T15:09:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-27 15:09:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7511634","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7511634","identity":"rs-7511634","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}