Late Pliocene growth of the West Antarctic Ice Sheet to near-modern configuration

Domain: earth_science
Published: 2025-07-21
Editorial outcome: major_revision

Abstract
Accurate prediction of a West Antarctic Ice Sheet (WAIS) collapse and its impact on sea level in a future warmer climate remains uncertain. Here, we provide evidence for the transition from a smaller-sized WAIS during the warm Pliocene to an expanded ice sheet closer to its modern configuration during the Pleistocene based on geochemical records from the proximity to the current maximum ice loss in the Amundsen Sea. In contrast to Pliocene ice sheet dynamics, the WAIS exhibited a relatively muted response throughout the Pleistocene despite substantial glacial-interglacial variations in atmospheric CO₂ levels, temperature, and orbital forcing. Our data suggest that critical tipping points for WAIS growth occurred under atmospheric-oceanic conditions of the Pliocene–Pleistocene transition. These findings highlight the importance of the Pliocene–Pleistocene transition in establishing the modern configuration of the WAIS and its importance as a key interval for understanding ice sheet stability under the changing climate.

Introduction
The West Antarctic Ice Sheet (WAIS) is largely marine-based (grounded below sea level) and, therefore, highly sensitive to climatic and oceanographic changes1. Over the past decades, the WAIS has been undergoing dramatic mass loss due to subglacial melting and contributed to sea-level rise at a faster rate than any other continental ice sheet on Earth1,2. Model-based simulations predict a complete collapse of the WAIS in the near future that would result in a global sea-level rise of 3.3-4.3 metres3,4. However, these model predictions differ for both past and future stability of ice sheets and have large uncertainties associated with the timing of the ice sheet collapse and resulting sea-level rise5. Thus, these numerical model-based projections require rigorous validation. A complementary approach based on geological evidence from proximal West Antarctic Ice Sheet margins can be utilised to constrain ice sheet sensitivity to climate forcing(s), particularly during geologic times when climatic conditions were similar to modern-day and/or the near future. Arguably, the best analogue in Earth’s history for the near-future global climate is the Pliocene (5.33–2.58 Ma)6. This epoch experienced 2–3°C higher global mean temperatures7 and atmospheric carbon dioxide concentrations (pCO₂) between 350 and 450 ppm, which are comparable to the early 21st century and 25–60% higher than pre-industrial values8–11. The transition period from the warm Pliocene to a cold Pleistocene climate is a critical interval to investigate the dynamics of ice sheet behaviour, given its analogous ice sheet boundary conditions of the Pleistocene to the modern period, as well as those of the Pliocene to likely near-future conditions in terms of atmospheric pCO₂, sea surface temperature and sea-level12,13. A recent study14 has demonstrated that Antarctic Ice Sheet dimensions are tied to a multitude of temperature thresholds beyond which ice loss is essentially irreversible, previously referred to as a “tipping point” due to the hysteresis behaviour of the ice sheet: that is, the currently observed ice-sheet volume and extent is not regained even if temperatures were reversed to present-day levels. Reconstructions of a WAIS collapse or a substantially smaller WAIS in the geological past will enable us to test ice sheet models that aim to predict future hysteresis behaviour14. Few attempts have been made earlier based on sediment cores retrieved from the western Ross Sea under the Antarctic Drilling (ANDRILL) project. However, these ANDRILL results15 are not representative of the WAIS in the Amundsen Sea sector, where maximum ice mass loss is taking place today16. The Amundsen Sea in West Antarctica is a key region for monitoring ice-sheet stability since the continental ice sheet in this sector is currently being lost at an accelerated pace, leading to rapid ice sheet retreat of Pine Island, Thwaites, and neighbouring glaciers16,17. Numerical model-based studies suggested that the Amundsen Sea sector is a key region for major West Antarctic Ice Sheet (WAIS) retreat or potential collapse during the most intense warm periods of the Plio-Pleistocene over the past 5 Ma3,4. However, evidence for such a collapse or smaller dimensions of the WAIS is, so far, indirect and mainly based on far-field data, such as sea-level records18. Direct geological evidence from ice-proximal records to WAIS is limited.

Here, we provide a record that constrains the behaviour of the WAIS in the Amundsen Sea sector during the late Pliocene and Pleistocene, based on sedimentological and geochemical data from marine sediment core Site U1532 (68°36.683′S, 107°31.500′W, 3961 m water depth) retrieved during IODP Expedition 379 in 201919 (Fig. 1, Supplementary Information). This site is located in close proximity to the WAIS, having recorded processes directly related to past WAIS dynamics. Based on the age-depth model, the cores of the present study represent the depositional history of the Pliocene-Pleistocene interval (Supplementary Fig. 1 and Supplementary Information).

Results
To constrain the dynamics of the West Antarctic Ice Sheet, we produced geochemical and radiogenic neodymium (Nd) and lead (Pb) isotope records, providing key information on climate-state dependent sediment sourcing from the late Pliocene into the Pleistocene based on detrital marine sediment signatures from IODP Site U1532. We used radiogenic isotope compositions of neodymium (143Nd/144Nd, expressed as εNd, which is the deviation of measured 143Nd/144Nd from the Chondritic Uniform Reservoir in parts per 10,000) and lead isotope ratios (here 208Pb/204Pb and 208Pb/207Pb) to trace sediment provenance. In conjunction, Nd and Pb isotopic signatures of the bulk sediments contain unique information about the continental source areas and are relatively conservative during transport and deposition, and thus can be used to delineate the sources. Our working hypothesis proposes that a major ice sheet destabilization would shift the subglacial erosion regime further inland, leading to erosion and sediment supply from new geological source regions to our sites, which would ultimately be recorded in proximal offshore marine sediments. The detrital εNd record based on a total of 140 sediment samples at IODP Site U1532 shows a major shift from less radiogenic values (-7±1) during the late Pliocene to substantially more radiogenic values (-3±1) during the Pleistocene. It is noteworthy to highlight that except for four anomalous data points (three being more radiogenic with an average εNd of ~-0.66±0.28 and one being less radiogenic ~-6, Fig. 2a), all the detrital εNd values (n=38) show a narrow range -4.3 to -2.0 with an average εNd of -3±1; almost invariant at across all sampled Pleistocene glacial-interglacial (G-I) cycles (Fig. 2a). The detrital Pb isotope records also followed similar trends with higher ratios during the late Pliocene and lower ratios in the Pleistocene (Fig. 2b, c). When shown in concert with a previously published West Antarctic sediment record (site ANT34/A2-1020, covering ~770 ka) ~421 nautical miles away from our core site in the northern edge of the Amundsen Sea (Fig. 1b), our detrital εNd record from Site U1532 show moderate and consistent variations throughout sampled late Pleistocene G-I periods (Fig. 2a). The overall trend derived from the εNd records of these two core sites clearly demonstrates a gradual and distinct shift from the supply of substantially less radiogenic Pliocene sediments (~-8) to more radiogenic Pleistocene sediments (-3±1, n=49) and, thereafter, largely invariant sediment provenance signature during the entire Pleistocene (Fig. 2a). The physical properties, lithological and geochemical parameters of bulk sediments exhibit consistent changes with the radiogenic isotope profiles, especially during the Pliocene-Pleistocene transition (Fig. 2). Since no other Nd and Pb isotope records extended into the Pliocene, these pronounced changes in sediment sourcing have not been previously detected.

This study investigates past erosion history and its connections to ice sheet dynamics and configuration during the Plio-Pleistocene climate transition and late Pleistocene glacial-interglacial cycles. Pine Island Glacier (PIG) and Thwaites Glacier (TG) are the two major ice streams draining around 32% of the West Antarctic Ice Sheet (WAIS) into Pine Island Bay within the Amundsen Sea Embayment (ASE) (Fig. 1, Supplementary Fig. 3). These glaciers, collectively termed the “weak underbelly” of the WAIS20, represent the most vulnerable part due to rapid current mass loss and are susceptible to rapid future collapse. These two glaciers supply glaciogenic detritus to the core sites (Fig. 1b). Glacially eroded fine-grained detritus delivered offshore by PIG is characterised by less radiogenic εNd (~-9) and is isotopically distinct from sediments supplied by TG (~-4)20,21 (Supplementary Fig. 3c, d). There is some overlap in εNd values between the Antarctic Peninsula (AP) and Western Amundsen Sea (AW) and western PIG and TG (Supplementary Fig. 3b, d, and Table S2); however, these can be distinguished with Pb isotope signatures (Fig. 3c, d, Supplementary Information). The Pb and Nd isotope data of Site U1532 in 208Pb/204Pb vs. 208Pb/207Pb and εNd vs. 208Pb/207Pb, show a binary mixing trend between the two distinct sources (Fig. 3e, f). Therefore, the substantial shift in εNd, 208Pb/204Pb, and 207Pb/208Pb records during the Pliocene-Pleistocene climate transition implies changes in regional sediment sourcing over this interval (Fig. 2a–c, Fig. 3, Supplementary Table 2).

The prominent shift in the radiogenic isotope profiles can either be explained by (i) variable mineralogical and grain size sorting, (ii) sediment dispersal and transport associated with transient ocean currents and (iii) changes in sediment provenance and erosion regime associated with ice-sheet dynamics and/or a combination of these factors. Detrital εNd measurements in the bulk samples of the present core U1532 and fine fraction (<63 μm) of the samples from the proximal core site ANT34/A2-1020 show similar values within their measurement uncertainty (Fig. 2a) and, thus, rule out potential effects of mineralogical or grain size sorting on the isotope compositions. The three anomalous radiogenic values (average of -0.66±0.28) and one less radiogenic value (-6) during the Pleistocene do not fit in the overall trend in the εNd profile. These radiogenic values could be due to the supply of volcanic material deposited directly over the region during the eruptions and/or transported by Ice Rafted Debris (IRD >250 μm detrital) sediments22 (Supplementary Fig. 4, 5). The geochemical fingerprints of glacially eroded bedrock from West Antarctica based on available radiogenic isotope and trace element data as evidenced via Sr-Nd isotope data in previous studies20–24 of glacial-marine sediments reveal a distinct contrast in IRD provenance between the AP, Bellingshausen Sea (BS), and the Sulzberger Bay (SB) sectors. The detrital thermochronology (hornblende 40Ar/39Ar ages) and bulk (<63 μ) Sm/Nd isotope systematics data25 from glacial-marine sediments in the AP sector showed relatively young ages compared to BS and AS (Supplementary Fig. 5a) and more radiogenic values that can be traced back to the west coast of the AP, while IRD from the BS and SB contributed less radiogenic sediments during interglacials (Supplementary Fig. 5). Detailed investigation22 suggested that the reorganization of ocean currents during MIS 16 significantly influenced IRD trajectories and sediment sources (see Supplementary Information, Section 3.1, and Supplementary Fig. 7). This shift contributed to a supply of less radiogenic sediments at site ANT34/A2-10 before MIS 16, which shifted to more radiogenic sediments thereafter.

The bathymetric map26 of the Pacific sector of Antarctica includes a network of seismic lines (black) in the Amundsen Sea sector27 (Supplementary Fig. 1a). It suggests that glaciogenic detritus originating from the continental shelf supplied most of the terrigenous drift sediments via gravity-driven transport through the channels, with bottom-current capture and subsequent deposition of their suspended load on the drift28,29. Hence, this core site sensitively recorded processes directly related to past WAIS dynamics in the form of sediment deposition after downslope transport, but also indirectly by current-related transport and deposition. The study site U1532 is located close to the Southern Antarctic Circumpolar Current Front, with its bottom waters influenced by Antarctic Bottom Water (AABW) derived from the western Ross Sea (Supplementary Fig. 5). Therefore, the down-core isotopic changes in Pliocene sediments at Site U1532 likely reflect a combined influence of past variations in ocean currents and detrital input from various source regions, linked to the extent of the WAIS. The ACC flows eastward at intermediate to abyssal water depths around Antarctica, while the Antarctic Slope Current (ASC) flows in the opposite direction along the Antarctic continental shelf and rise. Both these currents could influence sediment transport and deposition at our core site as a function of their respective strength and position. A recent study30 reconstructed ACC strength variations over the past ~5 Ma (Supplementary Fig. 6), revealing significant variations in its vigour during the Pleistocene glacial-interglacial periods. The reconstructed ACC record does not show any significant relation with these two detrital εNd records presented here that are distributed at geographically widespread locations within the Amundsen Sea at almost similar depths (Supplementary Figs. 5b, 6b). This indicates that the ACC did not play the dominant role in sediment transport and dispersal. However, the westward-flowing ASC could also have played an important role as it dominates iceberg transport near the coast31,32. The anomalous εNd values during the Pleistocene (~-6 and -0.66±0.28) are attributed to changes in IRD sources and iceberg transport by ocean currents. Nevertheless, IRD constitutes only a small fraction of the total sediment deposited at the core site, with hinterland erosion and downslope transport identified as the primary contributors. As a consequence, ocean currents only play a secondary role in controlling the observed isotopic signatures (see Supplementary Information, “Methods”). Thus, the provenance record from core site U1532 essentially reflects ice-sheet dynamics associated with the growth and retreat and/or configuration of the ice sheet further inland. The large variations in TOC/TN ratio (Fig. 2d) suggest a mixed input of terrestrial- and marine-derived matter, with a higher ratio indicating a greater contribution of terrestrial organic matter during the Pliocene33. Higher sedimentation rates (Fig. 2f) during the Pliocene warm period, together with higher TOC/TN, suggest enhanced erosion from the continental hinterland due to extended warming that resulted in an ice sheet margin retreat further inland and the supply of more terrestrial sediments from the interior, possibly under a stronger hydrological cycle. Based on the seismic correlation of sediment layers from the drill sites to the continental shelf, grounding zone wedges have been identified in the shelf sediments that predominantly formed during ice sheet retreat within an extended Pliocene warm period from ~4.2–3.2 Ma28. These findings from the seismic study indicate that the WAIS was highly dynamic and a regionally less extensive ice sheet along the Amundsen Sea margin during the Pliocene. Warmer regional climatic boundary conditions during the Pliocene would have resulted in a smaller and less extensive WAIS, which is consistent with the ice sheet model simulations for the Pliocene4,34,35. Consequently, substantial amounts of glacially eroded sediments were deposited in front of the Pliocene ice shelf front during glacial-interglacial fluctuations of the ice sheet and ultimately delivered over the continental shelf edge (Supplementary Fig. 8). This situation gradually changed with the expansion of the WAIS preceding the transition to the early Pleistocene cold climate during which large part of the marine-based ice-sheet extended to the ocean. Therefore, glacial-interglacial fluctuations at the terminal end of the extended marine ice sheet were mainly within the ocean and thus resulted in less sediment production associated with these fluctuations (Supplementary Fig. 8d, e). Sediment supply was reduced by almost fivefold compared to the Pliocene (Fig. 2f) due to extensive ice cover over the hinterland. Together, these traceable sedimentary features bear witness to the pronounced expansion of the WAIS and changes in its configuration during the Pliocene-Pleistocene transition. Last but not least, the reduced and relatively invariant or muted responses of Pleistocene sedimentation compared to the Pliocene also indicate that the terminal position of the ice sheet during the Pleistocene never retreated for prolonged interval to ice sheet margin positions near the substantially less radiogenic (older) source areas inland of West Antarctica during the Pliocene.

Sediments from two core sites in the Amundsen Sea (U1532 and ANT34/A2-10) reveal relatively low variability (-3±1, n=49) in detrital εNd records during the Pleistocene glacial-interglacial over the past ~750 ka (Fig. 4a). This contrasts sharply with the strong transient changes from ~-8 to ~-3 observed over ~550 ka across the Pliocene-Pleistocene transition. Distinct εNd signatures from Pine Island (εNd ~-9) and Thwaites (εNd ~-4) basins, along with subglacial lithologies in major ice drainage basins21 (Supplementary Fig. 3), suggest that almost uniform εNd values of the late Pleistocene reflect relatively stable and distinct sediment provenance compared to the Pliocene-Pleistocene transition. This isotopic consistency likely results from almost uniform sediment sources with a homogeneous εNd signature in the hinterland. Significant isotopic changes would require ice sheet retreat into geologically distinct terranes, such as the Ellsworth-Whitmore Mountains (EWM, εNd ~-8)36, which is located far interior at the southern flank of the West Antarctic Rift system (Fig. 3a, b). The absence of such variability implies that the ice sheet margins did not retreat far enough inland to erode and transport the sediments from the EWM during some of the Pleistocene interglacial sections captured by the detrital εNd record. Due to limited exposure of the bedrock and poorly constrained isotope signature in subglacial geology, it is difficult to quantify the exact extent of ice sheet retreat. However, the radiogenic isotopes of Nd and Pb detected in these sediments are sufficiently sensitive to record large-scale changes, such as seen during the Pliocene-Pleistocene transition. Prior to the Pliocene-Pleistocene transition, less radiogenic εNd values (~-8) suggest a WAIS of substantially smaller dimensions with an ice sheet margin being positioned deep in the interior of West Antarctica, reaching the EWM and delivering sediments with lower εNd values. In contrast, the Pleistocene data show no evidence of such extensive retreat during any of those interglacials sampled for the detrital records in the present study.

To investigate the relatively stable Pleistocene εNd signals, we re-examined the variability with much lower amplitude compared to that occurring during the Pliocene-Pleistocene transition. Although the resolution of the detrital εNd record in the Pleistocene interval is not sufficient to resolve all the glacial-interglacial cycles, these do not show changes at a near comparable extent that occurred during the Plio-Pleistocene transition. The high resolution records of magnetic susceptibility and geochemical proxies, including the first principal component (PC1) from PCA analysis of elemental ratios and K/Al ratio, primarily reflect changes in lithogenic inputs during MIS 5 (Fig. 4c–e). The comparison of these proxies suggests a different pattern of ice sheet retreat during the extreme Eemian interglacial (MIS 5e) compared to other Pleistocene interglacials. Unfortunately, the compiled two records could not capture the MIS 5e interval at the desired temporal resolution. In this context, it is noteworthy to mention that another two records (PC493 and PS58/254)37 from the proximity to our core site, present detrital records which captured the interval of the MIS 5e. These records reveal significant variation compared to other interglacials, yet are much smaller in extent compared to that observed during the Pliocene-Pleistocene transition. Further, the relatively muted response during other Pleistocene interglacials characterized by the high insolation38 implies minimal or insignificant ice sheet retreat during most of the interglacials of the late Pleistocene compared with those of the Pliocene. Previous studies based on geomorphological evidences and multiple cosmogenic in-situ 26Al, 10Be, and 21Ne derived exposure ages of quartz-bearing erratics from the southern Ellsworth Mountains suggest that the WAIS has fluctuated only modestly for at least the last 1.4 million years, while a regional ice sheet centered on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods39, which support our findings. In summary, we conclude that the WAIS exhibited less extensive retreat during the Pleistocene interglacials compared to the WAIS preceding the Pliocene-Pleistocene transition implied by the Nd and Pb isotopic constraints presented here. These findings do not align with ice-sheet models predicting widespread WAIS collapse during Pleistocene interglacials4,40. Instead, our findings of the Pliocene ice sheet behaviour align more closely with ice-sheet models, highlighting the relative resilience of the WAIS during the Pleistocene. This muted response, which contrasts with modern rapid WAIS mass loss, underscores the need to re-evaluate the underlying controls of past and future WAIS stability.

To investigate the forcing factors and determine the threshold of the boundary conditions for the retreat and growth of the WAIS, we compare the WAIS history inferred from previous provenance records (Fig. 5) with reconstructions of greenhouse/radiative forcing, specifically atmospheric pCO₂, and orbital forcing (solar insolation) (Fig. 5b, c). The WAIS was substantially smaller than its modern configuration at a pCO₂ of ~350–500 ppm during the Pliocene. No comparable retreat is apparent during extreme interglacial climate stages of the Pleistocene despite large variations in atmospheric temperature (+4 to -10°C) and atmospheric CO₂ concentrations (~180–280 ppm) during glacial-interglacial cycles. We made use of a change point detection analysis for the temperature record revealing a clear cooling trend between 3.25 Ma to 2.75 Ma (Supplementary Fig. 9a, d) with an onset of ~40 ka glacial-interglacial cycles paced by the orbital forcing (sharp increase in temperature variance at 32−64 ka band, Fig. 5d, Supplementary Fig. 9c) that coincided with changes in the configuration of the WAIS from a smaller ice sheet to a more expanded ice sheet extent afterward. This observation is consistent with previous findings reported from the Ross Ice Shelf based on AND-1B sediment core records retrieved under the ANDRILL Project that suggested 40 ka cyclic variations in ice-sheet extent during the Pliocene were linked to obliquity cycles15. Further, the AND-1B core record equally provides evidence for a smaller WAIS41, prolonged marine conditions in the Ross Embayment, and reduced sea ice extent before 3.3 Ma. Subsequent Southern Ocean cooling of ~2.5°C (Supplementary Fig. 10) in concert with a stepwise expansion of sea ice in the Ross Sea between 3.3 and 2.75 Ma coincided with the drawdown of atmospheric pCO₂ from ~400–280 ppm (Fig. 5b). We note that the major expansion of an ice sheet in the Ross Sea sector also initiated at ~3.3 Ma41. This orbital forcing paced cooling increased the seasonal persistence of Antarctic sea ice and led to an expansion of the westerly wind belt, resulting in the northward migration of oceanic fronts in the Southern Ocean42,43. The Pliocene records in the proximity of the WAIS margin in the Amundsen Sea and the Ross Sea provide direct evidence for continent-wide changes in the WAIS configuration. The evidence is consistent with an ice-sheet/ice-shelf model4 that simulates fluctuations in Antarctic ice volume associated with the loss of the WAIS, in response to ocean-induced melting paced by obliquity.

Surprisingly, no substantial changes were observed even during the glacial-interglacial cycles of the late Pleistocene, when global mean temperatures fluctuated substantially, ranging from +4 to -10°C relative to pre-industrial levels for the duration of 2−6 ka (Supplementary Fig. 10). We observed a muted response even during some of the intense super-interglacials44, which were subjected to the higher insolation values38 the than modern. This suggests that these extreme super interglacial conditions of the Pleistocene might have exerted insufficient thermal forcing for the collapse of the WAIS, which is contrary to previous reports45 from the Ross Sea Embayment. Further, our observation of only moderate Pleistocene ice sheet variability is also in contrast to the findings from the East Antarctic ice sheet13, which shows ice margin retreat or thinning in the vicinity of the Wilkes Subglacial Basin of East Antarctic during warm late Pleistocene interglacial intervals. Therefore, we suggest that the present mass loss of the West Antarctic Ice sheet is not comparable to the long-term climate trend of the last 2.7 Ma. Instead, it appears to be a recent phenomenon resulting from the rapidly progressing concomitant changes in atmospheric circulation and changes in the incursion strength and pattern of the circumpolar deep water circulation.

In conclusion, our data suggest a more stable WAIS during the Late Pleistocene relative to the Pliocene. Prolonged near total loss of its marine-based portions, with the ice sheet margin retreating near the Ellsworth-Whitmore Mountains, is unlikely to have occurred, even during the most intense interglacials of the late Pleistocene. Ice-sheet model predictions3,4,35 for the Pliocene are consistent with our proposition. However, it does not align with some of the model predictions for the Pleistocene interglacial periods3, and does not support earlier suggestions of WAIS contribution to the Pleistocene sea level change. Our findings suggest that the tipping point for the growth and stability of the WAIS may lie within the oceanic and atmospheric boundary conditions of the Pliocene-Pleistocene transition. These findings have significant implications for predicting future ice sheet behaviour and its contribution to sea level rise in a warming world.

Methods
IODP Expedition 379 drill sites and sediment cores
The IODP expedition 37927 in 2019 aimed to drill at six sites in the Amundsen Sea Embayment; however, the drilling operation was hindered by the excessive discharge of icebergs, rendering drilling operations impossible on the shelf in Amundsen Embayment. Finally, two sites such as U1532 (68°36.683′S, 107°31.500′W, 3961.5 m water depth) and U1533 (68°44′S, 109°0′W, water depth ~4180 m water depth) were successfully drilled (Supplementary Fig. 1a). These sites are located in close proximity to the WAIS, having recorded processes directly related to past WAIS dynamics. Out of these two sites, the U1532 site was chosen for this study because of its higher sedimentation rates (Fig. 2f) and, thus, better temporal resolution19. Sediment recovery from Site U1532 was ~90%46. This site is located on the western upper flank of a large sediment drift (Resolution Drift) on the continental rise, 270 km north of the Amundsen Sea Embayment shelf edge. This core site is the deepest drill site in close proximity to maximum modern ice mass loss, revealing sedimentary processes only affected by WAIS dynamics. Site U1532 contains a sequence of Pliocene and Pleistocene sediments with an almost complete paleomagnetic record for constraining high-resolution, suborbital-scale climate variability28. It provides continuous records of glacially eroded sediments, representing valuable archives of climatic and oceanographic changes throughout the Plio-Pleistocene glacial cycles.

The various cores of holes A to G of Site U1532 comprise mainly silty clay and clay with different amounts of biogenic content (Supplementary Fig. 1c). The cores comprise a single lithostratigraphic unit in which two subunits IA (0–92.6 mbsf, Pliocene to recent), IB (92.6–~130 mbsf, Pliocene) are targeted47 in this study (Supplementary Fig. 1b). Physical property data measured onboard were used to carry out a core-log seismic integration with drill records. To tie core-log information to seismic profiles, gamma ray attenuation bulk density and P-wave velocity were used to calculate synthetic seismograms. Furthermore, colour reflectance (a*), green/grey colour ratio, age constraints, sedimentation rate, diatom abundance, and lithological descriptions were obtained by the IODP Exp. 379 shipboard scientific party27 (Fig. 2, Supplementary Fig. 1c, d and e).

X-Ray Fluorescence (XRF) scanning for geochemical data
Post-cruise X-ray fluorescence (XRF) scans of the archive halves of sediment core sections were conducted at the IODP Gulf Coast Repository (College Station, Texas, USA)48 using a Avaatech XRF core scanner system. The scans were performed at a 2-cm resolution and analysed for a range of elements, providing semi-quantitative elemental data for Site U1532 sediment cores. Elemental ratios exhibit pronounced variations related to glacial-interglacial cycles. To extract common signals among the variations in elemental ratios, Principal Component Analysis (PCA) was performed using online Excel STAT software (https://www.xlstat.com/en/) (Supplementary Fig. 2). The first principal component (PC1) accounts for ~70% of the variance, related to lithogenic and biogenic variations during the glacial-interglacial cycles. Notably, the excursion observed in PC and PC2 reached their highest amplitude during the MIS 5e interglacial, much higher than those of other late Pleistocene interglacials (Supplementary Fig. 2).

Age model of IODP Site U1532
Age constraints used in this study were taken from the shipboard age-depth models, which were established based on biostratigraphy age datums in correlation with magnetostratigraphic polarity zones47. Based on shipboard analyses of Holes U1532A–U1532G, an age-depth model for Site U1532 was constructed using bio-stratigraphic age datums (Supplementary Table 1) to constrain correlation of magnetostratigraphic polarity zones at Site U1532 correlated to the Gradstein et al. (2012) geological timescale (GTS2012)49 (see Table T5 in the Expedition 379 methods chapter46). Bio-stratigraphic age control for Site U1532 is based on diatom and radiolarian datums46. Sufficient microfossils for bio-stratigraphic age assignment were only present in the upper ~0-10 m of the studied section (i.e. from 0 to 92 m; Lithostratigraphic Subunit IA) which provides an age of middle Pleistocene to recent (0–0.60 Ma). Based on diatom and radiolarian biostratigraphy, the interval between ~92 and 156 m are assigned a mid-to-late Pliocene age of 3.2–3.8 Ma. Using these bio-stratigraphic age control points, the interpreted correlation of magnetostratigraphic polarity reversals identified at Site U1532 (Table T16R)27 to the GTS2012 is relatively unambiguous. The interval between 0 and ~45 m is assigned a Pleistocene age, and the interval between ~45 and 150 m represents Pliocene age. Because of an absence of siliceous microfossils, there is no bio-stratigraphic age control between ~10 and 92 m in Hole U1532A-B27. For Hole U1532A, a reliable shipboard magneto-stratigraphy consisting of four normal and four reversed polarity intervals was obtained. These intervals are the Brunhes–Matuyama polarity transition (0.781 Ma), the termination and beginning of the Olduvai Subchron (1.778 and 1.945 Ma), the Matuyama–Gauss polarity transition (2.581 Ma), the termination and beginning of the Kaena Subchron (C2An.1r; 3.032 and 3.116 Ma) and the termination and beginning of the Mammoth Subchron (C2An.2r; 3.207 and 3.330 Ma, respectively) (see Supplementary Table 1). Paleomagnetic measurements in Hole U1532B identified the beginning of the Mammoth Subchron (C2An.2r; 3.330 Ma) and the Gauss–Gilbert polarity transition (3.596 Ma). Total eight magnetostratigraphic tie points were found between 0 and ~100 CSF-A(m) and two tie points between 101 and 146 CSF-A(m) for the basis of the chronology (Supplementary Table 1, Supplementary Fig. 1b). To improve the shipboard chronology further, we have identified more tie points in the present study based on the correlation between geochemical parameters and global benthic δ18O curve (LR04)44. Elemental ratios of (a) Ba/Al, (b) Ba/Rb, and (c) PC1 (first principal component) derived from Principal Component Analysis (PCA) of multiple elemental ratios were compared with the LR04 curve (Supplementary Fig. 1f–i). In addition to previously determined tie points, nine additional new tie points were identified based on the excursions in the geochemical parameters and their correspondence with the glacial-interglacial signals in the LR04 δ18O curve (shown in Supplementary Fig. 1f–i). Finally, the Matlab™-based programme “Undatable”50 was used to generate an age-depth model with uncertainty. The advantage of using Undatable over other available age-depth modelling programmes is that it allows for the input of uncertainties in both age and depth and for a series of different types of age control points to be incorporated. Undatable was run using 100,000 simulations50. A probability density cloud illustrating the uncertainty envelope around the modelled age-depth points was computed using Monte Carlo iterations. Blue and black dotted lines show 1σ and 2σ uncertainty, respectively. This revised model is based on sixteen tie-points within the study interval (0–3.5 Ma, Supplementary Fig. 1j, and Supplementary Table 1). The age-depth model for the Pleistocene interval is better constrained than the Pliocene interval due to the availability of more tie points/ages and therefore Pleistocene glacial-interglacial variations can be resolved with confidence.

Detrital sediment Nd and Pb isotope measurements
Nd isotopes were measured in the detrital phases of the bulk sediments following the method adopted from earlier studies13,51. We first conducted mild leaching for a shorter duration (ten seconds) without attacking the detrital fraction followed by a second leach for a duration of 24 h to ensure complete removal of the authigenic fractions52–54. Approximately 0.3 g of powdered and homogenized sediment samples were agitated with a mixture solution of 0.005 M hydroxylamine hydrochloride, 1.5% acetic acid, and 0.003 M Na-EDTA, buffered to pH 4 with NaOH. Then leachates were removed by centrifugation and washed with Milli-Q water thoroughly. Residual sediment samples were decarbonated by treating with 0.6 N HCl at 80°C for ~30 min and then the supernatant was discarded, and the acid-free residue was washed with Milli-Q water. The above steps were repeated to ensure complete decarbonation of the samples and washed with Milli-Q water and checked with pH paper to ensure that carbonates are removed from the sediments. Subsequently, samples were washed thoroughly with Milli-Q water and dried in the oven at 80°C. Dried samples were then ashed at 600°C to remove organic matter. Approximately 50 mg of ashed samples were digested in precleaned Teflon vials using HF-HNO3-HCL mixture at 120°C. Standard Reference Materials BCR-2 and BHVO-2 were also digested along with the samples. The digested samples were divided into two aliquots for the column chromatography of Nd and Pb. The dissolved samples were subjected to purification by column chromatography. Samples were passed through columns filled with cation-exchange resin AG50W-X8 (200–400 micron) to separate Rare Earth Elements (REE). Then REE fractions were passed through the column filled with Eichrom LN specTM (50–100 micron) resin to separate Nd from the REEs55.

Nd isotope analysis
Nd isotope ratios were measured using a Multi-Collector Inductively Coupled Plasma Mass Spectrometer (Thermo Fisher Scientific, Neptune Plus) at the National Centre for Polar and Ocean Research (NCPOR), Goa. Instrumental mass fractionation was corrected using the ratio of 146Nd/144Nd = 0.7219 and an exponential law. A correction for direct 144Sm interference was also applied, with all samples which was below (<0.1% of the 144Nd signal). Every five samples were bracketed with concentration matched Nd JNdi-1, and all the mass bias corrected 143Nd/144Nd ratios were normalised to the accepted JNdi-1 standard 143Nd/144 value of 0.51211556. The obtained long-term average ratios of measured JNdi-1 over the period of the analysis of these samples at 10 analytical seasons were 0.512115 ± 0.000049 (2σ, n=51). The external reproducibility calculated for each session was 0.12–0.27 εNd (2σ) units based on the repeated measurements of JNdi-1. Several procedural blanks were also processed along with the samples and ascertained an average blank of ~70 pg for the samples (n=9), which is several orders of magnitude lower than the total Nd typically analysed in samples. Hence, no blank correction was applied. Replicates have an average εNd variation of ±0.17 (n=16). To ensure the quality of the measurements, International reference rock standards BCR-2 and BHVO-2 were processed along with the samples and measured which gave 143Nd/144Nd = 0.512641 ± 0.000030 (2σ, n=7) and 143Nd/144Nd = 0.512997 ± 0.000027 (2σ, n=6) respectively, in agreement with reported values57 (Supplementary Data 2).

Pb isotope analysis
Pb isotope was analysed in the same aliquot in which Nd isotope was measured. The Pb cuts in the detrital dissolved were purified by column chromatography filled with ~80 μL AG1-X8 resin. Pb isotopes were measured using a Thermo Scientific Neptune Plus MC-ICP-MS at GEOMAR Helmholtz Centre for Ocean Research Kiel. Mass bias correction during Pb isotope measurements was performed externally using the Tl-doping technique52,58 with added NIST997 Tl standard solution and a Pb/Tl ratio of ~4. Given that Pb and Tl isotopes undergo slightly different mass-dependent isotopic fractionation during measurements, the adequate SRM 997 Tl isotope composition was chosen on a session-by-session basis so that the offset of all six Pb isotope ratios (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 208Pb/206Pb, 207Pb/206Pb, 208Pb/207Pb) for NBS SRM 981 Pb isotope standard were zero. Detailed information about the measurement procedure can be found in Süfke et al.58 and Huang et al.52. The resultant external intermediate reproducibility of all SRM NBS981 standard solutions were as follows: 206Pb/204Pb = 0.0011, 207Pb/204Pb = 0.0010, 208Pb/204Pb = 0.0029, 208Pb/206Pb = 0.00007, 207Pb/206Pb = 0.00002, 208Pb/207Pb = 0.00006 (n=39). The total procedure blanks were ~500 pg which represents <0.1% of the sample signal. Blank corrected and uncorrected ratios do not show significant differences and hence blank uncorrected data is reported in this study. The reproducibility of the rock standard BCR-2 and BHVO-2 is listed in the Supplementary Data 2. As shown in the table, all measured standard Pb isotopic ratios are within the error of published compositions.

Robustness of the detrital sediment Nd and Pb isotope records
Unlike other radiogenic isotope systems (for example, Sr and Hf), Nd isotopes are relatively insensitive to grain size variations59, making them a robust indicator of sediment provenance. Their insensitivity to grain size variations makes them more reliable tracers of sediment provenance. However, it is crucial to consider potential complications in provenance interpretations if changes in sediment transport processes result in changing the isotope compositions. In such cases, a link between grain size and Nd isotopes could emerge, impacting the reliability of using these isotopes for provenance analysis. To assess the robustness of Nd isotopes, Simões Pereira (2018)37 analysed Nd isotopes in fine-grained fraction (<63 μm) of sediment cores from two locations (PS58/254 and PC493) near our core site U1532 (Fig. 1b). The results of this investigation ruled out any significant influence of grain-size variations on the Nd isotope compositions, reinforcing the suitability of Nd isotopes as a dependable proxy for sediment provenance in this particular study area. Among various combinations of Pb isotope ratios (six in total), we have used 208Pb/204Pb and 208Pb/207Pb ratios as these displayed the most distinctive, clearest, and smoothest signal compared to other ratios, and both these ratios co-vary in concert with the εNd record. Observation of changes in the paired Nd-Pb isotope records is more robust to decipher the changes in the sediment provenances than either of the two trace metal isotope compositions alone. This finding further validates the robustness of using these isotopes as tracers of sediment sources and transport processes in the specific study region. Pertinent to this, it is important to mention that Pliocene erosional history and ice loss from the East Antarctic Ice Sheet (EAIS) were successfully reconstructed previously using detrital εNd records from the Adélie Land sector of East Antarctica12,13. Distinct sediment sourcing associated with the growth and retreat of the ice sheet margin and multiple collapse events establish a close link between ice sheet dynamics, erosion, and variable regional sediment supply. Therefore, our extensive analysis in the present study and successful demonstration in the previous study from this region provide confidence in the applicability of detrital radiogenic isotope compositions of Nd and Pb provide confidence for deciphering sediment sources and transport processes in the studied area.

Wavelet and scaled-average variance of wavelet power analysis
Wavelet transforms decompose time series into time-frequency space and can therefore find localized intermittent periodicities. We used Continuous Wavelet Transform (CWT) i.e. Morlet wavelet to decompose the time series into time-frequency space which enable us to identify the modes of variability and how those modes vary with time60. Statistical significance is estimated against a red noise model. Monte Carlo methods were used to assess the statistical significance against red noise backgrounds61. Wavelet analysis of the temperature record was performed using online Matlab codes http://grinsted.github.io/wavelet-coherence/ to identify nonstationary power at certain frequency bands60,61. Temperature variability at ~40 ka and ~100 ka bands is shown in the wavelet analysis. More detailed information on wavelet analysis is provided elsewhere60,61. Further, to examine fluctuations in power over a range of scales (a band), we used scale-averaged wavelet power which is a time series of the average variance in a certain band. This can be used to examine the modulation of one time series by another, or the modulation of one frequency by another within the same time series. We have performed this analysis using online Matlab codes http://paos.colorado.edu/research/wavelets/. The scaled average variance of the temperature at 32−64 ka and 64 -100 ka band captured the wavelet analysis show how the ~40 ka and ~100 ka periodicities evolved with time (Supplementary Fig. 9c).

Change-point detection using a Bayesian Ensemble Algorithm (BEAST)
Abrupt changes in the temperature time series were detected using a MATLAB based Bayesian model averaging time-series decomposition algorithm (BEAST)62 (Supplementary Fig. 9d). This algorithm offers a robust method to detect abrupt change points and nonlinear trends in the Antarctic temperature record. The code and software are available at https://github.com/zhaokg/Rbeast. The Bayesian algorithm—BEAST decomposition time series into three contrasting components: abrupt change, periodic/seasonal change, and trend. Mathematically, BEAST is rigorously formulated, with its key equations being analytically tractable. Practically, BEAST provides an estimate of probabilities of change point occurrence, detects both large and low-magnitude disturbances, and uncovers complex nonlinear trend dynamics. The details of the Bayesian Ensemble Algorithm (BEAST) are discussed elsewhere62.

Data availability
The datasets from IODP Expedition 379 used in this study, including paleomagnetic intensity, magnetic susceptibility, colour reflectance, biostratigraphy, and trace element data from shore-based XRF analyses, are available through the IODP LIMS Reports portal (https://web.iodp.tamu.edu/LORE/). A comprehensive overview of the available datasets can also be accessed via the International Ocean Discovery Program at http://publications.iodp.org/proceedings/379/datasets.html. Bulk detrital Nd and Pb isotope composition of sediments from Sites U1532 generated in this study have been deposited in the National Polar Data Centre at National Centre for Polar and Ocean Research (NCPOR, Goa; https://ncpor.res.in/) under accession link: https://npdc.ncpor.res.in/npdc/search_mf_data.action?expedition_type=Antarctic&parameter=MF-1233772888&userType=user. This dataset is also provided in the Supplementary Data.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Rahaman et al.’s manuscript entitled “Late Pliocene Growth of the West Antarctic Ice Sheet to Near-Modern Configuration” presents a long record of silicate (bulk sediment) derived neodymium and lead isotopes from IODP U1532. The authors argue that the West Antarctic Ice Sheet (WAIS) transitioned from a small and dynamic configuration in the Pliocene to a larger, more stable configuration in the Pleistocene, akin to modern-day conditions. They also claim that the WAIS has been relatively stable during the Pleistocene, which contrasts with previous studies suggesting otherwise.\nHaving reviewed the previous submission, my comments will consider both my earlier feedback and the subsequent improvements made. I find the overall conclusion of the study somewhat surprising, given what we know about the sensitivity of the WAIS. Therefore, the study may be deemed controversial by some. However, I believe it is an important contribution that could encourage the ice sheet dynamics community to reconsider their model parameters.\nComments:\nThe authors have done a thorough job addressing previous review comments, resulting in a version that is logically coherent and reads well. Significant effort is evident in the creation of provenance maps and the succinct explanation of tracer sensitivities, as well as how different currents, while present, may not affect the results.\nHowever, I have a few comments and concerns regarding the data generation:\n1. This study generates detrital data using marine sediments. I am unclear about the purpose of the short leach (first for ten seconds followed by a second leach lasting 24 hours). While this may not directly impact the results, it seems odd that the authors would conduct a short leach unless it is intended to obtain seawater samples. This is more of a comment than a concern.\n2. My primary concern relates to how Nd isotopes are reported. The authors state, “To ensure the quality of measurement, the international standard JNdi-1 was matrix matched and measured every five samples.” I am curious about how one matrix matches JNdi-1. Is this even possible without investing significant efforts? If something similar to real matrix matching was done, that should be reported.\n3. They also report obtaining the Tanaka value for JNdi-1, which is somewhat puzzling. The original 143Nd/144Nd of JNdi-1, as reported by Tanaka, is an average of several labs (who measured using TIMS) and not measured by a single lab or instrument. Generally, multi-collector measures a somewhat different value and that is why normalization to Tanaka value is done. While in one hand the authors mention that they normalized their results to Tanaka value (i.e., 0.512115), they also report that they can measure Tanaka value. So, I do not see the need for normalization. And hence becomes a point of serious concern, because now I am unsure how the data were treated.\nAdditionally, the authors mention an error of 10 ppm (2 sigma, n=51), yet in the next sentence, they report external reproducibility within a range of 0.12–0.27. How was this external reproducibility calculated? I thought researchers typically use JNdi-1 measurements during the analytical session to determine external reproducibility, which does not seem to be the case here. Furthermore, when converted to epsilon units, 10 ppm corresponds to 0.1, not what is reported. Internal error is generally expressed as 2SE, but here it is presented as 2 sigma.\nI am therefore concerned about the analytical methodologies employed. Interpretations come and go but the data remain forever, therefore, it is essential that both data and metadata are generated and reported with utmost care.\nAs stated, the Pb isotope section appears correct. Error reporting is, however, missing.", "reviewer_2": "As mentioned in my previous review, the data presented by Rahaman et al. are a useful contribution towards unravelling WAIS history. The authors have improved the manuscript since the previous submission and I am happy with the changes to the title and inclusion of the Wang et al. (2022) and Lamy et al. (2024) records. I also appreciate the more detailed discussion of subglacial geology in the supplement.\nHowever, I still do not believe the data available are sufficient to support the conclusion that the WAIS remained close to its modern extent throughout the Pleistocene.\n• Not satisfactorily explaining the εNd value of ~-6 in the Pleistocene: I previously commented that the outliers in the dataset were not properly discussed. It is certainly feasible that the outliers with more radiogenic εNd values could be influenced by volcanic detritus and welcome the addition of this text. However, there remains no discussion of the single datapoint with a less radiogenic εNd value (~-6) in the Pleistocene. This is not easily explained as volcanogenic, as such material would have εNd values of ~+5. I still feel this data point is not well enough explained, as it could suggest a significant change in provenance. This would likely translate to a change in ice sheet extent, in contrast to the manuscript’s conclusion of Pleistocene WAIS stability. Some discussion of this data point is needed, ideally in the context of the other types of data available.\n• Lack of glacial-interglacial change in the Pleistocene: It is difficult to reconcile that there is no cyclic pattern in the provenance data with the unequivocal evidence for major change to WAIS extent over glacial-interglacial cycles. This points to a lack of sensitivity of the provenance proxies used here to ice extent changes in this region; looking at these data alone, for instance, would suggest that there was no ice advance in the last glacial period which is clearly false. I think it is therefore impossible to say that the site is sensitive to any retreat of Pine Island/Thwaites glaciers.\n• Ice sheet margin retreat may not result in erosion of rocks with different isotopic signatures: The isotopic proxies used may be insensitive lack of change in the geology further inland. Although Thwaites and Pine Island glaciers do indeed have a distinct isotopic signature, it could easily be the case that this signature in relatively invariant far inland in an along-flow direction, until a very different geological terrane is reached (e.g., the Ellsworth-Whitmore Mountains). Retreat of the ice sheet margin may therefore not lead to any change in these provenance proxies at core sites offshore. The authors also argue that “… erosion was restricted from the Pine Island basin located interior compared to the Thwaites basin” (line 184). Retention of Pine Island Glacier when Thwaites Glacier is lost is not feasible or compatible with models of WAIS collapse, which lose both glaciers when marine ice sheet instability takes effect (e.g. DeConto et al., 2021; Golledge et al., 2021, etc.). Even if retreat initiates from Thwaites Glacier, Pine Island Glacier is not laterally constrained once Thwaites Glacier is lost.\n• Ocean transport is dismissed: I appreciate the inclusion of a new section on ocean current transport, which was not sufficiently acknowledged in the previous version of the manuscript. The authors argue against ocean current influence on the record here due to: 1) The lack of variability over glacial-interglacial cycles in this (and nearby) provenance records, 2) The lack of correlation with the Lamy et al. (2024) ACC record, and 3) the kaolinite present, which is the dominant clay mineral beneath Thwaites Glacier. However, I still think it is very likely that detritus at this site may be sourced, at least partly, from the Bellingshausen Sea/Antarctic Peninsula region at present and in the past. For instance, the path of modern icebergs, which will also carry fine-grained detritus, is predominantly to the top of the continental shelf above U1532 (see modelling of Rackow et al., 207, DOI:10.1002/2016JC012513), where such debris can flow down-slope to this core site. Rocks from the Antarctic Peninsula are a feasible isotopic endmember, as shown here in Fig. 3. The consistent provenance signature through the Pleistocene could potentially reflect a lack of isotopic variation in the source region(s) towards the Antarctic Peninsula, resulting in no glacial-interglacial variation. Furthermore, the kaolinite present in the record is not sufficiently abundant to be certain that the bulk sediment is derived predominantly from the Amundsen Sea Embayment. I therefore suggest that it should be acknowledged that the Antarctic Peninsula/Bellingshausen Sea cannot be excluded as a potential source region, now and in the past, using the available data.\nTo summarise, I would argue that the isotopic proxies used here are not sensitive enough to changes in ice sheet extent in this region to argue that there was no significant retreat into the Amundsen Sea sector of the WAIS in the Pleistocene. It is also impossible to exclude a sediment source from the Antarctic Peninsula or Bellingshausen Sea catchment. The εNd value of ~-6 in the Pleistocene also requires explanation. I do not feel the datasets presented here are able to identify loss of large parts of the Amundsen Sea sector of the WAIS because, even if Site U1532 directly records the Amundsen Sea sector of the WAIS, subglacial geology is potentially isotopically uniform enough further inland that a provenance change may not be recorded until a very different geological province is reached. This would likely be the Ellsworth-Whitmore Mountain block, requiring a near-complete WAIS collapse. A broadly uniform isotopic composition of the source geology parallel to ice flow for this region is also consistent with the lack of glacial-interglacial cyclicity in the record here.\nI would suggest that the “Evidence for a largely stable Pleistocene WAIS” section is removed, as well as this conclusion at line 264-266. Potentially, the interpretation of the data could be pushed as far as saying there were few, if any, complete collapses of the WAIS in the Pleistocene (except, perhaps the εNd value of ~-6), and this is a useful finding. However, I do not think it is possible to fully eliminate the possibility of a reasonably large-scale retreat of the WAIS in the Pleistocene. I would therefore suggest refocussing the manuscript with emphasis on the Pliocene ice sheet being significantly retreated, which is a novel and useful finding in this region well worthy of publication in Nature Communications.\nThe authors also still do not reference the major compilation of seafloor surface sediment provenance indicators from this sector by Simões Periera et al. (2018, DOI: 10.1016/j.earscirev.2018.04.011). This highly relevant piece of literature should be cited.\nLine-by line comments:\nLines 24-26: see major comments – I do not think that the data are able to support the statement that the Pliocene-Pleistocene transition represents the tipping point for WAIS stability.\nLine 184: “erosion was restricted from the Pine Island basin located interior compared to the Thwaites basin” – as outlined in my other comments, losing Thwaites Glacier but keeping Pine Island Glacier seems unlikely – I would suggest the signature comes from further inland (potentially the Ellsworth-Whitmore Mountain block).\nLine 191: I agree the degree of retreat seen in the Pliocene seems unlikely for the Pleistocene but would add a statement that some retreat cannot be excluded using these provenance proxies alone because of potentially homogenous subglacial geology and lack of ability to detect glacial-interglacial cycles.\nLine 225: As discussed above, I do not believe the data are sufficient to call it “stable”.\nLine 232: I’m not clear on what evidence there is to say that this smaller ice sheet was “dynamic”? There are no rapid fluctuations in the provenance data?\nLine 247: I would clarify that that it a new model simulation, as the ice sheet model itself is not new.\nLine 266-267: More than one ice sheet model simulation exists, so I would change this sentence to “An ice-sheet model prediction for the Pliocene is consistent with our proposition (reference)”.\nFigure 3 a): The caption should be adjusted as the map does not show subglacial geology, only exposed geology.\nFigure 3 b): The interpolated sub-ice estimate of εNd values is still incorrect – for instance, it is known that Pine Island and Thwaites glaciers are underlain by substrate with very different εNd values (Simões Periera et al., 2020), but here they are both shaded a uniform orange.\nLine 336: Is there a reason the 2020 geological timescale is not being used? Either this more up to date age scale should be used, or the reasoning for using the 2012 one should be explained."}, "author_response": "Response to Reviewer’s comments\nManuscript No.: NCOMMS-24-49341\nManuscript Title: Late Pliocene growth of the West Antarctic Ice Sheet to near-\nmodern configuration\nManuscript submitted to the Journal: Nature Communications\nSummary of the revision:\nThe key concerns raised by Rev- 1 regarding the Nd and Pb data and their associated\nerrors have been thoroughly addressed in the revised manuscript. We have addressed\nthe major concerns raised by Rev- 2, particularly regarding the anomalous Nd isotope\nvalues during the Pleistocene and the sensitivity of the proxies used to detect\nPleistocene ice sheet changes. To address these points, we have added a new\nparagraph to the main text and included Section 3.1 in the supplementary material,\nalong with Supplementary Fig. 7, to explain the anomalous values. The Pleistocene\ninterval has been carefully re-examined to resolve second-order variability, and the\ndiscussion has been revised accordingly. The revised interpretation suggests that\nsignificant retreat occurred during MIS 5e but it was geographically less extensive\ncompared to the Pliocene.\nA point-by-point reply to the reviewers’ comments is provided below. Blue colour text\nindicate reply to the comments.\nReviewer #1 (Remarks to the Author):\nRahaman et al.’s manuscript entitled “Late Pliocene Growth of the West Antarctic Ice\nSheet to Near-Modern Configuration” presents a long record of silicate (bulk sediment)\nderived neodymium and lead isotopes from IODP U1532. The authors argue that the\nWest Antarctic Ice Sheet (WAIS) transitioned from a small and dynamic configuration\nin the Pliocene to a larger, more stable configuration in the Pleistocene, akin to\nmodern-day conditions. They also claim that the WAIS has been relatively stable\nduring the Pleistocene, which contrasts with previous studies suggesting otherwise.\nfeedback and the subsequent improvements made. I find the overall conclusion of the\nstudy somewhat surprising, given what we know about the sensitivity of the WAIS.\nTherefore, the study may be deemed controversial by some. However, I believe it is\nan important contribution that could encourage the ice sheet dynamics community to\nreconsider their model parameters.\nComments:\nThe authors have done a thorough job addressing previous review comments,\nresulting in a version that is logically coherent and reads well. Significant effort is\nevident in the creation of provenance maps and the succinct explanation of tracer\nsensitivities, as well as how different currents, while present, may not affect the results.\nHowever, I have a few comments and concerns regarding the data generation:\n1. This study generates detrital data using marine sediments. I am unclear about the\npurpose of the short leach (first for ten seconds followed by a second leach lasting 24\nhours). While this may not directly impact the results, it seems odd that the authors\nwould conduct a short leach unless it is intended to obtain seawater samples. This is\nmore of a comment than a concern.\nReply: First of all, we thank for the constructive comments. In this study, we focused\non the generation of detrital Nd isotope ( ) and Pb isotope records to trace sediment\nNd\nprovenance. Even if only the detrital signature is wanted, it is essential to remove the\nauthigenic phase first to avoid any potential bias in the signal. This is common\nprocedure (e.g. Gutjahr et al., 2007, Chem. Geol.; Parker et al. 2022, QSR) Therefore,\nwe conducted very mild leaching for a very short duration. Subsequently, to measure\nNd in the detrital silicate phase, we conducted leaching for a long duration to remove\nall the authigenic phases. This two-step leaching process ensures the complete\nremoval of all authigenic phases, prior to the digestion of the residual phase.\n2. My primary concern relates to how Nd isotopes are reported. The authors state,\n“To ensure the quality of measurement, the international standard JNdi-1 was matrix\nmatched and measured every five samples.” I am curious about how one matrix\nmatches JNdi-1. Is this even possible without investing significant efforts? If something\nsimilar to real matrix matching was done, that should be reported.\nterminology should be “concentration matched”. This is corrected in the revised\nmanuscript (Line 515). The samples were not matrix-matched since these were\npurified prior to mass spectrometric measurement.\n3. They also report obtaining the Tanaka value for JNdi-1, which is somewhat puzzling.\nThe original 143Nd/144Nd of JNdi-1, as reported by Tanaka, is an average of several\nlabs (who measured using TIMS) and not measured by a single lab or instrument.\nGenerally, multi-collector measures a somewhat different value and that is why\nnormalization to Tanaka value is done. While in one hand the authors mention that\nthey normalized their results to Tanaka value (i.e., 0.512115), they also report that they\ncan measure Tanaka value. So, I do not see the need for normalization. And hence\nbecomes a point of serious concern, because now I am unsure how the data were\ntreated.\nReply: We have modified the text in the revised manuscript (Line No. 517-518). The\nentire confusion arises from the fact that the long-term mean of our measured JNdi-1\nratios is the same 0.512115 ± 0.000049 (2σ, n= 51) as that of the reported (accepted)\nvalue 0.512115 (Tanaka et al., 2000). However, the average composition for repeated\nstandard measurements during individual auto sequences may still be a little offset. If\nthis was observed, all Nd isotopic compositions have been normalised to this literature\nratio. For example, our reported value of JNdi-1 is an average of 143Nd/144Nd of JNdi-\n1 (n=51) measured over the period of ten analytical seasons. 143Nd/144Nd of JNdi-1 for\nthe various season was measured with following ratio: 0.512111 ± 0.000006 (n=4),\n0.512100 ± 0.000008 (n=4), 0.512126 ± 0.000009 (n=2), 0.512102 ±0.000010 (n=7),\n0.512070 ±0.000011 (n=3), 0.512127 ±0.000012 (n=4), 0.512083 ±0.000012 (n=4),\n0.512102 ±0.000014 (n=8), 0.512144 ± 0.000014 (n=13). The method section has\nbeen revised accordingly. For illustration for the reviewer, we have provided a plot\nbelow showing season-wise measurements of JNdi-1 values and their mean with 2SD\n(see the Figure below). The final plot compiled of all seasons of measured JNdi-1’s\n143Nd/144Nd ratios shown in one plot with a mean value of 0.512115 representing long-\nterm mean for the entire measurement season (see the Figure in the next page)\nsentence, they report external reproducibility within a range of 0.12–0.27. How was\nthis external reproducibility calculated? I thought researchers typically use JNdi-1\nmeasurements during the analytical session to determine external reproducibility,\nwhich does not seem to be the case here. Furthermore, when converted to epsilon\nunits, 10 ppm corresponds to 0.1, not what is reported. Internal error is generally\nexpressed as 2SE, but here it is presented as 2 sigma. I am therefore concerned about\nthe analytical methodologies employed. Interpretations come and go but the data\nremain forever, therefore, it is essential that both data and metadata are generated\n4\nand reported with utmost care. As stated, the Pb isotope section appears correct. Error\nreporting is, however, missing.\nReply: We agree with the reviewer’s comment regarding the use of “JNdi-1\nmeasurements during the analytical session to determine the external reproducibility”.\nIn the present manuscript (Line No. 518-520), the external reproducibility of the\nsamples ranging from 0.12–0.27 was determined based on the repeat measurements\nof the JNdi-1 in each analytical session as can be seen in the figure provided for the\ncomment above. Therefore, this is the same as the researchers typically use JNdi-1\nmeasurements during the analytical session to determine external reproducibility.\nWe sincerely would like to thank reviewer for the comments and suggestions to\nimprove the clarity on the Nd isotope data reporting. In view of the comments, we have\nclarified and illustrated the reliability of our measurements more clearly in the revised\nversion of the manuscript.\nReviewer #2 (Remarks to the Author):\nAs mentioned in my previous review, the data presented by Rahaman et al. are a\nuseful contribution towards unravelling WAIS history. The authors have improved the\nmanuscript since the previous submission and I am happy with the changes to the title\nand inclusion of the Wang et al. (2022) and Lamy et al. (2024) records. I also\nappreciate the more detailed discussion of subglacial geology in the supplement.\nHowever, I still do not believe the data available are sufficient to support the conclusion\nthat the WAIS remained close to its modern extent throughout the Pleistocene.\nReply: We thank for the insightful comments and suggestions. We have addressed\nmost of the points raised and incorporated all the suggestions into the revised\nmanuscript.\nIn response to the comment on one of the conclusions i.e. “the WAIS remained close\nto its modern extent throughout the Pleistocene”, we re-examined the Pleistocene ε\nNd\nrecords, focusing on the low-amplitude variations (Line No. 244-261). We have added\na new figure (Fig. 4) in the revised manuscript with a closer look at the Pleistocene \nNd\nvariability at narrower scale and added magnetic susceptibility, as well as geochemical\n5\ndata such as K/Al and principal component analysis of elementals ratios to derive the\nsignal that related to lithogenic changes driven by source variations (Fig. 4a). Our\ninvestigations presenting these additional data in the revised manuscript reveals\nmoderate ice-sheet fluctuations towards the end of late Pleistocene interglacials (Fig.\n4a), with the most prominent excursion during the MIS 5e which are consistent in all\nproxy records. However, other interglacial periods display more muted responses. Our\nreassessment supports significant ice-sheet retreat during MIS 5e; however, this\nretreat did clearly not reach the extent that occurred in the Pliocene. Further, our data\ndo not support large-scale retreat or collapse of the WAIS during other Pleistocene\ninterglacials, including the most intense super interglacial MIS 31 (1081-1062 ka),\nwhich was subject to the highest insolation values of the last ~5 Ma (Laskar et al.,\n2004), driven by high obliquity, eccentricity, and precession that led to an unusually\nwarm and prolonged interglacial. Based on these findings, we have revised our\ndiscussion and conclusions in the revised manuscript. We hope these revisions are\neasier to follow hence strengthening our conclusions.\n• Not satisfactorily explaining the ε value of ~-6 in the Pleistocene: I previously\nNd\ncommented that the outliers in the dataset were not properly discussed. It is certainly\nfeasible that the outliers with more radiogenic ε values could be influenced by\nNd\nvolcanic detritus and welcome the addition of this text. However, there remains no\ndiscussion of the single data point with a less radiogenic ε value (~-6) in the\nNd\nPleistocene. This is not easily explained as volcanogenic, as such material would have\nε values of ~+5. I still feel this data point is not well enough explained, as it could\nNd\nsuggest a significant change in provenance. This would likely translate to a change in\nice sheet extent, in contrast to the manuscript’s conclusion of Pleistocene WAIS\nstability. Some discussion of this data point is needed, ideally in the context of the\nother types of data available.\nReply: With regard to this comment, we have thoroughly re-examined the outliers,\nincluding the less radiogenic ε value (~-6) that was found to be associated with\nNd\nelevated IRD supply by ocean currents.\nOur ε measurements at Site U1532 were conducted on bulk detrital sediments, and\nNd\nhence most likely these outliers could reflect contributions from coarse-grained\niceberg-rafted debris (IRD). Wang et al. (2022, Geochemistry, Geophysics,\ncore ANT3434/A2 in the Amundsen Sea, which offers a continuous late Pleistocene\nIRD provenance record (spanning 770 ka) based on detrital Sr-Nd isotopes. Their\nstudy identified a distinct shift in IRD sediment provenance during MIS 16, linked to\n∼\nregional ocean circulation changes. Wang et al. suggested that prior to MIS 16, an\nexpanded Ross Gyre controlled iceberg trajectories, transporting less radiogenic\nsediments from Sulzberger Bay to the site ANT3434/A2. After MIS 16, the Ross Gyre\ncontracted due to the poleward shift of the Amundsen Sea Low at the end of the Mid-\nPleistocene Transition. This contraction reduced connectivity between the Southern\nBoundary of the Antarctic Circumpolar Current (SBACC) and these sites, allowing the\nAntarctic Slope Current (ASC) to deliver more radiogenic sediments from sources\nsuch as the Antarctic Peninsula coast, the western Amundsen Sea, or volcanic regions\nlike Marie Byrd Land. In view of this interpretation, we plotted our bulk detrital ε data\nNd\nwith Wang et al.'s IRD records. We find that the less radiogenic ε value (~-6) in our\nNd\nrecord aligns closely with the IRD value from core ANT3434/A2 during MIS 16 (see\nsupplementary Fig. 7, same shown below).\n.\nNd\niceberg trajectories influenced by ocean currents. (a) Post-MIS 16 iceberg trajectories are similar to\nmodern patterns indicated by black dashed lines, adapted from Wang et al. (2022). (b) Iceberg\ntrajectories prior to MIS 16, is depicted with black dashed lines, reflecting the expanded influence of the\nRoss Gyre during this period.\nThis supports the interpretation that these less radiogenic sediments originated from\nthe Sulzberger Bay under the influence of an expanded Ross Gyre and more\nradiogenic sediments from the Antarctic Peninsula coast, western Amundsen Sea, or\nvolcanic regions like Marie Byrd Land. We have added this discussion in the main text\n(Line No. 148 to 161) and also included a supplementary section 3.1 along with a\nfigure (supplementary Fig. 7, same as shown above) in the supplementary material.\nWe hope that the addition of this figure and extended discussion strengthen our\ninterpretation of the outliers in the revised version.\n• Lack of glacial-interglacial change in the Pleistocene: It is difficult to reconcile that\nthere is no cyclic pattern in the provenance data with the unequivocal evidence for\nmajor change to WAIS extent over glacial-interglacial cycles. This points to a lack of\nsensitivity of the provenance proxies used here to ice extent changes in this region;\nlooking at these data alone, for instance, would suggest that there was no ice advance\nin the last glacial period which is clearly false. I think it is therefore impossible to say\nthat the site is sensitive to any retreat of Pine Island/Thwaites glaciers.\nReply: The lack of pronounced glacial-interglacial cyclicity in the provenance data\ncould be due to a lower sensitivity of these proxies and sites to changes in ice sheet\nextent during the Pleistocene. However, please note that our detrital  record shows\nNd\na clear and distinct change during the Pliocene-Pleistocene transition. Therefore, the\nsite and the proxies (detrital  , Pb isotope) are indeed sensitive to Pliocene –\nNd\nPleistocene changes when ice-sheet retreat progressed far inland reaching and\nexposing a distinct lithology with less radiogenic values (e.g. Ellsworth Mountain\nblock). However, our Nd and Pb isotope records were less sensitive to Pleistocene\nglacial-interglacial changes when variability in the ice-sheet extent was restricted\nwithin the Pine Island and Thwaites basins. Due to limited exposure of the bed rock\nand poorly constrained isotope signature in subglacial geology, it is difficult to quantif<\nthe exact extent of ice sheet retreat. We have modified the discussion accordingly in\nthe revised manuscript to acknowledge this caveat.\nin the Pleistocene”, we have re-examined the entire detrital ε dataset, equally\nNd\nfocusing more closely on Pleistocene sequences. In doing so, we identified systematic\ncyclic patterns towards the end of the late Pleistocene, particularly a pronounced\npositive ε excursion during the MIS 5e based on the trend derived from a Loess fit\nNd\non the compiled records (a non-parametric fit, see Figure below panel b).\nThis observation is also consistent with new geochemical data (principal component\nanalysis of elemental ratios, PC1) and magnetic susceptibility data related to lithogenic\nvariations shown in the new figure (Fig. 4) in the revised manuscript. However, it is\n9\nintriguing that similar shifts in sediment sources were not observed in other\nPleistocene intervals including during the so-called “super interglacials”. We have\nmodified our interpretation in the revised section “West Antarctic ice sheet dynamics\nduring Pleistocene glacial-interglacial cycles” of the manuscript and added a new\nfigure (Figure 4, same as shown below) in the main text.\n• Ice sheet margin retreat may not result in erosion of rocks with different isotopic\nsignatures: The isotopic proxies used may be insensitive lack of change in the geology\nfurther inland. Although Thwaites and Pine Island glaciers do indeed have a distinct\nisotopic signature, it could easily be the case that this signature in relatively invariant\nfar inland in an along-flow direction, until a very different geological terrane is reached\n(e.g., the Ellsworth-Whitmore Mountains). Retreat of the ice sheet margin may\ntherefore not lead to any change in these provenance proxies at core sites offshore.\nThe authors also argue that “… erosion was restricted from the Pine Island basin\nlocated interior compared to the Thwaites basin” (line 184). Retention of Pine Island\nGlacier when Thwaites Glacier is lost is not feasible or compatible with models of WAIS\ncollapse, which lose both glaciers when marine ice sheet instability takes effect (e.g.\nDeConto et al., 2021; Golledge et al., 2021, etc.). Even if retreat initiates from Thwaites\nGlacier, Pine Island Glacier is not laterally constrained once Thwaites Glacier is lost.\nReply: We agree that significant isotopic shifts caused by ice sheet retreat would likely\nonly occur if the retreat extended far into the interior, up to Ellsworth-Whitmore\nMountains (EWM, ε -8, Robinson et al., 2021, Chemical Geology). The shift from\nNd\nPliocene ε values around -8 to Pleistocene values near -3 suggests that the present\nNd\ncore site U1532 and  proxy are sensitive to a substantial inland retreat reaching the\nNd\nEWM. However, if the ice-sheet fluctuations are moderate and confined within the\nThwaites and Pine Island regions, only moderate isotopic variability would be expected\nwhich is the case throughout the Pleistocene. Due to the rock exposure and poorly\nconstrained isotopic compositions, tracing the precise lithology at the extent of the ice-\nsheet retreats remains challenging.\nIn response to the major concern about the apparent stability of Pleistocene ε\nNd\nsignals, we have carefully re-examined the variability. In our earlier versions, the full\n10\nrecord was always plotted on a broad scale to accommodate the large shift from less\nradiogenic Pliocene (-8) values to more radiogenic Pleistocene values, including\nradiogenic outliers (ε ~ -0.66 ± 0.28, n=3). On this scale, moderate glacial-interglacial\nNd\nvariability in the Pleistocene is often difficult to resolve. To resolve these subdued\nvariations, the scale was zoomed in on the Pleistocene data (ε scale: -4.5 to -2.5),\nNd\nrevealing the emergence of cyclic pattern towards the end of the Pleistocene with the\nmost prominent positive excursion during the MIS 5e. This excursion aligns with\nvariations in other geochemical (first principal component PC1 from the PCA analysis\nof elemental rations, K/Al ratio) and magnetic susceptibility data, indicating significant\na retreat during MIS 5e. However, the muted response during other interglacials\nsuggests no major ice sheet retreat. We have revised the manuscript accordingly.\n• Ocean transport is dismissed: I appreciate the inclusion of a new section on ocean\ncurrent transport, which was not sufficiently acknowledged in the previous version of\nthe manuscript. The authors argue against ocean current influence on the record here\ndue to: 1) The lack of variability over glacial-interglacial cycles in this (and nearby)\nprovenance records, 2) The lack of correlation with the Lamy et al. (2024) ACC record,\nand 3) the kaolinite present, which is the dominant clay mineral beneath Thwaites\nGlacier. However, I still think it is very likely that detritus at this site may be sourced,\nat least partly, from the Bellingshausen Sea/Antarctic Peninsula region at present and\nin the past. For instance, the path of modern icebergs, which will also carry fine-\ngrained detritus, is predominantly to the top of the continental shelf above U1532 (see\nmodelling of Rackow et al., 207, DOI:10.1002/2016JC012513), where such debris can\nflow down-slope to this core site. Rocks from the Antarctic Peninsula are a feasible\nisotopic endmember, as shown here in Fig. 3. The consistent provenance signature\nthrough the Pleistocene could potentially reflect a lack of isotopic variation in the\nsource region(s) towards the Antarctic Peninsula, resulting in no glacial-interglacial\nvariation. Furthermore, the kaolinite present in the record is not sufficiently abundant\nto be certain that the bulk sediment is derived predominantly from the Amundsen Sea\nEmbayment. I therefore suggest that it should be acknowledged that the Antarctic\nPeninsula/Bellingshausen Sea cannot be excluded as a potential source region, now\nand in the past, using the available data.\nsource region and have expanded the discussion on ocean currents in the revised\nmanuscript (line no. 150 to 156, and supplementary section 3 “Role of bathymetry and\nocean currents in sediment transport and dispersal”).\nTo summarise, I would argue that the isotopic proxies used here are not sensitive\nenough to changes in ice sheet extent in this region to argue that there was no\nsignificant retreat into the Amundsen Sea sector of the WAIS in the Pleistocene. It is\nalso impossible to exclude a sediment source from the Antarctic Peninsula or\nBellingshausen Sea catchment. The ε value of ~-6 in the Pleistocene also requires\nNd\nexplanation. I do not feel the datasets presented here are able to identify loss of large\nparts of the Amundsen Sea sector of the WAIS because, even if Site U1532 directly\nrecords the Amundsen Sea sector of the WAIS, subglacial geology is potentially\nisotopically uniform enough further inland that a provenance change may not be\nrecorded until a very different geological province is reached. This would likely be the\nEllsworth-Whitmore Mountain block, requiring a near-complete WAIS collapse. A\nbroadly uniform isotopic composition of the source geology parallel to ice flow for this\nregion is also consistent with the lack of glacial-interglacial cyclicity in the record here.\nReply: We agree and address these major points in the revised manuscript (as\noutlined above). However, we nevertheless want to reiterate that the extent of the\nnear-coastal geology inland from Pine Island and Thwaites Glacier is unknown given\nthat it is covered by ice, yet may be more heterogeneous than implied by the reviewer.\nPresent sites and proxies are sensitive to large-scale changes, particularly the retreat\nof the ice sheet during the Pliocene and subsequent growth during the Pliocene-\nPleistocene transition. However, we observed a moderate and/or muted response\nduring the glacial-interglacial cycles of the Pleistocene. The less radiogenic ε values\nNd\nof -8 indicate a large-scale retreat or collapse of the ice sheet, potentially extending\ndeep interior reaching up to the Ellsworth-Whitmore Mountains, which would supply\nless radiogenic (ε -8, Robinson et al., 2021, Chemical Geology) sediments. In\nNd\ncontrast, variability during the Pleistocene is much smaller. However, closer insights\nof the Pleistocene records (in the current revised manuscript) show the emergence of\nmoderate cyclicity towards the end of the Pleistocene with the most prominent\nexcursion during the MIS5e, which indicates significant ice-sheet retreat, but not up to\n12\nthe extent observed during the Pliocene. Due to limited exposure of the bedrock and\npoorly constrained isotope signature in subglacial geology, it is difficult to quantify the\nexact extent of ice sheet retreat. We acknowledge this caveat and the text is modified\nin the revised manuscript accordingly (line 235 -237).\nOur revised conclusion for the Pleistocene is (i) Significant ice sheet retreat during the\nMIS5e but our data does not support any evidence for the large-scale retreat in the\nother interglacials, (ii) Though our investigation reveals significant retreat in the ice\nsheet during MIS5e but was not as extensive as occurred in the Pliocene. We have\nrevised our discussion in the revised manuscript to clarify these points and\nincorporated your suggestions.\nI would suggest that the “Evidence for a largely stable Pleistocene WAIS” section\nis removed, as well as this conclusion at line 264-266. Potentially, the interpretation of\nthe data could be pushed as far as saying there were few, if any, complete collapses\nof the WAIS in the Pleistocene (except, perhaps the ε value of ~-6), and this is a\nNd\nuseful finding. However, I do not think it is possible to fully eliminate the possibility of\na reasonably large-scale retreat of the WAIS in the Pleistocene. I would therefore\nsuggest refocussing the manuscript with emphasis on the Pliocene ice sheet being\nsignificantly retreated, which is a novel and useful finding in this region well worthy of\npublication in Nature Communications.\nReply: Yes, we agree and have modified the section heading and revised our\ndiscussion accordingly (line 222).\nUpon re-examining the detrital ε records for Pleistocene variability, we observed an\nNd\napparent cyclic pattern towards the end of the late Pleistocene, with the most\npronounced during the MIS 5e, suggesting significant retreat. However, no\nunequivocal evidence for a similar retreat during any of the so-called “Super\nInterglacials” in the Pleistocene. Therefore, based on the re-evaluation of the variability\nin detrital  records and including additional data and their analysis, we agree on the\nNd\nsuggestion of the significant retreat of ice sheet retreat during the MIS 5e and revised\nthe manuscript accordingly.\nThe authors also still do not reference the major compilation of seafloor surface\nsediment provenance indicators from this sector by Simões Periera et al. (2018, DOI:\n13\n10.1016/j.earscirev.2018.04.011). This highly relevant piece of literature should be\ncited.\nReply: Cited in the revised manuscript.\nLine-by line comments:\nLines 24-26: see major comments – I do not think that the data are able to support\nthe statement that the Pliocene-Pleistocene transition represents the tipping point for\nWAIS stability.\nReply: This sentence has been modified in the revised abstract. However, comparing\nthe reconstructed WAIS record of the Pliocene-Pleistocene transition with the climate\nrecords and forcing factors (CO levels and orbital forcing), allows us to infer the range\nof conditions for the growth of the ice-sheet with a reasonable level of confidence. As\n₂\nper the suggestion, the text is modified in the revised manuscript. And we would like\nto point out again that the late Pliocene underwent substantial changes that led to this\nclearly distinct sediment sourcing during the Pleistocene.\nLine 184: “erosion was restricted from the Pine Island basin located interior compared\nto the Thwaites basin” – as outlined in my other comments, losing Thwaites Glacier\nbut keeping Pine Island Glacier seems unlikely – I would suggest the signature comes\nfrom further inland (potentially the Ellsworth-Whitmore Mountain block).\nReply: Agreed. We have revised our discussion and incorporated the suggestion of\nthe source of the Ellsworth-Whitmore Mountain block which could provide less\nradiogenic sediments during the Pliocene.\nLine 191: I agree the degree of retreat seen in the Pliocene seems unlikely for the\nPleistocene but would add a statement that some retreat cannot be excluded using\nthese provenance proxies alone because of potentially homogenous subglacial\ngeology and lack of ability to detect glacial-interglacial cycles.\nReply: We have revised the discussion as suggested in the revised version (line 235-\n237).\nReply: Agreed. This has been modified in the revised manuscript.\nLine 232: I’m not clear on what evidence there is to say that this smaller ice sheet was\n“dynamic”? There are no rapid fluctuations in the provenance data?\nReply: The text has been revised. This was based on seismic (Gohl et al., 2021; GRL)\nand model study (Halberstadt et al., 2024; Nat Comms) from the same site (Line No.\n199-206).\nLine 247: I would clarify that it a new model simulation, as the ice sheet model itself\nis not new.\nReply: Text has been revised.\nLine 266-267: More than one ice-sheet model simulation exists, so I would change\nthis sentence to “An ice-sheet model prediction for the Pliocene is consistent with our\nproposition (reference)”.\nReply: Thanks for the suggestions. This sentence has been revised (Line 331 -332).\nFigure 3 a): The caption should be adjusted as the map does not show subglacial\ngeology, only exposed geology.\nReply: The caption text has been revised (Line 370).\nFigure 3 b): The interpolated sub-ice estimate of ε values is still incorrect – for\nNd\ninstance, it is known that Pine Island and Thwaites glaciers are underlain by substrate\nwith very different ε values (Simões Periera et al., 2020), but here they are both\nNd\nshaded a uniform orange.\nReply: Figure 3b has been revised.\nLine 336: Is there a reason the 2020 geological timescale is not being used? Either\nthis more up to date age scale should be used, or the reasoning for using the 2012\none should be explained.\non-board paleomagnetic (PMAG) analyses conducted for correlating\nmagnetostratigraphic polarity zones at Site U1532. At that time, the latest available\ngeological timescale for such correlations was GTS2012 from Gradstein et al. (2012).\nThis timescale was chosen to ensure consistency with the analyses performed during\nthe expedition. The GTS2012 includes orbitally tuned reversals between Chron C1n\nand the base of Subchron C5r.2n (0–11.657 Ma).\n16"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I have now read Rahaman et al.'s manuscript entitled “Late Pliocene Growth of the West Antarctic Ice Sheet to Near-Modern Configuration” multiple times (across various versions). Initially, I had concerns similar to those of my fellow reviewer. However, I believe the authors have made significant improvements to the manuscript over time. While I agree with Review 2 on several points, the data presented here is valuable to the relevant scientific community.\nThe authors have satisfactorily addressed my comments in relation to the analytical nuts and bolts. I only wish they would had been more careful in reporting these in the first place.\nMinor comments:\nLines 183-190: The text should be re-evaluated as it seemed contradictory to me.", "reviewer_2": "The authors have once more improved the manuscript substantially and addressed most of my previous remarks satisfactorily. I particularly welcome the new discussion of the outlying data points. I am also pleased to see more appreciation regarding the potential role of ocean currents at this site (e.g., lines 170-172). I agree that IRD could contribute to the anomalous data points (lines 184-185) as the measurements are on the bulk sediment. The anomalous point with an εNd value of ~-6 coinciding with less radiogenic IRD in the Wang et al. (2022) record is also a useful observation.\nI also appreciate the new discussion of potentially isotopically uniform geology to explain the broadly consistent Pleistocene signature (i.e., without glacial-interglacial cycles; lines 222-239). This addresses my point that it is impossible to say there was no change in Pleistocene, only that there was reduced sustained large-scale retreat compared to the Pliocene.\nI do, however, have the more major points on the new section addressing MIS 5e:\n• Evidence for a provenance shift during the MIS 5e interglacial is discussed. However, performing a Loess smoothing through data through multiple sites has the potential to bias the curve depending on the density of data points from different sites. Although εNd values are broadly similar across different sites, PC493 appears on average to be slightly more radiogenic. Simply having more samples from this site, particularly in the latter part of MIS 5e, could therefore easily result in the pattern seen. Although I welcome examination of these smaller amplitude changes, I would encourage the authors to think of a way to overcome this problem and better visualise this subtle change over MIS 5e.\n• Furthermore, a positive εNd excursion during the MIS 5e interglacial has already been described in reference 20 (Simões Pereira, 2018). This reference must be clearly cited (around line 250) to make clear that this observation is not original. Furthermore, “younger mafic rocks” (line 254) as the source lithology were also suggested by reference 20, which should be referenced again here.\nLine by line comments:\nLine 43: I wouldn’t say it’s an alternative approach. Maybe best to say a complimentary approach?\nLine 127: “…and are thereby…”\nLine 128: Remove streams: “These two glaciers supply…”\nLine 133: “…Table S2; however, …”\nLines 152-156: this reads as if the authors have looked at IRD provenance in this record, which I don’t think is the case. The paper(s) doing this characterisation should be cited here. Also, on line 154 the authors state “The AP sector showed relatively young ages…” but it is not clear what ages these are?\nLine 162: “…the continental shelf…”\nLines 162-165: This statement regarding sediment routing is not supported. There should be a reference here (to the cruise report maybe?).\nLin 191: I would call it a provenance record rather than an erosion record, as there will be some transport element.\nLine 208: I do not understand why the ice shelf front would be broader in the Pliocene?\nLine 219: “…compared to the Pliocene…”\nLine 221: I would be more specific about the degree of retreat into the interior of West Antarctica by suggesting erosion near the Ellsworth-Whitmore Mountains.\nLine 235: ”… far enough inland to erode and transport sediments from this location throughout the Pliocene”?\nLine 247: “reduced the y-axis scale”?\nLines 250-251: I do not think the positive excursion in the Loess fit during MIS 5e is particularly “prominent” and would suggest removing this word.\nLine 260: More pronounced than what? Do you mean inland of the present-day position?\nLines 265-266 and 316-318: There are only two data points in MIS 31, neither of which are from the new record presented here. Making interpretations regarding this time period therefore seems a bit of a stretch.\nLine 272: I would suggest adding “…may have occurred during the MIS 5e…” to express greater uncertainty.\nLine 319-320: I suggest again adding “…Pleistocene may have exerted insufficient thermal forcing…” to express uncertainty.\nLine 329-331: I suggest amending this to: “In conclusion, our data suggest a more stable WAIS during the Late Pleistocene relative to the Pliocene. Near total loss of its marine-based portions, with the ice sheet margin retreating near to the Ellsworth-Whitmore Mountains, is unlikely to have occurred, even during the most intense interglacials of the late Pleistocene.”. This is more specific about the amount of retreat likely to be required to see an isotopic shift.\nLine 455: Should this be “i.e. from 0 to 10 m…” ?\nThe author’s name for reference 20 is still spelt wrong (author is the same as the first author for references 22 and 23).\nComments on the supplement:\nSupplement lines 105-108: Simões Pereira, P. et al. 2018 (main references 23) should be included as a reference here.\nSupplementary Fig. 4: The arrow directions in panel f) are confusing as the Antarctic Coastal Current flows consistently westwards, rather than converging in the Amundsen Sea."}, "author_response": "Response to Reviewer’s comments\nManuscript No.: NCOMMS-24-49341A\nManuscript Title: Late Pliocene growth of the West Antarctic Ice Sheet to Near-modern\nconfiguration\nManuscript submitted to the Journal: Nature Communications\nREVIEWER COMMENTS\nReviewer #1 (Remarks to the Author):\nI have now read Rahaman et al.'s manuscript entitled “Late Pliocene Growth of the\nWest Antarctic Ice Sheet to Near-Modern Configuration” multiple times (across various\nversions). Initially, I had concerns similar to those of my fellow reviewer. However, I\nbelieve the authors have made significant improvements to the manuscript over time.\nWhile I agree with Review 2 on several points, the data presented here is valuable to\nthe relevant scientific community.\nThe authors have satisfactorily addressed my comments in relation to the analytical\nnuts and bolts. I only wish they would had been more careful in reporting these in the\nfirst place.\nReply: We thank reviewer #1 again for his/her thorough and constructive review of the\nmanuscript.\nMinor comments:\nLines 183-190: The text should be re-evaluated as it seemed contradictory to me.\nReply: Text has been revised (Line no. 187-195)\nReviewer #2 (Remarks to the Author):\nThe authors have once more improved the manuscript substantially and addressed\nmost of my previous remarks satisfactorily. I particularly welcome the new discussion\nof the outlying data points. I am also pleased to see more appreciation regarding the\npotential role of ocean currents at this site (e.g., lines 170-172). I agree that IRD could\ncontribute to the anomalous data points (lines 184-185) as the measurements are on\nthe bulk sediment. The anomalous point with an ε value of ~-6 coinciding with less\nNd\nradiogenic IRD in the Wang et al. (2022) record is also a useful observation.\nReply: We also want to thank reviewer #2 again for the constructive criticism towards\nour manuscript.\nI also appreciate the new discussion of potentially isotopically uniform geology to\nexplain the broadly consistent Pleistocene signature (i.e., without glacial-interglacial\ncycles; lines 222-239). This addresses my point that it is impossible to say there was\nno change in the Pleistocene, only that there was reduced sustained large-scale\nretreat compared to the Pliocene.\nReply: We agree and are thankful for this earlier suggestion.\nI do, however, have the more major points in the new section addressing MIS 5e:\n• Evidence for a provenance shift during the MIS 5e interglacial is discussed. However,\nperforming a Loess smoothing through data through multiple sites has the potential to\nbias the curve depending on the density of data points from different sites. Although\nε values are broadly similar across different sites, PC493 appears on average to be\nNd\nslightly more radiogenic. Simply having more samples from this site, particularly in the\nlatter part of MIS 5e, could therefore easily result in the pattern seen. Although I\nwelcome examination of these smaller amplitude changes, I would encourage the\nauthors to think of a way to overcome this problem and better visualise this subtle\nchange over MIS 5e.\nReply: There seems to be a misunderstanding towards the Loess fit approach taken\nhere. The Loess fit is a non-parametric smoothing technique that accounts for\nvariations in data density, as it is based on localized regression rather than assuming\na global trend. This approach helps minimize potential biases arising from uneven data\ndistribution across sites.\nIn response to the concern raised, we have re-examined individual records by plotting\nthem separately. A new figure is provided in the supplementary (Supplementary Fig.\n8). Please see the same below. Our analysis of PC493, PS58/254, and U1532 shows\na distinct shift toward more radiogenic values during MIS 5e. This is captured across\nthe individual records and is also consistent with the trend in the Loess fit, confirming\nthat the observed radiogenic excursion during MIS 5e is a real signal rather than an\nartifact of data density bias.\nFurther, we acknowledge that a similar pattern has been previously reported for the\ncore site PS58/254 which is close to our site and site PC493 (Simoes Parera, 2019),\nand we have now included this reference in the main text.\nSupplementary Fig. 8 (this new figure is added in the supplementary)\n• Furthermore, a positive ε excursion during the MIS 5e interglacial has already been\nNd\ndescribed in reference 20 (Simões Pereira, 2018). This reference must be clearly cited\n(around line 250) to make clear that this observation is not original. Furthermore,\n“younger mafic rocks” (line 254) as the source lithology were also suggested by\nreference 20, which should be referenced again here.\nReply: As suggested, reference is included in the revised manuscript.\nLine by line comments:\nLine 43: I wouldn’t say it’s an alternative approach. Maybe best to say a complimentary\napproach?\nReply: Suggestion incorporated (line no. 43).\nLine 127: “…and are thereby…”\nReply: Sentence modified (line no. 127-128).\nLine 128: Remove streams: “These two glaciers supply…”\nReply: Suggestion incorporated (line no. 128).\nLine 133: “…Table S2; however, …”\nReply: Suggestion incorporated (line no. 133).\nLines 152-156: this reads as if the authors have looked at IRD provenance in this\nrecord, which I don’t think is the case. The paper(s) doing this characterisation should\nbe cited here. Also, on line 154 the authors state “The AP sector showed relatively\nyoung ages…” but it is not clear what ages these are?\nReply: IRD provenance paper(s) has been cited (Line no. 152 and 154) and also the\ntext has been modified (Line no. 156-159).\nLine 162: “…the continental shelf…”\nReply: Incorporated (Line no. 168).\nLines 162-165: This statement regarding sediment routing is not supported. There\nshould be a reference here (to the cruise report maybe?).\nReply: As suggested, necessary references are provided (Line no. 167-170).\nLin 191: I would call it a provenance record rather than an erosion record, as there will\nbe some transport element.\nReply: Suggestion incorporated (line no. 196).\nLine 208: I do not understand why the ice shelf front would be broader in the Pliocene?\nReply: Text has been revised (Line no. 212-214).\nLine 219: “…compared to the Pliocene…”\nReply: Suggestion incorporated (Line no. 224).\nLine 221: I would be more specific about the degree of retreat into the interior of West\nAntarctica by suggesting erosion near the Ellsworth-Whitmore Mountains.\nReply: As suggested, the text has been revised (Line no. 226).\nLine 235: ”… far enough inland to erode and transport sediments from this location\nthroughout the Pliocene”?\nReply: This sentence is revised accordingly (Line no. 241).\nLine 247: “reduced the y-axis scale”?\nReply: Sentence has been modified (Line no. 253).\nLines 250-251: I do not think the positive excursion in the Loess fit during MIS 5e is\nparticularly “prominent” and would suggest removing this word.\nReply: Removed (Line no. 259-260).\nLine 260: More pronounced than what? Do you mean inland of the present-day\nposition?\nReply: More pronounced than other Pleistocene Interglacials. The text has been\nrevised accordingly (Line 269).\nLines 265-266 and 316-318: There are only two data points in MIS 31, neither of which\nare from the new record presented here. Making interpretations regarding this time\nperiod therefore seems a bit of a stretch.\nReply: Yes, we agree. These sentences have been revised (Line no 272-275 and 324-\n325).\nLine 272: I would suggest adding “…may have occurred during the MIS 5e…” to\nexpress greater uncertainty.\nReply: Agreed and revised (Line no. 281).\nLine 319-320: I suggest again adding “…Pleistocene may have exerted insufficient\nthermal forcing…” to express uncertainty.\nReply: Suggestion incorporated (Line no. 326).\nLine 329-331: I suggest amending this to: “In conclusion, our data suggest a more\nstable WAIS during the Late Pleistocene relative to the Pliocene. Near total loss of its\nmarine-based portions, with the ice sheet margin retreating near to the Ellsworth-\nWhitmore Mountains, is unlikely to have occurred, even during the most intense\ninterglacials of the late Pleistocene.”. This is more specific about the amount of retreat\nlikely to be required to see an isotopic shift.\nReply: Suggestion has been incorporated (Line no. 336-340).\nLine 455: Should this be “i.e. from 0 to 10 m…” ?\nReply: Corrected (Line no. 463).\nThe author’s name for reference 20 is still spelt wrong (author is the same as the first\nauthor for references 22 and 23).\nReply: Thanks. We have taken care in the revised manuscript.\nComments on the supplement:\nSupplement lines 105-108: Simões Pereira, P. et al. 2018 (main references 23) should\nbe included as a reference here.\nReply: Reference has been added.\nSupplementary Fig. 4: The arrow directions in panel f) are confusing as the Antarctic\nCoastal Current flows consistently westwards, rather than converging in the\nAmundsen Sea.\nReply: This figure has been revised."}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have satisfactorily addressed most of the concerns I raised in earlier iterations of this manuscript. I do, however, have two major concerns remaining:\n1. I do not completely oppose the use of the Loess fit and agree that plotting these datasets separately in Fig. S8 is useful. However, I do not see how the fit will remain unbiased if there happen to be more data from a site with a more/less radiogenic mean signature. In my attached synthetic example, I show a scatter plot with data from two ‘sites’ (red and blue) with constant ’provenance values’ of 1 and 3, respectively. I run a Loess fit through these (black line). In panel a), samples from the two sites are equally distributed over depths 1-10. However, if I take an example where the blue site has a lower sample density at depths 6-10 (panel b), the Loess curve is fitted closer to the data from the red site, simply because it has a higher sample density.\nThis distinction is important because the current text misleadingly suggests that there is a positive Nd isotope excursion at all of the sites, when this is in fact limited to sites PC493a and PS58/254, with no obvious excursion at Site U1532 if that record is examined alone. I therefore suggest rewriting the sentences on lines 257-259, currently: “This pattern is consistent with the previous report of shifting detrital eNd values towards more radiogenic values as captured in individual records from the core sitePS58/254 and PC49320.” To: “As we have few datapoints for MIS5e at Site U1532, this pattern in the Loess fit is primarily a result of shifting detrital eNd values towards more radiogenic values at sites PS58/254 and PC493, as previously reported20.”. Similarly, at line 261-268 the authors are presumably describing changes at U1532 (where there is no clear Nd isotope excursion), but this is never stated. Although I believe the conclusion, there should again be some acknowledgement here that there is no clear Nd isotope excursion at U1532 during MIS5e due to a lack of samples and that this interpretation is based off data from the other sites.\n2. This leads on to my primary concern that the current version of this manuscript contains interpretations of WAIS extent during MIS5e based entirely on data from sites PC493 and PS58/254. I am pleased that the authors have improved their citing of the Simões Pereira (2018) PhD thesis, which contains the PC493 and PS58/254 data. However, I echo my comments to the editor on the first draft of this manuscript stating that whilst this thesis is now publicly accessible, I am aware that no effort was made to contact the data generator or their PhD advisors despite them remaining active scientists. Given that the site PC493 and PS58/254 datasets have not been published in peer-reviewed literature before, I would strongly encourage the authors to reach out to the thesis author and/or their supervisors so that their considerable efforts generating these records can be properly acknowledged.\nMinor and line-by-line points:\n• The Ellsworth-Whitmore Mountains are stated as the main source region during the Pliocene on line 226, but the signature of this source region is not identified until line 238. I feel the signature needs to be discussed first, as otherwise it is not clear at line 226 why the EWM are being mentioned.\n• Line 105: As mentioned in the comment above, these datasets are not yet “published” in peer-reviewed literature.\n• Line 131: “We observe some overlap…” would be better as “There is some overlap…”, as at the moment it reads like a new observation from this study, which is not the case.\n• Line: 158-159: “… relatively young ages…” Relative to what? It would be better to be more quantitative.\n• Line 165: Worth adding that this is at site ANT34/A2-10.\n• Line 166: Change “comprises” to “includes”?\n• Line 263: The younger rocks are not all mafic. I suggest deleting the word mafic or specifying that Cenozoic volcanic rocks are being referred to.\n• Line 270-272: Which ice stream is being discussed? This sentence is not clear. Also, I am not aware of any mafic sedimentary rocks on Thurston Island? I would recommend clarifying this - maybe replacing “mafic sediments” with “detritus”?\n• Line 284: It is not clear which data are being referred to here."}, "author_response": "Response to Reviewers' comments\nReviewer #2 (Remarks to the Author):\nThe authors have satisfactorily addressed most of the concerns I raised in earlier\niterations of this manuscript. I do, however, have two major concerns remaining:\n1. I do not completely oppose the use of the Loess fit and agree that plotting these\ndatasets separately in Fig. S8 is useful. However, I do not see how the fit will remain\nunbiased if there happen to be more data from a site with a more/less radiogenic mean\nsignature. In my attached synthetic example, I show a scatter plot with data from two\n‘sites’ (red and blue) with constant ’provenance values’ of 1 and 3, respectively. I\nrun a Loess fit through these (black line). In panel a), samples from the two sites are\nequally distributed over depths 1-10. However, if I take an example where the blue site\nhas a lower sample density at depths 6-10 (panel b), the Loess curve is fitted closer\nto the data from the red site, simply because it has a higher sample density.\nReply: We thank Reviewer #2 for his/her latest comments. In the revised manuscript,\nwe have removed two detrital ε records—PS58/254 and PC493 (see detailed\nNd\nexplanation below). Consequently, the Loess fit is no longer necessary to derive the\nweighted average trend from the two records (our record U1532 and another record\nANT34/A2-10) and has been removed from the updated version of Figure 4b. We have\nalso removed Fig. S8 from the supplementary of the revised version.\nThis distinction is important because the current text misleadingly suggests that there\nis a positive Nd isotope excursion at all of the sites, when this is limited to sites PC493a\nand PS58/254, with no obvious excursion at Site U1532 if that record is examined\nalone. I therefore suggest rewriting the sentences on lines 257-259, currently: “This\npattern is consistent with the previous report of shifting detrital  values towards more\nNd\nradiogenic values as captured in individual records from the core site PS58/254 and\nPC49320.” To: “As we have few datapoints for MIS5e at Site U1532, this pattern in the\nLoess fit is primarily a result of shifting detrital  values towards more radiogenic\nNd\nvalues at sites PS58/254 and PC493, as previously reported20.”. Similarly, at line 261-268 the authors are presumably describing changes at U1532 (where there is no clear Nd\nisotope excursion), but this is never stated. Although I believe the conclusion, there should again be some acknowledgement here that there is no clear Nd isotope excursion at U1532 during MIS5e due to a lack of samples, and that this interpretation is based on data from the other sites.\nReply: In the revised version of the manuscript, the detrital ε records from PS58/254\nNd\nand PC493, as well as the Loess fit, have been removed from Figure 4b. Accordingly,\nthe discussion in this section has been revised to avoid suggesting a basin-wide\npositive ε excursion, which now reflects the site-specific nature of the signal more\nNd\naccurately.\nSimilarly, at line 261-268 the authors are presumably describing changes at U1532\n(where there is no clear Nd isotope excursion), but this is never stated. Although I\nbelieve the conclusion, there should again be some acknowledgement here that there\nis no clear Nd isotope excursion at U1532 during MIS5e due to a lack of samples, and\nthat this interpretation is based on data from the other sites.\nReply: We have modified the text accordingly (Line 268-271).\n2. This leads on to my primary concern that the current version of this manuscript\ncontains interpretations of WAIS extent during MIS5e based entirely on data from sites\nPC493 and PS58/254. I am pleased that the authors have improved their citing of the\nSimões Pereira (2018) PhD thesis, which contains the PC493 and PS58/254 data. However, I echo my comments to the editor on the first draft of this manuscript, stating\nthat whilst this thesis is now publicly accessible, I am aware that no effort was made\nto contact the data generator or their PhD advisors despite them remaining active\nscientists. Given that the site PC493 and PS58/254 datasets have not been published\nin peer-reviewed literature before, I would strongly encourage the authors to reach out\nto the thesis author and/or their supervisors so that their considerable efforts\ngenerating these records can be properly acknowledged.\nReply: We appreciate and understand Rev-2’s comment, and accordingly, we\ncontacted Dr. Patric Simões Pereira (thesis author) and Prof. Tina van de Flierdt\n(thesis supervisor). They have requested to remove the data from the present\nmanuscript, even though the data are already publicly available since 2018.\nIn view of the major concern of the Rev-2 on the clarification of using data from this\nparticular thesis, we also contacted the Open Access team at Imperial College London\n(ask@imperial.ac.uk). They confirmed that, under the CC-BY-NC-ND license, the data\ncan be reused for non-commercial purposes with proper citation. I quote, “you will\nonly need to cite and reference the thesis and author, as long as the re-use is\nnon-commercial. As this thesis is under an CC-BY-NC-ND license. However, if\nyou need to re-use the data for commercial use, you will have to request\npermission directly from the author.”\nGiven that Dr. Simões Pereira requested not to use his data, we have decided to\nremove these two Pleistocene detrital  records (PC493 and PS58/254) from our\nNd\nmanuscript. Please note that the removal of this data does not impact the main\nconclusion of our study, which focuses on the late-Pliocene interval and, accordingly,\nthe title of our manuscript based on our data.\nIn this context, we would also reiterate a comment made by Rev-2 in the original\nversion (1st submission) “I would therefore suggest refocusing the manuscript\nwith emphasis on the Pliocene ice sheet being significantly retreated, which is\na novel and useful finding in this region well worthy of publication in Nature\nCommunications.”\nWe have already revised the manuscript and refocused on the Pliocene-Pleistocene\ntransition.\nMinor and line-by-line points:\n• The Ellsworth-Whitmore Mountains are stated as the main source region during the\nPliocene on line 226, but the signature of this source region is not identified until line\n238. I feel the signature needs to be discussed first, as otherwise it is not clear at line\n226 why the EWM are being mentioned.\nReply: We have modified the text as suggested (lines 235-237).\n• Line 105: As mentioned in the comment above, these datasets are not yet “published”\nin peer-reviewed literature.\nReply: We acknowledge that the datasets from the Simões Pereira (2018) thesis have\nnot been published in peer-reviewed journals and have taken the data out of the\nmanuscript (see reply above).\n• Line 131: “We observe some overlap…” would be better as “There is some\noverlap…”, as at the moment it reads like a new observation from this study, which is\nnot the case.\nReply: The Text has been modified (line 137).\n• Line: 158-159: “… relatively young ages…” Relative to what? It would be better to be\nmore quantitative.\nReply: We have modified the text as suggested (line 165).\n• Line 165: Worth adding that this is at site ANT34/A2-10.\nReply: Appreciated and now mentioned in the text (171).\n• Line 166: Change “comprises” to “includes”?\nReply: Done (Line 173).\n• Line 263: The younger rocks are not all mafic. I suggest deleting the word mafic or\nspecifying that Cenozoic volcanic rocks are being referred to.\nReply: This sentence is deleted.\n• Line 270-272: Which ice stream is being discussed? This sentence is not clear. Also,\nI am not aware of any mafic sedimentary rocks on Thurston Island? I would\nrecommend clarifying this - maybe replacing “mafic sediments” with “detritus”?\nReply: These sentences are deleted, and the text has been revised (280-282)\n• Line 284: It is not clear which data are being referred to here.\nReply: We are referring to in-situ 26Al, 10Be, and 21Ne derived exposure ages of quartz-\nbearing erratics from the southern Ellsworth Mountains (Hein et al., 2016, Nature\nComm, doi.org/10.1038/ncomms10325)."}, {"round": 4, "reviewer_comments": {"reviewer_2": "The authors have further improved the manuscript since the last submission. I am glad the authors picked up on my comment on the first submission and have refocussed the manuscript on the Pliocene-Pleistocene transition, which is the most robust element of their data. I appreciate that Dr. Simões Pereira’s data were publicly available, so thank the authors for their kind decision to not publish these data without consent. I think the brief discussion on lines 278-282 is a suitable compromise.\nIn general, I feel the manuscript is almost ready for publication. However, after the refocussing since the previous submission, there are some instances where I feel the wording of sentences must be adjusted so that the statements can be supported by the data presented here. Although subtle changes that should be quick to implement, these are important:\n• Lines 32-34 (last sentence of abstract): This statement is not supported by the data presented here. Mass loss similar to that observed at present (i.e., thinning near the grounding zone) may well have occurred in Pleistocene interglacials – we simply don’t have the data to test this hypothesis. I would suggest this sentence is replaced by something more similar to the last concluding sentence (lines 354-356), focussing on the Plio-Pleistocene transition.\n• Line 120: Rather than saying “invariant sediment sourcing”, I would say “invariant sediment provenance signature”. As mentioned in previous reviews, it is possible to get ice sheet change without provenance change if source regions are not isotopically distinct.\n• Lines 235-237: I would add “for prolonged intervals” to this. The sampling resolution is not high enough to be certain that short periods with less radiogenic values have simply been missed.\n• Lines 266-268: I do not follow this sentence.\n• Lines 274-276: I do not think the data available support the statement suggesting “… a more pronounced ice sheet retreat during extreme Eemian interglacial (MIS5e) compared to other Pleistocene interglacials.”. The interglacial does clearly appear distinct in the PCA analysis, which is a useful observation. However, source rocks are not identified, so it seems too big a step to say this is definitely ice sheet retreat. I would instead refer to this as a *different* ice sheet extent in MIS5e, which is more correct and would imply retreat without explicitly saying it without clear evidence to back the statement up.\n• Lines 282-284: Again, a lack of provenance change does not mean a lack of retreat because geology inland may be isotopically homogenous. I would add “…compared to those of the Pliocene.” (or similar) to the end of this sentence, as the long-term provenance change from the Pliocene to Pleistocene is the robust finding of this study.\n• Line 290: I would remove the word “substantially” as the difference is hard to quantify.\n• Line 303: Change “erosion” to “provenance”.\n• Line 306: Change “substantial” to “comparative”. As mentioned above, quantification of change is difficult so the word substantial is not suitable.\n• Line 313: Change “resulted in” to “coincided with”. There is no proof that one caused the other.\n• Line 328: Change “orbitaly induced” to “continent-wide”. The record presented here lacks the resolution to show orbital-scale variation, and the long-term trend seems very unlikely to be driven by orbital forcing alone.\n• Lines 336-337: Higher than what? Modern?\n• Line 344: What “long term climate cycles” are being referred to? I suggest replacing “cycles” with “trend”.\n• Line 349: Add “Prolonged” to the beginning of the sentence currently starting “Near total mass loss…”. As mentioned above, the isotopic data are necessarily low resolution, so it is not possible to eliminate the possibility of brief major retreat.\n• Line 353: Not all ice sheet model experiments result in WAIS collapse for the Pleistocene, so I would suggest changing “align with the predictions” to “align with *some* predictions”.\n• Line 356: Suggest adding “…WAIS *may* lie within…”.\n• Fig. 2: Are error bars on the Pb isotopes smaller than the symbols? If so, this should be stated in the caption. Also, datasets from the cruise report should be cited in the caption.\n• Fig. 3b. I am glad the subglacial map is no longer interpolated inaccurately. The Robinson et al. (2021) data point at 180 longitude, -80 latitude of ~-20 is most certainly incorrect, so I would recommend removing this point from the map (and also doing a quick quality check of their table, which is a global compilation and not perfect).\n• Fig. 3f. I do not know what the dashed error bar for the PIG 208Pb/207Pb ratio means?\n• Fig. S3b: The Bellingshausen Sea has mafic granitoids??\n• Fig. S8: Not critical, but the debris seems very unrealistically high in the ice column. Also, for the caption in supplement line 381, I’d recommend removing “exposed large areas with the broader front” as the lateral extent of the calving front is not shown in the figure."}, "author_response": "Response to Reviewers' comments\nReviewer #2 (Remarks to the Author):\nThe authors have further improved the manuscript since the last submission. I am glad\nthe authors picked up on my comment on the first submission and have refocussed\nthe manuscript on the Pliocene-Pleistocene transition, which is the most robust\nelement of their data. I appreciate that Dr. Simões Pereira’s data were publicly\navailable, so thank the authors for their kind decision not to publish these data without\nconsent. I think the brief discussion on lines 278-282 is a suitable compromise.\nReply: Thank you very much for your comments and suggestions. We sincerely\nappreciate your suggestions and comments. Incorporating these suggestions has\nimproved our manuscript.\nIn general, I feel the manuscript is almost ready for publication. However, after\nrefocusing since the previous submission, there are some instances where I feel the\nwording of sentences must be adjusted so that the statements can be supported by\nthe data presented here. Although subtle changes that should be quick to implement,\nthese are important:\nReply: We have incorporated all the suggestions in the revised version.\n• Lines 32-34 (last sentence of abstract): This statement is not supported by the data\npresented here. Mass loss similar to that observed at present (i.e., thinning near the\ngrounding zone) may well have occurred in Pleistocene interglacials – we simply don’t\nhave the data to test this hypothesis. I would suggest this sentence is replaced by\nsomething more similar to the last concluding sentence (lines 354-356), focussing on\nthe Plio-Pleistocene transition.\nReply: Yes, we agree. We have modified the last sentence as per the suggestion\n(Lines No. 31-34).\n• Line 120: Rather than saying “invariant sediment sourcing”, I would say “invariant\nsediment provenance signature”. As mentioned in previous reviews, it is possible to\nget ice sheet change without provenance change if source regions are not isotopically\ndistinct.\nReply: Good point. Incorporated (Line No. 119)\n1\n• Lines 235-237: I would add “for prolonged intervals” to this. The sampling resolution\nis not high enough to be certain that short periods with less radiogenic values have\nsimply been missed.\nReply: Done (Line No. 235).\n• Lines 266-268: I do not follow this sentence.\nReply: This sentence has been modified (Line No. 266-267).\n• Lines 274-276: I do not think the data available support the statement suggesting “…\na more pronounced ice sheet retreat during extreme Eemian interglacial (MIS5e)\ncompared to other Pleistocene interglacials.”. The interglacial does clearly appear\ndistinct in the PCA analysis, which is a useful observation. However, source rocks are\nnot identified, so it seems too big a step to say this is definitely ice sheet retreat. I\nwould instead refer to this as a *different* ice sheet extent in MIS5e, which is more\ncorrect and would imply retreat without explicitly saying it, without clear evidence to\nback the statement up.\nReply: Yes, we agree. Text has been modified as per the suggestion (Line No. 274-\n276).\n• Lines 282-284: Again, a lack of provenance change does not mean a lack of retreat\nbecause geology inland may be isotopically homogenous. I would add “…compared\nto those of the Pliocene.” (or similar) to the end of this sentence, as the long-term\nprovenance change from the Pliocene to Pleistocene is the robust finding of this study.\nReply: Yes, agreed. Suggestion incorporated (Line No. 284-285).\n• Line 290: I would remove the word “substantially” as the difference is hard to quantify.\nReply: Done (Line No. 290).\n• Line 303: Change “erosion” to “provenance”.\nReply: Done (Line No. 303).\n2\n• Line 306: Change “substantial” to “comparative”. As mentioned above, quantification\nof change is difficult, so the word substantial is not suitable.\nReply: Changed to “comparable” (Line No. 306).\n• Line 313: Change “resulted in” to “coincided with”. There is no proof that one caused\nthe other.\nReply: Done (Line No. 313).\n• Line 328: Change “orbitally induced” to “continent-wide”. The record presented here\nlacks the resolution to show orbital-scale variation, and the long-term trend seems very\nunlikely to be driven by orbital forcing alone.\nReply: Done (Line No. 329).\n• Lines 336-337: Higher than what? Modern?\nReply: Corrected. Higher than modern insolation. (Line No. 338).\n• Line 344: What “long-term climate cycles” are being referred to? I suggest replacing\n“cycles” with “trend”.\nReply: Done (Line No. 346).\n• Line 349: Add “Prolonged” to the beginning of the sentence currently starting “Near\ntotal mass loss…”. As mentioned above, the isotopic data are necessarily low\nresolution, so it is not possible to eliminate the possibility of brief major retreat.\nReply: Done (Line No. 351).\n• Line 353: Not all ice sheet model experiments result in WAIS collapse for the\nPleistocene, so I would suggest changing “align with the predictions” to “align with\n*some* predictions”.\nReply: Done (Line No. 355).\n• Line 356: Suggest adding “…WAIS *may* lie within…”.\nReply: Done (Line No. 358).\n3\n• Fig. 2: Are error bars on the Pb isotopes smaller than the symbols? If so, this should\nbe stated in the caption. Also, datasets from the cruise report should be cited in the\ncaption.\nReply: Indeed, the error bars are smaller than the symbols. This is now mentioned in\nthe figure caption of the revised manuscript. We have also cited the data obtained\nduring the IODP379 expedition in the figure caption of the revised manuscript (lines\n387).\n• Fig. 3b. I am glad the subglacial map is no longer interpolated inaccurately. The\nRobinson et al. (2021) data point at 180 longitude, -80 latitude of ~-20 is most certainly\nincorrect, so I would recommend removing this point from the map (and also doing a\nquick quality check of their table, which is a global compilation and not perfect).\nReply: We have checked the original citation in the compilation of Robinson et al.\n(2021), and we found the data referred for this location (180° longitude, -80° latitude)\nwas taken from the original paper by Hergt et al. (1989)1, doi: 10.1007/BF00373722.\nThe data table (Table 2) is copied and provided below. The average measured Nd\nisotope ratio (143Nd/144Nd, ~0.511564) corresponds to the  value of -20.9 provided\nNd\nin the compilation and, plotted in the spatial map (Fig. 3b). So, we found that it is\ncorrect and no changes were made.\n• Fig. 3f. I do not know what the dashed error bar for the PIG 208Pb/207Pb ratio means?\nplotting limits in both directions, reflecting the full variability of the Pb isotope\nendmember values. The same is mentioned in the figure caption (Line No. 407-409)\n• Fig. S3b: The Bellingshausen Sea has mafic granitoids??\nReply: Yes, it is present in the hinterland lithology of the Bellingshausen Sea, such as\nMafic (magnetite-rich) and felsic (ilmenite-rich) granitoids (Simoes Pereira, 20182; PhD\nthesis, Pereira et al., 20183; Earth-Science Reviews).\n• Fig. S8: Not critical, but the debris seems very unrealistically high in the ice column.\nAlso, for the caption in supplement line 381, I’d recommend removing “exposed large areas with the broader front” as the lateral extent of the calving front is not shown in the figure.\nReply: Thanks for the suggestion. Yes, we agree, and debris is reduced in the revised\nfigure.\nReferences:\ndolerites from Portal Peak, Antarctica. Contributions to Mineralogy and Petrology 102,\n298-305, doi:10.1007/BF00373722 (1989).\nsheet behaviour from isotopic sedimentary provenance studies PhD Thesis thesis,\nImperial College London, (2018).\nWest Antarctica: Detrital thermochronology, radiogenic isotope systematics and trace\nelement geochemistry in Late Holocene glacial-marine sediments. Earth-Science\nReviews 182, 204-232, doi:https://doi.org/10.1016/j.earscirev.2018.04.011 (2018).\n5"}]

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