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The Aurora Subglacial Basin (ASB) catchment contains 3-5 m of sea-level equivalent ice volume that drains to the Sabrina Coast, East Antarctica via the Totten Glacier system. Observed thinning and retreat of Totten Glacier indicate regional sensitivity to oceanographic and atmospheric warming. Paleoclimate studies of climatically sensitive catchments are required to understand the evolution of the East Antarctic Ice Sheet (EAIS) and its outlet glacier systems. Recent seismic and sediment studies from the Sabrina Coast document the evolution of the EAIS in the ASB catchment, suggesting that the region has long been sensitive to climatic changes. This study presents new palynological and biomarker data from Sabrina Coast continental shelf sediments. Detailed palynological records were obtained from four short jumbo piston cores (JPC; NBP14-02 JPC-30, -31, -54 and -55), enabling reconstructions of regional vegetation and environments prior to and during Cenozoic EAIS development. The Sabrina Flora is dominated by angiosperms, with Gambierina spp. often exceeding 40% of the assemblage, and diverse Proteaceae, Battenipollis spp., Forcipites spp., Nothofagidites spp., fern, and conifer palynomorphs indicative of an open shrubby ecosystem. Excellent preservation and frequent occurrence of Gambierina spp. clusters suggest that a majority of the Sabrina Flora assemblage is penecontemporaneous with sedimentation; however, some uncertainties remain whether this sedimentation occurred in the Late Cretaceous or the Paleogene. Despite that uncertainty, high abundances of Gambierina spp. and Battenipollis spp., in combination with relatively low (

A physical oceanographic, geophysical and marine geological survey of Edward VIII Gulf, Kemp Coast, collected data from conductivity–temperature–depth casts, multi-beam bathymetric swath mapping and 3.5 kHz sub-bottom surveying. Modified circumpolar deep water (mCDW) is observed in Edward VIII Gulf, as well as notable bathymetric features including mega-scale glacial lineations and a 1750 m-deep trough. Sedimentological, geochemical, rock-magnetic and micropalaeontological analysis of two kasten cores document regional palaeoclimate and palaeo-oceanographic conditions over the past 8000 years, with a warm period occurring fromc.8 to 4 ka and a shift to cooler conditions beginning atc.4 ka and persisting until at least 0.9 ka. Sediment packages > 40 m thick within deep troughs in Edward VIII Gulf present potential targets for higher-resolution Holocene and deglacial climate studies. Despite the presence of mCDW on the shelf, inland bed topography consisting of highland terrain suggests the likelihood of relative stability of this sector of the East Antarctic Ice Sheet.

The Miocene to Pliocene (Neogene) occurred between 23.04 and 2.58 million years ago and includes intervals of peak global warmth where Earth’s average surface temperature was up to 8℃ warmer than present. Major cooling steps also occurred, across which Antarctica’s ice sheets advanced to the continental shelf for the first time and sea ice expanded across the Southern Ocean. Knowledge of Antarctic environmental change and ice sheet variability through this dynamic period in Earth history has advanced over the past 15 years. Major field and ship-based efforts to obtain new geological information have been completed and significant advances in numerical modelling approaches have occurred. Integration of ice proximal data and coupled climate-ice sheet model outputs with high-resolution reconstructions of ice volume and temperature variability from deep sea δ18O records now offer detailed insight into thresholds and tipping points in Earth’s climate system. Here we review paleoenvironmental data through key episodes in the evolution of Neogene climate to include the Miocene Climatic Optimum (MCO), Middle Miocene Climate Transition (MMCT), Tortonian Thermal Maximum (TTM), Late Miocene Cooling (LMC), and Pliocene Warm Period (PWP). This review shows that Antarctica’s climate and ice sheets remained dynamic throughout the Neogene. Given the analogous nature of warm episodes in the Miocene and Pliocene to future projections, the environmental reconstructions presented in this chapter offer a stark warning about the potential future of the AIS if warming continues at its current rate. If average global surface warming above pre-industrial values exceeds 2℃, a threshold will be crossed and AIS instabilities would likely be irreversible on multi-century timescales.

The past three decades have seen a sustained and coordinated effort to refine the seismic stratigraphic framework of the Antarctic margin that has underpinned the development of numerous geological drilling expeditions from the continental shelf and beyond. Integration of these offshore drilling datasets covering the Cenozoic era with Antarctic inland datasets, provides important constraints that allow us to understand the role of Antarctic tectonics, the Southern Ocean biosphere, and Cenozoic ice sheet dynamics and ice sheet–ocean interactions on global climate as a whole. These constraints are critical for improving the accuracy and precision of future projections of Antarctic ice sheet behaviour and changes in Southern Ocean circulation. Many of the recent advances in this field can be attributed to the community-driven approach of the Scientific Committee on Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) research programme and its two key subcommittees: Paleoclimate Records from the Antarctic Margin and Southern Ocean (PRAMSO) and Palaeotopographic-Palaeobathymetric Reconstructions. Since 2012, these two PAIS subcommittees provided the forum to initiate, promote, coordinate and study scientific research drilling around the Antarctic margin and the Southern Ocean. Here we review the seismic stratigraphic margin architecture, climatic and glacial history of the Antarctic continent following the break-up of Gondwanaland in the Cretaceous, with a focus on records obtained since the implementation of PRAMSO. We also provide a forward-looking approach for future drilling proposals in frontier locations critically relevant for assessing future Antarctic ice sheet, climatic and oceanic change.

High-resolution seismic data from the Sabrina Coast continental shelf, East Antarctica, elucidate the Cenozoic evolution of the East Antarctic Ice Sheet. Detailed seismic stratigraphic and facies analysis reveal the Paleogene to earliest Pliocene glacial evolution of the Aurora Basin catchment, including at least 12 glacial expansions across the shelf indicated by erosional surfaces and chaotic acoustic character of strata. Differences in facies composition and seismic architecture reveal several periods of ice-free conditions succeeded by glacial expansions across the shelf. A deep (∼100 m), undulating erosional surface suggests the initial appearance of grounded ice on the shelf. Following the initial ice expansion, the region experienced an interval of open-marine to ice-distal conditions, marked by an up to 200-m-thick sequence of stratified sediments. At least three stacked erosional surfaces reveal major cross-shelf glacial expansions of regional glaciers characterized by deep (up to ∼120 m) channel systems associated with extensive subglacial meltwater. The seismic character of the sediments below the latest Miocene to earliest Pliocene regional unconformity indicates intervals of glacial retreat interrupted by advances of temperate, meltwater-rich glacial ice from the Aurora Basin catchment. Our results document the Paleogene to late Miocene glacial history of this climatically sensitive region of East Antarctica and provide an important paleoenvironmental context for future scientific drilling to constrain the regional climate and timing of Cenozoic glacial variability.

Knowledge of how the Antarctic Ice Sheet (AIS) responded in the geologic past to warming climates will provide powerful insight into its poorly understood role in future global sea level change. Study of past natural climate changes allows us to determine the sensitivity of the AIS to higher-than-present atmospheric carbon dioxide (CO) concentrations and global temperatures, thereby providing the opportunity to improve the skill and performance of ice sheet models used for Intergovernmental Panel on Climate Change (IPCC) future projections. Antarctic and Southern Ocean (south of 60°S latitude) marine sediment records obtained over the last 50 years by seven scientific ocean drilling expeditions have revolutionized our understanding of Earth’s climate system and the evolution and dynamics of the Antarctic ice sheets through the Cenozoic (0–65 million years ago). These records document an ice-free subtropical Antarctica between ~52 and 40 million years ago when CO was ~1,000 ppm; the initiation of continental-scale Antarctic ice sheets ~34 million years ago as CO dropped below 800 ppm; evidence for a dynamic, largely terrestrial, ice sheet driving global sea level changes of up to 40 m amplitude between 34 and 15 million years ago; and colder periods of highly dynamic, marine-based ice sheets contributing up to 20 m of global sea level rise when CO levels were in the range of 500–300 ppm between ~14 and 3 million years ago. Notwithstanding these discoveries, paleoenvironmental records obtained around Antarctica are still limited in their geographical coverage and do not provide a basis for comprehensive understanding of how different sectors of Antarctica respond to climate perturbations. Transects of drill cores spanning ice-proximal to ice-distal environments across the continental margin and at sensitive locations that have been identified by models and recent observations are needed to fully understand temporal and spatial ice volume changes that result from complex ice sheet-ocean-atmosphere interactions. These records are also critical for reconstructing equator-to-pole temperature gradients through time to better understand global climate change, interhemispheric long-distance transmission of changes through the atmosphere and ocean (teleconnec-tions), and the amplification of climate signals in the polar regions. Future Antarctic scientific ocean drilling will remain key to obtaining records of past Antarctic Ice Sheet dynamics that can be integrated into coupled ice sheet-climate models for improved projections of sea level change. Thus, keeping an eye on ice sheet stability is critical for improving the accuracy and precision of predictions of future changes in global and regional temperatures and sea level rise., The authors are thankful for the opportunity to undertake this Antarctic scientific ocean drilling 50-year review and outlook into the future. We are especially thankful to two formal reviewers and to Anthony Koppers and Debbie Thomas for their useful comments on various aspects of the manuscript. Support for C. Escutia to conduct this activity comes from Grant CTM2017-89711-C2-1-P, CGL2016-75679P, co-funded by the European Union through FEDER funds.

During the late Miocene, meridional sea surface temperature gradients, deep ocean circulation patterns, and continental configurations evolved to a state similar to modern day. Deep-sea benthic foraminiferal stable oxygen (δ18O) and carbon (δ13C) isotope stratigraphy remains a fundamental tool for providing accurate chronologies and global correlations, both of which can be used to assess late Miocene climate dynamics. Until recently, late Miocene benthic δ18O and δ13C stratigraphies remained poorly constrained, due to relatively poor global high-resolution data coverage.Here, I present ongoing work that uses high-resolution deep-sea foraminiferal stable isotope records to improve late Miocene (chrono)stratigraphy. Although challenges remain, the coverage of late Miocene benthic δ18O and δ13C stratigraphies has drastically improved in recent years, with high-resolution records now available across the Atlantic and Pacific Oceans. The recovery of these deep-sea records, including the first astronomically tuned, deep-sea integrated magneto-chemostratigraphy, has also helped to improve the late Miocene geological timescale. Finally, I will briefly touch upon how our understanding of late Miocene climate evolution has improved, based on the high-resolution deep-sea archives that are now available.

Oscillations in ice sheet extent during early and middle Miocene are intermittently preserved in the sedimentary record from the Antarctic continental shelf, with widespread erosion occurring during major ice sheet advances, and open marine deposition during times of ice sheet retreat. Data from seismic reflection surveys and drill sites from Deep Sea Drilling Project Leg 28 and International Ocean Discovery Program Expedition 374, located across the present-day middle continental shelf of the central Ross Sea (Antarctica), indicate the presence of expanded early to middle Miocene sedimentary sections. These include the Miocene climate optimum (MCO ca. 17–14.6 Ma) and the middle Miocene climate transition (MMCT ca. 14.6–13.9 Ma). Here, we correlate drill core records, wireline logs and reflection seismic data to elucidate the depositional architecture of the continental shelf and reconstruct the evolution and variability of dynamic ice sheets in the Ross Sea during the Miocene. Drill-site data are used to constrain seismic isopach maps that document the evolution of different ice sheets and ice caps which influenced sedimentary processes in the Ross Sea through the early to middle Miocene. In the early Miocene, periods of localized advance of the ice margin are revealed by the formation of thick sediment wedges prograding into the basins. At this time, morainal bank complexes are distinguished along the basin margins suggesting sediment supply derived from marine-terminating glaciers. During the MCO, biosiliceous-bearing sediments are regionally mapped within the depocenters of the major sedimentary basin across the Ross Sea, indicative of widespread open marine deposition with reduced glacimarine influence. At the MMCT, a distinct erosive surface is interpreted as representing large-scale marine-based ice sheet advance over most of the Ross Sea paleo-continental shelf. The regional mapping of the seismic stratigraphic architecture and its correlation to drilling data indicate a regional transition through the Miocene from growth of ice caps and inland ice sheets with marine-terminating margins, to widespread marine-based ice sheets extending across the outer continental shelf in the Ross Sea.

The Asian-Pacific tropics likely instigated millennial-scale climate changes

Palynological analyses of 13 samples from two sediment cores retrieved from the Sabrina Coast, East Antarctica provide rare information regarding the paleovegetation within the Aurora Basin, which ...

Our understanding of the response of the Antarctic ice sheet to climate and ocean changes requires the improvement of current ice-atmosphere-ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals, so that satellite gravity observations and isostatic models can be adjusted. However, large portions of the Antarctic margin remain understudied or lack suitable data. One key area where data are lacking, is the Sabrina Coast portion of the East Antarctic Ice Sheet (EAIS) margin where the Totten Glacier, which has the largest ice discharge in East Antarctica, is accelerating, thinning and loosing mass at high rates. In this work, we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the Dalton Ice Tongue and Moscow University ice shelf, east of the Totten Glacier. The data presented include multibeam swath bathymetry and multichannel seismic, focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre- and post-Miocene glacial strata. Sea floor scouring and iceberg keel marks on the outer shelf, associated with gullies on the upper slope indicate that ice expanded in the past and grounded ~5 km from the shelf edge at ~450–500 mbsl, extending ~155 km north of the current Moscow University Ice Shelf. A nearly 1000 m deep area in the inner-middle shelf, oriented NW with paleo-ice flow direction indicated by mega scale glacial lineations (MSGL) and drumlins, is interpreted as a cross shelf glacial trough. A series of geomorphic associations on the north-eastern side of the glacial trough includes glacial lobes, grounding zone wedges (GZW), glacial lineations and transverse ridges, which indicates slower ice, grounding line stabilization and collapse. These geomorphic associations are organized in 4 four sets representing different past ice-flow configurations reflecting changes in ice flow direction, grounding line position, location of fast and slow ice areas, and retreat pattern. Some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage, and others are with rapid grounding line collapse. A well-preserved series of GZWs occurring at different water depths implies they were formed during different glacial stages or cycles. The inferred diminishing ice thickness for consecutives GZWs indicates that the margin of the Antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles. The identification of different ice flow configurations, evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes. We observe that some of the described morphological associations are similar to those found in the Amundsen sea sector of the West Antarctic Ice Sheet (WAIS) where they are associated with ice sheet and ice stream collapse. Although further studies are needed to assess the precise timing and rates of the glacial processes involved, we conclude that there is enough evidence to support the hypothesis that the EAIS margin can behave as dynamically as the WAIS margin, especially during glacial retreat and icesheet margin collapse.

Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate forcing, but future El Nino-Southern Oscillation (ENSO) behavior is unclear. Understanding of extreme hydroclimate variability and magnitude prior to human-influences is limited by short instrumental records, however, continuous sedimentary archives of past hydroclimate variability can complement and extend these records. Laminated Santa Barbara Basin (SBB) sediment cores MV0508-33JPC, −21JPC, and −29JPC preserve annually-resolved, multi-centennial-scale precipitation records from Termination V (T V ), the transition from glacial Marine Isotope Stage (MIS) 12 to interglacial MIS 11 at 424 ka. These records provide insights into the subtropical hydroclimate response to warming. Foraminiferal δ 18 O variations indicate rapid warming and/or salinity changes, and were used to verify the T V age assignment. A paleoprecipitation proxy was developed using the first principal component of scanning XRF elemental counts (PC1), which has high loadings for siliciclastic sediment-associated elements K, Ti, and Si. Sedimentary laminae couplets identified in PC1 were annually-tuned to investigate T V paleoprecipitation variability, as modern SBB laminae represent annual deposits. Extreme flooding and decadal-to-centennial droughts were identified, with magnitudes exceeding modern observations. ENSO-like (2–7 year) paleoprecipitation periodicities coincide with wetter intervals, but ENSO variability is reduced during droughts. A 1500-year arid interval may be related to poleward shifting of general atmospheric circulation as ice sheets melted, such that the subtropical dry zone intersected California. Southern California paleoprecipitation reconstructions from past warm climates provide insight into precipitation variability and magnitude on interannual timescales, and can reduce uncertainties in predictions of interannual climate, including ENSO.

The southeast Atlantic Ocean is dominated by two major oceanic systems: the Benguela Upwelling System, one of the world's most productive coastal upwelling cells and the Agulhas Leakage, which is important for transferring warm salty water from the Indian Ocean to the Atlantic Ocean. Here, we present a multi-proxy record of marine sediments from ODP Site 1087. We reconstruct sea surface temperatures (U37 K′ and TEX86 indices), marine primary productivity (total chlorin and alkenone mass accumulation rates), and terrestrial inputs derived from southern Africa (Ti/Al and Ca/Ti via XRF scanning) to understand the evolution of the Southeast Atlantic Ocean since the late Pliocene. In the late Pliocene and early Pleistocene, ODP Site 1087 was situated within the Benguela Upwelling System, which was displaced southwards relative to present. We recognize a series of events in the proxy records at 3.3, 3.0, 2.2, 1.5, 0.9 and 0.6 Ma, which are interpreted to reflect a combination of changes in the location of major global wind and oceanic systems and local variations in the strength and/or position of the winds, which influence nutrient availability. Although there is a temporary SST cooling observed around the initiation of Northern Hemisphere glaciation (iNHG), proxy records from ODP Site 1087 show no clear climatic transition around 2.7 Ma but instead most of the changes occur before this time. This observation is significant because it has been previously suggested that there should be a change in the location and/or strength of upwelling associated with this climate transition. Rather, the main shifts at ODP Site 1087 occur at ca. 0.9 Ma and 0.6 Ma, associated with the early mid-Pleistocene transition (EMPT), with a clear loss of the previous upwelling-dominated regime. This observation raises the possibility that reorganisation of southeast Atlantic Ocean circulation towards modern conditions was tightly linked to the EMPT, but not to earlier climate transitions.

Antarctica’s continental-scale ice sheets have evolved over the past 50 million years1,2,3,4. However, the dearth of ice-proximal geological records5,6,7,8 limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations9,10,11. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago1,2,3,4. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys12 associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming10,11. Cooling since the late Miocene13 resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment14,15,16. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections10,11,15,17 may be under-estimated.

This study presents the first analysis of benthic megafauna and habitats from the Sabrina Coast shelf, encompassing a proposed Marine Protected Area. Sea bed imagery indicated an abundant benthic fauna compared to other parts of the Antarctic shelf, dominated by brittle stars, polychaete tubeworms, and a range of other sessile and mobile taxa. The distribution of taxa was related (ρ=0.592, PAnoxycalyx joubini and branching hydrocorals exhibited a more restricted distribution, probably related to water depth and limited dispersal capability, respectively. Dropstones were associated with significant increases in taxa diversity, abundance and biological cover, enhancing the overall diversity and biomass of this ecosystem.

Orbital-scale climate variability during the latest Miocene-early Pliocene is poorly understood due to a lack of high-resolution records spanning 8.0–3.5 Ma, which resolve all orbital cycles. Assessing this variability improves understanding of how Earth's system sensitivity to insolation evolves and provides insight into the factors driving the Messinian Salinity Crisis (MSC) and the Late Miocene Carbon Isotope Shift (LMCIS). New high-resolution benthic foraminiferal Cibicidoides mundulus δ18O and δ13C records from equatorial Pacific International Ocean Drilling Program Site U1338 are correlated to North Atlantic Ocean Drilling Program Site 982 to obtain a global perspective. Four long-term benthic δ18O variations are identified: the Tortonian-Messinian, Miocene-Pliocene, and Early-Pliocene Oxygen Isotope Lows (8–7, 5.9–4.9, and 4.8–3.5 Ma) and the Messinian Oxygen Isotope High (MOH; 7–5.9 Ma). Obliquity-paced variability dominates throughout, except during the MOH. Eleven new orbital-scale isotopic stages are identified between 7.4 and 7.1 Ma. Cryosphere and carbon cycle sensitivities, estimated from δ18O and δ13C variability, suggest a weak cryosphere-carbon cycle coupling. The MSC termination coincided with moderate cryosphere sensitivity and reduced global ice sheets. The LMCIS coincided with reduced carbon cycle sensitivity, suggesting a driving force independent of insolation changes. The response of the cryosphere and carbon cycle to obliquity forcing is established, defined as Earth System Response (ESR). Observations reveal that two late Miocene-early Pliocene climate states existed. The first is a prevailing dynamic state with moderate ESR and obliquity-driven Antarctic ice variations, associated with reduced global ice volumes. The second is a stable state, which occurred during the MOH, with reduced ESR and lower obliquity-driven variability, associated with expanded global ice volumes.

The East Antarctic continental margin, which extends from the Weddell Sea to the Ross Sea (Fig. 1h), surrounds the largest and oldest ice mass on Earth; however, it has only been studied at a few locations because of its remoteness and persistent sea ice. The shelf is 100–150 km wide over most of its length but broadens where major crustal structures intersect it, such as in Prydz Bay (Fig. 1a) where the shelf is 200–300 km wide. This paper reviews what is known presently about the geomorphology of the best-studied sectors of the East Antarctic margin: the deep re-entrant of Prydz Bay and the narrower shelves of George V and Mac.Robertson Land (Fig. 1h). Only a small proportion of the East Antarctica shelf has been surveyed with multibeam bathymetry, so this review is also dependent on compilations of single-beam bathymetry, seismic-reflection profiles and side-scan sonar data. In particular, we use George V Digital Elevation Model (GVDEM, Beaman et al. 2011) and International Bathymetric Chart of the Southern Ocean (IBCSO; Arndt et al. 2013). The slope has been more widely studied, with large amounts of seismic-reflection data available (e.g. Kuvaas & Leitchenkov 1992; Escutia et al. 2000; Solli et al. 2007; Close et al. 2007). Fig. 1. ( a ) Prydz Bay and sub-Amery Ice Shelf bathymetry. (IBCSO v. 1.0; Arndt et al. 2013). ( b ) Long profile of Amery Ice Shelf from upstream of the modern grounding zone to the trough-mouth fan on the continental slope. VE×140. ( c ) Cross-section of Amery Ice Shelf valley at its southern end. VE×20. ( d ) Shaded-relief image of multibeam data collected by N. B. Palmer in 2001 (Leventer et al. 2005). The image covers the transition from streamlined bedrock to moulded basin sediment in the Svenner Channel. Image from GEOMAPAPP (www.geomapapp.org). ( e ) Seismic …

This work was funded by NERC studentship NE/I528185/1 awarded to W.R.G., NERC studentship NE/1492942/1 to B.T., NERC grant NE/N011716/1 awarded to J.W.B.R and A.B., and NERC grant NE/I013377/1 awarded to A.E.S. The interplay between ocean circulation and biological productivity affects atmospheric CO2 levels and marine oxygen concentrations. During the warming of the last deglaciation, the North Pacific experienced a peak in productivity and widespread hypoxia, with changes in circulation, iron supply and light limitation all proposed as potential drivers. Here we use the boron-isotope composition of planktic foraminifera from a sediment core in the western North Pacific to reconstruct pH and dissolved CO2 concentrations from 24,000 to 8,000 years ago. We find that the productivity peak during the Bølling–Allerød warm interval, 14,700 to 12,900 years ago, was associated with a decrease in near-surface pH and an increase in pCO2, and must therefore have been driven by increased supply of nutrient- and CO2-rich waters. In a climate model ensemble (PMIP3), the presence of large ice sheets over North America results in high rates of wind-driven upwelling within the subpolar North Pacific. We suggest that this process, combined with collapse of North Pacific Intermediate Water formation at the onset of the Bølling–Allerød, led to high rates of upwelling of water rich in nutrients and CO2, and supported the peak in productivity. The respiration of this organic matter, along with poor ventilation, probably caused the regional hypoxia. We suggest that CO2 outgassing from the North Pacific helped to maintain high atmospheric CO2 concentrations during the Bølling–Allerød and contributed to the deglacial CO2 rise. Postprint

The marine-based West Antarctic Ice Sheet (WAIS) is currently retreating due to shifting wind-driven oceanic currents that transport warm waters toward the ice margin, resulting in ice shelf thinning and accelerated mass loss of the WAIS. Previous results from geologic drilling on Antarctica's continental margins show significant variability in marine-based ice sheet extent during the late Neogene and Quaternary. Numerical models indicate a fundamental role for oceanic heat in controlling this variability over at least the past 20 My. Although evidence for past ice sheet variability has been collected in marginal settings, sedimentologic sequences from the outer continental shelf are required to evaluate the extent of past ice sheet variability and the associated oceanic forcings and feedbacks. International Ocean Discovery Program Expedition 374 drilled a latitudinal and depth transect of five drill sites from the outer continental shelf to rise in the eastern Ross Sea to resolve the relationship between climatic and oceanic change and WAIS evolution through the Neogene and Quaternary. This location was selected because numerical ice sheet models indicate that this sector of Antarctica is highly sensitive to changes in ocean heat flux. The expedition was designed for optimal data-model integration and will enable an improved understanding of the sensitivity of Antarctic Ice Sheet (AIS) mass balance during warmer-than-present climates (e.g., the Pleistocene "super interglacials," the mid-Pliocene, and the late early to middle Miocene). The principal goals of Expedition 374 were to • Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates; • Reconstruct ice-proximal atmospheric and oceanic temperatures to identify past polar amplification and assess its forcings and feedbacks; • Assess the role of oceanic forcing (e.g., sea level and temperature) on AIS stability/instability; • Identify the sensitivity of the AIS to Earth's orbital configuration under a variety of climate boundary conditions; and • Reconstruct eastern Ross Sea paleobathymetry to examine relationships between seafloor geometry, ice sheet stability/instability, and global climate. To achieve these objectives, we will • Use data and models to reconcile intervals of maximum Neogene and Quaternary Antarctic ice advance with far-field records of eustatic sea level change; • Reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach; • Reconstruct Neogene and Quaternary sea ice margin fluctuations in datable marine continental slope and rise records and correlate these records to existing inner continental shelf records; • Examine relationships among WAIS stability/instability, Earth's orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and • Constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics. Expedition 374 was carried out from January to March 2018, departing from Lyttelton, New Zealand. We recovered 1292.70 m of high-quality cores from five sites spanning the early Miocene to late Quaternary. Three sites were cored on the continental shelf (Sites U1521, U1522, and U1523). At Site U1521, we cored a 650 m thick sequence of interbedded diamictite, mudstone, and diatomite, penetrating the Ross Sea seismic Unconformity RSU4. The depositional reconstructions of past glacial and open-marine conditions at this site will provide unprecedented insight into environmental change on the Antarctic continental shelf during the early and middle Miocene. At Site U1522, we cored a discontinuous upper Miocene to Pleistocene sequence of glacial and glaciomarine strata from the outer shelf, with the primary objective to penetrate and date seismic Unconformity RSU3, which is interpreted to represent the first major continental shelf-wide expansion and coalescing of marine-based ice streams from both East and West Antarctica. At Site U1523, we cored a sediment drift located beneath the westerly flowing Antarctic Slope Current (ASC). Cores from this site will provide a record of the changing vigor of the ASC through time. Such a reconstruction will enable testing of the hypothesis that changes in the vigor of the ASC represent a key control on regulating heat flux onto the continental shelf, resulting in the ASC playing a fundamental role in ice sheet mass balance. We also cored two sites on the continental slope and rise. At Sit e U1524, we cored a Plio-Pleistocene sedimentary sequence on the continental rise on the levee of the Hillary Canyon, which is one of the largest conduits of Antarctic Bottom Water delivery from the Antarctic continental shelf into the abyssal ocean. Drilling at Site U1524 was intended to penetrate into middle Miocene and older strata but was initially interrupted by drifting sea ice that forced us to abandon coring in Hole U1524A at 399.5 m drilling depth below seafloor (DSF). We moved to a nearby alternate site on the continental slope (U1525) to core a single hole with a record complementary to the upper part of the section recovered at Site U1524. We returned to Site U1524 3 days later, after the sea ice cleared. W e then cored Hole U1524C with the rotary core barrel with the intention of reaching the target depth of 1000 m DSF. However, we were forced to terminate Hole U1524C at 441.9 m DSF due to a mechanical failure with the vessel that resulted in termination of all drilling operations and a return to Lyttelton 16 days earlier than scheduled. The loss of 39% of our operational days significantly impacted our ability to achieve all Expedition 374 objectives as originally planned. In particular, we were not able to obtain the deeper time record of the middle Miocene on the continental rise or abyssal sequences that would have provided a continuous and contemporaneous archive to the high-quality (but discontinuous) record from Site U1521 on the continental shelf. The mechanical failure also meant we could not recover sediment cores from proposed Site RSCR-19A, which was targeted to obtain a high-fidelity, continuous record of upper Neogene and Quaternary pelagic/hemipelagic sedimentation. Despite our failure to recover a shelf-to-rise transect for the Miocene, a continental shelf-to-rise transect for the Pliocene to Pleistocene interval is possible through comparison of the high-quality records from Site U1522 with those from Site U1525 an d legacy cores from the Antarctic Geological Drilling Project (ANDRILL).

A.J. Drury was funded by a Janet Watson studentship from Imperial College London. The late Miocene-early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here, we present the first continuous late Miocene-early Pliocene (8.0-4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0-3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest mean sea-surface-temperatures (SSTs) are ~27.8±1.1°C (1σ) between 6.4-5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2-6.1 Ma and an up to 3°C warming between 6.1-4.4 Ma, consistent with observed tropical alkenone paleo-SSTs. Diverging fine-fraction-to-foraminiferal δ13C gradients likely suggest increased upwelling from 7.1-6.0 and 5.8-4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene-early Pliocene. Between 8.0-6.5 and 5.2-4.4 Ma, low east-west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5-5.7 Ma, with larger east-west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric pCO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction). Publisher PDF

Instrumental data suggest changes in the intensity of the East Asian Monsoon system over the past century, possibly in response to anthropogenic climate change. To understand modern observations and explore past variations in East Asian summer monsoon (EASM) strength, we conducted grain size, geochemical, and pollen assemblage studies on a lacustrine sediment sequence from an earthquake-dammed paleolake on the eastern Tibetan Plateau. The chronology, generated from eight optically stimulated luminescence and two pollen concentrate radiocarbon dates, indicates deposition of the lacustrine sequence between 600 and 1250 C.E. Fine grain sizes and low arboreal pollen percentages are associated with regional aridity (790–916, 1020–1080, 1125–1150 C.E.) and a weak EASM, whereas coarser grain sizes and higher arboreal pollen percentages are associated with increased precipitation and a stronger EASM (1090–1125, 1160–1230 C.E.). Although observed variations in our paleodata are predominantly driven by climate, the sequence is also influenced by regional tectonics, as evident from seismites, a ~90-year hiatus (917–1004 C.E.) during a period of regional seismicity, and an abrupt increase in regional sedimentation rates. Human disturbance is also observed to increase during weak EASM intervals. On decadal to millennial scales, our paleodata are highly correlated with reconstructions of EASM strength from northeastern China and sea surface temperature reconstructions from the tropical Pacific Ocean, indicating that the Medieval Climate Anomaly was associated with a strong EASM and prolonged La Nina-like state. Our data also suggest decadal-scale EASM variability associated with solar intensity, but an inconsistent response suggests additional complexity in EASM forcing. The inverse relationship between modern EASM weakening with anthropogenic warming, and a strong EASM during the warm Medieval Climate Anomaly, suggests that the complexity of the decadal to centennial-scale EASM response may be related to changes in the mean state of the tropical Pacific Ocean.

In PNAS, two companion studies by Levy et al. (1) and Gasson et al. (2) underscore the importance of ice-proximal geologic data for improving computer models of Antarctic ice sheet response to oceanic and atmospheric warming. Current knowledge of Antarctic ice sheet evolution (∼40–0 Ma) is based on deep-sea records of global ice volume, deep ocean temperature, and carbon cycling preserved in the calcium carbonate shells of benthic foraminifera (3, 4). Shackleton and Kennett (5) hypothesized, from moderate-resolution southwest Pacific Ocean benthic foraminifer stable oxygen (δ18O) and carbon (δ13C) isotope compilations, that the deep ocean cooled ∼15 °C through the Cenozoic and that Antarctic ice sheets expanded significantly at the Eocene–Oligocene boundary, varied dynamically until the middle Miocene climate transition (MMCT; 14.2–13.8 Ma), and then rapidly expanded and stabilized. Over the last 41 y, paleoceanographers have used deep-sea sediments recovered by scientific ocean drilling programs, including the International Ocean Discovery Program (2013–2023), to increase the resolution of the global deep-sea stable isotope record (3⇓–5), develop geochemical methods to separate ice volume and temperature signals contained in the δ18O signal (4), and resolve climate forcings and feedbacks involved in Antarctic ice growth and global climate evolution (4, 6). Because of a lack of high-quality ice-proximal drill sites, only a handful of studies (e.g., refs. 1 and 7) directly link Antarctic ice sheet variability to far-field deep-sea δ18O (3⇓–5) and passive margin sea-level records (8). Such linkages are required to improve understanding of the timing and magnitude of ice volume fluctuations, relative contributions of Antarctica’s ice sheets to global eustacy, individual histories of the East and West Antarctic ice sheets, and climatic boundary conditions favorable for ice growth and decay (3). In PNAS, Levy et … [↵][1]1Email: ashevenell{at}usf.edu. [1]: #xref-corresp-1-1

The Prydz Bay continental shelf was sculpted by the Lambert Glacier–Amery Ice Shelf system, a large outlet glacier that drains 16% of the East Antarctic Ice Sheet (Allison 1979; Fig. 1a). Prydz Channel (71–73° E; Fig. 1b) is a NW-trending cross-shelf trough (500–700 m deep) in western Prydz Bay that formed in the Pliocene, when the Lambert-Amery system first developed a fast-flowing ice stream (Fig. 1b; Cooper & O'Brien 2004). In Prydz Channel mega-scale glacial lineations (MSGLs) delineate the direction and orientation of past ice flow, and large grounding-zone wedges (GZWs; Batchelor & Dowdeswell 2015) in the inner channel mark the limit of the Last Glacial Maximum (LGM) ice advance about 250 km from the shelf edge (Fig. 1c, d, e). Fig. 1. Multibeam swath bathymetry and seismic-reflection profile of Prydz Channel, East Antarctica. ( a ) Location of study area (red box; map from IBCSO v. 1.0). ( b ) General bathymetry of Prydz Channel, delineated by the 500 m contour, and other relevant regional features. ( c ) Multibeam swath bathymetry of mega-scale glacial lineations (MSGLs) in Prydz Channel and grounding-zone …