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Continental Rift systems often involve narrow regions, which accommodate all the stretching. In some cases, the initial extension occurs with a diffuse style and may successively produce a narrow rift. An example is the West Antarctica Rift System, bearing evidence of the concurrent formation of multiple basins normal to the rift axis. This rift system has undergone extension between the Cretaceous and the middle Neogene age (105 to 11 Ma [1, 2]), due to the sea floor spreading in the northwestern Ross Sea. It is composed of three main basins (Victoria Land Basin, Central Trough, and Eastern Basin), which cover a present-day length of 900-1000 km, encompassing the lateral contact between the cratonic domains of East Antarctica and West Antarctica Phanerozoic lithosphere. The different basins, bounded by structural highs, exhibit significant variations in the thickness and thinning of the underlying crust and lithosphere. This multiple-basin pattern suggests that, at least for some part of the rifting, the deformation occurred in a diffuse way, instead of being localized in a small portion of the rift system [3].The factors controlling these deformation styles have been identified in the inheritance of structures and thermal/rheological heterogeneities [4], which acted concurrently with the extensional kinematics in shaping the present-day rift architectures. Therefore, an improved knowledge on how different thermo-structural initial conditions (e.g. lateral contacts, thermal transients, accumulated strain softening) influence the outcome of rifting may help identify the most likely state at the onset of rifting. To this purpose, we implement a series of numerical models, testing several starting structural conditions (rheology, temperature, prior damage) and distribution of extensional velocity (a single phase or multiple pulses, for the same total extension) that could trigger this peculiar diffuse deformation pattern.To build a 2-D simplified geometry of the structures of the rift system, we took as a reference the seismic profiles BGR-02 and ACRUP2, normal to the rift axis, along the 77° S parallel [5]. We assumed an initial crustal thickness of about 50 km and a kinematic pattern consisting of two main distinct extension phases, covering the Cretaceous-Cenozoic interval [1, 6].Modelling was carried out using the open source Underworld2 code [7], which relies on Lagrangian integration point finite element approach and provides a Python API to construct, run, and visualize the output of geodynamic models. The results show that the models that are more consistent with the observations require the existence of peculiar a-priori inherited features. In addition to the role of inheritance, diffuse patterns are favoured, for the same extension amount, by slow and long-lasting rifting phases, with respect to fast and short time pulses.This work was carried out in the context of PNRA project "Onset of Antarctic Ice Sheet Vulnerability to Oceanic conditions (ANTIPODE)".[1] Behrendt et al. (1991) https://doi.org/10.1029/91TC00868[2] Granot & Dyment (2018) https://doi.org/10.1038/s41467-018-05270-w[3] Huerta & Harry (2007) https://doi.org/10.1016/j.epsl.2006.12.011[4] Perron et al. (2021) https://doi.org/10.1051/bsgf/2020038[5] Trey et al. (1999) https://doi.org/10.1016/S0040-1951(98)00155-3[6] Davey & De Santis (2006) https://doi.org/10.1007/3-540-32934-X_38[7] Mansour et al. (2020) https://doi.org/10.21105/joss.01797

The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~ 17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~ 15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma.

Analysis of multichannel seismic profiles collected on the continental rise off the Sabrina Coast, East Antarctica, has allowed the determination of the acoustic features that are indicative of major evolution steps of the East Antarctic Ice Sheet (EAIS) and highlights the role of meltwater that originated from Totten Glacier in shaping the margin architecture. The arrival of marine-terminating glaciers into the coastal region was recorded by an enhanced sediment input on the continental rise and the nucleation of channel-levees. Downslope sedimentary processes were dominant throughout the Late Cenozoic, testifying to the progressive growth of a highly dynamic, temperate ice sheet on the continent. The last evolutionary step marks the transition to when a full polar glacial regime occurred. The development of a prograding wedge with steeply dipping foresets on the continental shelf and slope exemplifies sedimentation at this time. Other sub-sea-floor observations indicate that downslope fluxes, triggered by glacial meltwater, were still able to deeply erode and deliver sediments to the rise area. This study's findings have led to the identification of expanded and well-preserved sedimentary successions, which we suggest should be considered as priority targets for future International Ocean Discovery Program deep drilling due to the sensitivity of the ice sheet in this area., This study is funded by Italian Programma Nazionale di Ricerche in Antartide (PNRA) under the TYTAN Project. The Marine National Facility Survey IN2017-V01 survey was supported by the Australian Government through Australian Antarctic Science grant AAS#4333 and Australian Research Council grant DP170100557. G. Leitchenkov acknowledges the Russian Science Foundation grant 16-17-10139.

A new multidisciplinary, international research program aims to tackle one of the grand challenges in climate science: resolving the Antarctic Ice Sheet’s contribution to future sea level rise.

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.

Technological advances in the study and dating of both land and marine glacial geologic features, combined with both glaciological and post-glacial isostatic rebound modelling, have developed knowledge and understanding of the Antarctic Ice Sheets at the Last Glacial Maximum (LGM) and their subsequent changes. Here, we review geological evidence for the extent and timing of the maximum advance of the East and West Antarctic Ice Sheets and the Antarctic Peninsula Ice Sheet during the most recent glacial cycle. We also discuss evidence for the rate and timing of post-LGM ice-sheet retreat. Geological data provide a very important ‘first-hand’ record of ice-sheet changes over a range of time periods. They are also useful for constraining and improving models that have the potential to both fill in the gaps where geological data are unavailable, and to make predictions about the future. In reviewing the glacial geological evidence, we provide a benchmark against which future ice-sheet modelling exercises can be assessed.

The legacy of the Scientific Committee on Antarctic Research’s (SCAR) PAIS strategic research programme includes not only breakthrough scientific discoveries, but it is also the story of a long-standing deep collaboration amongst different multi-disciplinary researchers from many nations, to share scientific infrastructure and data, facilities, and numerical models, in order to address high priority questions regarding the evolution and behaviour of the Antarctic ice sheets (AIS). The PAIS research philosophy is based on data-data and data-model integration and intercomparison, and the development of ‘ice-to-abyss’ data transects and paleo-environmental, extending from the ice sheet interior to the deep sea. PAIS strives to improve understanding of AIS dynamics and to reduce uncertainty in model simulations of future ice loss and global sea level change, by studying warm periods of the geological past that are relevant to future climate scenarios. The multi-disciplinary approach fostered by PAIS represents its greatest strength. Eight years after the start of this programme, PAIS achievements have been high-profile and impactful, both in terms of field campaigns that collected unique data sets and samples, and in terms of scientific advances concerning past AIS dynamics, that have measurably improved understanding of ice sheet sensitivity in response to global warming. Here we provide an overview and synthesis of the new knowledge generated by the PAIS Programme and its implications for anticipating and managing the impacts of global sea-level rise.

Our appreciation of Antarctic climate evolution has grown significantly in the last decade. Characterised by international cooperation, and leadership from the Scientific Committee on Antarctic Research (SCAR), we now have a better understanding of how and why Antarctica’s ice sheets have developed and influenced global climate change. While the nature of, and explanations for, significant glacial events has improved, gaps in our knowledge of the rate and impact of processes responsible remain. Such processes are critical if we are to understand how the palaeo record can inform us about the vulnerability of the Antarctic ice sheet during periods of greenhouse gas–driven warming. Hence, establishing further precision of past changes, at a resolution helpful to process-based modelling, is an important next step to better constraining future Antarctic change and its sea-level consequences.

Antarctic Climate Evolution – second edition is a result of both SCAR programmes and documents the state of knowledge concerning the ice and climate evolution of the Antarctic continent and its surrounding seas through the Cenozoic era to present day and into the future. Most of the subcommittees in ACE and PAIS have been responsible for individual chapters and, in this way, we have been able to cover the complete history of the Antarctic Ice Sheet and its climate evolution. The book will be of interest to research scientists from a wide range of disciplines including glaciology, palaeoclimatology, sedimentology, climate change, environmental science, oceanography and palaeontology. It will also be valuable as a supplementary text for undergraduate courses.

The Oligocene-Miocene transition (OMT) is one of the most enigmatic periods (~23.3–22.9 Ma) in Earth’s Cenozoic climate history. It is characterised in deep-sea benthic foraminiferal (δ18O) records by an increase of up to +1‰ spanning a 200–300 kyr interval associated with global cooling and growth in Antarctic ice volume to as much as 120% of present day (Mi-1 glaciation). The Mi-1 glaciation was then terminated by a −1.2‰, δ18O decrease that occurred in less than 100 kyrs, implying rapid Northern Hemisphere-style ice retreat, and potentially continental-scale deglaciation of Antarctica. Antarctic margin ocean drill core records and seismic reflection profiles display evidence of ice-proximal glacimarine deposition or glacimarine erosion, and imply continent-wide advance of the ice sheet terminus into the marine realm during the Mi-1 glaciation. This major transient glaciation occurred within a ~400 kyr-duration eccentricity cycle and appears to be coupled with an orbitally-paced perturbation of the carbon cycle. Atmospheric CO2 reconstructed from geological proxy records imply a long-term decrease during the Oligocene from about 500 to less than 300 ppm. Atmospheric CO2 declining below a threshold (~400 ppm), together with an extreme cold orbital configuration, enabled widespread seasonal sea-ice formation and the development of extensive marine-based ice margins around Antarctica. Atmospheric CO2 concentration appears to rebound rapidly following the Mi-1 glaciation, with some proxy estimates as high as 1000 ppm by the earliest Miocene. The OMT challenges our current understanding of orbitally-paced, ocean-atmosphere carbon exchange and associated feedbacks in the climate system. Prior to the OMT, between ~27 and 24 Ma, a trend towards lower δ18O values suggested an extensive period of global warmth, polar ice volume decrease and global sea-level rise. This is in contrast with widespread evidence from Ross Sea drill cores that show cooling of near surface ocean and land temperatures, and glacial advance calving ice bergs at the coastline. However, on the Wilkes Land margin cooling begins later, after ~25 Ma. Here, we summarise new evidence of the relative influences of tectonics, atmospheric carbon dioxide, ocean dynamics and orbital forcing on the evolution of the Antarctic Ice Sheet (AIS) during the Late Oligocene and across the OMT. We revisit the longstanding conundrums and provide some insights for the future (in)stability of the Antarctic Ice Sheet.

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.

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.

In this paper we analyze how oceanic circulation affects sediment deposition along a sector of the Ross Sea continental margin, between the Iselin Bank and the Hillary Canyon, and how these processes evolved since the Late Miocene. The Hillary Canyon is one of the few places around the Antarctic continental margin where the dense waters produced onto the continental shelf, mainly through brine rejection related to sea ice production, flow down the continental slope and reach the deep oceanic bottom layer. At the same time the Hillary Canyon represents a pathway for relatively warm waters, normally flowing along the continental slope within the Antarctic Slope Current, to reach the continental shelf. The intrusion of warm waters onto the continental shelf produces basal melting of the ice shelves, reduces their buttressing effect and triggers instabilities of the ice sheet that represent one of the main uncertainties in future sea level projections. For this study we use seismic, morpho-bathymetric and oceanographic data acquired in 2017 by the R/V OGS Explora. Seismic profiles and multibeam bathymetry are interpreted together with age models from two drilling sites (U1523 and U1524) of the International Ocean Discovery Program (IODP) Expedition 374. Oceanographic data, together with a regional oceanographic model, are used to support our reconstruction by showing the present-day oceanographic influence on sediment deposition. Regional correlation of the main seismic unconformities allows us to identify eight seismic sequences. Seismic profiles and multibeam bathymetry show a strong influence of bottom current activity on sediment deposition since the Early Miocene and a reduction in their intensity during the mid-Pliocene Warm Period. Oceanographic data and modelling provide evidence that the bottom currents are related to the dense waters produced on the Ross Sea continental shelf and flowing out through the Hillary Canyon. The presence of extensive mass transport deposits and detachment scarps indicate that also mass wasting participates in sediment transport. Through this integrated approach we regard the area between the Iselin Bank and the Hillary Canyon as a Contourite Depositional System (ODYSSEA CDS) that offers a record of oceanographic and sedimentary conditions in a unique setting. The hypotheses presented in this work are intended to serve as a framework for future reconstructions based on detailed integration of lithological, paleontological, geochemical and petrophysical data.

Paleo-bathymetric reconstructions provide boundary conditions to numerical models of ice sheet evolution and ocean circulation that are critical to understanding their evolution through time. The geological community lacks a complex open-source tool that allows for community implementations and strengthens research synergies. To fill this gap, we present PALEOSTRIPv1.0, a MATLAB open-source software designed to perform 1D, 2D, and 3D backtracking of paleo-bathymetries. PALEOSTRIP comes with a graphical user interface (GUI) to facilitate computation of sensitivity tests and to allow the users to switch all the different processes on and off and thus separate the various aspects of backtracking. As such, all physical parameters can be modified from the GUI. It includes 3D flexural isostasy, 1D thermal subsidence, and possibilities to correct for prescribed sea level and dynamical topography changes. In the following, we detail the physics embedded within PALEOSTRIP, and we show its application using a drilling site (1D), a transect (2D), and a map (3D), taking the Ross Sea (Antarctica) as a case study. PALEOSTRIP has been designed to be modular and to allow users to insert their own implementations.

The five sites drilled during International Ocean Discovery Program (IODP) Expedition 374 recovered the distal geological component of a Neogene latitudinal and depth transect across the Ross Sea continental shelf, slope and rise, that can be combined with previous records of ANDRILL and the Deep Sea Drilling Project Leg 28. This transect provides clues into the ocean and atmospheric forcings on marine ice sheet instabilities and provides new direct constraints for reconstructing the Antarctic Ice Sheet contribution to global sea level change. Site U1521 recovered a middle Miocene record that allows identification of the different processes that lead to the expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. This site also recovered a semi-continuous, expanded, high-resolution record of the Miocene Climatic Optimum in an ice-proximal location. Site U1522 recovered a Pleistocene to upper Miocene sequence from the outer shelf, dating the step-wise continental shelf–wide expansion and coalescing of marine-based ice streams from West Antarctica. Thin diatom-rich mudstone and diatomite beds were recovered in some intervals that provide snapshot records of a deglaciated outer shelf environment in the late Miocene. Site U1523 targeted a Miocene to Pleistocene sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time. Changes in ASC vigor is a key control on regulating heat flux onto the continental shelf, making the ASC a key control on ice sheet mass balance. Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon. The upper ~50 m at Site U1525 belong to a large trough-mouth fan deposited to the west of the site. The lower 100 m at Site U1525 and the entire 400 m succession of sediment at Site U1524 recovered near-continuous records of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. Analyses of Exp. 374 sediments is ongoing, but following initial shipboard characterization, the intial results of sample analysis, the correlation between downhole synthetic logs and the associated seismic sections provide insight into the ages and the processes of erosion and deposition of glacial and marine strata. Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming.

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the Ross Sea continental shelf break has been inferred to directly influence sedimentary processes occurring on the continental slope. Sediment delivery to the shelf edge by grounded ice sheets during past glacials may have influenced turbidity current and debris flow activity, thus the records of these processes can be used to study the past history of the WAIS. However, the continental slope record may also be affected by density-driven or geostrophic oceanic bottom currents, therefore additionally providing an archive on their history and interplay with depositional mechanisms that are driven by ice sheets. Here, we investigate the upper 120.94m of one sediment core (length: 208.58mbsf) from Hole U1525A collected by International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the south-western levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interaction at the eastern Ross Sea continental shelf break/slope for the past 2.4 Ma. The earliest Pleistocene interval (2.4-1.35 Ma) is interpreted as a largely hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Microfossil barren, finely interlaminated sediments are interpreted as contourites deposited under the presence of multi-year sea-ice. During the latter part of the early Pleistocene (1.35-0.8 Ma), bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Much of the fine-grained sediments were probably deposited via gravitational settlement from turbid plumes, and a sustained nepheloid layer. The thickest interval of turbidite interlamination occurs after ~1 Ma, following the onset of the “Mid-Pleistocene Transition” (MPT), interpreted as a time when most terrestrial ice sheets increased in size and glacial periods were longer and more extreme. Sedimentation in the mid-late Pleistocene (< ~0.8 Ma) was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental shelf prograded and expanded over the site. More frequent and longer-lasting fully-extended glacial conditions allowed the continued progradation of the trough-mouth fan across the core site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the formation and growth of the WAIS under distinct oceanographic conditions.

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.

International audience; A new method merges conventional and quantitative biostratigraphic approaches, supported by magnetic polarity data, to develop a chronological framework for sediment core MD03-2595 retrieved on the continental rise off Wilkes Land, East Antarctica before proceeding to paleoceanographic and paleoclimatic analysis. This combined method helped to identify climatic cycles, highlight stratigraphic discontinuities and reworking, and assess regional sedimentological and diatom biostratigraphic evolution. Core MD03-2595 spans the last 0.8 Ma, from the Mid Pleistocene Transition (MPT) to the Early Holocene. A hiatus including Marine Isotope Stages (MIS) 19, 18 and 17 was identified, and a decreasing trend in sediment accumulation rates from MIS 16 to the Holocene was observed. This quantitative diatom biostratigraphic dataset, placed in its own sedimentological and paleomagnetic context, provides new information regarding the paleobiogeographic distribution and ecological responses of biostratigraphically significant diatom species, such as Thalassiosira elliptipora and T. fasciculata, for the Matuyama-Brunhes (M-B) transition, and Actinocyclus ingens, Hemidiscus karstenii and Rouxia spp. for the middle and late Pleistocene diatom biozonation.

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions.

The Prydz Bay region of Antarctica is the immediate recipient of ice and sediments transported by the Lambert Glacier, the single largest outflow from the East Antarctic Ice Sheet. The continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information. Marine geological and geophysical data collected from the continental shelf and adjacent slope of Prydz Bay, Antarctica, including seismic reflection data, bathymetry, and core records from ODP drilling sites, reveal the history of glacial sediment transport and deposition since the early Pliocene times. Seismic facies are interpreted in terms of episodes of slope progradation, contourite, turbidite, trough-mouth fan, and mass transport deposition. Two seismic units with estimated age of early to late Pliocene and late Pliocene to recent have been analyzed in detail for the area immediately offshore the Lambert Glacier and Prydz Bay and the adjacent Mac. Robertson margin. The upper slope is dominated by episodic mass transport deposits, many of which accumulated to form a trough mouth fan since Early Pliocene times. The trough mouth fan contrasts with the adjacent steep (4–6°) continental slope of the Mac. Robertson margin, where glacigenic sediments have been transported down slope as high-velocity turbidity currents via submarine channels. The distal region exhibits evidence for contrasting effects of high-energy, traction-dominated versus lower-energy, fallout-dominated suspension flows. The counter-clockwise Coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel-levee architecture. Since the early Pliocene, turbidite sedimentation surpassed the amount of sediment reworked and transported by westward-flowing contour currents along the base of slope. On the continental rise, contourites and sediment waves were deposited in response to enhanced bottom-water formation, which is consistent with climatic cooling since late Pliocene times. This study, based on existing seismic reflection and ODP data, highlights the need for a future scientific ocean drilling proposal on the Prydz Bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin.

An undergraduate thesis submitted in partial application for the Honors degree in Earth Sciences.

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