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Extensive ice coverage largely prevents investigations of Antarctica’s unglaciated past. Knowledge about environmental and tectonic development before large-scale glaciation, however, is important for understanding the transition into the modern icehouse world. We report geochronological and sedimentological data from a drill core from the Amundsen Sea shelf, providing insights into tectonic and topographic conditions during the Eocene (~44 to 34 million years ago), shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from >40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a >1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.

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.

Geothermal heat flow in the polar regions plays a crucial role in understanding ice-sheet dynamics and predictions of sea level rise. Continental-scale indirect estimates often have a low spatial resolution and yield largest discrepancies in West Antarctica. Here we analyse geophysical data to estimate geothermal heat flow in the Amundsen Sea Sector of West Antarctica. With Curie depth analysis based on a new magnetic anomaly grid compilation, we reveal variations in lithospheric thermal gradients. We show that the rapidly retreating Thwaites and Pope glaciers in particular are underlain by areas of largely elevated geothermal heat flow, which relates to the tectonic and magmatic history of the West Antarctic Rift System in this region. Our results imply that the behavior of this vulnerable sector of the West Antarctic Ice Sheet is strongly coupled to the dynamics of the underlying lithosphere.

The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet (WAIS) because of the great water depth at the grounding line, a subglacial bed seafloor deepening toward the interior of the continent, and the absence of substantial ice shelves. Glaciers in this configuration are thought to be susceptible to rapid or runaway retreat. Ice flowing into the Amundsen Sea Embayment is undergoing the most rapid changes of any sector of the Antarctic ice sheets outside the Antarctic Peninsula, including substantial grounding-line retreat over recent decades, as observed from satellite data. Recent models suggest that a threshold leading to the collapse of WAIS in this sector may have been already crossed and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. Drill cores from the Amundsen Sea provide tests of several key questions about controls on ice sheet stability. The cores offer a direct offshore record of glacial history in a sector that is exclusively influenced by ice draining the WAIS, which allows clear comparisons between the WAIS history and low-latitude climate records. Today, relatively warm (modified) Circumpolar Deep Water (CDW) is impinging onto the Amundsen Sea shelf and causing melting under ice shelves and at the grounding line of the WAIS in most places. Reconstructions of past CDW intrusions can assess the ties between warm water upwelling and large-scale changes in past grounding-line positions. Carrying out these reconstructions offshore from the drainage basin that currently has the most substantial negative mass balance of ice anywhere in Antarctica is thus of prime interest to future predictions. The scientific objectives for this expedition are built on hypotheses about WAIS dynamics and related paleoenvironmental and paleoclimatic conditions. The main objectives are To test the hypothesis that WAIS collapses occurred during the Neogene, QC 20230814

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The goal of core-log-seismic integration is to glean new scientific understanding from diverse datasets that span the millimeter to kilometer scale. Germany plays an important role in international scientific drilling, with major core curation and data management centres, as well as broad expertise in seismicdata acquisition, borehole logging and sediment core investigations. Springboarding from this solid foundation, we propose to establish a virtual Core-Log-Seismic Integration Research Centre to act as a nucleus for conceiving and running research projectsthat harvest the untapped potential of hundreds of scientific boreholes. We envisage that scientists from Germany, in collaboration with key international partners, should work closely together and provide the critical mass and long-term expertise to sustain the research centre. We see this an ideal way to foster collaboration within Germany and globally.In this presentation we will describe this new initiative and provide some examples of on-going and developing research projects that are underpinned by core-log-seismic integration methods. The examples will include investigations into submarine landslide processes (offshore New Zealand), gas hydrate formation (offshore Taiwan) and continental collision (onshore Sweden).

Highlights • Common HIMU end member in adjacent continental and oceanic volcanic provinces. • End member St. Helena HIMU derived from deep upwelling(s)/plume(s). • Plateau collision & plume interaction with Gondwana active margin causes breakup. • Hybrid volcanic-tectonic margins resulted from Zealandia – Antarctica breakup. Abstract Margins resulting from continental breakup are generally classified as volcanic (related to flood basalt volcanism from a starting plume head) or non-volcanic (caused by tectonic processes), but many margins (breakups) may actually be hybrids caused by a combination of volcanic and tectonic processes. It has been postulated that the collision of the Hikurangi Plateau with the Gondwana margin ∼110 Ma ago caused subduction to cease, followed by large-scale extension and ultimately breakoff of the Zealandia micro-continent from West Antarctica through seafloor spreading which started at ∼85 Ma. Here we report new geochemical (major and trace element and Sr-Nd-Pb-Hf isotope) data for Late Cretaceous (99-69 Ma) volcanism from Zealandia, which include the calc-alkalic, subduction-related Mount Somers (99-96 Ma) and four intraplate igneous provinces: 1) Hikurangi Seamount Province (99-88 Ma), 2) Marlborough Igneous Province (98-94 Ma), 3) Westland Igneous Province (92-69 Ma), and 4) Eastern Chatham Igneous Province (86-79 Ma). Each of the intraplate provinces forms mixing arrays on incompatible-element and isotope ratio plots between HIMU (requiring long-term high U/204Pb) and either a depleted (MORB-source) upper mantle (DM) component or enriched continental (EM) type component (located in the crust and/or upper mantle) or a mixture of both. St. Helena end member HIMU could be the common component in all four provinces. Considering the uniformity in composition of the HIMU end member despite the type of lithosphere (continental, oceanic, oceanic plateau) beneath the igneous provinces, we attribute this component to a sublithospheric source, l

We present GlobSed, a new global 5-arc-minute total sediment thickness grid for the world's oceans and marginal seas. GlobSed covers a larger area than previously published global grids and incorporates updates for the NE Atlantic, Arctic, Southern Ocean, and Mediterranean regions, which results in a 29.7% increase in estimated total oceanic sediment volume. We use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude. An analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time. This study provides a much-needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

We present GlobSed, a new global 5-arc-minute total sediment thickness grid for the world's oceans and marginal seas. GlobSed covers a larger area than previously published global grids and incorporates updates for the NE Atlantic, Arctic, Southern Ocean, and Mediterranean regions, which results in a 29.7% increase in estimated total oceanic sediment volume. We use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude. An analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time. This study provides a much-needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

The second generation Antarctic magnetic anomaly compilation for the region south of 60°S includes some 3.5 million line-km of aeromagnetic and marine magnetic data that more than doubles the initial map’s near-surface database. For the new compilation, the magnetic data sets were corrected for the International Geomagnetic Reference Field, diurnal effects, and high-frequency errors and leveled, gridded, and stitched together. The new magnetic data further constrain the crustal architecture and geological evolution of the Antarctic Peninsula and the West Antarctic Rift System in West Antarctica, as well as Dronning Maud Land, the Gamburtsev Subglacial Mountains, the Prince Charles Mountains, Princess Elizabeth Land, and Wilkes Land in East Antarctica and the circumjacent oceanic margins. Overall, the magnetic anomaly compilation helps unify disparate regional geologic and geophysical studies by providing new constraints on major tectonic and magmatic processes that affected the Antarctic from Precambrian to Cenozoic times.

The second generation Antarctic magnetic anomaly compilation (ADMAP‐2) for the region south of 60oS includes some 3.5 million line‐km of aeromagnetic and marine magnetic data that more than doubles the initial map's near‐surface database. For the new compilation, the magnetic datasets were corrected for the International Geomagnetic Reference Field, diurnal effects, and high‐frequency errors, and levelled, gridded, and stitched together. The new magnetic data further constrain the crustal architecture and geological evolution of the Antarctic Peninsula and the West Antarctic Rift System in West Antarctica, as well as Dronning Maud Land, the Gamburtsev Subglacial Mountains, the Prince Charles Mountains, Princess Elizabeth Land, and Wilkes Land in East Antarctica, and the circumjacent oceanic margins. Overall, the magnetic anomaly compilation helps unify disparate regional geologic and geophysical studies by providing new constraints on major tectonic and magmatic processes that affected the Antarctic from Precambrian to Cenozoic times.

A multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7% and 76%. We deployed the MARUM-MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.

On parts of glaciated continental margins, especially the inner shelves around Antarctica, grounded ice has removed pre-existing sedimentary cover, leaving subglacial bedforms on eroded substrates (Anderson et al. 2001; Wellner et al. 2001). While the dominant subglacial bedforms often follow a distinct, relatively uniform pattern that can be related to overall trends in palaeo-ice flow and substrate geology (Wellner et al. 2006), others are more randomly distributed and may reflect local substrate variations. Here we describe and discuss examples of large, isolated crag-and-tail features that are recognized on the Amundsen Sea continental shelf.

The seafloor of inner continental shelves on glaciated margins is sometimes stripped of most of the softer sediments, leaving bedrock exposed (Wellner et al. 2001). Examples of such exposed bedrock regions have been observed in the inner parts of several cross-shelf troughs on the West Antarctica margin, including those in the Amundsen Sea (Lowe & Anderson 2003; Graham et al. 2009) and Marguerite Bay (Anderson & Fretwell 2008). The detailed morphology of these areas consists of various features of glacial origin, predominantly parallel grooves or striations. These areas can also contain sinuous channels that are incised deeply into the rock substrate.

About 30% of ice draining the West Antarctic Ice Sheet discharges through several glacier systems into the Amundsen Sea Embayment (ASE) (Fig. 1a). Two major ice-stream outlets, Pine Island and Thwaites glaciers, have undergone significant twentieth century changes (e.g. Rignot et al. 2008) and much effort has focused upon understanding their late Quaternary glacial history (Larter et al. 2014). At the Last Glacial Maximum (LGM), the ice sheet in the ASE expanded to reach the outer shelf and is postulated to have reached the shelf edge (Graham et al. 2010). The Pine Island and Thwaites glaciers combined regularly through Quaternary glaciations to carve out a >500 km long trough that extends from the shelf break back to the modern-day grounding line and beyond. Geophysical data exist for the breadth of this transect, including sub-ice-shelf bathymetry (Jenkins et al. 2010), making it one of the most complete palaeo-ice-stream landsystems known offshore of Antarctica. Deglaciation of the trough was underway by c. 20 cal. ka BP and was episodic, reaching a mid-shelf position by c. 13.5–12 cal. ka BP and retreating rapidly to the inner ASE by c. 11–9 cal. ka BP (Kirshner et al. 2012; Hillenbrand et al. 2013; Smith et al. 2014). Repeated pauses and several phases of ice-shelf break-up have been interpreted to have taken place during deglaciation based upon a well-preserved landform and sediment record (Lowe & Anderson 2002; Graham et al. 2010; Jakobsson et al. 2011).

Large ice streams that drain the West Antarctic Ice Sheet (WAIS) into the Amundsen Sea Embayment (ASE) are currently thinning, accelerating and retreating rapidly (e.g. Rignot et al. 2014). These ice streams are assumed to have reached the continental shelf edge during the Last Glacial Maximum (LGM; c. 23–19 cal ka BP), some 450 km north of the modern grounding line (e.g. Larter et al. 2014). Recent modelling results suggest that the expanded LGM ice sheet was characterized by fast-flowing regions across the entire ASE shelf (Golledge et al. 2013). However, the original geomorphological imprint of former fast ice-flow has usually only been preserved within deep palaeo-ice stream troughs, for example as mega-scale glacial lineations (MSGLs) (Clark 1993). In contrast, the morphological record in inter-ice stream settings is believed to have been subsequently obliterated by ploughing iceberg keels (e.g. Dowdeswell & Bamber 2007). As a result, evidence for palaeo-ice sheet dynamics in these regions, which make up a substantial portion of the former ice-sheet bed, remain largely understudied (Ottesen & Dowdeswell 2009). The undisturbed geomorphological record from a palaeo-inter-ice stream setting in the ASE, north of Burke Island, revealed an assemblage of subglacial landforms that is entirely different from those in the deep troughs (Klages et al. 2013). The geomorphological record therefore provides new insights into basal conditions of the former WAIS in the Amundsen Sea sector that is also relevant to other sectors and to ice-sheet beds outside Antarctica. Description The seafloor in the inter-ice stream setting between the Pine Island (PIT) and the Abbot (AT) palaeo-ice stream troughs in the ASE (Fig. 1a) is characterized by a unique assemblage of glacial landforms that includes the following features (Klages et al. 2013, 2015).

Within Earth's ice sheets, fast-flowing ice streams are the principal components through which ice and sediment are discharged, accounting for c. 90% of the ice lost from the Antarctic today (Bamber et al. 2000). The processes occurring at ice-stream beds, therefore, lie at the heart of resolving how and why major ice-stream systems may change in the future. Although drill-cores and ice-surface seismic methods have been employed to survey the beds of some of West Antarctica's ice streams, studies are still hampered by the logistical and technological challenges associated with understanding a dynamic and spatially extensive interface buried beneath kilometre-thick continental ice (Larter et al. 2009). Here, a multibeam swath-bathymetric dataset acquired from the Dotson–Getz palaeo-ice-stream bed, offshore of West Antarctica, is described (Fig. 1a). In contrast to the modern ice-sheet base, the spatial coverage and quality of the marine data allow us to analyse landform evolution along an entire ice-stream bed that is both completely exposed and well preserved.

On parts of glaciated continental margins, especially the inner shelves around Antarctica, grounded ice has removed pre-existing sedimentary cover, leaving subglacial bedforms on eroded substrates (Anderson et al. 2001; Wellner et al. 2001). While the dominant subglacial bedforms often follow a distinct, relatively uniform pattern that can be related to overall trends in palaeo-ice flow and substrate geology (Wellner et al. 2006), others are more randomly distributed and may reflect local substrate variations. Here we describe and discuss examples of large, isolated crag-and-tail features that are recognized on the Amundsen Sea continental shelf.