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Lack of foraminiferal carbonate in marine sediments deposited at high latitudes results in traditional oxygen isotope stratigraphy not playing a central role in Quaternary age control for a large portion of the globe. This limitation has affected the interpretation of Quaternary sediment drifts off the Antarctic Peninsula in a region critical for documenting past instability of the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). Here we use piston cores recovered from these sediment drifts in 2015 during cruise JR298 of the RRS James Clark Ross to test the usefulness for age control of relative paleointensity (RPI) data augmented by scant δ 18 O data. Thermomagnetic and magnetic hysteresis data, as well as isothermal remanent magnetization (IRM) acquisition curves, indicate the presence of prevalent magnetite and subordinate oxidized magnetite (“maghemite”) in the cored sediments. The magnetite is likely detrital. Maghemite is an authigenic mineral, associated with surface oxidation of magnetite grains, which occurs preferentially in the oxic zone of the uppermost sediments, and buried oxic zones deposited during prior interglacial climate stages. Low concentrations of labile organic matter apparently led to arrested pore-water sulfate reduction explaining oxic zone burial and downcore survival of the reactive maghemite coatings. At some sites, maghemitization has a debilitating effect on RPI proxies whereas at other sites maghemite is less evident and RPI proxies can be adequately matched to the RPI reference template. Published RPI data at ODP Site 1101, located on Drift 4, can be adequately correlated to contemporary RPI templates, probably as a result of disappearance (dissolution) of maghemite at sediment depths >∼10 m.

The Drake Passage is an oceanic gateway of about 850 km width located between South America and the Antarctic Peninsula that connects the southeastern Pacific Ocean with the southwestern Atlantic Ocean. It is an important gateway for mantle flow, oceanographic water masses, and migrations of biota. This sector developed within the framework of the geodynamic evolution of the Scotia Arc, including continental fragmentation processes and oceanic crust creation, since the oblique divergence of the South American plate to the north and the Antarctic plate to the south started in the Eocene. As a consequence of its complex tectonic evolution and subsequent submarine processes, as sedimentary infill and erosion mainly controlled by bottom currents and active tectonics, this region shows a varied physiography. We present a detailed map of the bathymetry and geological setting of the Drake Passage that is mainly founded on a new compilation of precise multibeam bathymetric data obtained on 120 cruises between 1992 and 2015, resulting in a new Digital Bathymetric Model with 200 × 200 m cell spacing. The map covers an area of 1,465,000 km2 between parallels 52°S and 63°S and meridians 70°W and 50°W at scale 1:1,600,000 allowing the identification of the main seafloor features. In addition, the map includes useful geological information related to magnetism, seismicity and tectonics. This work constitutes an international cooperative effort and is part of the International Bathymetric Chart of the Southern Ocean project, under the Scientific Committee on Antarctic Research umbrella.

Faunal assemblages at hydrothermal vents associated with island-arc volcanism are less well known than those at vents on mid-ocean ridges and back-arc spreading centres. This study characterizes chemosynthetic biotopes at active hydrothermal vents discovered at the Kemp Caldera in the South Sandwich Arc. The caldera hosts sulfur and anhydrite vent chimneys in 1375–1487 m depth, which emit sulfide-rich fluids with temperatures up to 212°C, and the microbial community of water samples in the buoyant plume rising from the vents was dominated by sulfur-oxidizing Gammaproteobacteria. A total of 12 macro- and megafaunal taxa depending on hydrothermal activity were collected in these biotopes, of which seven species were known from the East Scotia Ridge (ESR) vents and three species from vents outside the Southern Ocean. Faunal assemblages were dominated by large vesicomyid clams, actinostolid anemones, Sericosura sea spiders and lepetodrilid and cocculinid limpets, but several taxa abundant at nearby ESR hydrothermal vents were rare such as the stalked barnacle Neolepas scotiaensis. Multivariate analysis of fauna at Kemp Caldera and vents in neighbouring areas indicated that the Kemp Caldera is most similar to vent fields in the previously established Southern Ocean vent biogeographic province, showing that the species composition at island-arc hydrothermal vents can be distinct from nearby seafloor-spreading systems. δ13C and δ15N isotope values of megafaunal species analysed from the Kemp Caldera were similar to those of the same or related species at other vent fields, but none of the fauna sampled at Kemp Caldera had δ13C values, indicating nutritional dependence on Epsilonproteobacteria, unlike fauna at other island-arc hydrothermal vents.

The mid-Cretaceous was one of the warmest intervals of the past 140 million years (Myr) driven by atmospheric CO2 levels around 1000 ppmv. In the near absence of proximal geological records from south of the Antarctic Circle, it remains disputed whether polar ice could exist under such environmental conditions. Here we present results from a unique sedimentary sequence recovered from the West Antarctic shelf. This by far southernmost Cretaceous record contains an intact ~3 m-long network of in-situ fossil roots. The roots are embedded in a mudstone matrix bearing diverse pollen and spores, indicative of a temperate lowland rainforest environment at a palaeolatitude of ~82°S during the Turonian–Santonian (92–83 Myr). A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric CO2 contents of 1120–1680 ppmv and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo in high-CO2 climate worlds.

Late Miocene to Recent sediments offshore from the Antarctic Peninsula are predominantly lithogenic, having originated through glacial erosion. Sediments that accumulated during interglacial periods commonly have a greater biogenic component, but deposits in which this constitutes a substantial fraction are rare. Only a small fraction of the continental block is above sea level and even during interglacial periods temperatures are only warm enough to generate significant melt at low elevations for a few weeks each summer, so sediment input to the sea from surface runoff is minor. Sediment transport to the continental margin takes place mainly at the ice bed during glacial periods when the grounding line advances to the shelf edge. On the Pacific margin, downslope transport from the shelf edge region occurs mainly through gravitational mass transport processes. These processes are likely most active during glacial periods when rapid delivery of glacial sediment leads to instability on the uppermost slope and discharge of sediment-laden subglacial meltwater at the shelf edge grounding line initiates turbidity currents. The lack of obvious large slide scars along most of the relatively steep continental slope suggests that most individual failures are small in volume. Dendritic networks of small channels on the lower slope feed into large turbidity current channels that run out across the continental rise for hundreds of kilometres. Between the channels are giant sediment drifts, some with more than a kilometre of relief, which are composed predominantly of finely-bedded silt and clay layers. The drifts have been produced through entrainment of the fine-grained components of turbidity currents in the ambient bottom current that flows southwestward along the margin. Results from Ocean Drilling Program Leg 178 showed that these drifts contain high-resolution records of ice sheet and oceanographic changes, although unfortunately insufficient core material was recovered to

Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet modulate ice flow velocities over periods of months to years. Although subglacial lake drainage events have been observed from satellite altimetric data, little is known about their role in the long term evolution of ice sheet basal hydrology. Here, we systematically map and model past water flow through an extensive area containing over 1000 subglacial channels and 19 former lake basins exposed on over 19,000 km2 of seafloor by the retreat of Pine Island and Thwaites glaciers, West Antarctica. At 560 m wide and 50 m deep on average, the channels offshore of present day Pine Island and Thwaites glaciers are approximately twice as deep, three times as wide, and cover an area over 400 times larger than the terrestrial meltwater channels comprising the Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock offshore of contemporary Pine Island and Thwaites glaciers would have been capable of accommodating discharges of up to 8.8 × 106 m3 s−1. We suggest that the channels were formed by episodic, high magnitude discharges from subglacial lakes trapped during ice sheet advance and retreat over multiple glacial periods. Our results document the widespread influence of episodic subglacial drainage events during past glacial periods, in particular beneath large ice streams similar to those that continue to dominate contemporary ice-sheet discharge.

Bathymetric data of unprecedented resolution are used to provide insights into former ice dynamics and glacial processes in a western Antarctic Peninsula embayment. An assemblage of submarine glacial landforms, which includes subglacially produced streamlined features and ice-marginal ridges, reveals the former pattern of ice flow and retreat. A group of more than 250 small (< 1–3 m high, 10–20 m wide) and relatively evenly spaced recessional moraines was identified beyond the margin of Philippa Glacier. The small recessional moraines are interpreted to have been produced during short-lived, possibly annual re-advances of a grounded ice margin during overall retreat. This is the first time that these features have been shown to be part of the assemblage of landforms produced by tidewater glaciers on the Antarctic Peninsula. Glacier-terminus changes during the last four decades, mapped from LANDSAT satellite images, were analysed to determine whether the moraines were produced during recent still-stands or re-advances of Philippa Glacier and to further investigate the short-term (annual to decadal) variability in ice-marginal position in tidewater glacier systems. The asynchronous response of individual tidewater glaciers in Darbel Bay is interpreted to be controlled mainly by local topography rather than by glacier catchment-area size.

Basal hydrological systems play an important role in controlling the dynamic behaviour of ice streams. Data showing their morphology and relationship to geological substrates beneath modern ice streams are, however, sparse and difficult to collect. We present new multibeam bathymetry data that make the Anvers-Hugo Trough west of the Antarctic Peninsula the most completely surveyed palaeo-ice stream pathway in Antarctica. The data reveal a diverse range of landforms, including streamlined features where there was fast flow in the palaeo-ice stream, channels eroded by flow of subglacial water, and compelling evidence of palaeo-ice stream shear margin locations. We interpret landforms as indicating that subglacial water availability played an important role in facilitating ice stream flow and controlling shear margin positions. Water was likely supplied to the ice stream bed episodically as a result of outbursts from a subglacial lake located in the Palmer Deep basin on the inner continental shelf. These interpretations have implications for controls on the onset of fast ice flow, the dynamic behaviour of palaeo-ice streams on the Antarctic continental shelf, and potentially also for behaviour of modern ice streams.

Trough mouth fans (TMFs) are sediment depocentres that form along high-latitude continental margins at the mouths of some cross-shelf troughs. They reflect the dynamics of past ice sheets over multiple glacial cycles and processes operating on (formerly) glaciated continental shelves and slopes, such as erosion, reworking, transport and deposition. The similarities and differences in TMF morphology and formation processes in the Arctic and Antarctic regions remain poorly constrained. We analyse the dimensions and geometries of 15 TMFs from Arctic and Antarctic margins and the grain size distribution of 82 sediment cores centred on them. We compare the grain size composition of sub- and proglacial diamictons deposited on the shelves and glacigenic debris flows deposited on the adjacent TMFs and find a significant difference between Arctic and Antarctic margins. Antarctic margins show a coarser grain size composition for both glacigenic debris flows and shelf diamictons. This significant difference provides insight into high-latitude sediment input, transportation and glacial–interglacial regimes. We suggest that surface runoff and river discharge are responsible for enhanced fine-grained sediment input in the Arctic compared with the Antarctic.

It is becoming increasingly apparent that bathymetry plays a crucial role in determining the behavior of marine-terminating glaciers. This is because variations in the shape of the bed can produce both pinning points where glaciers (or their floating tongues) can ground and stabilize, as well as pathways for warm waters to move across the shelf and access the grounding line. Ahead of the first ITGC field season we present the existing state of knowledge about the bed in front of Thwaites Glacier (TG). We have compiled existing multibeam-bathymetric datasets from the UK, the USA and international partners (Korea, Germany) to produce a high-resolution grid (50-m cells) for the area. From this grid we identify possible pathways for warm Circumpolar Deep Water to the TG grounding line, a topographic high – as shallow as 130 m in places - that likely acted as a pinning point and is less than 18 km from the current eastern ice-shelf margin, and landforms indicative of the past behavior of the glacier (e.g. meltwater channels and basins, streamlined landforms). This exercise also highlights important data gaps to target for surveying in 2019, including for example, the area left vacant by the calving of the B-22 iceberg. Secondly, we explore existing sub-bottom and seismic-reflection profiles from the Amundsen Sea Embayment to investigate the nature of the substrate in front of TG. Unlithified sediment cover is generally thin (<5 m) over scoured crystalline bedrock but thickens to up to 40 m in basins. We discuss potential coring targets close to pathways for warm water incursions, and former stability points including the possibility of unknown basins in front of TG.

Iceberg calving accounts for between one third and a half of the mass loss from Thwaites Glacier and Pine Island Glacier ice shelves. If increased calving results in ice-shelf retreat or break up, the loss of buttressing can be expected to lead to further flow acceleration and dynamic thinning of the glaciers. It has been suggested that if ice-shelf breakup exposes a floating terminus exceeding a critical thickness of ~1000 m, this will be structurally unstable and rapid retreat through Marine Ice Cliff Instability (MICI) could be initiated. Despite their importance, the factors controlling calving remain poorly understood. Two recent studies show how sea-bed topography can influence calving. Prior to 2015, despite rapid thinning for more than 20 years, the position from which large tabular icebergs calved from Pine Island Glacier had varied little since its ice shelf was first observed in 1947. In August 2015 calving occurred at a position ~15 km further upstream than on any previous occasion and the new calving front had a different orientation from previous ones. The area that the ice shelf retreated from at this time encompassed a former pinning point. Multibeam bathymetry data were collected over this area on RV Polarstern expedition PS104 in 2017. Consideration of a series of satellite images from 2002 to 2017 in the context of the detailed new bathymetry data suggests that calving events in 2007 and 2013 were triggered by interactions between the ice shelf and bathymetric highs (Arndt et al., 2018). Further offshore, an unusual episode of calving during the last deglaciation of the continental shelf is recorded by iceberg-keel plough marks in Pine Island Trough that are identified in multibeam bathymetry data collected on icebreaker Oden expedition OSO0910 in 2010. The relatively small size (width <450 m) and great depth (up to 848 m) of these plough marks, together with the fact that they formed during a short period of rapid retreat constrained by radiocarb

Past ice sheet conditions in the southern Weddell Sea remain poorly known. Previous studies have led to contradicting scenarios of maximum ice extent during the Last Glacial Maximum (LGM). Scenario A is mainly based on terrestrial data indicating limited ice sheet thickening in the hinterland and suggests a LGM grounding-line position on the inner shelf. Scenario B is based on marine geological/-physical data and concludes that the grounding line was located on the outer shelf (~650 km further offshore than in scenario A). In addition, studies suggest a complex history of ice retreat and drainage pattern since the LGM that needs further constraint. We investigated hydroacoustic data acquired during 17 expeditions. A key finding is a previously unknown stacked grounding zone wedge (GZW) located in Filchner Trough on the outer shelf showing that a palaeo-ice stream stabilized at this position at least twice. Radiocarbon dates from sediment cores indicate that (i) the GZW was formed in the early Holocene and (ii) grounded ice did not extend seaward at the LGM. Hence, the grounding line in Filchner Trough experienced dynamic changes in the Holocene and ice sheet retreat after the LGM was not linear. Ice-flow switches in the hinterland possibly explain this behaviour. Further interesting findings are made in Brunt Basin suggesting the existence of cold-based ice or impacts of large icebergs. In addition, new data will be acquired in the area with RV Polarstern in Jan-Mar 2018.

Pine Island Glacier is the largest current Antarctic contributor to sea-level rise. Its ice loss has substantially increased over the last 25 years through thinning, acceleration and grounding line retreat. However, the calving line positions of the stabilising ice shelf did not show any trend within the observational record (last 70 years) until calving in 2015 led to unprecedented retreat and changed the alignment of the calving front. Bathymetric surveying revealed a ridge below the former ice shelf and two shallower highs to the north. Satellite imagery shows that ice contact on the ridge was likely lost in 2006 but was followed by intermittent contact resulting in back stress fluctuations on the ice shelf. Continuing ice-shelf flow also led to occasional ice-shelf contact with the northern bathymetric highs, which initiated rift formation that led to calving. The observations show that bathymetry is an important factor in initiating calving events.

Pine Island Glacier (PIG) currently experiences the largest negative mass balance in comparison to other outlet glaciers in Antarctica and hence is the largest contributor to modern sea-level rise. Due to the glacier’s topographic setting, a bed that deepens beyond the grounding line to the deep interior basin of the West Antarctic Ice Sheet (WAIS), it has been suggested that this increased ice loss may be a precursor of WAIS collapse. Despite the increased mass loss, however, the calving front of PIG remained more or less stable since the earliest observations in the mid-20th century. Large icebergs where calved at intervals of a few years but subsequently the calving front re-advanced close to or even beyond its former position. This pattern changed in 2015 when a calving event resulted in a reoriented (45°-25° clockwise compared to previous calving lines) and most retreated calving line position ever observed. This new calving geometry was confirmed by a calving event in September 2017. In February 2017 we were able to access the formerly ice-shelf covered area during RV Polarstern expedition PS104. Bathymetric data from this area revealed a bathymetric ridge that has acted as a pinning point of PIG in the past. We use these bathymetric data in combination with satellite data from the last decades to investigate the correlation of bathymetric features to the calving dynamics of Pine Island Glacier.

The sedimentary sequences of the Amundsen Sea Embayment (ASE) shelf contain records that have the potential to reveal the environmental and ice sheet evolution from pre-glacial to glacial times for a very dynamic sector of the West Antarctic Ice Sheet (WAIS). The currently observed massive loss of continental ice in this region may be a precursor to a partial or full collapse of the WAIS. Deciphering paleoclimate and paleo-ice sheet records from the shelf sediments is therefore a major scientific objective for studying processes of past warm times that can be considered as analogues to the present and future WAIS behavior. In previous work, the seismic stratigraphic model of the shelf was based solely on long-distance jump correlation with seismic records from the Ross Sea shelf. New MeBo70 seabed drill cores collected in early 2017 from the ASE shelf contain unconsolidated to highly consolidated sediments spanning time periods from the Holocene to Cretaceous. We are now able to correlate the mapped seismic horizons and units with the physical property and age information from the drill cores to obtain new insight into the sedimentary and paleoenvironmental development of the entire shelf. The drill records and seismo-stratigraphic units of the ASE provide new constraints on the timing of the transition from the pre-glacial terrestrial environment of the Cretaceous–Paleocene to marine transgression thereafter, and the first advances of grounded ice across the shelf.

The sedimentary sequences of the Amundsen Sea Embayment (ASE) shelf contain records that have the potential to reveal the environmental and ice sheet evolution from pre-glacial to glacial times for a very dynamic sector of the West Antarctic Ice Sheet (WAIS). The currently observed massive loss of continental ice in this region may be a precursor to a partial or full collapse of the WAIS. Deciphering paleoclimate and paleo-ice sheet records from the shelf sediments is therefore a major scientific objective for studying processes of past warm times that can be considered as analogues to the present and future WAIS behavior. In previous work, the seismic stratigraphic model of the shelf was based solely on long-distance jump correlation with seismic records from the Ross Sea shelf. New MeBo70 seabed drill cores collected in early 2017 from the ASE shelf contain unconsolidated to highly consolidated sediments spanning time periods from the Holocene to Cretaceous. We are now able to correlate the mapped seismic horizons and units with the physical property and age information from the drill cores to obtain new insight into the sedimentary and paleoenvironmental development of the entire shelf. The drill records and seismo-stratigraphic units of the ASE provide new constraints on the timing of the transition from the pre-glacial terrestrial environment of the Cretaceous–Paleocene to marine transgression thereafter, and the first advances of grounded ice across the shelf.

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise and establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the early Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop durin

The study of ice-sheet behaviour is needed to better our understanding of glacial dynamics under the influence of a changing climate. Marked differences in palaeo-ice stream growth, retreat and pathways, have been reported to exist between the easternmost (east of Burke Island) and western Amundsen Sea Embayment, West Antarctica. Previously collected seismic reflection and bathymetric data have suggested a slower retreat of the ice-stream east of Burke Island than west of it, which is interpreted to be the result of smaller, colder drainage basins and less meltwater production. In order to verify this hypothesis a set of high-resolution seismic reflection profiles was collected across a grounding zone wedge east of Burke Island during cruise PS104 with RV Polarstern in February/March 2017. First results of this survey will be presented.

Grounding-zone wedges (GZW) have been mapped on the sea floor in various sectors of formerly glaciated continental shelf around Antarctica. In most cases, these wedges record periods of grounding-line stillstands during ice-sheet retreat following the Last Glacial Maximum (~26-19 ka BP). The presence of GZWs along the axis of a palaeo-ice stream trough therefore indicates a style of episodic retreat of the grounding line from its LGM to modern position. However, information about their composition and internal structure is sparse, and precise chronological constraints for both the onset and duration of stillstands they represent are still lacking. Consequently, the role of grounding-zone wedge formation in modulating post-LGM ice-sheet retreat cannot be reliably quantified. This information is vital, however, for calculating reliable retreat rates during the past, which are essential for evaluating and understanding the significance of modern retreat rates. Here we present the currently known inventory of GZWs on the continental shelf of the Amundsen Sea Embayment (ASE), West Antarctica, and introduce newly acquired data from one particular middle shelf GZW revealing the first information of its internal structure and composition. We will also discuss geological preconditions at the ice sheet bed that led to GZW formation. Furthermore, we will present our approach to i) reliably date the onset of GZW development, and ii) constrain the duration of these stillstands, including better estimations for subglacial sediment delivery rates. This knowledge will help refine available post-LGM retreat chronologies, which, in turn, serve as a basis for validating and improving ice-sheet models in an area where these are urgently needed.