Search

The Ekström Ice Shelf is one of numerous small ice shelves that fringe the coastline of western Dronning Maud Land, East Antarctica. Reconstructions of past ice-sheet extent in this area are poorly constrained, due to a lack of geomorphological evidence. Here, we present a compilation of geophysical surveys in front of and beneath the Ekström Ice Shelf, to identify and interpret evidence of past ice-sheet flow, extent and retreat. The sea floor beneath the Ekström Ice Shelf is dominated by an incised trough, which extends from the modern-day grounding line onto the continental shelf. Our surveys show that mega-scale glacial lineations cover most of the mouth of this trough, terminating 11 km away from the continental shelf break, indicating the most recent minimal extent of grounded ice in this region. Beneath the front ∼30 km of the ice shelf measured from the ice shelf edge towards the inland direction, the sea floor is characterised by an acoustically transparent sedimentary unit, up to 45 m thick. This is likely composed of subglacial till, further corroborating the presence of past grounded ice cover. Further inland, the sea floor becomes rougher, interpreted as a transition from subglacial tills to a crystalline bedrock, corresponding to the outcrop of the volcanic Explora Wedge at the sea floor. Ice retreat in this region appears to have happened rapidly in the centre of the incised trough, evidenced by a lack of overprinting of the lineations at the trough mouth. At the margins of the trough uniformly spaced recessional moraines suggest ice retreated more gradually. We estimate the palaeo-ice thickness at the calving front around the Last Glacial Maximum to have been at least 305 to 320 m, based on the depth of iceberg ploughmarks within the trough and sea level reconstructions. Given the similarity of the numerous small ice shelves along the Dronning Maud Land coast, these findings are likely representative for other ice shelves in this region and provide e

The Antarctic Ice Sheet extent in the Weddell Sea Embayment (WSE) during the Last Glacial Maximum (LGM; ca. 19-25 calibrated kiloyears before present, cal. ka BP) and its subsequent retreat from the shelf are poorly constrained, with two conflicting scenarios being discussed. Today, the modern Brunt Ice Shelf, the last remaining ice shelf in the northeastern WSE, is only pinned at a single location and recent crevasse development may lead to its rapid disintegration in the near future. We investigated the seafloor morphology on the northeastern WSE shelf and discuss its implications, in combination with marine geological records, for reconstructions of the past behaviour of this sector of the East Antarctic Ice Sheet (EAIS), including ice-seafloor interactions. Our data show that an ice stream flowed through Stancomb-Wills Trough and acted as the main conduit for EAIS drainage during the LGM. Post-LGM ice-stream retreat occurred stepwise, with at least three documented grounding line still stands, and the trough had become free of grounded ice by ~10.5 cal. ka BP. In contrast, slow-flowing ice once covered the shelf in Brunt Basin and extended westwards toward McDonald Bank. During a later time period, only floating ice was present within Brunt Basin, but large ‘ice slabs’ enclosed within the ice shelf occasionally ran aground at the eastern side of McDonald Bank, forming ten unusual ramp-shaped seabed features. These ramps are the result of temporary ice-shelf grounding events buttressing the ice further upstream. To the west of this area, Halley Trough very likely was free of grounded ice during the LGM, representing a potential refuge for benthic shelf fauna at this time.

The geometry of the sea floor immediately beyond Antarctica's marine-terminating glaciers is a fundamental control on warm-water routing, but it also describes former topographic pinning points that have been important for ice-shelf buttressing. Unfortunately, this information is often lacking due to the inaccessibility of these areas for survey, leading to modelled or interpolated bathymetries being used as boundary conditions in numerical modelling simulations. At Thwaites Glacier (TG) this critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project. We present more than 2000 km2 of new multibeam echo-sounder (MBES) data acquired in exceptional sea-ice conditions immediately offshore TG, and we update existing bathymetric compilations. The cross-sectional areas of sea-floor troughs are under-predicted by up to 40 % or are not resolved at all where MBES data are missing, suggesting that calculations of trough capacity, and thus oceanic heat flux, may be significantly underestimated. Spatial variations in the morphology of topographic highs, known to be former pinning points for the floating ice shelf of TG, indicate differences in bed composition that are supported by landform evidence. We discuss links to ice dynamics for an overriding ice mass including a potential positive feedback mechanism where erosion of soft erodible highs may lead to ice-shelf ungrounding even with little or no ice thinning. Analyses of bed roughnesses and basal drag contributions show that the sea-floor bathymetry in front of TG is an analogue for extant bed areas. Ice flow over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting at the grounding zone today. We conclude that more can certainly be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. This work also addresses the requi

The coastal bathymetry of Thwaites Glacier (TG) is poorly known yet nearshore sea-floor highs have the potential to act as pinning points for floating ice shelves, or to block warm water incursions to the grounding line. In contrast, deeper areas control warm water routing. Here, we present more than 2000 km2 of new multibeam echo-sounder data (MBES) acquired offshore TG during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project on the RV/IB Nathaniel B. Palmer (NBP19-02) in February-March 2019. Beyond TG, the bathymetry is dominated by a >1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some sea-floor highs having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf. In addition, submarine landform evidence indicates at least some unconsolidated sediment cover on the highs, as well as in the troughs that separate them. Knowing that this offshore area of ridges and troughs is a former bed for TG, we also used a novel spectral approach and existing ice-flow theory to investigate bed roughness and basal drag over the newly-revealed offshore topography. We show that the sea-floor bathymetry is a good analogue for extant bed areas of TG and that ice-sheet retreat over the sea-floor troughs and ridges would have been affected by high basal drag similar to that acting in the grounding zone today. Comparisons of the new MBES data with existing regional compilations show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the oceanic heat flux may be significantly underestimated. This work supports the findings of recent numerical ice-sheet and ocean modelling studies that recognise the need for accurat

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian–Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

Past ice dynamics are so far only poorly resolved in the southern Weddell Sea. This is highlighted by previous studies that led to two contradicting scenarios for the grounding line location during the Last Glacial Maximum (LGM), which differed by up to ~650 km. Another study suggested that the maximum ice extent locally was not reached during the LGM but in the early Holocene, indicating that there was also a highly dynamic ice sheet system during deglaciation. There is ambiguity about the history of ice advance and retreat in the region offshore Brunt Ice Shelf based on current data. Only one radiocarbon dated marine geological core is available, contains age reversals, and can be interpreted as indicating ice free conditions during the LGM or having been overrun by grounded ice between 30.2-20.3 cal ka BP. Today, the Brunt Ice Shelf itself is a focus of interest due to the critical crack/fracture development since 2016. This endangers Halley research station, which is situated on the ice shelf, and has resulted in the third consecutive year of austral winter closure. Geophysical ice shelf investigations revealed that, unlike usual ice shelves, the Brunt Ice Shelf consists of numerous blocks of meteoric/glacial ice that are “glued” together by freezing sea ice and snow drift. It is hypothesized that the Brunt Ice Shelf sustains its stability due to buttressing at the McDonald Ice Rumples, which form the only remaining ice shelf pinning point. Improved understanding of the past development of the ice shelf system may also aid understanding the processes active today. We investigated hydroacoustic data that were acquired offshore Brunt Ice Shelf over the last decades with RV Polarstern and RRS James Clark Ross for geomorphological indications of past ice sheet dynamics. The identified landforms show that major ice discharge during the LGM was not via Brunt Basin just in front of the modern-day Brunt Ice Shelf, but via an ice stream that occupied Stancomb-Wills Troug

Swath bathymetric surveys in formerly ice shelf covered areas can reveal high-resolution images of former ice shelf pinning points. We present swath bathymetry from two formerly ice shelf covered areas of Antarctica and investigate their implications for ice-shelf processes. Pine Island Glacier currently experiences the largest negative mass balance in comparison to other outlet glaciers in Antarctica. Here, we were able to access an area with pinning points that were still in contact with the ice shelf less than two years before data acquisition. The bathymetric data revealed three bathymetric highs. These data were used in combination with satellite data from the last decades to investigate the correlation of the bathymetric highs to recent calving dynamics of Pine Island Glacier. In the southeastern Weddell Sea, swath bathymetry acquired offshore Brunt Ice Shelf revealed numerous ramp-shaped seafloor bedforms. The Brunt Ice Shelf is currently intensively monitored due to imminent risk of large-scale calving or even disintegration, which is threatening the British polar research station Halley VI. We interpret that these ramps on the seafloor indicate past ice-shelf grounding events that occurred sometime less than 19000 years ago at a time when the ice shelf was more extensive than today. Most likely, keels of thick glacial ice slaps enclosed within the ice shelf by perennial sea-ice mélange created these bedforms. An analogue pattern of such ice slaps is observed in the modern-day ice shelf. The presence of these bedforms indicate that the ice shelf experienced several phases of ice shelf pinning and unpinning in the last few thousand years.

High-resolution swath bathymetric data can provide clues to the geological history by revealing the seafloor geomorphology. Submarine glacial landforms, for example, can be used to reconstruct past ice sheet development and landslide debris may reveal areas of past tsunami formation. Here, a geomorphological investigation of swath bathymetric data acquired on five research expeditions of RV Polarstern in three glacier outlet systems of East Greenland (Kejser Franz Joseph Fjord, Kong Oscar Fjord, and Scoresby Sund) will be presented. The investigation refines the, so far, only poorly resolved reconstruction of East Greenland ice sheet development and, in addition, reveals a site of a large rock fall that most probably caused a major tsunami. Combination of the marine geomorphological record with published geological data was used to infer the post-LGM ice dynamics and extent in the study area. The investigation suggests that most ice streams likely reached the shelf edge, via cross-shelf troughs, in all three glacier-outlet systems, probably during the LGM. Ice marginal landforms on the shelf and at the fjord entrances indicate a dynamic ice margin with still stands, retreat phases and subsequent readvances. A tentative chronology was developed based on the geomorphological constraints and the geological record. It suggests that in the Allerød-Bølling interstadial, ice retreated to the fjord entrances at Kejser Franz Joseph Fjord and Kong Oscar Fjord, and most probably into the fjord at Scoresby Sund. A subsequent readvance up to a mid-shelf position likely took place in the Younger Dryas. Thereafter, Holocene retreat on the shelf and in the outer fjord areas most likely was rapid, except for two phases of stabilization at the entrance of Kong Oscar Fjord. Apart from glacial landforms, the swath bathymetry data revealed a large amount of landslide debris in the southern part of Scoresby Sund. The origin of this debris is an up to 1500 m high mountain cliff that likel

High-resolution swath bathymetric data can provide clues to the geological history by revealing the seafloor geomorphology. Submarine glacial landforms, for example, can be used to reconstruct past ice sheet development and landslide debris may reveal areas of past tsunami formation. Here, a geomorphological investigation of swath bathymetric data acquired on five research expeditions of RV Polarstern in three glacier outlet systems of East Greenland (Kejser Franz Joseph Fjord, Kong Oscar Fjord, and Scoresby Sund) will be presented (Arndt, 2018). The investigation refines the, so far, only poorly resolved reconstruction of East Greenland ice sheet development and, in addition, reveals a site of a large rock fall that most probably caused a major tsunami. A combination of the marine geomorphological record with published geological data was used to infer the post-LGM ice dynamics and extents. The investigation suggests that most ice streams likely reached the shelf edge, via cross-shelf troughs, in all three glacier-outlet systems, probably during the LGM. Ice marginal landforms on the shelf and at the fjord entrances indicate a dynamic ice margin with still stands, retreat phases and subsequent readvances. The inferred tentative chronology suggests that in the Allerød-Bølling interstadial, ice retreated to the fjord entrances at Kejser Franz Joseph Fjord and Kong Oscar Fjord, and most probably into the fjord at Scoresby Sund. A subsequent readvance up to a mid-shelf position likely took place in the Younger Dryas. Thereafter, Holocene retreat on the shelf and in the outer fjord areas most likely was rapid, except for two phases of stabilization at the entrance of Kong Oscar Fjord. Apart from glacial landforms, the swath bathymetry data revealed a large amount of landslide debris in the southern part of Scoresby Sund. The origin of this debris is an up to 1500 m high mountain cliff that likely collapsed sometime in the Holocene. On first approximation, the debris vol

The Drake Passage is an oceanic gateway of about 850km 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 200x200 m cell spacing. The map covers an area of 1,465,000km2 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.

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.

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 18 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 changing the drainage pattern of the West and East Antarctic Ice Sheets possibly explain this behaviour. In addition, new data were acquired in the southern Weddell Sea during expedition PS111 with RV Polarstern in Jan-Mar 2018. We intend to provide a brief update on the ongoing work and show some preliminary results.

The aim of the International Bathymetric Chart of the Southern Ocean (IBCSO) project is to create high-resolution bathymetric compilations for the waters off Antarctica. Detailed knowledge of seafloor morphology is fundamental to almost all marine and maritime scientific activities. The size, remoteness and harsh ice conditions around Antarctica necessitates strong international collaboration to map the Southern Ocean. This is facilitated via connections to international bodies such as the Scientific Committee on Antarctic Research (SCAR) and the General Bathymetric Chart of the Ocean (GEBCO) project, which operates under the joint auspices of the Intergovernmental Oceanographic Commission (IOC) and the International Hydrographic Office (IHO). In 2013, the first version of IBCSO was published, covering the area south of 60° S with a resolution of 500 x 500 m. Over 30 institutions from 15 countries contributed data and shared their expertise to generate the, so far, largest database of bathymetric data for the Southern Ocean. Since 2017, IBCSO is part of the new Nippon Foundation - GEBCO - Seabed2030 project and work on a second version has begun. The new version will include numerous new data sets of high-resolution swath bathymetry surveys, which will substantially improve previously unmapped areas. IBCSO V2.0 will also cover a larger area extending up to 50° S. With this extension, the new bathymetric model will now also include important features like the Drake Passage, the South Sandwich Arc, and the southern parts of the Kerguelen Plateau and Campbell Plateau. We will present the current status of the project, including the areas that will be most notably improved as compared to the previous version.

Reconstructions of ice sheet development in East Greenland, since the Last Glacial Maximum (LGM), are poorly constrained. This study compiles swath bathymetric data from five expeditions, to investigate the geomorphology of three glacier outlet systems (Kejser Franz Joseph Fjord, Kong Oscar Fjord, and Scoresby Sund) and reconstruct the post‐LGM ice dynamics and extent. The landforms suggest that ice streams probably reached the shelf edge, via cross‐shelf troughs, in all three systems at the LGM. Off Scoresby Sund, it remains unresolved as to whether a mid‐shelf grounding zone wedge marks a recessional stage or the LGM extent. In the Allerød–Bølling interstadial, ice retreated to the fjord entrances at Kejser Franz Joseph Fjord and Kong Oscar Fjord, as documented by partly overridden terminal moraines, and most probably into the fjord at Scoresby Sund. Subsequent overriding occurred by ice readvance, probably in the Younger Dryas. Large ice‐marginal deposition features, formed on the mid‐shelf and at the entrance of Scoresby Sund, probably mark the maximum ice‐sheet extent after the readvance. Holocene retreat was rapid, except for two phases of stabilization at the entrance of Kong Oscar Fjord. Landslide debris indicates that at least one tsunami affected Scoresby Sund at some time in the Holocene.

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 44 (2017): 11,051–11,061, doi:10.1002/2017GL074954., Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheet is 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which AW can access glaciers with marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to future oceanic forcing., National Aeronautics and Space Administration; Cryospheric Sciences Program Grant Number: NNX15AD55G; National Science Foundation's ARCSS program Grant Number: 1504230; NERC Grant Number: NE/M000869/1

We present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data-constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N-S trending Zambezi Channel could be imaged in the central Mozambique Basin. Maps are crucial not only for orientation but also to set scientific processes and local information in a spatial context. For most parts of the ocean seafloor, maps are derived from satellite data with only kilometer resolution. Acoustic depth measurements from ships provide more detailed seafloor information in tens to hundreds of meters resolution. For the southwest Indian Ocean, all available depth soundings from a variety of sources and institutes are combined in one coherent map. Thus, in areas where depth soundings exist, this map shows the seafloor in so-far unknown detail. This detailed map forms the base for subsequent studies of e.g. the direction of ocean currents, geological and biological processes in the southwest Indian Ocean.