Boris Dorschel

Ice shelves exert a buttressing effect on the Antarctic ice sheets that can reduce as basal melting drives their thinning and destabilization. This process is strongly affected by the depths and morphologies of the underlying cavity floors, which regulate ice-ocean interactions, but remain poorly constrained. We created a new model of the bathymetry beneath a section of the Ronne Ice Shelf downstream of the Evans Ice Stream by inversion of carefully selected airborne gravity data constrained by seismic and ice-penetrating radar depth references. The model reveals a deep, asymmetric and U-shaped trough aligned with the ice flow direction, reflecting glacial erosion and tectonic inheritance. The persistent retrograde slope of the seafloor potentially allows warm water intrusion from the open ocean up to the grounding line. Our model thus provides critical constraints for estimating basal melt rates and assessing ice shelf and ice sheet stability with regard to large-scale climate changes.

Benthic ecosystems are shaped by seafloor structure, yet linking geomorphology and biology across environmental gradients remains challenging. Here, we integrate seafloor imagery, multiscale bathymetry, and predictive modelling to quantify benthic biodiversity and its environmental drivers along the Powell Basin flank of the Antarctic Peninsula. Steep geomorphological landforms (terraces and steep slopes) hosted maximal densities and distinct communities, with significant enrichment of corals, sponges, ophiuroids, and sea pens. The marked congruence of slope across bathymetric resolutions enabled regional upscaling, estimating a standing stock of ∼96 billion individuals across 7,400 km² of the basin flank. Decadal oceanographic models indicate that benthic densities peak in cold bottom water below −0.15 °C. We identified four biodiversity hotspots (∼33 km ² ) with slopes >35° and depths >1,700 m, with up to threefold higher densities. Hotspots align with the pathway of Weddell Sea Deep Water, where thermal decoupling between bottom and overlying waters indicates dynamic hydrography along steep, biodiverse terrain. Furthermore, contrasting sea-ice cover and stratification regimes suggest distinct cryo-pelagic-benthic coupling around hotspots. The concentration of biodiversity through seafloor geomorphology and ocean circulation bridges Antarctic benthic ecology from habitat to biogeography, with implications for monitoring change and guiding conservation in the warming Weddell Sea.

Seamounts number in the hundreds of thousands across all ocean basins and constitute a fundamental component of the ocean floor. They provide constraints on intraplate magmatism, mantle melting processes, lithospheric stress and flexure, and the evolution of oceanic plates. At the same time, seamounts are hotspots of biodiversity, and their morphology modifies ocean circulation and mixing, further influencing benthic ecosystems. Addressing these aspects requires high-resolution bathymetric mapping, yet most seamounts inferred from satellite-derived gravity data have never been directly surveyed. The German marine research community contributes to systematic seafloor mapping during transits of the large German research vessels through the underway research-data project coordinated within the German Marine Research Alliance (DAM). While this approach steadily improves coverage and contributes to international efforts such as Seabed 2030, the scale of the remaining mapping gap of about 75% motivates complementary strategies that increase scientific return without substantially increasing ship time. Within the SEAMAP project, we pursue a collaborative approach in which research vessel transits are actively planned to intersect previously uncharted seamounts, with minimal impact on cruise logistics and primary scientific objectives. The goal is to link underway data acquisition to active research questions in geodynamics and ocean sciences.We present initial results from SEAMAP. Modified transits have so far been planned for five research cruises, resulting in new multibeam bathymetric coverage of approximately 80 previously unmapped seamounts across a range of tectonic settings and plate ages. The acquired data are being integrated into studies addressing intraplate volcanic construction, machine-learning-based bathymetry prediction and validation, and flow–topography interactions, including enhanced mixing and turbulence in seamount wakes. In parallel, SEAMAP supports rapid data availability by integrating new bathymetric products into the harmonized data streams for German research vessels established by DAM. These results illustrate how targeted seamount mapping during transit legs can efficiently improve seafloor coverage while supporting interdisciplinary ocean science on the role of seamounts within the Earth system.

The ice sheets of the Antarctic continent are supported and stabilised by floating ice shelves. Any future decrease in ice shelf mass and stability is expected to increase ice sheet drainage thus potentially contributing to a rise in the global sea level. Basal melting is a critical factor concerning ice shelf stability. Its rates are strongly dependent on the bathymetry underneath the ice shelves, as this directly influences sub-ice water circulation and its interactions with the open ocean. Therefore, accurate knowledge of sub-ice bathymetry is crucial to estimate the exchange of water masses and heat with the open ocean. We have created a model of the seafloor topography beneath the Evans Ice Stream - draining into the Ronne Ice Shelf, one of the world’s largest ice shelves - by the inversion of legacy airborne gravity data constrained by seismic and ice-penetrating radar depth references. The new bathymetric model is a distinct improvement over existing topographic compilations based on interpolated depths, providing a range of new information on topographic characteristics beneath the ice shelf with increased resolution and detail. The model shows a deep, asymmetric and U-shaped trough beneath the Evans Ice Stream that follows the ice stream’s flow direction. The bathymetry shows that the retrograde slope of the seafloor on the continental shelf and beneath the outer Ronne Ice Shelf continues as far as the ice stream’s grounding line. Should warm water masses from the open ocean cross the continental shelf edge, this slope would permit intrusion of these water masses all the way up to the grounding line. The new bathymetric model thus enables a step towards being able to more confidentially estimate basal melt rates beneath the Evans Ice Stream and their effect on ice shelf and ice sheet stability. The depth and shape of the seabed beneath numerous other ice shelves and areas of permanent sea ice coverage around the Antarctic margins remains poorly constrained or completely unknown. As well as the Evans cavity model, new data and plans for upcoming bathymetric modelling of some of these other areas are highlighted.

We present Bedmap3, the latest suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60 °S. Bedmap3 incorporates and adds to all post-1950s datasets previously used for Bedmap2, including 84 new aero-geophysical surveys by 15 data providers, an additional 52 million data points and 1.9 million line-kilometres of measurement. These efforts have filled notable gaps including in major mountain ranges and the deep interior of East Antarctica, along West Antarctic coastlines and on the Antarctic Peninsula. Our new Bedmap3/RINGS grounding line similarly consolidates multiple recent mappings into a single, spatially coherent feature. Combined with updated maps of surface topography, ice shelf thickness, rock outcrops and bathymetry, Bedmap3 reveals in much greater detail the subglacial landscape and distribution of Antarctica’s ice, providing new opportunities to interpret continental-scale landscape evolution and to model the past and future evolution of the Antarctic ice sheets.

Marine geophysical data combined with radiocarbon dated sediment cores provide a record of the advance and retreat of the ancestral Northeast Greenland Ice Stream (NEGIS) across the continental shelf offshore of NE Greenland during the last glaciation. Today, NEGIS is the largest ice stream to drain the Greenland Ice Sheet (GrIS), holding a sea-level equivalent of 1.1-1.4 m. However, the longer-term history of the ice stream, especially on the adjoining outer continental shelf has, to date, been poorly constrained. Streamlined subglacial landforms record grounded ice flow in the outer shelf section in cross shelf bathymetric troughs, with mega-scale glacial lineations recording former streaming flow towards the shelf edge. Flow transverse landforms in the form of downlow-tapering, sediment wedges occur at the shelf edge and on the outer-mid shelf of the bathymetric troughs. These landforms differ in their morphology from the classic ‘ramp-step’ form of typical grounding wedges but are similarly interpreted as a form of grounding-zone wedge in which sediment prograded and thinned away from the grounding-zone. The wedges record a shelf-edge terminating, grounded ancestral NEGIS, as well as the subsequent episodic retreat of the ice stream inshore during deglaciation. Beyond the shelf edge, glacigenic debris flows imaged on acoustic stratigraphic profiles and recovered in sediment cores document sediment delivery onto the slope; such deposits are typical of submarine slopes offshore of shelf-edge terminating palaeo-ice streams. On the outer shelf subglacial tills and grounding-zone proximal sediments overlain by deglacial stratified glacimarine sediments record ice stream advance and retreat in the troughs. Radiocarbon dates from glacimarine sediments in these cores indicate early deglaciation from the shelf edge but with relatively slow rates of subsequent ice-stream retreat across the outer shelf.

Knowledge about seafloor depth, or bathymetry, is crucial for various marine activities, including scientific research, offshore industry, safety of navigation, and ocean exploration. Mapping the central Arctic Ocean is challenging due to the presence of perennial sea ice, which limits data collection to icebreakers, submarines, and drifting ice stations. The International Bathymetric Chart of the Arctic Ocean (IBCAO) was initiated in 1997 with the goal of updating the Arctic Ocean bathymetric portrayal. The project team has since released four versions, each improving resolution and accuracy. Here, we present IBCAO Version 5.0, which offers a resolution four times as high as Version 4.0, with 100 × 100 m grid cells compared to 200 × 200 m. Over 25% of the Arctic Ocean is now mapped with individual depth soundings, based on a criterion that considers water depth. Version 5.0 also represents significant advancements in data compilation and computing techniques. Despite these improvements, challenges such as sea-ice cover and political dynamics still hinder comprehensive mapping.

Ocean ecosystems are at the forefront of the climate and biodiversity crises, yet we lack a unified approach to assess their state and inform sustainable policies. This blueprint is designed around research capabilities and cross-sectoral partnerships. We highlight priorities including integrating basin-scale observation, modelling and genomic approaches to understand Atlantic oceanography and ecosystem connectivity; improving ecosystem mapping; identifying potential tipping points in deep and open ocean ecosystems; understanding compound impacts of multiple stressors including warming, acidification and deoxygenation; enhancing spatial and temporal management and protection. We argue that these goals are best achieved through partnerships with policy-makers and community stakeholders, and promoting research groups from the South Atlantic through investment and engagement. Given the high costs of such research (€800k to €1.7M per expedition and €30–40M for a basin-scale programme), international cooperation and funding are integral to supporting science-led policies to conserve ocean ecosystems that transcend jurisdictional borders.