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One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and the ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future surveys and gridded datasets accessible under the Findable, Accessible, Interoperable, and Reusable (FAIR) data principles. With the goals of making the gridding process reproducible and allowing scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (https://bedmap.scar.org, last access: 1 March 2023) created to provide unprecedented open access to these important datasets through a web-map interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk (last access: 5 May 2023​​​​​​​). See the Data availability section for the complete list of datasets.

New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors (SDRs), which are found to decrease in size both northwards and southwards from a central point at 75° N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the SDRs have been emplaced over a period of 2‐4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40 Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The break‐up of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southwards, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone. Key Points Polyphase Cenozoic volcanic rifting and consecutive emplacement of breakup‐related lava flows units along the northern East Greenland margin Breakup along restricted margin segments is followed by north to south directed progressive opening of the Greenland Sea Widespread post‐middle Eocene (< 40 Ma) offshore magmatism, associated with the breakup of the Jan Mayen microcontinent from East Greenland

We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60� S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved datacoverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72m lower and the area of ice sheet grounded on bed below sea level is increased by 10 %. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets.

The Northern Baffin Bay between Greenland and Canada is a remote Arctic area restricted in primary production by seasonal ice cover, with presumably low sedimentation rates, carbon content and microbial activities in its sediments. Our aim was to study the so far unknown subseafloor geochemistry and microbial populations driving seafloor ecosystems. Shelf sediments had the highest organic carbon content, numbers of Bacteria and Archaea, and microcosms inoculated from Shelf sediments showed highest sulfate reduction and methane production rates. Sediments in the central deep area and on the southern slope contained less organic carbon and overall lower microbial numbers. Similar 16S rRNA gene copy numbers of Archaea and Bacteria were found for the majority of the sites investigated. Sulfate in pore water correlated with dsrA copy numbers of sulfate-reducing prokaryotes and differed between sites. No methane was found as free gas in the sediments, and mcrA copy numbers of methanogenic Archaea were low. Methanogenic and sulfate-reducing cultures were enriched on a variety of substrates including hydrocarbons. In summary, the Greenlandic shelf sediments contain vital microbial communities adapted to their specific environmental conditions.

Baffin Bay is an Arctic basin between Canada and Greenland, connected via Davis Strait with the Labrador Sea in the south. Due to its shallow water depth of only 500 m, Davis Strait acts as a gateway for the Arctic water exchange between Baffin Bay and the Atlantic. The nature of Baffin Bay and Davis Strait crust has long been a subject of debate. Either oceanic or stretched continental crust have been proposed by different authors from sonobuoy readings, seismic reflection and potential field data. We here present the new results of two seismic refraction lines acquired with ocean bottom seismometers. P-wave velocity models for both lines are constrained and complemented by density models, seismic reflection and magnetic anomaly data. Line AWI-20080500/AWI-20100400, in southern Baffin Bay, is oriented across a proposed Eocene spreading centre. This line confirms the existence of oceanic crust in southern Baffin Bay and allows for a regional mapping of the oceanic crust. With a plate kinematic model we depict the evolution of this basin and can distinguish between Palaeocene and Eocene oceanic crust. Line AWI-20080700 in Davis Strait crosses the Ungava Fault Complex, a major transform fault, where extension was followed by a stage of transpression. We here find deformed blocks of continental crust that are separated by transform faults of the Ungava Fault Complex. Between these blocks a region of 50 km is characterized by high P-wave velocities and a thin crust that we interpret as stretched and highly intruded crust. Tectonic modelling depicts a great lateral movement of 310 km of the continental blocks along the Ungava Fault complex. The compressional component is visible in a 70 km wide overlap of crust that had to be compensated by deformation of the blocks. With our new models and the compilation of published Moho depth and seismic stratigraphy we try to estimate the paleo bathymetry and the role of Davis Strait as a polar gateway.

Während des Merian-Fahrtabschnitts MSM09/3 wurden Ende 2008 in einer Kooperation zwischen dem Alfred-Wegener-Institut für Polar- und Meeresforschung (AWI), der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), dem Geologischen Dienst von Dänemark und Grönland (GEUS) und der Dalhousie University geophysikalische Untersuchungen in der Baffinbucht und Davisstraße zwischen Grönland und dem kanadischen Baffininsel durchgeführt. Als Teilvorhaben des IPY-2007/08-Kernprojekts Plate Tectonics and Polar Gateways in the Earth System (PLATES & GATES) hat das Projekt DAVIS GATE das Ziel, eine tektonische und sedimentäre Rekonstruktion des Öffnungsprozesses dieser Meeresstraße zu entwickeln. Die Baffinbucht und Davisstraße spielen eine wichtige Rolle für den Flachwasseraustausch zwischen dem arktischen und dem atlantischen Ozean. Die plattentektonische Entwicklung sowie die magmatischen Ereignisse im Laufe dieser Entwicklung sind bisher kaum bekannt und erforderten eine eindringliche geophysikalische Untersuchung, um akkurate paläobathymetrische und paläogeographische Datensätze für eine vollständige geodynamische Rekonstruktion dieses Gateway zu erstellen. Entlang von drei refraktions/weitwinkelseismischen Profilen unter Nutzung von Ozeanbodenseismometern auf insgesamt 62 Stationen sowie dem Einsatz der Mehrkanal-Reflexionsseismik mit einem 3000 m langen Streamer sind Daten von der sedimentären Bedeckung bis in die tiefe Kruste und teilweise vom obersten Mantel gewonnen worden. Weitere seismische Profildaten ergänzen diese Messungen und lassen Einblicke in die Strukturen des Grundgebirges sowie der dominanten Verwerfungszonen, z.B. der Ungava-Störung, zu. Eine parallel angelegte Magnetfeldvermessung ist auf die Auflösung der zeitlichen Entwicklung der ozeanischen Kruste der Baffinbucht ausgerichtet worden. Ausdünnung und Absenkung der kontinentalen Kruste und Übergangskruste in der Davisstraße und die Entwicklung der ozeanischen Kruste der Baffinbucht konnten mit diesen g

Baffin Bay is the northwest extension of the Labrador Sea spreading system. The transition zone between these two areas is characterized by the sinistral Ungava transform-fault system across Davis Strait. The crustal type within Baffin Bay is considered to be oceanic based on a few refraction seismic experiments of older vintage. However, the velocity-depth profiles obtained from these experiments also indicate deviations from normal oceanic crust. A refraction profile in northern Baffin Bay indicates that spreading there was amagmatic and that serpentinized mantle is encountered beneath the sedimentary sequence. In addition, no magnetic anomalies related to seafloor spreading could be detected in Baffin Bay so far. This leaves a relative uncertainty about the geodynamic evolution of the Davis Strait and Baffin Bay region. For this reason, a geophysical study was carried out onboard the research vessel Maria S. Merian in 2008, collecting wide-angle reflection/refraction seismic data, supplemented by coincident and additional deep reflection seismic profiles, potential field measurement, swath bathymetry and high-resolution sediment profiling (Parasound). The refraction seismic data set comprises three lines running across the centre part of Davis Strait and southern Baffin Bay extending from Greenland to Baffin Island. The seismic source was an airgun array with a total volume of 7006 cubic inches and the shots were recorded by up to 25 ocean bottom seismometers (OBS) deployed along each line. Initial velocity models will be presented for line AWI-20080600 extending from the Sisimiut Basin off Greenland across the Hellefisk well, farther towards the NW and parallel to the assumed extinct spreading axis (based on gravity data) up to the Baffin Island continental margin some 60 km to the south of ODP site 645. The record sections indicate considerable lateral variations of the crustal structure and character along the line.

The Davis Strait is a bathymetric high that separates the southern Baffin Bay and the northern Labrador Sea. These basins are the result of Cretaceous and Paleogene rifting and seafloor spreading between the North American plate and Greenland. Being one of the main tectonic features of the Davis Strait, the Ungava Fault Zone is associated with transform motion related to a northward movement of Greenland relative to North America during rifting and seafloor spreading in Baffin Bay and Labrador Sea. The plate tectonic reconstruction of the Davis Strait contributes significantly to the understanding of the geodynamic history of the North-American - Greenland plates, not only the Davis Strait area but also the area of Lancaster Sound and Nares Strait, where it could shed light into the so-called Nares Strait Conflict. It is still under debate whether the spreading between Greenland and Baffin Island was compensated by sinistral transform motion along the proposed Wegener-Fault. Thus Nares Strait (trace of the Wegener Fault) and Lancaster Sound (failed arm rift) are relicts of this scenario. The lack of evidence for transform motion between Greenland and Ellesmere Island contradicts this model and provokes the conflict. As major compression along the Eurekan Fold Belt overprinted the proposed transform motion along the Wegener Fault, the Ungava Fault Zone in the Davis Strait could give the missing information for the plate tectonic reconstruction. The onshore-offshore geology and structural setting of Baffin Island is analysed by recent publications that show an essentially non-volcanic continental margin at Baffin Island that is interrupted by a volcanic-style margin around Cape Dyer. Intensive magmatic activity during the initial opening phase is indicated by widespread seaward-dipping-reflector sequences (SDRS) north of Cape Dyer. On the other hand, the structural setting of the Greenland margin side is unclear. The identification of the corresponding conjugate patte

Measurements of ice thickness on the Antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database. From these data, a seamless suite of digital topographic models have been compiled for Antarctica and its surrounding ocean. This includes grids of ice sheet thickness over the grounded ice sheet and ice shelves, water column thickness beneath the floating ice shelves, bed elevation beneath the grounded ice sheet, and bathymetry to 60°S, including the sub-ice-shelf cavities. These grids are consistent with a recent high-resolution surface elevation model of Antarctica. While the digital models have a nominal spatial resolution of 5 km, such high resolution is justified by the original data density only over a few parts of the ice sheet. The suite does, however, provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps. The total volume of the Antarctic ice sheet calculated from the BEDMAP grid is 25.4 million km3, and the total sea level equivalent, derived from the amount of ice contained within the grounded ice sheet, is 57 m, comprising 52 m from the East Antarctic ice sheet and 5 m from the West Antarctic ice sheet, slightly less than earlier estimates. The gridded data sets can be obtained from the authors.