The Skytrain plate and tectonic evolution of southwest Gondwana since Jurassic times

Uncertainty about the structure of the Falkland Plateau Basin has long hindered understanding of tectonic evolution in southwest Gondwana. New aeromagnetic data from the basin reveal Jurassic-onset seafloor spreading by motion of a single newly-recognized plate, Skytrain, which also governed continental extension in the Weddell Sea Embayment and possibly further afield in Antarctica. The Skytrain plate resolves a nearly century-old controversy by requiring a South American setting for the Falkland Islands in Gondwana. The Skytrain plate’s later motion provides a unifying context for post-Cambrian wide-angle paleomagnetic rotation, Cretaceous uplift, and post-Permian oblique collision in the Ellsworth Mountains of Antarctica. Further north, the Skytrain plate’s margins built a continuous conjugate ocean to the Weddell Sea in the Falkland Plateau Basin and central Scotia Sea. This ocean rules out venerable correlation-based interpretations for a Pacific margin location and subsequent long-distance translation of the South Georgia microcontinent as the Drake Passage gateway opened

Quantifying the effect of ocean bed properties on ice sheet geometry over 40 000 years with a full-Stokes model

Simulations of ice sheet evolution over glacial cycles require integration of observational constraints using ensemble studies with fast ice sheet models. These include physical parameterisations with uncertainties, for example, relating to grounding-line migration. More complete ice dynamic models are slow and have thus far only be applied for  50 % under almost equal forcing. Grounding-line positions differ by up to 49 km, show significant hysteresis, and migrate non-steadily in both scenarios with long quiescent phases disrupted by leaps of rapid migration. The simulations quantify the evolution of two different ice sheet geometries (namely thick and slow vs. thin and fast), triggered by the variable grounding-line migration over the differing ocean beds. Our study extends the timescales of 3D full-Stokes by an order of magnitude compared to previous studies with the help of parallelisation. The extended time frame for full-Stokes models is a first step towards better understanding other processes such as erosion and sediment redistribution in the ice shelf cavity impacting the entire catchment geometry

Ice-ocean interactions at Riiser-Larsen Ice Shelf assessed by unveiling of seabed beneath it

The Riiser-Larsen ice shelf is the fourth largest ice shelf on Earth. The detailed depth and shape of the seabed beneath the ice shelf is entirely unknown. Since bed topography beneath ice shelves generally poses the controlling factor of heat exchange between the open ocean and water cavities, this unknown factor inhibits proper assessment of ice-ocean interactions. In coastal Dronning Maud Land, the intrusion of Warm Deep Water – a warm intermediate water mass transported by the Weddell Gyre – into the ice shelf cavities is strongly dependent on seabed depth. We are addressing this shortcoming by generating a bathymetric model beneath the ice shelf based on the inversion of gravity data and complementary data sets of magnetic and ice penetrating radar data, all acquired during the joint AWI-BGR airborne campaign ‘RIISERBATHY’ in 2022/23. The resulting model will have a resolution of 5 to 10 km and is complemented offshore by shipborne hydroacoustic data. We present the first versions of the model here. Modelled depths can be compared to thermocline depths of available in-situ oceanographic data close to and at the calving fronts. In doing so, we will identify key regions of possible entry for Warm Deep Water into the cavity beneath the ice shelf

Recent and past processes at the ice-sheet base of Jutulstraumen drainage basin (Antarctica)

Future sea-level predictions require that the history and physical state of the Antarctic ice sheet is well understood and constrained by observations. Much of the ice sheets’ ice-dynamic properties are governed by processes at the ice-bed interface which can be imaged with radar sounding surveys. Moreover, certain processes at the ice-sheet base can have an effect all the way to the ice surface, which in turn can be observed with satellites. Here we use a combination of ultra-wideband radio-echo sounding data, satellite radar and laser altimetry data to characterize the evolution of the subglacial morphology of the Jutulstraumen drainage basin (western Dronning Maud Land, Antarctica). Based on the classification of the bed topography, we reconstruct the step-by-step modifications the subglacial landscape has experienced since the beginning of the glaciation of Antarctica, 34 million years ago. In addition, between 2017 and 2020, we find evidence of active episodic cascade-like subglacial water transport along the subglacial valley network. The combination of these observations will represent an important step towards a better understanding of large-scale ice-sheet dynamics in western Dronning Maud Land

Ice-flow history and observations from the ice base of Jutulstraumen drainage basin (Antarctica)

Future sea-level predictions require that the history of the Antarctic Ice Sheet is well understood and constrained by observations. Much of the ice sheets’ ice-dynamic properties are governed by processes at the ice-bed interface which can be imaged with radar sounding surveys. Here we use a combination of ultra-wideband radio-echo sounding data, satellite radar and laser altimetry data, as well as electromagnetic waveform modeling to characterize the properties of the ice base and the evolution of the subglacial morphology of the Jutulstraumen drainage basin (western Dronning Maud Land, Antarctica). Based on the classification of the bed topography, we reconstruct the step-by-step modifications the subglacial landscape has experienced since the beginning of the glaciation of Antarctica, 34 million years ago. Between 2017 and 2020, we find evidence of active episodic cascade-like subglacial water transport along the subglacial valley network. In addition, our high-resolution radio-echo sounding data reveal a cluster of anomalous basal ice units whose material properties we constrain by electromagnetic waveform modeling. Through this, we aim to derive the physical conditions at the ice base, and establish a link to the subglacial hydrology system. The combination of these observations will represent an important step towards a better understanding of large-scale ice-sheet dynamics in western Dronning Maud Land

Bathymetry Beneath Ice Shelves of Western Dronning Maud Land, East Antarctica, and Implications on Ice Shelf Stability

Antarctica's ice shelves play a key role in stabilizing the ice streams that feed them. Since basal melting largely depends on ice-ocean interactions, it is vital to attain consistent bathymetry models to estimate water and heat exchange beneath ice shelves. We have constructed bathymetry models beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data and incorporating seismic, multibeam, and radar depth references. Our models reveal deep glacial troughs beneath the ice shelves and terminal moraines close to the continental shelf breaks, which currently limit the entry of Warm Deep Water from the Southern Ocean. The ice shelves buttress a catchment that comprises an ice volume equivalent to nearly 1 m of eustatic sea level rise, partly susceptible to ocean forcing. Changes in water temperature and thermocline depth may accelerate marine-based ice sheet drainage and constitute an underestimated contribution to future global sea level rise

Relevance of field observations as boundary conditions for understanding ice-sheet-ocean interactions

The direct contact of warm ocean water with the front and base of ice shelves is the main driver for accelerated mass loss of the Antarctic ice sheet. We present a compilation of observations from various projects and methodological approaches applied over the last decade along the Dronning Maud Land coast and highlight their importance for understanding the ice-ocean interactions. With a focus on the Ekström ice shelf, these include spatially continuous seismic observations in combination with airborne gravity inversion to yield sub-shelf bathymetry and geomorphological evidence of past ice-flow activity; ice-dynamic numerical modelling to investigate the role of seafloor/subglacial substrate characteristics to enhance or reduce ice-sheet extent and advance/retreat rates; sub-shelf CTD measurements to determine ocean properties driving basal melting; satellitebased remote sensing to determine ice-shelf height changes and spatially-distributed basal melting; and point measurements of basal melt with surface-based phase-sensitive radar to determine ocean-driven melt and validate remote-sensing products. As the Dronning Maud Land coast plays a critical role in preconditioning the water mass of the coastal current before it enters the Filcher ice-shelf cavity, we argue that a coordinated inter- and transdisciplinary observational network is required to facilitate monitoring a potential ice-sheet mass loss in this part of Antarctica

Topography beneath the ice shelves and ice sheets of Dronning Maud Land: Implications for ice shelf stability and glacial history

Der Großteil der Landmasse Antarktikas ist von Eisschilden bedeckt, die eine Mächtigkeit von mehreren Kilometern erreichen können. Gestützt werden diese massiven Eisschilde von vorgelagerten Schelfeisen, die sich in den Ozean erstrecken. Schelfeise und Eisschilde bilden ein wechselwirkendes System, das nach Gleichgewicht strebt. Massenverluste am Schelfeis durch Schmelz- oder Abkalbungsprozesse werden durch eine erhöhte Dränung des gekoppelten Eisschildes in Richtung Ozean, sowie durch Massengewinn im System, wie beispielsweise Schneefall, ausgeglichen. Ein Nettoverlust in diesem System trägt zum Anstieg des globalen Meeresspiegels bei. Vor diesem Hintergrund ist es von entscheidender Bedeutung, Massengewinne und -verluste der Eisschild-Schelfeis-Systeme korrekt zu quantifizieren, um deren Stabilität bewerten zu können. Der Massenverlust durch basales Schmelzen an Schelfeisen ist in hohem Maße abhängig von der vorherrschenden Bathymetrie, welche den Wasser- und Wärmeaustausch zwischen dem offenen Ozean und dem mit Wasser gefüllten Hohlraum zwischen dem Schelfeis und dem Meeresboden beeinflusst. In dieser Arbeit werden neu entwickelte bathymetrische Modelle für die Schelfeisregionen des Dronning Maud Landes in der Ostantarktis vorgestellt. Die modellierte subglaziale Bathymetrie ist geprägt durch tiefe Tröge unterhalb der Schelfeise, welche durch die landwärtige Erhebung flacher bathymetrischer Schwellen entlang der Kontinentalschelfkante begrenzt werden. Diese Schwellen befinden sich nahe der Kalbungsfronten und werden von vereinzelten Gateways durchbrochen, deren Tiefe das Eindringen von warmen und tiefen Wassermassen aus dem offenen Ozean in die Schelfeishöhlen entweder ermöglicht oder verhindert. Eine individuelle Beurteilung der Stabilität dieser Schelfeise wird vorgenommen

Bathymetric model beneath Nivl and Lazarev ice shelves, and across Astrid Ridge

Attached data comprise a bathymetric model of central Dronning Maud Land, including the seabed beneath the Nivl Ice Shelf and the Lazarev Ice Shelf, as well as the offshore Astrid Ridge and adjacent parts of the Riiser-Larsen Sea. It gives seabed and ice base depths relative to WGS84 at a resolution of 2.5 km. The bathymetric model is generated by complementing existing topographic data sets - such as seismic data, ice penetrating radar data, and shipborne hydroacoustic data - with the inversion of airborne gravity data towards bathymetry. The airborne gravity data used for the inversion consist of data acquired during aerogeophysical campaigns VISA from the early 2000s and WEGAS from the austral summer of 2009/2010