Ocean melting has thinned Antarctica's ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new highresolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local oceanatmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet.
The southern sector of Antarctica's Ross Embayment beneath the Ross Ice Shelf (RIS; area ∼480,000 km 2 ) is poorly resolved because the region is not accessible to conventional seismic or geophysical surveying. Rock exposures on land suggest that Ross Ice Shelf (RIS) crust consists of early Paleozoic post-orogenic sediments, intruded in places by mid-Paleozoic and Cretaceous granitoids (Goodge, 2020;Luyendyk et al., 2003). Following the onset of extension in the mid-Cretaceous, grabens formed and filled with terrestrial and marine deposits, continuing into the Cenozoic (e.g., Coenen et al., 2019;Sorlien et al., 2007), as the Ross Embayment underwent thermal subsidence (Karner et al., 2005;Wilson & Luyendyk, 2009). The physiography of this region then responded to the onset of glaciation in the Oligocene (Paxman et al., 2019), coinciding with localized extension in the western Ross Sea until 11 Ma (Granot & Dyment, 2018). The Oligocene-early-Miocene paleo-landscape of the Ross Sea sector was revealed by marine seismic data (e.g., Brancolini et al., 1995;Pérez et al., 2021) and offshore drilling that penetrated crystalline basement (DSDP Site 270; Ford & Barrett, 1975) (Figure 1). Recognition of the role of elevated topography in Oligocene formation of the Antarctic Ice Sheet (DeConto & Pollard, 2003;Wilson et al., 2013) and the likely influence of subglacial topography upon ice sheet processes during some climate states (Austermann et al., 2015;Colleoni et al., 2018) motivated our effort to determine basement topography beneath the RIS.
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