Seafloor Depth of George VI Sound, Antarctic Peninsula, From Inversion of Aerogravity Data

Abstract

George VI Sound is an~600 km-long curvilinear channel on the west coast of the southern Antarctic Peninsula separating Alexander Island from Palmer Land. The Sound is a geologically complex region presently covered by the George VI Ice Shelf. Here we model the bathymetry using aerogravity data. Our model is constrained by water depths from seismic measurements. We present a crustal density model for the region, propose a relocation for a major fault in the Sound, and reveal a dense body,~200 km long, flanking the Palmer Land side. The southern half of the Sound consists of two distinct basins~1,100 m deep, separated by a −650 m-deep ridge. This constricting ridge presents a potential barrier to ocean circulation beneath the ice shelf and may account for observed differences in temperature-salinity (T-S) profiles. Plain Language Summary Knowing the seafloor depth beneath ice shelves is crucial for understanding the interaction between the ocean and the overlying ice, as the shape of the sea floor influences water circulation pathways. We present a new bathymetric model of the seafloor beneath George VI Ice Shelf on the Antarctica Peninsula. The data for our model were collected from airborne surveys, including the ice surface elevation, ice thickness, and gravity field measurements. We first present a new geological model of the Sound and use our improved data coverage to relocate a previously interpreted geological fault. The new bathymetry model shows that in the southern segment of the Sound, an area with shallow bathymetry and deep ice might be acting as a barrier to the water flow. This information can change our understanding of the circulation between the northern and southern segments of the Sound and can be used in models of how this impacts the melt in the base of the ice shelf. High basal melt rates around Antarctica have been interpreted as responses to variations in oceanic temperature and circulation (e.g., Holland et al., 2008; Jacobs et al., 2011). Over George VI Ice Shelf, estimated basal melt rates range from 2.8 m/a (Corr et al., 2002) to 6.0 m/a (Dinniman et al., 2012) with a recent study report-ing~4 m/a over a 23 year period (Adusumilli et al., 2018). Future changes in basal melt depend on changes in ocean temperature as well as subsurface currents, steered by the cavity shape, highlighting the importance of accurate bathymetry data for future predictions (e.g.,

The Scientific Legacy of NASA’s Operation IceBridge

“…Mapping this bathymetry at large scales is challenging due to the presence of ice mélange in Greenlandic fjords and thick (tens of meters to more than a kilometer) ice shelves in Antarctica, combined with the present operational limits of underwater autonomous vehicles in ice‐covered seas. To address this challenge, OIB regularly collected high‐accuracy airborne gravity data to infer both fjord and sub‐ice‐shelf bathymetry (An et al., 2017, 2019; Boghosian et al., 2015; Cochran & Bell, 2012; Cochran et al., 2015, 2020; Constantino et al., 2020; Greenbaum et al., 2015; Millan et al., 2017, 2018, 2020; Muto et al., 2013; Schodlok et al., 2012; Tinto & Bell, 2011; Tinto et al., 2015; Wei et al., 2020). These studies variously combined OIB gravity data from airborne (both fixed‐wing and helicopter) surveys with information from other sources because bathymetric inferences from gravity data alone are non‐unique.…”

British Antarctic Survey’s Aerogeophysical Data: Releasing 25 Years of Airborne Gravity, Magnetic, and Radar Datasets over Antarctica

“…These surveys contributed to a new bathymetric map of Thwaites, Crosson and Dotson ice shelves from gravity measurements, revealing a deep (>800 m) marine channel extending beneath the ice shelf adjacent to the front of Thwaites Glacier (Jordan et al, 2020). These datasets have also contributed to a new bathymetry model of George VI Sound (Constantino et al, 2020) and Thwaites Glacier (Hogan et al, 2020).…”

Bathymetry Beneath the Amery Ice Shelf, East Antarctica, Revealed by Airborne Gravity

“…The mean and standard deviation of the differences between the of 10 pseudo-observed gravity anomalies and the one forward computed from the gravity-estimated seafloor topography (Figure S1b in Supporting Information S1) are −0.2 and 2.1 mGal, respectively. This gravity misfit and the 1 mGal uncertainty in gravity data translate into a nominal root-mean-square error of 62 m in bed elevation if we use a conversion factor of 5 mGal per 100 m of water (An et al, 2019;Constantino et al, 2020;Millan et al, 2020). In comparison, the mean and standard deviation of the differences computed using the seafloor topography in BMA model (Figure S1c in Supporting Information S1) are 6.9 and 17.5 mGal, respectively.…”