Airborne Geophysical Investigation beneath Antarctica's Ross Ice Shelf

The Ross Ice Shelf controls the flow of ice into the ocean from catchments consisting of both the East and West Antarctic Ice Sheets. These catchments hold a volume of ice equivalent to ∼12 m of global sea level rise. To adequately understand how this ice will respond to a warming world requires knowledge of the properties and parameters which influence how the ice sheet behaves. These boundary conditions include fundamental knowledge of the Earth, such as the shape of the bed beneath the ice, the seafloor, and the geologic structures of the upper crust. Knowledge of the physiography and sub-surface geology is severely lacking beneath ice shelves due to their inaccessibility.Here, we use airborne geophysical data from an extensive survey over the Ross Ice Shelf to better understand these boundary conditions. From the analysis of airborne magnetics data, we model the thickness of sediment, the shape of the crystalline basement, and the likely locations of faults throughout the crust under the Ross Ice Shelf. We find a continuous drape of sediment over the seafloor, including deep and narrow fault-bound sedimentary basins beneath the Siple Coast.Using airborne gravity data, and distributed seismic constraints over the ice shelf, we develop and implement a gravity inversion to recover a higher-resolution bathymetry model beneath the ice shelf. This bathymetry model and our quantification of spatial uncertainty highlight locations likely important for sub-ice shelf ocean circulation and possible recent pinning points. In the process of these geophysical investigations, we reveal a wide range of insights relating to how bathymetry and geology play a critical role in the past, present, and future dynamics of the ice sheet, and how this region has developed over its tectonic history.</p

Slides: Addressing bathymetry uncertainty beneath the Ross Ice Shelf

These slides were presented at the 2023 New Zealand Australia Antarctic Science Conference in Christchurch, NZ.Abstract:The bathymetry underlying Antarctica’s Ross Ice Shelf exterts a strong control on it’s stability. The bathymetry guides the circulations of melt-inducing water masses and defines the geometry of pinning points. Collecting sub-ice shelf bathymetry data using typical polar surveying methods (e.g. seismic surveying or direct observations) can be inefficient, expensive or unfeasible. Gravity inversions provide a more practical alternative, in which observed variations in Earth's gravitational field are used to predict the bathymetry. Here we present a gravity inversion algorithm designed specificy to model sub-ice shelf bathymetry. Features include several methods to separate the regional gravity field, various options to impose model regularization, and the ability to quantify spatially variable model uncertainties. Here, we use this inversion with airborne gravity data from the Ross Ice Shelf and model the underlying bathymetry. Our results build upon the Tinto et al. 2019 model by using the new algorithm as well as incorporating additional gravity data and bathymetric constraints, collected since 2019.Gravity Inversion Github Repository: https://github.com/mdtanker/RIS_gravity_inversion</p

Poster: Revealing sub-ice shelf sediment basins with airborne magnetics

Poster presented at WAIS Conference and Workshop 2022.  Abstract The bedrock geology beneath Antarctica's southern Ross Embayment is concealed by 100– 1000s of meters of sedimentary deposits, seawater, and the floating Ross Ice Shelf (RIS). Our research strips away those layers to discover the shape of the consolidated bedrock below, which we refer to as the basement. To do this, we use the contrast between non-magnetic sediments and magnetic basement rocks to map out the depth of the basement surface under the RIS. Our primary data source is ROSETTA-Ice airborne measurements of the variation in Earth's magnetic field across the ice shelf, from flight lines spaced 10-km apart. We use the resulting basement topography to highlight sites of possible influence upon the Antarctic Ice Sheet and to further understand the tectonic history of the region. The basement features we image are characteristic of extensional tectonics, consistent with the setting in the West Antarctic Rift System. These features show continuity with Ross Sea basement features, suggesting a common tectonic development. In the center of the ice shelf, we delineate a broad, segmented, N-S basement high with thin (0–500m) sedimentary cover. We discover contrasting basement characteristics on either side of the RIS. The West Antarctic side displays evidence of active faults, which may localize geothermal heat, accommodate movements of the solid earth caused by changes in the size of the Antarctic Ice Sheet, and control the flow of groundwater between the ice base and aquifers. The East Antarctic side contains a wide and deep basin, with sediments over 3 km thick. This work contributes critical information about Ross Embayment basement topography and subglacial boundary conditions that arise from an interplay of geology, tectonics, and glaciation.  GitHub repository for this poster GitHub repository for the GRL paper GRL 2022 paper </ul