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

Anthropogenic warming forces extreme annual glacier mass loss

Glaciers are unique indicators of climate change. While recent global-scale glacier decline has been attributed to anthropogenic forcing, direct links between human-induced climate warming and extreme glacier mass-loss years have not been documented. Here we apply event attribution methods to document this at the regional scale, targeting the highest mass-loss years (2011 and 2018) across New Zealand’s Southern Alps. Glacier mass balance is simulated using temperature and precipitation from multiple climate model ensembles. We estimate extreme mass loss was at least six times (2011) and ten times (2018) (>90% confidence) more likely to occur with anthropogenic forcing than without. This increased likelihood is driven by present-day temperatures ~1.0 °C above the pre-industrial average, confirming a connection between anthropogenic emissions and high annual ice loss. These results suggest that as warming and extreme heat events continue and intensify, there will be an increasingly visible human fingerprint on extreme glacier mass-loss years in the coming decades