Using seismic and gravity data to examine the seafloor geology in the vicinity of the Discovery Deep shelfal basin, Ross Ice Shelf, Antarctica

The Discovery Deep Basin, located beneath the Ross Ice Shelf, adjacent to the Trans-Antarctic Mountains and south of Minna Bluff, is the deepest (>1500 m water depth) shelfal basin in the Ross Sea.  Its tectonic origin and sedimentary and glacial evolution are poorly constrained, and direct investigations are hindered by the ice cover of the Ross Ice Shelf. Understanding of bathymetry and seafloor geology in the region is based on limited surface investigations and inversions of regional airborne geophysical datasets. However, its proximity to outflow glaciers from East Antarctica and great depth mean that it is likely to contain sedimentary records of past glacial cycles and environmental change.

We present the results of two seasons of explosive-source seismic exploration of the basin in the summers of 2021/22 and 2023/24, for which the primary objectives were to identify the basin’s deepest point, obtain high-resolution imagery of seafloor sediment accumulations, and constrain subsurface structure and stratigraphy. More than 65 km of seismic reflection imaging was complemented by surface collected gravity data. These data provide localised coverage of the sub-ice-shelf ocean and sediments in a region where ROSETTA-Ice airborne-gravity data identified a regional gravity low. During the first season, data were collected using explosive charges frozen into 25-m-deep hot-water-drilled holes that are recorded by 96 conventional geophones buried in the firn with a 10-m spacing; the shot spacing was 240 m. During the second season, data were collected using  surface-detonated Cordtex detonating cord sources (10 m lengths at 10 g/m) recorded by a 300-m-long 96-geophone snow streamer with a 60 m shot spacing. Both seismic reflection data sets were processed into seismic images using GLOBE Claritas.

Processed seismic data show a gently dipping layered seafloor lying beneath the ocean cavity with a maximum depth of 1650 m and at least 200 m of layered and dipping sedimentary strata containing several mappable unconformities and distinct geological structures (e.g., a regional anticline and several faults). Given its depth and substantial sediment accumulation, this site may offer one of the highest resolution climate records in Antarctica. The study also provides a critical bathymetric tie for regionally inverted airborne gravity data (Tinto et al., 2019; Tankersley et al., 2022) by confirming a greater basin depth than previously modelled and relocating the deepest point of Discovery Deep towards the NW. These findings will contribute to an improved understanding of RIS basin geodynamics, ice sheet stability, ocean currents, and tectonic activity and emphasise the importance of future exploration drilling to refine our knowledge of past climate conditions.