Abstract
Covering an area of 580,000 km2, the Ross Ice Shelf (RIS) is the largest ice shelf in the world. It is the one of the main outflows for both the East Antarctic Ice Sheet and the West Antarctic Ice Sheet. The RIS is currently in a period of stability; no advancement or retreat in its areal extent is occurring, but this is not the case for many of the other ice shelves grounded below sea-level around Antarctica. Understanding how and why the RIS is in a period of stability
in the face of increasing global warming and future sea-level rise is vital to our understanding of ice shelf dynamics and possibly in preventing a collapse and rapid ice loss from the centre of Antarctica. Improving our understanding
of previous changes in the ice regime of Antarctica, how the ice sheets, ice shelves, and glaciers change in response to climatic forcings, will improve future modelling.
We aim to answer three research questions in this study: first, to characterise the seafloor and substrate in the area of a future hot water drill site and make a suggestion on a proposed coring/drilling target, secondly, to compare a conventional spiked geophone array with buried shots to a snow streamer array with surface shots, and finally, to use gravity data to model and constrain the basin evolution.
Field data collection was completed over the 2021/2022 Austral summer, ∼150 km south of Scott Base at Discovery Deep. A spiked geophone array collected 30 km of seismic data. Then, a 2.6 km subsection was resampled with a snow streamer system to compare acquisition methods. The snow streamer was about four times as fast to collect data and had a smaller crewing requirement as the spiked array and produced high quality data.
Seismic interpretation revealed two distinct seismic units in the upper 200 m of the geological strata. An erosional feature divides the two seismic units. The lower unit, seismic unit one, comprises regular continuous deformed
reflectors. The upper unit, seismic unit two, has irregular semi-continuous draped reflectors. The boundary between the units is interpreted as recording a change in the glacial regime of Antarctica, changing from an earlier wetbased
(seismic unit two) to cold-based (seismic unit one) glacial regime that occurred around 3 Ma. During or between the deposition of these units, tectonic processes resulted in the deformation observed in seismic unit one. No
location is recommended for a potential hot water drilling site due to a lack of clear evidence of Holocene strata; instead further seismic surveys are recommended. This seismic study did not image the basement beneath the seafloor sedimentary units. Instead, gravity models were used to propose different shapes of the basin. The controlling point in the basement modelling was a gravity low located in the centre of the seismic line. The seismic surveys provided control points and the seismic bathymetry indicated a shallowly dipping seafloor to the south-east, forcing the gravity models to have a central low in the basement topography reaching depths of 3,650 to 5,000mbelow the seafloor. Due to the complexities of the geological evolution of this part of Antarctica, resulting
in many sedimentary layers that are unconstrained under Discovery Deep, a simple layer cake model like those used in this study are not sufficient to provide a fully constrained history of basin evolution.