How much, how deposited, how old – what can we learn from sediments in Pine Island Bay?

A number of studies have defined a boundary in the Amundsen Sea embayment between an inner continental shelf, which contains areas where crystalline bedrock is at or near the seabed, and the shelf further offshore, which is underlain by sedimentary strata that increase in overall thickness oceanward. Other studies have shown that much of the inner shelf in Pine Island Bay is covered by a drape of sandy mud averaging about 1 m in thickness, interpreted as having been deposited from meltwater plumes during the mid-late Holocene. Much thicker sediments have been shown to be present in isolated deep basins based on acoustic sub-bottom profiles and sparse seismic reflection profiles, including an estimated maximum thickness of >400 m in one basin close to the front of Pine Island Glacier.  Thus, the widespread impression exists that, apart from the thin Holocene drape, sedimentary cover in Pine Island Bay is restricted to isolated basins.

Here we examine the distribution and thickness of sediments in Pine Island Bay using a network of high-resolution seismic reflection profiles collected in 2020 on RV Nathaniel B Palmer cruise NBP20-02. We show that more extensive thick sediments are present near the front of Pine Island Glacier than have been reported previously. In some places sediment units exhibit characteristics that suggest their deposition was influenced by bottom currents. We also show that sedimentary deposits are present over the tops and on the flanks of some bathymetric highs that must have been former ice shelf pinning points. Finally, we consider what the extent, thickness and character of the sedimentary units identified tell us about glacial/glacimarine processes and ice sheet history in the area, and what could be learned by further study and sampling.