SEDIMENT TRANSPORT AND DEPOSITIONAL PROCESSES IN ICE-COVERED EXPLORERS COVE, ANTARCTICA

At its summer minimum, sea ice covers 3 x 10⁶ km² of the ocean around Antarctica, over four times the size of Texas. However, transport and depositional processes that deliver sediment to the sea floor under semi-permanent sea ice (SPSI) are poorly constrained and the characteristics of sub-SPSI facies are not well documented. Sedimentation processes in Explorers Cove (EC), a bay at the mouth of Taylor Valley (Dry Valleys area) where sea ice has not melted out since 1999, were investigated by textural analysis of subaerial (moraine, delta, sea-ice surface) sediment and of seafloor sediment from short cores taken at depths of 7 – 20 m. Subaerial and submarine samples from two areas adjacent to the Wilson and Bowers Piedmont Glaciers (W-BPG) also were analyzed. Analysis was by sieving and, for the <1 mm fraction, by a laser diffraction particle-size analyzer (Malvern Mastersizer 2000). Matches between subaerial and seafloor grain size in two settings allowed identification of two processes transferring sediment to the sea floor: 1) Deltaic processes from a delta built by Wales Stream, a small ephemeral glacier-fed stream; 2) supra-ice eolian sediment streaming down cracks associated with pressure ridges that form where sea ice is grounded; this has been observed by divers. Both processes probably operate only during months when grounded sea ice melts to form a shallow moat a few tens of meters wide at the shoreline. In other areas in EC and in W-BPG the seafloor sediment, particularly in the top few cm, is finer grained than that of nearby subaerial deposits, including the overlying supra-sea ice sediment; W-BPG sediment also includes more outsized boulders than EC sediment. Possible causes for the fine texture of the surficial sea-floor sediment relative to subaerial sediment include: 1) widespread dispersal of fine grained component of deltaic sediment, in spite of minimal current activity, and 2) repeated resuspension of sediment by megafauna including scallops that make divots in the sediment by their swimming and clapping activities, also obliterating primary lamination. The reason why the eolian supra sea-ice sediment is coarser than subaerial morainal or deltaic sediment as well as seafloor sediment is also not clear; the finer fraction may be winnowed by wind and deposited on ice further offshore.