SEDIMENT TEXTURE IN EXPLORERS COVE, ANTARCTICA: HOW IS SEDIMENT TRANSPORTED FROM THE TAYLOR DRY VALLEY TO THE ICE COVERED SEAFLOOR

As part of a study of sedimentological, taphonomic, and bioturbation processes on the nearshore seafloor of Explorers Cove at the mouth of the Taylor Dry Valley, we investigated grain size distributions of sediment on the sea ice, in shallow cores from the sea floor, and from the adjacent land. Sea ice in Explorers Cove has not melted in 10 years, so wind-blown sediment is abundant on the sea-ice surface. We predicted that the on-land moraine sediment would be coarse and poorly sorted and would contrast to fine-grained and well-sorted eolian sediment on the sea ice; the seafloor substrate would resemble the on-ice sediment above. Results of textural analysis (sieve and Malvern Mastersizer 2000) do not support the predictions. Sediment is universally poorly sorted, and sediments from all settings have overlapping textural characteristics. This reflects a heterogeneous source as well as limited sorting by transport processes. Surfaces of moraines are armored by pebbly surface deposits which are the coarsest sediments in the region, but underlying subsurface morainal sediments are the finest (fine-grained sand). Surface sediments of deltas formed by small glacier meltwater streams are coarser grained than subsurface delta deposits, also indicating winnowing. Sea-ice sediment typically is medium-grained sand, coarser than the fine-grained sand in the upper centimeters of the underlying seafloor substrate. Seafloor surface sediment from water depths of 20 m is finer grained than that from shallower depths. Seafloor sediment is coarsest near a small delta and near a tidal crack observed to be a conduit for transfer of sediment from sea ice to seafloor. Differences in texture between sea ice and seafloor sediments as well as fining in surface sediments at greater depth indicate transport and winnowing processes other than by wind. Pervasive downward coarsening in cores to a layer of medium-grained sand beneath 10 cm possibly reflects sea-ice melt and introduction of coarse windblown sea-ice deposits. Overall, sediment transport processes from land with heterogeneous source sediment to the seafloor in nearshore areas with semi-permanent sea ice are complex and yield variable poorly sorted coarse-grained sandy deposits with few clues to their origin.