Mixed diatom assemblages in glacigenic sediment from the central Ross Sea, Antarctica

We have investigated diatom assemblages and their distribution in piston and trigger cores from six sites in the central Ross Sea, including analysis of absolute abundance of diatom valves and diatom fragments, with the aim of characterising different glacigenic sediment facies and sediment packets. These data provide a new perspective on the current texturally based classification of diamicton, mud, and diatomaceous mud. All samples investigated include diatom taxa characteristic of the modern Ross Sea flora, thus all deposits evaluated are interpreted to be upper Quaternary in age. Reworked diatoms are ubiquitous, but they vary in terms of species content and concentration. Sediment units classified as diamicton are enriched in robust reworked valves of long-ranging taxa such as Paralia spp., Stephanopyxis spp., and Stellarima microtrias, but different diamicton packets can be distinguished based on variable concentrations of biostratigraphically constrained taxa including Denticulopsis spp., Thalassiosira spp., and Actinocyclus spp. Absolute abundance of diatoms and diatom fragments provide another useful criterion for distinguishing sedimentary processes. Together, these criteria permit interpretations of past glacial and glacial marine processes with greater certainty than allowed by textural analyses alone. We are able to distinguish between tills deposited beneath ice streams from those emplaced by slow-moving ice—information that is important in ice sheet reconstruction.