PARTICULATE CARBON DISTRIBUTION AND COMPOSITION BENEATH ICE SHELVES, EXAMPLES FROM THE LARSEN SYSTEM, ANTARCTICA

A conceptual model of particulate carbon transport beneath ice shelves greatly expands our understanding of benthic ecosystems and the sedimentologic history of ice shelf systems. Such research is a major step to deciphering the carbon cycle across some 1.5 million km2 of mostly unexplored seafloor and water column. We can most effectively study the problem by sampling beneath the former extent of recently collapsed shelves, such as the Larsen system. Thus, we evaluate the content of total organic carbon (TOC) from 30 surface samples collected in water depths of 446-1181 m from sites formally located beneath the Larsen B and A Ice Shelves in the NW Weddell Sea. Swath bathymetry clearly delineates the sub-ice shelf system into at least five glacial drainage pathways that lead to contributory valley glaciers along the Peninsula coast (i.e. Drygalski, Crane, Hektoria, Evans, Leppard Glaciers). The TOC composition of the surface samples was evaluated by C/N ratios and biomarker (sterol) total abundances. Sources of particulate TOC may be related to advection from outside the ice shelf, hemipelagic settling from glacier grounding lines or undermelt of basal debris, or even in situ production via chemoautotrophy. Results show that mean TOC within the surface sediment samples is 0.41% with a standard deviation of 0.14%. NBP0603 KC5, collected north of the SCAR Inlet and 24 nm from the Crane Glacier terminus, is adjacent to a known cold seep site and shows the lowest TOC at 0.17% at the surface. The average C/N ratio of the samples is within the bounds of the Redfield Ratio with a standard deviation of 3.21. Biomarker analysis of LMG0502 KC21, collected in the Larsen A area, demonstrates evidence of a recent influx of phytoplankton by-products. The average background level of sterols indicative of eukaryotic phytoplankton at 19-43 cm below the surface is 0.03 ug/g. From a depth of 19 cm, sterol levels climb and then significantly increase near the surface (around 5 cm) to 1.38 ug/g. Conversely, cores in the Hektoria Basin, located in the northern region of the Larsen B area, lack any detectable sterols at the sampled depths. The patterns we outline suggest significant differences in particulate carbon transport and distribution between the two ice shelves and within each glacial trough system.