The Effects of Ice Shelf Break-up on Changes in Particulate Carbon Distribution and Composition, 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 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. It is important to evaluate how biogeochemical processes such as those that govern particulate carbon transport in southern polar regions are affected by the loss of permanent ice cover. Thus, we investigate how open marine and ice-covered benthic environments vary in terms of the amount, source, and isotopic composition of total organic carbon (TOC) at the surface and at depth in the Larsen System. We evaluate stable isotopic carbon and the content of TOC from 30 surface samples and one Kasten core collected in water depths of 446-1181m from sites formally located beneath the Larsen A & B Ice Shelves in the NW Weddell Sea. We evaluated the content of TOC within the surface samples with C/N ratios and δ13C values. Sources of particulate TOC may be related to advection from outside the ice shelf system, hemipelagic settling from glacier grounding lines or undermelt of basal debris, or in situ production via chemoautotrophy. δ13C variations among surface and downcore samples (formerly beneath the Larsen Ice Shelf) show remarkable uniformity. The mean value for δ13C is -23.86‰ with a standard deviation of 0.27‰ and a range of 1.41‰ across an area of 7*103 km2. Such uniformity suggests that a similar provenance of particulate carbon transport may exist over time and space, despite differences in sediment source and accumulation beneath the ice shelf. δ13C variations among surface samples located in open marine environments show a similar mean δ13C value (-23.53‰), but the standard deviation (0.76‰) and the range (2.32‰) show that the values are not as uniform as beneath the ice shelf. Mean TOC within all surface sediment samples is 0.41% with a standard deviation of 0.14%; the average C/N ratio of the samples is within the bounds of the Redfield Ratio with a standard deviation of 3.21. Our preliminary δ13C and TOC data suggest dynamic changes in particulate carbon transport due to the removal of permanent ice cover via ice shelf break-up along the Antarctic Peninsula.