Towards estimation of blue carbon sink potential of sub-Antarctic continental shelf benthos

Continental shelves around Antarctica are a globally important carbon sink, due to both oceanographic CO2 absorption and biological fixation and trophic cascading. Most carbon passing through the foodweb is pelagic and is recycled through microbial loops. However significant masses are accumulated and immobilized (within calcareous skeletons of benthos), accounting for sequestration potential of 106 tonnes per year. Burial potential is enhanced by being largely untrawled by human harvesting and too deep for iceberg scouring. Yet these are also true for subAntarctic island shelves where there are considerable phytoplankton blooms, little or no sea ice and warmer sea temperatures (enabling faster meal processing time by benthos) – yet their potential as a carbon sink has been largely ignored. We report on the Antarctic Seabed Carbon Capture Change (ASCCC) project which sampled most of the high southern latitude continental shelves during the 2016/17 Antarctic Circumnavigation Expedition (ACE). Video and photo- equipped trawls collected imagery and benthos samples allowing us to estimate changes in intra and inter-shelf variability in benthos density and biomass. Growth models constructed from age structure of sampled species with growth check lines (e.g. bryozoans, bivalves, brachiopods etc) enable annual carbon accumulation to be estimated. Preliminary data and analyses suggest that continental shelves of 40-55°S may be globally significant, both in terms of absolute carbon storage but also in trying to reduce error in climate models. See www.asccc.co.u