%0 Journal Article
%T Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment
%A S. F. Henley
%A A. L. Annett
%A R. S. Ganeshram
%A D. S. Carson
%A K. Weston
%A X. Crosta
%A A. Tait
%A J. Dougans
%A A. E. Fallick
%A A. Clarke
%J Biogeosciences (BG) & Discussions (BGD)
%D 2012
%I Copernicus Publications
%X A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (¦Ä13CPOC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting ¦Ä13CPOC in the coastal western Antarctic Peninsula sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/06 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10 ¡ë negative isotopic shift in ¦Ä13CPOC that cannot be explained by a concurrent change in concentration or isotopic signature of CO2. We hypothesise that the ¦Ä13CPOC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms (CCMs) in different diatom species. Specifically, very low ¦Ä13CPOC in P. inermis may be caused by the lack of a CCM, whilst some diatom species abundant at times of higher ¦Ä13CPOC may employ CCMs. These short-lived yet pronounced negative ¦Ä13CPOC excursions drive a 4 ¡ë decrease in the seasonal average ¦Ä13CPOC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4 ¡ë difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean ¦Ä13CPOC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary ¦Ä13CPOC. We also find significantly higher ¦Ä13CPOC in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of HCO3  and production of exopolymeric substances. This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for ¦Ä13CPOC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based ¦Ä13CPOC in the sedimentary record.
%U http://www.biogeosciences.net/9/1137/2012/bg-9-1137-2012.html