Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment.

A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ¹³C_POC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ¹³C_POC in the coastal western Antarctic Peninsula (WAP) 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 2005/2006 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10‰ negative isotopic shift in δ¹³C_POC that cannot be explained by a con10 current change in concentration or isotopic signature of CO₂. We hypothesise that the δ¹³C_POC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms in different diatom species. These short-lived yet pronounced negative δ¹³C_POC excursions drive a 4‰ decrease in the seasonal average δ¹³C_POC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ¹³C_POC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary δ¹³C_POC. We also find significantly higher δ¹³C_POC 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 Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and production of exopolymeric substances (EPS). This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ¹³C_POC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ¹³C_POC in the sedimentary record. A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ¹³C_POC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ¹³C_POC in the coastal western Antarctic Peninsula (WAP) 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 2005/2006 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10‰ negative isotopic shift in δ¹³C_POC that cannot be explained by a con10 current change in concentration or isotopic signature of CO₂. We hypothesise that the δ¹³C_POC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms in different diatom species. These short-lived yet pronounced negative δ¹³C_POC excursions drive a 4‰ decrease in the seasonal average δ¹³C_POC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ¹³C_POC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary δ¹³C_POC. We also find significantly higher δ¹³C_POC 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 Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and production of exopolymeric substances (EPS). This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ¹³C_POC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ¹³C_POC in the sedimentary record. [ABSTRACT FROM AUTHOR]