Blue sky and green bugs – How physical parameters and algal speciation influence DMSP and DMS profiles in Antarctic winter sea ice

Due to the unique and extreme physico-chemical conditions in sea ice, i.e. the high salinity and the icy matrix, it constitutes a favourable habitat for the production of high levels of dimethylsulfoniopropionate (DMSP) by the inhabiting microalgae. High concentrations of DMSP and DMS (dimethylsulfide) are frequently found in sea ice during spring and summer. Records of production during winter are still scarce, but first evidence indicates the potential importance for global budgeting. Our study presents profiles of DMS(P) in sea ice cores collected during the AWECS (Antarctic Winter Ecosytem Climate Study) cruise on RV Polarstern (ANT29-6) in the Weddell Sea. Results show that significant DMS(P) production also occurs during winter in sea ice of the Weddell Sea. This stands in contrast to previous measurements in Arctic winter sea ice (CFL-IPY cruise in the Circumpolar Flaw Lead Polynya), where DMS(P) concentrations were very low. Possible explanations for the differences between DMS(P) levels in the Arctic and Antarctic might be the different snow cover and thus insulation, light regimes and also microbial community structure within the ice. The DMS profiles mirrored the permeability of the sea ice, following elevated DMSP levels in the impermeable areas while showing losses to the ice surface and ice-water interface in the more permeable regions. DMS(P) levels were generally correlated with chlorophyll A concentrations, although the details are complex and seem to be influenced by species composition and species specific DMSP/Chla ratios. Three mayor trends determined in situ reflect values of 136 (±93), 32 (±15) and 5 (±2) mmol DMSP/g Chla resembling published values for cultures of dinoflagellates, haptophytes and diatoms. Preliminary microscopy data confirm that dinoflagellate dominated sea ice layers display higher DMSP/ChlA ratios than diatom dominated ones