Land-fast ice off Adélie Land (Antarctica): short-term variations in nutrients and chlorophyll just before ice break-up

This study focused on the short-term variations of sea ice microalgal biomass and nutrients, in Adélie Land coastal area (Antarctica). The annual land-fast ice, “platelet ice-like” layer (PLI) and under-lying seawater were sampled during the 1999 austral spring. The study was conducted during 33 days preceding the ice break-up, with a daily sampling when the meteorological conditions were favourable. Time-series for salinity, chlorophyll a (Chl a), NH4+, NO2−, NO3−, PO4− and Si(OH)4 are shown. We also provide satellite data and meteorological variables for the same period. During the study period, the solid ice thickness varied from 1.47 to 1.05 m. Pigments were concentrated in bottom ice, but progressively invaded the PLI. Phaeo a increased in the PLI during the last weeks, in parallel with increasing NO2− concentration. Si(OH)4, in lowest concentrations in bottom ice, increased progressively in the under-ice water (UIW) and PLI, this was because of offshore water inputs. NH4+ concentrations were high in every sea ice component (particularly in the bottom ice) and were inversely correlated to pigments in the bottom ice. NH4+ concentrations progressively increased in the PLI and underlying seawater just before the break-up. In the bottom ice, PO4− concentrations were related to high pigment concentrations, but with a short lag close to the break up period, indicating in situ regeneration. Neither NO3− nor NH4+ concentrations were exhausted in the bottom ice. NO2− and NH4+ concentrations increased in PLI and under-ice water just before the break-up period, which might indicate strong inorganic nitrogen recycling in land-fast ice. Approximately 0.4 kmol km−1 linear coast of NH4+ (1 kmol NO3− and 2 kmol PO4−) were released to the under-ice seawater during break-up, along with 0.12 tons km−1 Chl a (9.6 tons POC km−1 equivalent). These nutrient sea ice inputs to the coastal zone waters, during the ice recession and break-up, may vary annually depending upon the local meteorological conditions that control ice formation, duration of ice cover and melting.