Enhanced winter biogeochemical activity in Antarctic first-year sea ice

The study of Antarctic first-year ice as a biogeochemical habitat has been limited by samples mostly collected in pack ice during summer. Fewer winter data are available, and due to the harsh conditions, data from the marginal ice zone (MIZ) are even more difficult to obtain. The MIZ is broad and circumpolar in the Southern Ocean; it is found at different latitudes during the year with sufficient light and nutrients to sustain primary production and affect ecosystem functioning. We present the first dataset of biogeochemical properties of first-year ice collected in the Atlantic sector of the Southern Ocean during winter 2019, obtained from young pancake ice and consolidated first-year ice. Temperature, salinity, crystal structure, δ18O, chl-a and bulk macronutrient data were used to investigate the winter habitat and explain the transition from young ice to first year ice through exchanges with the ocean biogeochemistry. Data suggests that the sea ice sampled at the consolidated station was a result of thermodynamic processes combined with possibly multiple cycles of breaking and rafting induced by waves and dynamics, which ultimately enhanced the biogeochemical activity beyond what expected for first-year ice. A numerical model was used to support the hypothesis that winter first-year ice buffers biogeochemical components differently from the upper ocean winter concentrations, and this may determine the conditions for the biogeochemical development later in spring.