A time series study during spring transition in the fast ice at Davis station, Antarctica: preliminary resul

While representing less than 5% of the total ice cover around Antarctica, fast ice is nevertheless an important habitat with highest biomass and production occurring in the bottom (Archer et al., 1996). Sea--‐ice algae are playing a key role in structuring the ecosystem, as they are an essential food source for krill. With the annual melting of the sea ice there is a strong release of nutrients and algae to the water, possibly fertilizing and/or seeding algae the underlying water column. A time series was sampled during the Austral spring of 2015 (Oct. 27th – Dec. 11th), in the vicinity of Davis station (68°35’ S, 77°58’ E, Prydz Bay, Antarctica). Fast ice, snow cover and underlying water column were sampled with focus on the nitrogen and carbon cycle and the pivotal role of sea--‐ice algae for higher tropic levels. Different parameters such as nutrients, particulate matter (PM) and isotopic signatures for nitrate, ammonium and PM will be measured. Primary production and uptake rates for different nitrogen substrates were also measured using in--‐situ stable isotope incubation experiments to study the change in algae growth rates. That campaign was performed in close relation with colleagues from the Institute of Marine and Antarctic Studies (Hobart, Australia) to link our findings with the availability of trace metals such as iron. Temperature profiles in the ice showed a clear change halfway the sampling campaign with increasing temperatures, likely accompanied by an increase in permeability throughout the ice. Results show a large accumulation of biomass in the bottom few 5 cm (particulate organic carbon reaching up to 1300 μmol l‐1). Preliminary data also shows a large accumulation of nitrate at the bottom with concentrations exceeding those in the underlying water. Preliminary results will be presented and discussed.