Multi-scale variability of ambient conditions, fast ice dynamics and biogeochemistry in the coastal zone of Victoria Land (Ross Sea)

Interannual and seasonal variability of the biogeochemical characteristics of fast ice were analysed in relation to ambient conditions, water column properties and ice biota. According to Zubov's Law, the annual atmospheric cooling should generate 2.5m thick fast ice sheets in this coastal zone, but katabatic wind peaks in July-August often cause ice breakouts, resulting in highly variable growth periods (2-9 months) and thickness (1.0-2.5 m). In spring, atmospheric forcings significantly modulate brine content (5-20%) and drainage in fast ice, as well as salinity oscillations in bottom and platelet layers (15 psu). In the water column, the formation of nutrient-impoverished Summer Surface Waters is triggered by seawater warming (-1.9 to 0.78 C), ice melting (0.03 m d-1) and pelagic production. Negative NO3 and SiO2 balances and positive NH4 balances (-41, -153 and 1173 kg km-2, respectively) were estimated in fast ice in spring, whereas nutrient budgets in the platelet layer are regulated by its variable level of isolation from seawater. The large accumulation of dissolved organic carbon (3890 kg km-2) in the ice system and its release in seawater in late spring are important features of the carbon cycle in these Antarctic coastal zones, with possible implications for the modulation of climate.