Seasonal development of algal biomass in snow-covered fast ice and the underlying platelet layer in the Weddell Sea, Antarctica

The seasonal changes of the nutrient regime and the development of algal co mmunities in snow-covered fast ice and the underlying platelet layer was in vestigated in the eastern Weddell Sea during autumn, winter, and spring 199 5. In the upper sea ice, an autumnal diatom community became enclosed durin g subsequent ice growth in winter, declined, and was replaced by a flagella te dominated community in spring. In this layer, nitrate was completely exh austed at the end of spring, although nutrients had been partly regenerated in early spring. The progressive congelation of platelet ice contributed s ignificantly to sea ice growth thus influencing algal inoculation of the se a ice bottom. Biomass, present in the uppermost section of the platelet lay er, could be found in the sea ice bottom after this section congealed to so lid ice. After incorporation, species composition changed from larger and c hain-forming species to species of smaller cell size. Concurrently, net gro wth rate slowed down from 0.07 day(-1) within the platelet layer to 0.03 da y(-1) within the sea ice. Despite a thick snow cover of more than 20 cm, ma ximum biomass yield was 210 mg chi a m(-2) in the platelet layer and 40 mg chi a m(-2) in the sea ice respectively, while 95% of the latter was locate d within consolidated platelet ice. Total fast ice biomass observed here is significantly lower than that observed in snow-free fast ice of the Ross S ea, but because snow cover of the southern Weddell Sea is representative of most fast ice areas in the Antarctic, the data presented here are of gener al value.