Changes in the sea-ice brine community during the spring-summer transition, McMurdo Sound, Antarctica. I. Photosynthetic protists

Abstract

During the austral spring, a characteristic microbial community develops in the subsurface brine pockets and channels of the annual land-fast sea-ice in McMurdo Sound. This community is distinct from the diatom-dominated community that develops in the channels at the base of the sea-ice, at the seawater/ice interface, and in the platelet layer. The photosynthetic biomass in the brine pockets is dominated by athecate dinoflagellates. Chrysophyte statocysts and <5 μm photosynthetic flagellates are also characteristically found in this assemblage. In December, chlorophyll a content and biomass peak, and photosynthetic gymnodinioid dinoflagellates can reach densities >103 ml-1 of brine. The photosynthetic dinoflagellates form cysts during late December and early January, and chrysophyte statocysts also become abundant. During austral summer, total autotrophic biomass in the upper ice brine decreases due to dilution by melt water, flushing of brine into the water column, and grazing. By late summer, the annual sea-ice in McMurdo Sound has broken out. -from Authors