Seasonal Variation in Ice Algal Assemblages in the Fast Ice Near Syowa Station in 1983/84

Abstract

Ice algal assemblages in the fast ice near Syowa Station were investigated from March 1983 to January 1984. Peaks in the standing crop (chlorophyll a) occurred in April–June and October–November; the largest (125 mg chlorophyll a m−2) occurred in mid-November at a site with moderate snow cover. Chlorophyll was most highly concentrated in the bottom of the ice, where the diatoms Amphiprora kufferathii, Berkeleya rutilons, Nitzschia lecointei, N. stellata, N. turgiduloides and Pleurosigma directum were dominant. The chlorophyll concentration within the ice developed mainly in May with little change during the following months at heavily snow-covered sites. Centric diatoms, e.g. Chaetoceros spp., Eucampia antarctica and Rhizosolenia alata were major components in the interior assemblage. The chlorophyll concentration increased in the upper consolidated snow layer during October-January. The dominant species there, Tropidoneis sp., was a minor component of the interior and bottom ice layers. These results suggest that the interior ice algal assemblage was formed by mechanical inclusion of microalgae at the time of sea ice formation, and did not grow in the ice. However, the bottom assemblage grew when irradiance was high enough. The surface assemblage, which was presumed to be inoculated by an interior assemblage through vertical channels, grew in spring.