Ice Flora (Bottom Type): A Mechanism of Primary Production in Polar Seas and the Growth of Diatoms in Sea Ice

Abstract

A yellowish-brown layer at the bottom of summer sea ice, upturned by an icebreaker, off the coast at Point Barrow, Alaska, extended up to 30 cm from the bottom. It consisted of large diatom colonies which were found to have been formed in brine included in fissures between vertically oriented ice crystals. Grazing by zooplankton was highly restricted because the structure of the ice microhabitat prevented their entry. The chlorophyll content of the layer studied was 100 times greater than that of sea water under the ice. This suggests that the most important primary production of the Arctic is in the sea ice. The biological environment of the colored layer at the bottom of the sea ice is summarized, viz: relatively stable temperature (-3 to 0 C), sufficient nutrient supply, variable osmotic pressure, stronger light conditions than in sea water below, limited grazing by zooplankton, and probable abundance of organic matter.