Production and Decomposition of Organic Matter in a Bay of the Japan Sea During the Winter Diatom Bloom

The winter bloom of diatoms studied under the ice of a bay in the Japan Sea consisted mainly of species of Thalassiosira and Chaetoceros, having a low temperature optimum (9°C) for photosynthesis and a low optimum of illumination (2 klux). Photosynthesis proceeded to 8–15 m in water under the ice at −1.8°C. The cause of the bloom is related to optimal illumination and nutrient supply during this period. Microbial biomass was sufficiently high to sustain the normal feeding on zooplankton. Thus, an active process of biological production takes place there even in winter at subzero temperature.