Chlorophyll a and Hydrography of Sea Ice and Water Column in Lagoon Notoro-ko during Ice Covered Periods in 2012

Abstract

Lagoon Notoro-ko is a large brackish lake on the Okhotsk Sea coast of Hokkaido. It is completely covered with sea ice during winter and the hydrographic and biological conditions during this season are unknown. We conducted a winter investigation into the temporal changes of chlorophyll a and environmental variables in the sea ice and water column beneath the surface during the period from February 6 to April 5, 2012. Integrated chlorophyll a at 18 m ranged 22.4-295.6 mg/m². In contrast, chlorophyll a levels in 24-45 cm thick ice ranged 0.2-8.6 mg/m², or relatively less than in the water column. However, because chlorophyll a was largely concentrated in the bottom-most part of the ice, it might be available to grazers in the underlying water. While the ice is melting, a large proportion of the populations released from the ice likely sink to the sea bottom rather than remaining in the water column. During the ice melting period, a large part of the populations released from the ice likely sink to the sea bottom rather than stayed in the water column. In summary, it can be said that the ice is a unique ecological platform, where microalgae perform the three roles of the primary producers, i.e., to produce rich products（pasture）, to avail grazers to feed on the products（meadow）and to send the products to a benthic community（feeder）.