Observation and modeling of the ice-covered ecosystem in the lagoon

A field observation was conducted in ice-covered coastal lagoon, Saroma-ko (Hokkaido, Japan) during the period from late February to mid March in 2004. The samples of the ice core and water were collected and the concentration of chlorophyll a, particulate organic matter and nutrients in both ice and water were measured. As a result, a bloom of ice algae was observed at the end of the February whereas the bio mass of pelagic phytoplankton had remained low during the observational period. In order to quantitatively clarify the behavior of material transport in the ecosystem, a coupled ice-ocean ecosystem model developed in our previous study is used. The model reproduced the observed bloom of the ice algae with good accuracy. The model results show that the organic matter accumulated in the ice by the production of the ice algae was effectively transported into the pelagic system by means of physical releasing effects, which is effective especially in the ice-melting period and that the nutrients consumed by the activity of biological production were effectively transported from the water by the above effects.