Estimation of standing stock of chlorophyll a and primary production from Remote-Sensed Ocean Color in the Oyashio region, the Western Subarctic Pacific, during the spring bloom in 1997

In order to examine the applicability of remotely-sensed ocean color for the estimation of phytoplankton biomass and primary production in the Oyashio region, the western subarctic Pacific, vertical distributions of chlorophyll a concentration and primary production were observed in April and May 1997. Spring bloom was observed in both April and May, and the surface concentration of chlorophyll a exceeded 40 mg m-3. The relationship between the standing stocks of chlorophyll a within the layer from the sea surface to one optical depth (0-1/k layer) and the surface chlorophyll a concentration is expressed as a Michaelis-Menten equation. The mean ratio of the standing stock of chlorophyll a in the euphotic layer to that in the 0-1/k layer was 4.41, this ratio did not significantly differ from 4.61 which was obtained at homogeneous distribution of chlorophyll a within the euphotic layer. These facts suggest that the distribution of chlorophyll a could be assumed to be homogeneous in the euphotic layer during the spring bloom. Results of primary production measurements by simulated in situ method were compared with those by an algorithm with two variables; chlorophyll a and non-spectral PAR. Daily primary production in the euphotic layer estimated by the algorithm varied in a range of 38-274% of that estimated by incubation, although the primary productions by the algorithm agreed with those by the incubation at a half of stations. Primary production within the euphotic layer calculated using simply the surface data was the same as that estimated using vertical distribution of chlorophyll a. These results show that the primary production in the euphotic layer may be estimated from the remote sensed measurements during the spring bloom in the Oyashio region.