OCTS-Derived Chlorophyll-a Concentration and Oceanic Structure in the Kuroshio Frontal Region off the Joban/Kashima Coast of Japan

As a preliminary study on the use of Ocean Color Temperature Scanner (OCTS) chlorophyll-a (Chl-a) maps for fishery and oceanographic studies, version 3.0 OCTS Chl-a products were validated with sea surface Chl-a data and compared with the oceanic structure, current field, and fishing grounds in temperate coastal Pacific waters east of Japan during April to June 1997. Underestimation of OCTS values for high Chl-a concentrations and ghost patterns in coastal areas suggest that the OCTS ocean color algorithm needs to be improved. OCTS images depicted detailed Chl-a distributions associated with the oceanic fields observed by hydrographic data. The Chl-a-rich coastal waters correlated closely with the cold waters, suggesting that coastal upwelling might enhance nutrient supply and phytoplankton production. The high Chl-a frontal eddies near the meander crest of the Kuroshio Extension (KE) may be caused by a combination of advection of coastal waters by the KE front and an upwelling due to the cyclonic circulation. Fishing grounds reported during this period were often distributed in and around the high Chl-a area of the frontal eddy and around another coastal eddy. These results suggest that high Chl-a waters can be one of the important factors enhancing fishing ground formation. OCTS Chl-a images are useful to clarify the detailed biological processes in the Kuroshio frontal region off the Joban/Kashima coast of Japan.