Validation of chlorophyll algorithm in Ulleung Basin, East/Japan Sea

Abstract

The results of our observation in May 2000 indicated that the SeaWiFS algorithm(OReilley et al., 1998), which was adopted for OSMI data processing, overestimated the actualchlorophyll values. This was rather unexpected in that there were good reasons to expect that the bio-optical properties of East/Japan Sea belonged to Case 1 water and in such case, the OC2 algorithmwould give unbiased estimates of actual chlorophyll a values. In November 2000, a cruise conducted bio-optical surveys in the same area. This time we added HPLC (High Performance Liquid Chromatography)method for measuring chlorophyll a concentration to the standard fluorometric method, which we havebeen using during the past. Fluorometric method with acidification is known to result inunder/overestimation of chlorophyll values in many parts of the world oceans, while it is easier andcheaper than HPLC method. To our surprise, the comparison of HPLC chlorophyll and fluorometricchlorophyll values show that fluorometric values gave an underestimation up to 50%. This error was dueto the presence of accessory pigments such as chlorophyll b. Considering this error, our previous result ofMay 2000 (Yoo et al., 2000) might have to be reinterpreted. Calculation of reflectance at 490 and555nm, however, indicated that this is not still enough to explain the discrepancies.