Estimation of interdecadal change of spring bloom timing, in the case of the Japan Sea

A new method to estimate past chlorophyll a variation from available satellite, ship and buoy data is proposed. Satellite chlorophyll a variations during spring from 1998 to 2003 in the Japan Sea were described well by a Gaussian curve, and the parameters were correlated with physical variables obtained from other sources. Start and peak timing of spring bloom had positive/negative correlation with average wind speed in February and March and strength of stratification during spring ship observation, respectively. Spring bloom timing estimated for past 20 years showed that in mid‐1980s the bloom started and peaked relatively earlier in early March and the duration was shorter. Primary production during 1980s was estimated not to be high. The method is also applicable to understanding of past chlorophyll a conditions in other areas.