Satellite-Observed Chlorophyll-a Concentration Variability and Its Relation to Physical Environmental Changes in the East Sea (Japan Sea) from 2003 to 2015

The spatio-temporal variability of the chlorophyll-a (chl-a) concentration in the East Sea (Japan Sea) (EJS) was investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) data over 13 years from 2003 to 2015 to understand the impact of physical environmental changes on low-trophic level marine ecosystems. The chl-a images were composited to produce gridded monthly chl-a images using a weighted average method after applying a speckle removal algorithm to each path image. Missing pixels without any satellite observations because of cloud coverage were objectively filled using three-dimensional optimal interpolation. The first empirical orthogonal function (EOF) mode of the monthly chl-a images, accounting for 14% of the total variance, showed higher eigenvectors values in the eastern part of the EJS and distinct annual peaks each spring. The amplitudes of the first EOF mode, despite the dominant year-to-year variations in chl-a, tended to increase during spring over time. The recent 13-year trend of chl-a showed differences between the southwestern part and the northeastern part of the EJS, and this difference clearly appeared in the monthly trend maps for March and April. The eastern coast of Korea showed a highly positive trend during summer, particularly during August. The changes in chl-a over the decade were related to the physical environmental changes in sea surface wind, mixed layer depth, and stratification of upper sea water in the EJS.