The Changjiang Diluted Water (CDW) detection by SeaWiFS chlorophyll-a

Abstract

It is known that the Changjiang Diluted Water (CDW), which mixed Changjiang summer freshwater discharge and Kuroshio Surface Water and/or Taiwan Warm Water, spreads eastwards over the broad area of the East China Sea and reaches as far as Jeju Island to Tsushima Strait. It is expected that the distribution of CDW is controlled by the Changjiang summer freshwater discharge and showed significant interannual variations. Here we analyzed the Sea-viewing Wide field-of-view Sensor (SeaWiFS) chlorophyll-a during 1998-2006 and showed that interannual variations of the spatial distribution of high satellite chlorophyll-a (>0.9-0.4 mg m-3) was well corresponded with distribution of low salinity CDW (<30-32) and that interannual variation of the CDW area was associated with the interannual variation of the Changjiang summer freshwater discharge. In order to decide the criteria of the higher satellite chlorophyll-a area showing CDW, K-means clustering method was used to decide the boundaries. Correlation analysis between the high satellite chlorophyll-a and summer freshwater discharge indicated that low salinity, high satellite chlorophyll-a CDW spread further in the East China Sea after 1 to 2 months time lag of the discharge. CDW area in 2006 was sharply reduced and this may be caused by partly operation of the Three Gorge Dam (TGD).