Decadal variability in the Yellow and East China Seas as revealed by satellite ocean color data (1979–2003)

Abstract

Satellite ocean color data from the Coastal Zone Color Scanner (CZCS) in 1979 to 1984 and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in 1998 to 2003 are examined to determine whether there have been changes in chlorophyll concentration and suspended sediment as indicated by changes in satellite-derived optical properties during the past two decades in the Yellow and East China Seas (YECS). We compare water-leaving radiance measurements at 443 and 555 nm [the CZCS band is centered at 550 nm, but we consider this comparable to the SeaWiFS 555-nm band] and discuss possible reasons for the changes observed. The shallow coastal areas of the YECS exhibited high water-leaving radiance in the 555-nm band (Lw555) during two time periods, indicating that these waters are sediment-dominated Case-2 waters. Between the CZCS era and the SeaWiFS era, Lw443 increased in these areas by 17%61%, and Lw555 increased by 67108%. In the deeper waters, Lw443 decreased by 25%31%, which would indicate an increase in absorbing materials such as chlorophyll and colored dissolved organic matter (CDOM). Between the CZCS and SeaWiFS eras, the average chlorophyll concentration (based on Case-1 algorithms) increased by 15-60% in these offshore deep waters. Periodical in situ measurements from 61 stations in the western coast of Korea from 1978 and 2002 were compared with the trends found in satellite data. The results show that there were increasing trends in temperature and zooplankton biomass, and decreasing trends in salinity and Secchi depth. The satellite data surrounding these stations showed an increase in Lw555 (49 %), a decrease in the Lw443 (12 %), and an increase in chlorophyll (46 %). From the results, it is inferred that there have been environmental changes in the Yellow Sea during the last two decades from 1979 to 2003.