SEASONAL AND INTERANNUAL VARIABILITY OF SEAWIFS CHLOROPHYLL A IN THE NORTHERN MALACCA STRAITS IN RELATION TO ASIAN MONSOON

摘要

Primary productivity in Malacca Straits (MS) is described as constant throughout the year.However, our analysis of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data (November1997–January 2003) using Geographical Information System (GIS) showed that chlorophyll a (chl a) innorthern MS exhibited seasonal variability. The SeaWiFS chl a during northeast monsoon (NEM)increased as much as twice compared to chl a during southwest monsoon (SWM). Besides, in situ datashowed chl a increased from 0.39 mg m-3 during SWM to 1.26 mg m-3 during NEM at northern MS.Monsoon wind influenced the spatial distribution and seasonal variation of the bloom. The bloom startedfrom eastern MS, and dispersed northwest towards Andaman Sea by northeasterlies. NEM wind createdpositive wind stress curl along 4.5° -6.5° N in the Straits which caused positive Ekman pumping resultingto upwelling. Consequently, upwelling helped replenish the surface water nutrients, thus, maintaining thephytoplankton bloom over the continental shelf. However, low chl a was observed during SWM, and thiswas attributed to negative wind stress curl and downwelling. In addition, large-scale atmospheric-oceanevents in both Indian and Pacific Oceans could possibly affect interannual variation of chl a in northernMS.