Offshore and nearshore chlorophyll increases induced by typhoon winds and subsequent terrestrial rainwater runoff

Abstract

The response of phytoplankton chlorophyll to Typhoon Damrey in the South China Sea (SCS) in September 2005 was studied by remote sensing. Chl a concentration increased in 2 areas after the typhoon: (1) An offshore bloom along Damrey's track exhibited a chl a peak (4 mg m-3) 5 d after the typhoon's passage. It was preceded by sea-surface cooling (-5°C), mainly on the right side of the typhoon track, and sea-level decrease (-25 cm) along the typhoon track 1 d post-typhoon. The offshore bloom was due to nutrient increase from mixing and upwelling. (2) A nearshore chl a increase succeeded typhoon rain (>300 mm on 26 September) on Hainan Island in the northwest SCS. In the bloom region, the water was rich in suspended sediments, phytoplankton, and colored dissolved organic matter, and was entrained by an eddy. This nearshore feature may have resulted from rainwater discharge and seaward advection by a typhoon-induced current. By these 2 mechanisms, both typhoon winds and rain can enhance production of marine phytoplankton. © Inter-Research 2007.