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Strong enhancement of chlorophyll a concentration by a weak typhoon
Recent studies demonstrate that chlorophyll a (chl a) concentrations in the
surface ocean can be significantly enhanced due to typhoons. The present study
investigated chl a concentrations in the middle of the South China Sea (SCS)
from 1997-2007. Only the Category1 (minimal) Typhoon Hagibis (2007) had a
notable effect on the chl a concentrations. Typhoon Hagibis had a strong
upwelling potential due to its location near the equator, and the forcing time
of the typhoon (>82 h) was much longer than the geostrophic adjustment time
(~63 h). The higher upwelling velocity and the longer forcing time increased
the depth of the mixed-layer, which consequently induced a strong phytoplankton
bloom that accounted for about 30% of the total annual chl a concentration in
the middle of the SCS. The implication is that the forcing time of a typhoon
should be long enough to establish a strong upwelling and consequently for the
induction of significant upper ocean responses.Comment: Typhoon-Ocean Environment interaction
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