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THE SPATIAL DISTRIBUTION OF CHLOROPHYLL- a
AND ITS RESPONSES TO OCEANOGRAPHIC
ENVIRONMENTS IN THE SOUTH CHINA SEA
HUI ZHAO and DANLING TANG
Laboratory for Tropical Marine Environmental Dynamics
South China Sea, Institute of Oceanology
Chinese Academy of Sciences, Guangzhou-510301, P. R. China
lingzistdl@126.com
This study investigates the spatial distribution of Chlorophyll a (Chl- a )inthe
summer season for the South China Sea (SCS) using satellite measurements
and discusses the mechanisms of spatial variation of phytoplankton. Results
show that Chl- a concentrations are higher in the west than in the east of the
SCS. Chl- a concentrations in the west central basin, southeast of Vietnam and
a jet like band east of Phan Ri Bay are evidently higher than in the rest of
the SCS. Their spatial characteristics are related to upwelling derived from
Ekman pumping, Ekman transport induced by southwest monsoon winds, and
the strong offshore current east of Vietnam.
1. Introduction
The South China Sea (SCS) is the largest marginal sea, in the western
Pacific Ocean covering 3.5 million km 2 from the equator to 23 Nandfrom
99 E to 121 E, with an average depth of 2000 m (Fig. 1). The monsoons
always play an important role in the dynamics of upper circulations of SCS
throughout the year, 1 , 2 as it is dominated by strong northeasterly monsoon
during winter (December-February) and southwesterly monsoon in summer
(June-August). 3 The seasonally reversing monsoons arouse considerable
changes in general oceanic circulations and hydrological features, 4 , 5 whilst
southwesterly winds and the orientation of the coastline provide favor-
able conditions for wind-induced upwelling along the SCS west coast. 1 , 4
In addition, a strong offshore current northeast of Vietnam, 1 , 4 , 6 may also
exert important influence on the growth of phytoplankton, especially the
chlorophyll- a (Chl- a ) close related to primary productivity in the northern
SCS, and possibly over the whole SCS, by bringing nutrients from sublayer
waters.
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