Chlorophyll a increase induced by surface winds in the northern South China Sea
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Chlorophyll a increase induced by surface winds in the northern South China Sea GAO Shan1,2∗ , WANG Hui2 , LIU Guimei2 , HUANG Liangmin3,4 , SONG Xingyu3,4 1
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College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China National Marine Environmental Forecasting Center, State Oceanic Administration, Beijing 100081, China State Key Laboratory of Oceanography in the Tropics, Guangzhou 510301, China Key Laboratory of Marine, Bio-resources Sustainable Utilization, Chinese Academy of Sciences, Guangzhou 510301, China
Received 25 January 2011; accepted 29 April 2011 ©The Chinese Society of Oceanography and Spring-Verlag Berlin Heidelberg 2012
Abstract The response of chlorophyll a (Chl a) concentration to wind stress is analyzed in the South China Sea (SCS), using in-situ data of Chl a and remote sensing data (QuikScat-sea surface wind (SSW), AVHRR-sea surface temperature (SST), AVISO merged-sea level anomalies (SLA), SeaWiFSderived Chl a and MODIS Terra-derived Chl a) in August/September/October 2004, 2006 and 2009. The variability of SSW, SST and SLA 7 d before in-situ Chl a sampling (including the work day of in-situ Chl a sampling) with the same latitude and longitude of the study area are investigated, and the correlation coefficients are calculated between these hydrographic factors and in-situ Chl a concentration. The results show that the Chl a-SSW correlation coefficients at upper layers (such as 0 m and 25 m) are more significant than those at deeper layers (such as 50, 75 and 100 m) 1–3 d before, which indicates that there is a time lag of strong surface winds stimulating phytoplankton bloom. By analyzing the relationship among the daily remote sensing derived (RSderived) SSW, SST, SLA and 3 d averaged SeaWiFS/MODIS-derived Chl a concentration in the northern SCS in September 2004 and 2009 respectively, it shows that the intensity and speed of surface winds could have great influence on extend of Chl a increase. If surface winds reach 4–5 m/s over, Chl a concentration would increase 1–3 d after the process of strong surface winds in open sea area of the northern SCS mainly during September. Key words: South China Sea, phytoplankton bloom, chlorophyll a, surface wind, vertical mixing and upwelling
Ocean, is located in the tropical monsoon zone between the equator and the Tropic of Cancer (Fig. 1a). The northern SCS connects to the Pacific Ocean in east through the Luzon Strait, and to the East China Sea in northeast through the Taiwan Strait, with wide continental shelf (Fig. 1a). The East Asian monsoon plays an important role in hydrological features and upper layer circulations of the SCS (Wyrtki, 1961; Lau and Li, 1984). Multi-time scale variations of monsoon over the SCS have direct influence on the hydrological conditions, therefore on the transport and distribution of nutrients, and ultimately on phytoplankton bloom (Ning et al., 2004; Wang Hui et al., 2008). The previous studies on phytoplankton bloom have been cond-
1 Introduction Marine phytoplankton, living nea
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