Multiple mechanisms for chlorophyll <i>a</i> concentration variations in coastal upwelling regions: a case study east of Hainan Island in the South China Sea
J. Li,
J. Li,
J. Li,
M. Li,
C. Wang,
Q. Zheng,
Q. Zheng,
Y. Xu,
T. Zhang,
L. Xie
Affiliations
J. Li
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
J. Li
College of Ocean and Meteorology, Key Laboratory of Climate,
Sources and Environments in Continent Shelf Sea and Deep Ocean, Zhanjiang,
China
J. Li
Key Laboratory of Space Ocean Remote Sensing and Application,
MNR, Beijing, China
M. Li
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
C. Wang
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
Q. Zheng
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
Q. Zheng
Department of Atmospheric and Oceanic Science, University of Maryland,
College Park, MD, USA
Y. Xu
Key Laboratory of Space Ocean Remote Sensing and Application,
MNR, Beijing, China
T. Zhang
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
L. Xie
College of Ocean and Meteorology, Laboratory of Coastal Ocean Variation and Disaster Prediction,
Guangdong Ocean University, Zhanjiang, China
Using satellite observations from 2003 to 2020 and cruise observations from 2019 and 2021, this study reveals an unexpected minor role of upwelling in seasonal and interannual variations in chlorophyll a (Chl a) concentrations in the coastal upwelling region east of Hainan Island (UEH) in the northwestern South China Sea (NWSCS). The results show strong seasonal and interannual variability in the Chl a concentration in the core upwelling area of the UEH. Different from the strongest upwelling in summer, the Chl a concentration in the UEH area reaches a maximum of 1.18 mg m−3 in autumn and winter, with a minimum value of 0.74 mg m−3 in summer. The Chl a concentration in summer increases to as high as 1.0 mg m−3 with weak upwelling, whereas the maximum Chl a concentration in October increases to 2.5 mg m−3. The analysis of environmental factors shows that, compared to the limited effects of upwelling, the along-shelf coastal current from the northern shelf and the increased precipitation are crucially important to the Chl a concentration variation in the study area. These results provide new insights for predicting marine productivity in upwelling areas, i.e., multiple mechanisms, especially horizontal advection, should be considered in addition to the upwelling process.
