30 Sep 2022
30 Sep 2022

Multiple mechanisms for chlorophyll-a concentration variations in coastal upwelling regions: A case study east of Hainan Island in the South China Sea

Junyi Li1,2,3, Min Li1, Chao Wang1, Quanan Zheng1,4, Ying Xu3, Tianyu Zhang1, and Lingling Xie1 Junyi Li et al.
  • 1Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
  • 2Key Laboratory of Climate, Sources and Environments in Continent Shelf Sea and Deep Ocean, Zhanjiang 524088, China
  • 3Key Laboratory of Space Ocean Remote Sensing and Application, MNR, Beijing, 100081, China
  • 4Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742, USA

Abstract. Using satellite observations from 2003 to 2020 and cruise observations in 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 summer Chl-a concentration increases to as high as 1.0 mg m−3 with weak upwelling during El Niño years, whereas the maximum Chl-a concentration in October increases to 2.5 mg m−3 during La Niña years. 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.

Junyi Li et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-969', Anonymous Referee #1, 31 Oct 2022
  • RC2: 'Comment on egusphere-2022-969', Manuel Vargas-Yáñez, 03 Nov 2022

Junyi Li et al.

Junyi Li et al.


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Short summary
This study reports existence of relatively low productivity area of upwelling east of Hainan Island (UEH), which is inconsistent with previous cognition. The reason for this phenomenon is the crucial role of the Guangdong Coastal Current and precipitation. The current and precipitation would induce a high productivity, which is interrupted by the upwelling processes. Therefore, the upwelling has a relatively limited effect on the Chl-a concentration in the UEH area.