Preprints
https://doi.org/10.5194/os-2020-26
https://doi.org/10.5194/os-2020-26

  02 Jun 2020

02 Jun 2020

Review status: this preprint was under review for the journal OS but the revision was not accepted.

The Influence of Turbulent Mixing on the Subsurface Chlorophyll Maximum Layer in the Northern South China Sea

Chenjing Shang1, Changrong Liang2,3, Guiying Chen2,3, and Yongli Gao4 Chenjing Shang et al.
  • 1Shenzhen Key Laboratory of Marine Bioresources and Eco-environmental Science, College of Life Science and Oceanography, Shenzhen University, Shenzhen 518060, PR China
  • 2State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
  • 3Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou 511458, China
  • 4Equipment Public Service Center, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China

Abstract. We present observations from deployments of a turbulent microstructure instrument and a CTD package in the northern South China Sea from April to May 2010. From these we determined the turbulent mixing (dissipation rate ε and diapycnal diffusivity κ), nutrients (phosphate, nitrate, and nitrite), nutrient fluxes, and chlorophyll a (Chl-a) in two transects (A and B). Transect A was located in region far away from the Luzon Strait where turbulent mixing in the upper 100 m was weak (κ~10−6–10−4 m2 s−1). Transect B was located in region near the Luzon Strait where the turbulent mixing in the upper 100 m was strong (κ~10−5–10−3 m2 s−1) due to the influence of the internal waves originating from the Luzon strait and the water intrusion from the western Pacific. In both transects, there was a thin subsurface chlorophyll maximum layer (SCML) (0.3–0.7 mg m−3) nested in the water column between ~50 and 100 m. The observations indicate that effects of turbulent mixing on the distributions of nutrient and Chl-a were different in different transects. In transect with weak turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water. Nutrients were sufficient to maintain a local SCML phytoplankton population and the SCML remained compact. In transect with strong turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water, which scatters the nutrients in the water column, and weakens and diffuses the SCML.

Chenjing Shang et al.

 
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Status: closed
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Chenjing Shang et al.

Chenjing Shang et al.

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Short summary
The South China Sea is characterized by abundant phytoplankton and energetic internal waves. The distribution of turbulent mixing is uneven in the South China Sea. It is not clear how turbulent mixing affects the distribution of nutrients and chlorophyll in the South China Sea. Investigating the impact of turbulent mixing on the distributions of nutrient and chlorophyll is important to understand the bio-dynamic process and improve the marine ecological model in the South China Sea.