scholarly journals Referee comments on The Influence of Turbulent Mixing on the Subsurface Chlorophyll Maximum Layer in the Northern South China Sea by authors: Chenjing Shang et al. MS No.: os-2020-26

2020 ◽  
Author(s):  
Anonymous
Keyword(s):  
South China Sea ◽  
South China ◽  
Turbulent Mixing ◽  
Northern South China Sea ◽  
China Sea ◽  
Chlorophyll Maximum ◽  
Subsurface Chlorophyll Maximum

scholarly journals Spatial distribution of the summer subsurface chlorophyll maximum in the North South China Sea

PLoS ONE ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. e0248715
Author(s):  
Ying Chen ◽  
Hui Zhao
Keyword(s):  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Light Attenuation ◽  
Masking Effect ◽  
Light Limitation ◽  
China Sea ◽  
Chlorophyll Maximum ◽  
Subsurface Chlorophyll Maximum ◽  
Nutrients Concentration

Based on the biological, nutrients and hydrological data in August 2018, the vertical chlorophyll a (Chl-a) concentration profiles and the relationship among surface Chl-a (Chl-a(0)) concentration, maximum Chl-a (Chl-a(m)) concentration and depth-integrated Chl-a (Chl-a(int)) concentration were studied in the Northern South China Sea (NSCS). The results indicate that there are 4 different patterns in the vertical Chl-a profiles in the NSCS: (i) Chl-a increases with depth from the surface (e.g. station 1); (ii) there exists subsurface chlorophyll maximum (SCM), with low Chl-a on the surface and at the bottom layers respectively (e.g. station 5); (iii) there is no SCM, only with high Chl-a on the surface and in the bottom (e.g. station 14); (iv) the 4th pattern is similar to (ii), with the higher Chl-a(0) (e.g. station 28). The SCM is observed at 95% stations in the NSCS and is not detected only at a few stations near the Pearl River (PR) estuary. These patterns are mainly regulated by alternative limitation of nutrients and light from the surface to the bottom of euphotic layer. For the pattern 1 (e.g. station 1), light is not a limited factor, and Chl-a and nutrients increase with depth. The pattern 2 (e.g. station 5) exists with the limitation of surface nutrients in offshore region. The nutrients increases with depth and the nutrients limitation turns to light limitation gradually from surface to bottom. And the SCM appears in the layer which need of the light and nutrients is roughly equivalent. Compared with that the offshore SCM, the nutrients for the pattern 3 (e.g. station 14) are rich on the surface with nutrients concentration and light irradiance. Therefore, it is seawater intrusion from the bottom that brings the higher nutrients concentration. The reason for the high Chl-a(0) on the pattern 4 (e.g. station 28) is terrestrial matter from the nearshore. High correlation (R2 = 0.5206, p<0.01) between the depth of SCM (Depth(m)) and Chl-a(0) indicates that the SCM depth is regulated by light masking effect of surface phytoplankton, generally with shallow nutriclines and fast light attenuation for high Chl-a(0) and vice versa low Chl-a(0) brings deeper nutriclines and light attenuate slowly with less shading effect. Further research results shows that Chl-a(int) and Chl-a(m) have a good correlation(R2 = 0.6397, p<0.01). However, the correlation between Chl-a(int) and Chl-a(0) is relative weak (R2 = 0.3202, p<0.01). That could be attributed to the availability of nutrients playing an important role in growth of phytoplankton, with high nutrients at upper euphotic layers for the stations with high Chl-a(0).

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

2020 ◽  
Author(s):  
Chenjing Shang ◽  
Changrong Liang ◽  
Guiying Chen ◽  
Yongli Gao
Keyword(s):  
South China Sea ◽  
Water Column ◽  
South China ◽  
Turbulent Mixing ◽  
Northern South China Sea ◽  
Luzon Strait ◽  
Nutrient Fluxes ◽  
Chl A ◽  
China Sea ◽  
Subsurface Chlorophyll Maximum

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.

Spatial structure of turbulent mixing of an anticyclonic mesoscale eddy in the northern South China Sea

2020 ◽  
Vol 39 (11) ◽  
pp. 69-81
Author(s):  
Yongfeng Qi ◽  
Chenjing Shang ◽  
Huabin Mao ◽  
Chunhua Qiu ◽  
Changrong Liang ◽  
...  
Keyword(s):  
South China Sea ◽  
Spatial Structure ◽  
South China ◽  
Turbulent Mixing ◽  
Northern South China Sea ◽  
Mesoscale Eddy ◽  
China Sea

scholarly journals Elevated Mixing in the Periphery of Mesoscale Eddies in the South China Sea

2017 ◽  
Vol 47 (4) ◽  
pp. 895-907 ◽  
Author(s):  
Qingxuan Yang ◽  
Wei Zhao ◽  
Xinfeng Liang ◽  
Jihai Dong ◽  
Jiwei Tian
Keyword(s):  
Kinetic Energy ◽  
South China Sea ◽  
South China ◽  
Turbulent Mixing ◽  
Field Experiments ◽  
Northern South China Sea ◽  
Mesoscale Eddies ◽  
China Sea ◽  
Mesoscale Dynamics ◽  
Forward Energy

AbstractDirect microstructure observations across three warm mesoscale eddies were conducted in the northern South China Sea during the field experiments in July 2007, December 2013, and January 2014, respectively, along with finestructure measurements. An important finding was that turbulent mixing in the mixed layer was considerably elevated in the periphery of each of these eddies, with a mixing level 5–7 times higher than that in the eddy center. To explore the mechanism behind the high mixing level, this study carried out analyses of the horizontal wavenumber spectrum of velocities and spectral fluxes of kinetic energy. Spectral slopes showed a power law of k−2 in the eddy periphery and of k−3 in the eddy center, consistent with the result that the kinetic energy of submesoscale motion in the eddy periphery was more greatly energized than that in the center. Spectral fluxes of kinetic energy also revealed a forward energy cascade toward smaller scales at the wavelength of kilometers in the eddy periphery. This study illustrated a possible route for energy cascading from balanced mesoscale dynamics to unbalanced submesoscale behavior, which eventually furnished turbulent mixing in the upper ocean.

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