Journal of Tropical Oceanography ›› 2018, Vol. 37 ›› Issue (5): 62-73.doi: 10.11978/2017121CSTR: 32234.14.2017121

Special Issue: 南海专题

• Orginal Article • Previous Articles     Next Articles

Vertical variability of chlorophyll a concentration and its responses to hydrodynamic processes in the northeastern South China Sea in summer

Wenlong XU1,2(), Guifen WANG1,3(), Wen ZHOU1, Zhantang XU1, Wenxi CAO1   

  1. 1. State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences), Guangzhou 510301, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    3. College of Oceanography, Hohai University, Nanjing 210098, China;
  • Received:2017-11-10 Revised:2018-03-07 Online:2018-09-20 Published:2018-10-13
  • Supported by:
    National Natural Science Foundation of China (41776045, 41376042, 41576030, 41776044);Open Project Program of the State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences) (LTOZZ1602)

Abstract:

Chlorophyll a (Chla) concentration is an important indicator of phytoplankton biomass for estimating primary production, which exhibits inhomogeneous vertical distribution. In this study, optical measurements with high vertical resolution were used for studying the spatio-temporal variability of Chla profiles and its influencing mechanism, providing us much insights for understanding marine environmental dynamics in the South China Sea. In this study, an optical inversion method was proposed to retrieve Chla profiles from in situ measurements with high-spectral absorption/attenuation spectrophotometer in the northeastern South China Sea. Based on the in situ data of the Kuroshio Cruise in summer 2015, an empirical relationship between the absorption line height at 676 nm and Chla was developed for inverting Chla with a high accuracy (Chla=49.96×(aLH(676) (676))0.9339, the coefficient of determination R2=0.87, the root mean square error RMSE=0.16 mg·m-3). Moreover, the response characteristics of Chla profiles to different hydrodynamic processes were studied. Results showed that large spatial differences existed in the vertical distribution of Chla. In the nearshore area, surface Chla varied from 0.42 to 1.57 mg·m-3, which generally followed a decreasing trend with depth. Uniform vertical distribution of Chla in upper ocean was observed in the coastal upwelling region. The Subsurface Chlorophyll Maximum (SCM) layer is nearly ubiquitous in stratified waters of the open ocean, with its vertical structure being influenced by mesoscale processes. The depth of SCM ranged between 34 and 100 m, which showed consistent variability with the isopycnal depth of 1023 kg·m-3. The SCM layer was uplifted to about 34 m due to the mixing effect in the upper ocean caused by Kuroshio intrusion in the western area of Luzon Island. The uplifting and widening of the SCM layer were also observed in the area affected by a cold eddy, with obviously different features in the eddy center from that on the eddy edge.

Key words: the northeastern South China Sea, vertical distribution of chlorophyll a concentration, Subsurface Chlorophyll Maximum, absorption line height, hydrodynamic processes

CLC Number: 

  • P733.3