Journal of Tropical Oceanography ›› 2022, Vol. 41 ›› Issue (1): 106-116.doi: 10.11978/2021030CSTR: 32234.14.2021030

• Marine Meteorology • Previous Articles     Next Articles

Multi-linear regression of partial pressure of sea-surface carbon dioxide in the South China Sea and its mechanism

QIU Shuang1,2(), YE Haijun1,3, ZHANG Yuhong1,2,3(), TANG Shilin1,2,3   

  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. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
  • Received:2021-03-04 Revised:2021-04-08 Online:2022-01-10 Published:2021-04-29
  • Contact: ZHANG Yuhong E-mail:qasisqius@163.com;zhangyuhong@scsio.ac.cn
  • Supported by:
    Strategic Priority Research Program of the Chinese Academy of Sciences(XDA13010404);National Natural Science Foundation of China(41806146);National Natural Science Foundation of China(41976024);National Natural Science Foundation of China(41830538);Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)(GML2019ZD0302);Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)(GML2019ZD0303);“Guangdong TeZhi Plan” Local Innovation and Entrepreneurship Team(2019BT02H594)

Abstract:

The partial pressure of carbon dioxide (pCO2) refers to the content of CO2 gas at the sea surface when the CO2 exchange between the sea surface and atmosphere is in dynamic equilibrium, which is an important factor to calculate air-sea CO2 flux. Based on the observations of pCO2 covering most of the South China Sea (SCS) from 2008 to 2014, combined with in-situ observations of sea-surface temperature (SST), sea-surface salinity (SSS) and Modis-Aqua satellite observations of chlorophyll a (Chla), we construct a regional inversion of sea-surface pCO2 based on a multi-linear regression method. The root mean square error is estimated to be 5.3 μatm in the area with depth shallower than 30 m, and 10.8 μatm in the remaining sea area, which are consistent with previous results based on cruise observations. Using the equation acquired from our method and combining with the HYbrid Coordinate Ocean Model (HYCOM) reanalysis SST and SSS data and MODIS-Aqua remote sensing Chla data, we obtained monthly sea-surface pCO2 of the SCS from 2004 to 2016 with spatial resolution of 5'×5'. The data can well reflect the seasonal variation of sea-surface pCO2 in the SCS under the influence of SST, which is high in spring and summer, and low in autumn and winter. These findings are similar to previous results based on cruise observations, indicating our method has rather high reliability. Further analysis shows the average sea-surface pCO2 of the SCS and adjacent sea areas has a significant quasi-decadal oscillation: a minimum value appeared around 2011, which first showed a decreasing trend and then an increasing trend. Due to the influence of sea-surface pCO2, the average air-sea CO2 flux in the SCS and adjacent areas decreased significantly before 2012, and changed into negative values during winter, then changed slowly since 2012. The variation of SSS in the SCS caused by the Pacific Decadal Oscillation is the main reason for the quasi-decadal oscillation of sea-surface pCO2 and air-sea CO2 fluxes. Our results indicate the variation of sea-surface pCO2 in the northern SCS is the most significant, which plays an important role in the seasonal and quasi-decadal oscillation of pCO2 in the whole area.

Key words: South China Sea, sea-surface pCO2 inversion, air-sea CO2 flux, sea-surface salinity, quasi-decadal oscillation

CLC Number: 

  • P732.6