Spatiotemporal variations and controlling factors of the surface pCO2 in the northern South China Sea

Abstract

The focal area of this study was the northern South China Sea (NSCS; 18.5°-22.5°N, 1.0°-8.0°E), located on the northwestern shelf of the SCS. The surface pCO2 (pCO2w), sea surface temperature (SST) and sea surface salinity (SSS) was measured by continuous measurement system during four field surveys to show their spatiotemporal variations in the NSCS. Low pCO2w in the southwestern region of PRE were observed in four seasons, particularly in spring and summer. The Pearl River diluted water (PRDW) discharged a large amount of nutrients into nearshore waters, which promoted phytoplankton propagation and CO2 uptake in spring and summer. On the contrary, primary productivity was low in winter and late autumn, runoff input of dissolved inorganic carbon (DIC) played important role in increasing the pCO2 in nearshore waters, so the PRDW controlled the spatiotemporal variations of pCO2w in the coastal and inner shelf. The pCO2w in the outer shelf and slope were relatively high in four seasons, and SST was the critical controlling factor of pCO2w, sea-air CO2 exchange also played role in the seasonal scales of pCO2w, the impact of weather and climate events on the variations of pCO2w and sea-air CO2 flux in the short term also were remarkable. Generally, the NSCS acted as sink of atmospheric CO2 in spring, late autumn and winter, particularly in latter two seasons, in contrast, it was weak CO21 source in summer.