Distributions of volatile halocarbons in the marine atmosphere and seawater of the northern South China Sea

Abstract

Concentrations of 4 volatile halocarbons (VHCs) in seawater and atmosphere of the Northern South China Sea (NSCS) were measured during summer 2015. Mean surface seawater concentrations of CH3I, CH3Br, CHBr3, and C2Cl4 were 2.0, 4.2, 15.7, and 12.5 pM, respectively; mean atmospheric concentrations were 0.4, 4.1, 8.0, and 7.2 ppt, respectively. The surface seawater concentrations of the 4 VHCs were significantly influenced by the coastal mixed water, South China Sea surface water, Kuroshio Current, and Qiongdong upwelling in summer, while atmospheric concentrations were affected by the prevailing southwest monsoon and terrigenous pollutants from the Southwest Asia region. Chl-a concentrations were positively correlated with CH3I and CHBr3, indicating that phytoplankton were an important source of these gases in the study area. The flux of the 4 VHCs showed that the NSCS was a net source to the atmospheric during the study period.