Impact of Marine Heatwaves and Coldwaves on CO2 in the South China Sea

Global warming is increasing the frequency and intensity of marine heatwaves (MHWs) in the South China Sea, while marine cold waves (MCWs) occur intermittently. Both phenomena influence the air-sea CO2 flux (FCO2) at the air-sea interface. This study uses inversion and reanalysis data, along with FCO2 diagnostic methods, to assess their impact on FCO2 in the South China Sea from 2003 to 2019. The results show that MHWs enhance CO2 release (+0.016 mmol/m²/d), whereas MCWs reduce it (-0.14 mmol/m²/d). The variation in FCO2 is primarily controlled by the sea-air partial pressure difference (∆pCO2) during both MHWs and MCWs, with the surface seawater CO2 partial pressure (pCO2sea) being the main factor influencing ∆pCO2. Specifically, MHWs increase pCO2sea, thus increasing ∆pCO2, while MCWs decrease pCO2sea, lowering ∆pCO2. Additionally, temperature factors were the primary drivers of changes in pCO2sea during both MHWs and MCWs, with their impact gradually intensifying over time. The South China Sea serves not only as a representative of a low-latitude marginal sea but also as a "mini-ocean," making these findings valuable for broader oceanographic research.