Seasonal to interannual variabilities of sea–air CO₂ exchange across Tropical Maritime Continent indicated by eddy–permitting coupled OGCM experiment

Abstract. The lack of long–term observational data has limited research on sea–air CO₂ exchange variabilities in the Tropical Maritime Continent (TMC). To address the issue, we utilized a three–dimensional high–resolution physical–biogeochemical ocean numerical model and applied it to simulate sea–air CO₂ exchange in the region over the last decade (2010–2019). Some key features like atmospheric CO₂ source signature and high sea surface pCO₂ environment inside the TMC were captured by the model. Within the TMC, model results indicated strong CO₂ degassing along the south of Java associated with the seasonal cycle of the upwelling system. Abundant supply of inorganic carbon during upwelling season and strong wind speed results in CO₂ degassing that could reach as high as 30 gC m^–2 year^–1 around the area. In addition to the region acting as a full–year atmospheric CO₂ source, the TMC also exhibited interannual modulation in both sea–air CO₂ flux and sea surface pCO₂ which can be related to the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Large–scale anomalous strong CO₂ degassing and high sea surface pCO₂ from 2015 to 2016 in response to the 2015/2016 El Niño evolution was observed and dominated by modulation within the TMC. It is further found that modulation of CO₂ degassing related to IOD were confined along the west of south of Java with a higher magnitude compared with anomalies related to ENSO which shows larger spatial scale but lower in the magnitude. Study conducted here may provide insight about possible variabilities of sea–air CO₂ exchange in the area that still poorly represented in many global–scale modelling and reconstruction efforts.