Exceptional decrease of Indian Ocean carbon uptake in 2015-2016 due to a remote effect of El Niño

The Indian Ocean experienced an extremely anomalous carbon flux with a magnitude of 0.1 PgC/yr in 2015-2016 according two pCO₂-based data products and MOM6 model simulations. However, the Indian Ocean Dipole (IOD) climate mode cannot well explain the anomalous interannual variability. We show that the Indian Ocean carbon flux anomaly is remotely driven by the extreme 2015-2016 El Niño which is the strongest El Niño in the 21st century. The El Niño is able to drive a basin-scale warming and high dissolved inorganic carbon (DIC) anomaly in the southeastern tropical Indian Ocean which increase ocean pCO2 and weaken the ocean carbon sink in the Indian Ocean. The basin-scale warming is induced by a more shortwave radiation and less latent heat flux loss in the Indian Ocean which is originated from El Niño through cloud-radiation-SST feedback and wind-evaporation-SST (WES) feedback. The high DIC in the southeastern tropical Indian Ocean is induced by a less dilution of weakened the fresh Indonesia Through Flow (ITF) and reduced freshwater flux associated with El Niño. The ocean carbon response to El Niño remote effect is different from IOD. This study complements the understanding of air-sea CO2 flux interannual variability in the Indian Ocean.