Weakening Indian Ocean carbon uptake in 2015: The role of amplified basin‐wide warming and reduced Indonesian throughflow

Abstract

In 2015, the Indian Ocean exhibits an exceptionally weakened CO₂ uptake, highlighting strong interannual variability of ocean carbon sink. By utilizing multiple ocean CO₂ partial pressure (pCO₂) data and a state‐of‐the‐art ocean biogeochemical model, we show that the 2015 ocean CO₂ anomaly is characterized by a basin‐wide amplification of ocean pCO₂, differing from ocean pCO₂ responses to other Indian Ocean Dipole events (e.g., 1997 and 2019). The distinct ocean pCO₂ anomaly is attributed to an amplified warming and an unprecedented weakening Indonesian Throughflow under the influence of co‐occurrence of positive IOD and extreme El Niño in 2015. The amplified warming drives higher ocean pCO₂ in the western and central Indian Ocean, while the ITF transports anomalously high ocean pCO₂ water from the Pacific Ocean to the southeastern Indian Ocean. This newly identified ocean carbon response provides deeper insights into the Indian Ocean carbon interannual variability.