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.