Exploring the Climate-change induced dissolved inorganic carbon trends in the Indonesian Seas and their link to a changing Indonesian Throughflow using a regional downscaling of future climates

The Indonesian Seas act as a main pathway of water transport from the Pacific to the Indian Ocean, known as the Indonesian Throughflow (ITF). Climate-induced changes in the regional water properties within the Indonesian Seas could have extensive impacts on the large-scale ocean budgets, as the ITF will carry these signals from the Indonesian Seas across the Indian Ocean’s upper thermocline. Here, we investigate the impacts of climate change on the Indonesian Seas’ dissolved inorganic carbon (DIC) budget using a regional ocean physics/biogeochemistry model for South East Asia that downscales climate projections from an Earth System Model under the RCP 8.5 scenario. The regional model has a horizontal resolution of about 9 km, uses a hybrid depth-terrain following vertical coordinate system and explicitly includes tides so as to better resolve the shelf-seas processes. A transport-based framework is used to explore the role of climate-induced changes of the ITF on the carbon storage within the Indonesian Seas. Specifically, the DIC trends are separated into: (i) an “added contribution” associated with the uptake of additional carbon from the atmosphere due to carbon emissions, and (ii) a “dynamic redistribution” of the pre-existing ocean DIC associated with changes in the circulation due to climate change. Our analysis reveals that in the next decades, although carbon emissions will lead to an ocean carbon uptake and an increase in the DIC within the Indonesian Seas, a plausible climate-induced weakening in the ITF can lead to either an increase or a decrease in the DIC at different depths associated with different water masses. Hence, the effects of global carbon emissions on the carbon budget within the Indonesian Seas, and particularly whether local waters will experience a lower or higher increase in DIC than the rest of the ocean, are controlled by the dynamical redistribution associated with the response of the ITF to climate change.