Photo (above): Ningaloo coastline by Ben Carless (Unsplash)
The circulation of the South Indian Ocean modulates marine life and global climate through important oceanic teleconnections with the Pacific, Atlantic and Southern Oceans. Previous studies indicate robust future changes to these teleconnections, however, future changes to South Indian Ocean circulation across a range of models and the corresponding driving mechanisms are not well understood.
Therefore, in this study, we examine long-term annual and seasonal transport changes of South Indian Ocean circulation using an ensemble of 28 climate models. We also investigate if the projected changes are due to changes in wind forcing via Sverdrup dynamics or due to changes in oceanic teleconnections with the Pacific and SouthernOceans.
The models project that all circulation features of the South Indian Ocean, including the Leeuwin Current and Undercurrent, North and South East Madagascar Currents, transport through the Mozambique Channel and Agulhas Current are projected to weaken significantly in the last half of the 21st century with unchecked greenhouse gas emissions.
Changes to the meridional pressure gradient off the west coast of Australia, which drives the anomalously southward flowing Leeuwin Current, explain the weakening of onshore transport into the Leeuwin Current. While the alongshore pressure gradient change is consistent with projected weakening of the Indonesian Throughflow, we found no inter-model relationship between these changes.
In the south-western Indian Ocean, the weakening of western boundary transport is related to reduced Indonesian Throughflow transport from the Pacific in combination with a substantial decrease of deep-water flow entering the Indian Ocean from the Southern Ocean.
- Paper: Stellema, A., Sen Gupta, A. & Taschetto, A.S. Projected slow down of South Indian Ocean circulation. SciRep 9, 17705 (2019) doi:10.1038/s41598-019-54092-3