[A-OS16] Physical, biogeochemical, and ecological processes and variability in the Indian Ocean

[AOS16-P03] Characteristics of ITF bifurcation in the eastern Indian Ocean at the decadal timescale

*Hiroki Iwasa¹, Yukio Masumoto¹ (1.Graduate School of Science, The University of Tokyo)

Keywords:Indonesian throughflow, decadal variability, Indian Ocean

The Indonesian throughflow (ITF) connects the tropical Pacific and Indian Oceans and plays an important role in the regional circulation as well as the global thermohaline circulation. After the ITF enters the eastern Indian Ocean, a part of it flows to the west as the South Equatorial Current, and a remaining part of it flows to the south as the Leeuwin Current. Although there are many studies on the seasonal and interannual variability in these currents, which are associated with the monsoons and short-term climate modes, such as the El Nino/Southern Oscillation and the Indian Ocean Dipole events, our understanding on their variability at the decadal timescale is limited, particularly on the mechanism responsible for the ITF bifurcation into the South Equatorial Current and Leeuwin Current. The period of global warming hiatus in the first decade of the 21th century is one example of the significant decadal variability in the Indian Ocean, during which the eastern part of the southern subtropical Indian Ocean experienced unprecedented warming in the upper layer temperature. Further investigations of possible mechanisms of the ITF bifurcation at the decadal timescale are a key for better understanding of hiatus and decadal climate variations in the Indo-Pacific sector. This study, therefore, aims to clarify the characteristics of the ITF bifurcation at decadal timescale with a particular focus on the processes during the hiatus period. The ocean and atmosphere re-analysis data show that the relation between wind and ocean heat content, and ocean currents on decadal timescale in the eastern Indian Ocean. The wind stress along the Australian coast is more important than the offshore wind stress curl for the decadal variability of ocean heat content and ocean currents. The roles of mesoscale eddies in the mid-latitude region on the decadal variability are also discussed.