The Indonesian Throughflow, its characteristics, drivers, and impact on the Indian Ocean
Arnold L. Gordon*, Laura
Lamont-Doherty Earth Observatory of Columbia University
Lamont-Doherty Earth Observatory Palisades, New York, United States Pincode: 10964-8000 Mobile: 8455361731 E-mail: email@example.com
The Makassar Strait throughflow of ~12 Sv, representing ~80% of the total Indonesian Throughflow (ITF), displays fluctuations over a broad range of time scales, from intraseasonal (Madden Julian Oscillations, Rossby and Kelvin Waves); to seasonal and interannual (ENSO) scales, reflecting their connectivity with the larger scale ocean and climate systems. It is driven by the Pacific to Indian Ocean pressure gradient profile, with regional sea surface salinity playing a surprisingly large role in governing the volume and heat transport. Strong southward transport during boreal summer, modulated by ENSO interannual signal: weaker southward surface layer flow, mainly in winter; a deeper subsurface velocity maximum weaker/deeper during El Niño; stronger/shallower during La Niña: modulates ITF heat flux into the Indian Ocean. Once in the Indian Ocean the ITF spreads westward as a relatively cool/fresh plume within the South Equatorial Current (SEC) thermocline between 10°-15° S (capped in the eastern Indian Ocean by a low salinity surface layer drawn from the Bay of Bengal) reaching the western tropical Indian Ocean, which mostly advects southward, but a branch turns northward towards the Arabian Sea. A ITF component spreads southward along the west coast of Australia, within the Leeuwin Current, reaching into the subtropical gyre regime. The ratio of between the SEC and Leeuwin pathways varies with time, with potential consequences to the tropical Indian Ocean heat/freshwater inventories. By one pathway or another the ITF water must exit the Indian Ocean within the Agulhas Current, mostly leaking into the Atlantic, with some curling back within the Agulhas Retroflection, towards the Pacific Ocean.