The Indonesian Throughflow: Its Place in the Global Ocean and Climate Systems (Invited Presentation)

The seas of the Maritime Continent (MC), including those of Indonesia, are gateways, providing as “Oceanic Tunnel”, for interaction between the Pacific and Indian Oceans. A time series of the Makassar Strait throughflow, accounting for ~80% of the average total ITF, spanning the period (with gaps) 1996-2017, reveals various attributes of the ITF and its links to the larger scale. The Indonesian Throughflow (ITF), with an upper thermocline velocity maximum, hence less heat flux than expected from the previously assumed warm surface intensified ITF, transfers ~15 Sv of Pacific water into the Indian Ocean. The ITF T/S and velocity profiles are drawn from the varied pathways from the North and South Pacific Oceans, governed by the large scale wind field, delivering heat and freshwater to the Indian Ocean. Fluctuations are evident, spanning from intraseasonal (Kelvin and Rossby Waves), seasonal (wet and dry monsoonal phases), to interannual (ENSO) scales. Archived data and proxy data (coral based timeseries) point to the existence of longer scales (decadal, century and beyond). But there is more than just the ITF linking the two oceans- there is the "Atmospheric Bridge". Convection over the MC, defines the ascending branch of the Walker Circulation that varies with ENSO; there are large meridional, seasonal shifts of the ITCZ, linked to the Asian-Australian monsoon; and there are intraseasonal Madden-Julian Oscillations (MJO). The reach and strength of eastward propagationof the MJO transecting the MC into the tropical Pacific, of importance to triggering ENSO phases, are influenced by the sea surface temperature and stratification of the upper layers of the Indonesian Seas. The “Oceanic Tunnel” and "Atmospheric Bridge" are partners in the ocean and climate system. The ITF mass, heat and freshwater signal spreads across the Indian Ocean and decades later, feed into the Agulhas leakage, impacting the Atlantic Meridional Overturning Cell (AMOC), as part of a global thermohaline circulation.