PATHWAYS OF WATER BETWEEN THE PACIFIC AND INDIAN OCEANS IN THE INDONESIAN SEAS

THE physical structure of the Pacific and Indian oceans is substantial ly affected by the inter-ocean transport of excess fresh water from th e North Pacific Ocean through the Indonesian seas(1,2). The efficiency of this transport is an important regulator of the meridional overtur ning of these oceans(1,2), and hence perhaps of the global thermohalin e circulation(3); in addition the seepage of warm water out of the Pac ific affects the volume of the western Pacific warm pool, and thus may influence El Nino events(24). But the sources, pathways and physical properties of the Indonesian throughflow are not well enough character ized to allow its influence on ocean circulation and the climate syste m to be quantified. Here we report salinity, temperature and chemical- tracer data from the Indonesian seas which show that the throughflow i s dominated by two components: one of low-salinity, well ventilated No rth Pacific water through the upper thermocline of the Makassar Strait , and the other of more saline South Pacific water through the lower t hermocline of the eastern Indonesian seas. Seasonal (monosonal) variat ions in the ratio of these components, perhaps modulated by El Nino co nditions, imply the existence of potentially important variable feedba cks to the ocean circulation and climate system.