Deep topographic barriers within the Indonesian seas

Abstract

Abstract Whereas at the surface and at thermocline depth the Indonesian throughflow can weave its way between basins towards the Indian Ocean on a quasi-horizontal plane, at greater depth numerous sills are encountered, resulting in circulation patterns governed by density-driven overflow processes. Pacific water spills over deep topographic barriers into the Sulawesi Sea and into the Seram and Banda seas. The western-most throughflow path flowing through Makassar Strait encounters shallower barriers than does the eastern path. The first barrier encountered by Pacific water directed towards Makassar Strait is the 1350-m deep Sangihe Ridge, providing access to the Sulawesi Sea. The 680-m deep Dewakang Sill separating the southern Makassar Strait from the Flores Sea is a more formidable barrier. Along the eastern path, Pacific water must flow over the 1940 m barrier of the Lifamatola Passage before passing into the deep levels of the Seram and Banda Seas. The deepest barrier encountered by both the western and eastern paths to the Indian Ocean is the 1300–1450 m (perhaps as deep as 1500 m) sill of the Sunda Arc near Timor. The Savu Sea while connected to the Banda Sea down to 2000 m depth, is closed to the Indian Ocean at a depth shallower than the Timor Sill. The density-driven overflows force upwelling of resident waters within the confines of the basins, which is balanced by diapycnal mixing, resulting in an exponential deep-water temperature profile. A scale depth (Z*=Kz/w) of 420–530 m is characteristic of the 300–1500 m depth range, with values closer to 600 m for the deeper water column. The upwelled water within the confines of the Banda Sea, once over the confining sill of the Sunda Arc, may contribute 1.8–2.3 Sv the interocean throughflow.