Dual overflows into the deep Sulu Sea

Abstract

[1] The Sulu Sea, isolated from the neighboring ocean below 570 m, is nearly isothermal below 1250 m but with a marked salinity increase with depth. The source of the deep Sulu Sea water has been attributed to South China Sea water overflowing the 570 m topographic sill of Panay Strait. However, the Panay overflow (estimated as 0.32 × 106 m3/sec) is an unlikely source for the saltier water Sulu Sea deep water. We propose that deep Sulu Sea ventilation is derived from the south, from the Sulawesi Sea through Sibutu Passage. Sulawesi Sea water between 245 to 527 m, is mixed and heaved over the Sibutu Passage 234 m sill by the energetic tidal environment. Oxygen concentrations within the deep Sulu Sea suggest that the Sulawesi overflow is 0.15 × 106 m3/sec, with a residence time of Sulu Sea deep water of 60 years. The deep tropical Sulu Sea has the unique distinction of being ventilated from two separate sources, whose ratio may fluctuate across a range of temporal scales, associated with regional thermocline depth changes.