Red Sea outflow during the last glacial maximum

Abstract

Abstract The Red Sea is connected to the Gulf of Aden, and hence to the Arabian Sea, via the Strait of Bab-el-Mandab, which is only about 20 km wide and 300 m deep. The shallowest part of the passage, however, lies about 140 km further basin-inward, near greater Hanish Island. That passage is only 137 m deep, while the channel deeper than 120 m is only 11 km wide. Foraminiferal and isotopic studies suggest that the inflow-outflow salinity contrast at Bab-el-Mandab was about 10‰ during the Last Glacial Maximum (LGM), compared with 3.1‰ at present. Calculation of maximal outflow during the LGM suggests that it was about 14% of the present-day value, while the density of this outflow was around 1035 kg m −3 , compared to the modern value of about 1029 kg m −3 . Therefore, it seems very likely that this outflow played no role of importance in the intermediate water ventilation of the Arabian Sea during the LGM. The Persian Gulf influence on this ventilation may be excluded as well, since the very shallow Persian Gulf was completely above sea level during the LGM. It is anticipated that, among other influences, LGM curtailment of these sources for intermediate depth ventilation should be reflected in the intensity and extent of the Oxygen Minimum Zone (OMZ) in the Arabian Sea. Other sources may have become important, such as northward penetration of Antarctic Intermediate Water. The Institute for Paleoenvironment and Paleoclimate Utrecht has recently participated in the 1992 Netherlands Indian Ocean Expedition, with the intention to determine Late Quaternary variations in the intensity and extent of the Arabian Sea OMZ in transects of cores recovered across its lower dept limit.