We used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the Red Sea in response to reduced sea level and modified atmospheric conditions during the Holocene. With Holocene sea level close to the modern level, the Red Sea was sensitive to changes in atmospheric conditions, and it only shows a relatively mild response to sea level change. Changes in the monsoon system influence the exchange flow through the Strait of Bab el Mandab, the meridional overturning circulation of the Red Sea, and its hydrography. Forced by humid conditions the (modeled) Red Sea temperature increased by ∼1.5C, while when arid conditions were imposed, the temperature decreased by ∼2.5C. Similar heating and cooling events during the early and late Holocene are seen in a sea surface temperature record from the northern Red Sea (derived from the temperature sensitive TEX86 molecular biomarker), which suggests that humid conditions prevailed during the early Holocene and more arid conditions prevailed during the late Holocene. The gradual decline in Red Sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength. This monsoon trend and the resulting changes in the Red Sea circulation are supported by the distribution of crenarchaea fossil lipids in Red Sea sediments from this period. Monsoon-driven changes in the exchange flow through the Strait of Bab el Mandab affected the crenarchaea population structure, and therefore, their molecular fossil distribution in the sediments of the Red Sea potentially provides an index for the summer monsoon strength during the Holocene.
Bibliographical noteFunding Information:
This work was supported by the European Research Council grant 647895 “GluActive”, the Deutsche Forschungsgemeinschaft ( German Research Foundation ) under Germany’s Excellence Strategy ( EXC-2049 – 390688087 ), and the Deutsche Forschungsgemeinschaft grants PL619/1-1 and PL 619/3-1 (to A.J.R.P.). H.S. was the recipient of a Long-Term Fellowship from Human Frontier Science Program.