Imprints of high-salinity water plumes originating from the red sea during termination II

The investigation of a core collected in the Socotran area (western Indian Ocean) provides new insights into water mass exchanges between the Red Sea and the Gulf of Aden through the strait of Bab el Mandeb during the penultimate deglaciation. The benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea-level rise. Plumes of warm and salty waters are recorded at the surface of the Arabian Sea and as far as the Socotran coast for each increase in sea-level. These plumes disappeared whenever global sea-level stopped rising, or showed a brief lowering. According to their high salinities, these plumes can only originate in the Red Sea. The sill of Bab el Mandeb, becoming deeper and wider during the deglaciation, allowed greater exchange between both seas, and stronger flow out of the Red Sea at each episode of sea level rise. Isotopic and faunal evidence suggest a strengthening of coastal upwelling in the Arabian Sea during these periods. This increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface. Moreover, the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column. The occurrence of at least high salinity salty water outflows during Termination II confirms the step-wise, non-linear structure of the penultimate deglaciation, providing a perfect example of the threshold concept in rapid climate changes.