Abstract Between 10 and 6 ka, one of the most devastating ecological events for marine life was occurring as the well-ventilated, oxygen-rich glacial eastern Mediterranean deep waters had turned into a dead zone and organic matter accumulated in thick sediment layers, called sapropels. Numerous hypotheses on sapropel formation have been put forward, but a thorough evaluation of the potential drivers is yet missing. Our numerical modelling study, from the Last Glacial Maximum to the Holocene, captures the onset and termination of sapropel formation S1. The predominant driver is the surface water buoyancy gain due to sea-level rise and surface warming during the deglaciation, which reduces ventilation and consequently causes a substantial oxygen decline at depth. During the African Humid Period, enhanced nutrient supply and continued low microbial activity in cold waters, where remineralisation occurs at greater depths, result in anoxia and S1 forms. Despite prevailing poor ventilation of the deep sea and continued high nutrient supply, S1 terminates at 7 ka due to higher microbial activity in a warming ocean, which curtails the flux of organic matter to depths.
Six et al. (Wed,) studied this question.