Simulating the Occurrence of the Last Sapropel Event (S1): Mediterranean Basin Ocean Dynamics Simulations Using Nd Isotopic Composition Modeling

Sapropels are sediments rich in black, pelagic organic matter which occur mainly in the Eastern Mediterranean, documenting anoxic environments and high biological productivity. The quasiperiodicity of deposition of sapropels -over millions of years- relates to the Earth's precession cycle, which directly enhances the African monsoon, ultimately increasing freshwater input from the Nile. The last sapropel event, S1, occurred about 10,000 years ago (Early Holocene), when the Mediterranean region was warmer and wetter than today. Several modeling studies reflect the impact of this climate and a stronger Nile influx on Mediterranean oceanic circulation, but the regional models used lacked the spatial resolution necessary to simulate winter intermediate and deep convection. Here, we investigate recently occurring changes in the convective areas in the Eastern Mediterranean, using a regional ocean–atmosphere coupled climate model of high spatial resolution, essential to the simulation of a realistic Mediterranean circulation for present-day conditions. We focused on the thermohaline circulation and the simulation of neodymium isotopic composition to compare our modeling results to modern data and paleo-proxies. A sensitivity experiment shows a radical response of the Mediterranean to enhanced Nile discharge, creating the appropriate conditions for sapropel formation. We thus demonstrate that increased discharge of the Nile River can trigger the shutdown of Eastern Mediterranean convection and create conditions favorable to the development of anoxic events.