Deep water circulation within the eastern Mediterranean Sea over the last 95 kyr: New insights from stable isotopes and benthic foraminiferal assemblages

Abstract

The response of eastern Mediterranean Sea (EMS) circulation to climate forcings over the last 95kyr BP was studied using core MD04-2722, collected at 1780m water depth within the Levantine Sea. Foraminiferal stable isotopes and benthic assemblages were combined in order to reconstruct deep water ventilation and oxygenation in relation to surface water freshening. Over the last deglaciation, benthic foraminiferal δ13C values and oxygen index decreased, while the δ18O gradient between benthic and planktonic foraminifera increased. The results, respectively, indicate slower ventilation, bottom water oxygen depletion, and stronger stratification prior to S1 sapropel deposition. A combination of deglacial sea level rise and fresher north Atlantic surface water contributions were determined to be a precondition for S1 formation within the Levantine Sea. Local Nile River freshwater supplied during the African Humid Period further strengthened water column stratification. As for S3 deposit, the central role of monsoonal precipitation was estimated. For the last glacial period, three events at around 53, 46 and 37ka BP were marked by a deep water circulation reduction at the core location. Considering the influence of north Atlantic surface water salinity on Mediterranean Sea circulation, we propose that the 46 and 37ka BP events are responses to Heinrich Events 4 and 5 that supplied fresher surface water to the Mediterranean Sea. Since the ‘53ka event’ was also characterized by the appearance of low oxygen benthic indicators as observed within the S1 and S3 layers, we tentatively attributed it to ‘missing’ sapropel S2. Our results indicate that intense stagnation within the EMS could occur when both the local freshwater supply and fresher north Atlantic surface water are contributors. The influence of north Atlantic conditions was significant to EMS circulation under warm and cold climate conditions.