Changes in the deep-water masses of the Eastern Mediterranean Sea during the last interglacial maximum - New constraints from neodymium isotopes in foraminifera

Abstract

The thermohaline circulation of the Mediterranean Sea was a key factor in the development of sapropel layers in the Eastern Mediterranean Sea (EMS). Sapropel formation is linked to stagnant deep-water conditions and/or increased sea surface productivity during boreal summer insolation maximum. However, debates persist regarding the complex interplay between high and low latitude climatic processes, circulation dynamics, and sapropel formation. Analyses of major and trace elements by XRF, δ¹⁸O of planktonic foraminifera, and neodymium isotopes (εNd) of foraminifera have been carried out on two cores collected in the southeastern Aegean Sea of the EMS and in the Sardinia Channel of the Western Mediterranean Sea (WMS), in order to constrain deep-water mass circulation during the last glacial-interglacial cycle (i.e. the past ∼150 ka), focusing on the last interglacial maximum. When combined with previous εNd records from the EMS, we identified two regional patterns of the εNd variations during the sapropel S5 interval (∼128-120 ka), suggesting that the initial freshwater influx from North Africa led to marked water stratification, limited deep-water formation, and shifted foraminiferal εNd towards a local signature due to an extended period of Nd exchange between seawater and marginal sediments. Cores strongly influenced from the Nile River discharge display radiogenic εNd values (−3.7), whereas those from the northern EMS exhibit more unradiogenic εNd values (−5.1). As S5 progressed, εNd records of all cores from the Levantine basin indicate a slight mixing of deep-water masses accompanied by a decrease in the εNd gradient between the northern and southern EMS. This was associated with the global decrease in temperature and reduced Nile River water input, which supported a slight deep-water recirculation from the Aegean Sea. This active circulation conveyed radiogenic εNd from the southern EMS to the north and the Western Mediterranean Sea. Overall, our new results suggest that hydrological conditions in Mediterranean Sea fluctuated during the S5 deposition, with a slight recirculation of Aegean deep-water in a pre-stage before the complete recovery of circulation in the EMS at the end of the sapropel S5 deposition.