Comparison of Holocene and Last Interglacial sapropels in the Gulf of Sirte (eastern Mediterranean)

The Mediterranean thermohaline circulation is sensitive to ongoing climate change and generally stagnant circulation is expected by the end of the 21^st century. In the past, the eastern Mediterranean Sea has experienced slower ventilation as demonstrated by rhythmic occurrence of organic-rich sediments “sapropels”. The two sapropels S1 (Holocene) and S5 (Last Interglacial) were formed under conditions of excess fresh water inputs via Nile river in relation to insolation-driven African monsoon intensification and deglacial meltwater inputs from the North Atlantic. In addition to the Nile river discharge, the paleodrainage toward Gulf of Sirte off Libya has been proposed although its contribution could be significantly different between S1 and S5 because of distinct monsoon intensification. Since the response of circulation to freshwater forcing could vary with the region of perturbation, comparison of S1 and S5 deposited in the Gulf of Sirte will provide key information on the Mediterranean ventilation sensitivity.

We applied a multi-proxy approach (bulk elemental composition by XRF scanning, redox sensitive elemental concentration, planktonic foraminiferal δ¹⁸O and benthic foraminiferal faunal assemblages) to core SL95 (32º46.46N, 19º11.46E; 1390 m water depth) from the eastern side of the Gulf of Sirte. Both S1 and S5 are marked by prominent peaks of Ba/Al and Ba/Ti with more pronounced Ba enrichment for S5. Redox sensitive elements such as U and Mo present enrichment prior to the Ba peaks that can be interpreted as reduced ventilation before sapropel deposition. However, expected reduced oxygenation is not synchronous with benthic foraminiferal faunal changes, suggesting possible remobilisation of the trace elements during sapropel interruption and/or post-sapropel oxygenation. Acquisition of high-temporal resolution data of Globigerinoides ruber δ¹⁸O and benthic foraminiferal assemblages is in progress. We will discuss potential influence of (partial) ventilation at intermediate water depths during sapropel interruption in association with 8.2 event and possible different freshwater inputs at S1 and S5 depositions.