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Evidence for the Presence of Oxygen-Depleted Sapropel Intermediate Water across the Eastern Mediterranean during Sapropel S1

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posted on 27.08.2019, 17:40 by Eleen Zirks, Michael D. Krom, Dongdong Zhu, Gerhard Schmiedl, Beverly N. Goodman-Tchernov
In the Eastern Mediterranean Sea (EMS), natural climate-driven changes that impacted its physical circulation and created deep-water anoxia have led to periods of distinctive deposits referred to as sapropels. The most recent sapropel event (S1) occurred between ∼6 and 10.8 kyr BP. Use of a global climate model has suggested that there was a previously unrecognized mid-depth (500–1800 m) water mass present at that time. Here, a broad review of cores previously analyzed from across the EMS was undertaken to determine if the field evidence was compatible with the presence of this intermediate water mass. The proxy records document a widespread oxygenated interruption centered around 8.2 ka BP in water depths between 500 and 1800 m, but not present in shallower or deeper water. We attribute this pattern to the formation and spread of a water mass, which we refer to as Sapropel Intermediate Water (SIW). It is shown that this water mass was formed in the Aegean Sea and became more depleted in oxygen, to anoxicity but not euxinicity, as it flowed west to the Adriatic and east across the Levantine basin. The rate of formation and flow of this water mass was estimated to be slow but not zero. An evolving oxygen minimum zone in the SE Levantine basin is posited where oxygen was depleted first in shallower water and expanded with time into deeper water. The presence of SIW obviates the need for the previously suggested thin anoxic blanket, since the 1300 m-thick SIW can be fully deoxygenated in 200–500 years.

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