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A 10-fold decline in the Eastern Mediterranean thermocline overturning circulation during the last interglacial period

Andersen, Morten, Matthews, A, Vance, D, Bar-Matthews, M., Archer, C and Souza, G de 2018. A 10-fold decline in the Eastern Mediterranean thermocline overturning circulation during the last interglacial period. Earth and Planetary Science Letters 503 , pp. 58-67. 10.1016/j.epsl.2018.09.013

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Abstract

Present-day Mediterranean deep-waters are well oxygenated, but the episodic formation of organic-rich sediments (sapropels) indicates that this pattern was frequently perturbed in the past. Both high export productivity and disruption of the thermohaline circulation, leading to reduced deep-water ventilation, have been proposed to account for sapropel deposition and anoxia. The last interglacial sapropel S5 is considered one of the most strongly developed. Here, we apply the redox-sensitive Mo and U (elemental and isotope) systems to quantify the intensity of anoxic deep-water conditions in the Eastern Mediterranean Sea from ODP core 967 (2550 mbsl). Both U and Mo show strong authigenic enrichment, coupled to progressive increase in δ98Moauth (+1.2–1.8‰ to +2.0–2.3‰) and decrease in δ238Uauth (+0.10‰ to −0.15‰) from the beginning to the end of S5, suggesting increasing water column euxinia and removal fluxes of Mo and U. Based on modern euxinic basins, we show that sedimentary Uauth can be used to derive estimates of water column U depletion and, ultimately, deep-water renewal rates. These principles are first tested on the modern Black Sea, which yields calculated deep-water renewal times of 830+690/−500 yrs, in good agreement with independent estimates. Applying these principles to the end of S5 suggests bottom-water U depletion of ∼50% and deep-water renewal times of 1030+820/−520 yrs. The significantly slower deep-water renewal rates in the Eastern Mediterranean Sea compared to today (∼100 yrs) would have played an important role in the formation of sapropel S5 and are consistent with the proposed suppression of overturning during the last interglacial, due to increased stratification resulting from higher riverine freshwater input under enhanced monsoon forcing.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Elsevier
ISSN: 0012-821X
Date of First Compliant Deposit: 24 September 2018
Date of Acceptance: 11 September 2018
Last Modified: 19 Oct 2019 13:40
URI: http://orca.cf.ac.uk/id/eprint/115189

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