TY - JOUR
T1 - A 10-fold decline in the deep Eastern Mediterranean thermohaline overturning circulation during the last interglacial period
AU - Andersen, M. B.
AU - Matthews, A.
AU - Vance, D.
AU - Bar-Matthews, M.
AU - Archer, C.
AU - de Souza, G. F.
N1 - Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/12/1
Y1 - 2018/12/1
N2 - 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 δ238Uauth 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.
AB - 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 δ238Uauth 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.
KW - last interglacial
KW - Mediterranean
KW - molybdenum isotopes
KW - sapropels
KW - uranium isotopes
UR - http://www.scopus.com/inward/record.url?scp=85054193037&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2018.09.013
DO - 10.1016/j.epsl.2018.09.013
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AN - SCOPUS:85054193037
SN - 0012-821X
VL - 503
SP - 58
EP - 67
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -