A 10-fold decline in the deep Eastern Mediterranean thermohaline overturning circulation during the last interglacial period
A 10-fold decline in the deep Eastern Mediterranean thermohaline overturning circulation during the last interglacial period
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DOI：
10.1016/j.epsl.2018.09.013
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发表时间：
2018-12
影响因子：
5.3
通讯作者：
M. B. Andersen;A. Matthews;D. Vance;M. Bar-Matthews;C. Archer;G. F. D. Souza
中科院分区：
文献类型：
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作者：
M. B. Andersen;A. Matthews;D. Vance;M. Bar-Matthews;C. Archer;G. F. D. Souza
如今的地中海深水区含氧良好，但富含有机物沉积物（腐泥）的偶发性形成表明，这种模式在过去经常受到干扰。人们提出，高出口生产率和温盐循环的破坏导致深水通风减少，是腐泥沉积和缺氧的原因。最后的间冰期腐泥 S5 被认为是最发达的间冰期腐泥之一。在这里，我们应用氧化还原敏感的 Mo 和 U（元素和同位素）系统，从 ODP 核心 967 (2550 mbsl) 量化东地中海深水缺氧条件的强度。 U和Mo均表现出强烈的自生富集，加上从S5开始到结束，δ 98 Mo auth逐渐增加（+ 1.2–1.8‰至+ 2.0–2.3‰），而δ 238 U auth逐渐减少（+ 0.10‰至− 0.15‰），表明水体存在增加，Mo和U的去除通量增加。我们表明，沉积物 δ 238 U auth 可用于估算水柱 U 消耗，并最终估算深水更新率。这些原理首先在现代黑海进行了测试，计算得出的深水更新时间为 830+ 690/− 500 年，与独立估计非常吻合。将这些原理应用到 S5 结束时表明，底水 U 消耗约为 50%，深水更新时间为 1030+ 820/− 520 年。与今天（约100年）相比，东地中海深水更新速度显着减慢，这在腐泥S5的形成中发挥了重要作用，并且与所提出的末次间冰期期间翻转抑制一致，因为季风强迫增强下河流淡水输入增加导致分层增加。
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 δ 98 Mo auth (+ 1.2–1.8‰ to+ 2.0–2.3‰) and decrease in δ 238 U auth (+ 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 δ 238 U auth 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.