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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Hydrogen isotopic compositions of long-chain alkenones record freshwater flooding of the Eastern Mediterranean at the onset of sapropel deposition
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Hydrogen isotopic compositions of long-chain alkenones record freshwater flooding of the Eastern Mediterranean at the onset of sapropel deposition

机译：长链烯酮的氢同位素组成记录了腐殖质沉积开始时东地中海的淡水驱替

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Sapropels are organic-rich sediment layers that were intermittently deposited in the Mediterranean Sea, especially in its eastern basin, during the last 10Myr. The associated anoxic events that gave rise to sapropel formation resulted indirectly from the impact of African monsoon maxima on the basin's hydrography. Sharp shifts in oxygen isotopes (delta O-18) to values more depleted in the heavy isotope (180) in carbonates from surface dwelling planktonic foraminifera, slightly preceding sapropel deposition, suggest that the Mediterranean was flooded by large amounts of freshwater leading to the development of a low salinity of the surface water and a strong density stratification of the water column. However, the degree of freshwater flooding and concomitant drop in sea surface salinity (SSS) remain elusive. Recent work has shown that the hydrogen isotope (delta D) values of long-chain alkenones produced by haptophyte algae depend mainly on the delta D of the water and on salinity, and may therefore offer a new tool for salinity reconstructions. Our analysis of the delta D of alkenones from last interglacial sapropel S5 from the Aegean Sea shows a large decrease in delta D of 25 parts per thousand at the onset of sapropel formation, suggesting a drop in SSS of 6, from 39 to 33. Although the absolute SSS L estimates should be interpreted with care as they are subject to relatively large uncertainties, the estimated SSS values appear quite reasonable as they, for example, yield SSS before sapropel deposition similar to that of the present day Aegean Sea. To reduce uncertainties in SSS estimates, the delta D-salinity relationship has to be better constrained with cultures and also tested in field studies. However, our results do illustrate the promise of a combined use of delta D of alkenones, U-37(k') of alkenones, and delta O-18 of surface dwelling planktonic foraminifera, for SSS reconstructions. (C) 2007 Elsevier B.V. All rights reserved.
机译：腐殖质是富含有机物的沉积物层，在过去的10年中间歇性地沉积在地中海，尤其是其东部盆地。引起腐殖质形成的相关缺氧事件是非洲季风最大值对流域水文学影响的间接结果。地表浮游有孔虫的碳酸盐中氧同位素（δO-18）的急剧变化使其碳同位素中的重同位素（180）更趋贫化，这早于腐殖质沉积，表明地中海被大量淡水淹没，导致了开发地表水的低盐度和水柱的强密度分层。但是，淡水的泛滥程度和随之而来的海面盐度（SSS）下降仍然难以捉摸。最近的工作表明，由触藻类藻类产生的长链烯酮的氢同位素（δD）值主要取决于水的δD和盐度，因此可能为盐度重建提供新的工具。我们对来自爱琴海的最后一个冰川间腐殖质S5中烯酮的δD的分析显示，在腐殖质形成开始时，δD大大降低了千分之二十五，表明SSS下降了6，从39降至33。绝对SSS L估计值应受到相对较大的不确定性的影响，应谨慎解释，因为它们的估计值似乎很合理，例如，与今天的爱琴海相似，在腐泥沉积之前产生SSS的估计值。为了减少SSS估计中的不确定性，必须更好地限制D-盐度关系与文化并在现场研究中进行测试。但是，我们的结果确实说明了将烯酮的D值，烯酮的U-37（k'）和表面居住的浮游有孔虫的δO-18结合起来用于SSS重建的希望。 （C）2007 Elsevier B.V.保留所有权利。

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