Quantification of African Monsoon Runoff During Last Interglacial Sapropel S5
Quantification of African Monsoon Runoff During Last Interglacial Sapropel S5
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DOI：
10.1029/2019pa003652
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发表时间：
2019-08-01
影响因子：
3.5
通讯作者：
Marino, Gianluca
中科院分区：
文献类型：
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作者：
Amies, Jessica D.;Rohling, Eelco J.;Marino, Gianluca
富含有机物的腐泥层点缀着地中海东部的沉积序列，记录了深海缺氧事件。腐泥沉积的时间与岁差极小值相吻合，这与北非季风雨带向北迁移有关。由此产生的增加，在撒哈拉沙漠的季风降水造成增加低三角洲O-18淡水径流到地中海东部的表面沃茨，这是反映了负三角洲O-18异常记录中的南极有孔虫方解石。然而，尽管对腐泥进行了广泛的研究，季风强度和淡水径流的大小，沿着对O-18三角洲的影响，仍然难以捉摸。在这里，我们提出了一个量化的非洲季风淡水径流到地中海东部的沉积期末次间冰期腐泥S5（类似于128.3-121.5万年）。我们的方法使用地中海的箱形模型，该模型代表不同的水团，并使用来自不同深度和季节性栖息地的浮游有孔虫物种的Delta O-18进行了校准。该模型与海平面和海表温度的现有记录约束，然后反演去卷积三角洲O-18信号的表面居住有孔虫物种Globigerinoides ruber（w）和计算淡水径流量。我们计算出的非洲季风径流表明，流入地中海东部的淡水流量大幅增加（相当于现代阿斯旺前尼罗河流量的8.8倍）。快速发病的S5沉积后，径流量的估计增加强烈表明，地中海东部腐泥沉积的预处理。我们的研究还提供了深入了解的分层和变暖的东地中海表面沃茨在S5的间隔。
Organic-rich sapropel layers punctuate the eastern Mediterranean sedimentary sequence, recording deep-sea anoxic events. The timing of sapropel deposition coincides with precession minima, which are associated with the northward migration of the monsoon rain belt over North Africa. The resultant increase in monsoon precipitation over the Sahara caused an increase in low-delta O-18 freshwater runoff into eastern Mediterranean surface waters, which is reflected by negative delta O-18 anomalies in the records of planktic foraminiferal calcite. However, despite extensive research on sapropels, the magnitude of monsoon intensification and freshwater runoff, along with its influence on delta O-18, remains elusive. Here, we present a quantification of African monsoon freshwater runoff into the eastern Mediterranean for the period of deposition of last interglacial sapropel S5 (similar to 128.3-121.5 ka). Our method uses a box model of the Mediterranean Sea, which represents different water masses, and has been calibrated using delta O-18 from planktic foraminiferal species of different depth and seasonal habitats. The model was constrained with existing records of sea level and sea surface temperature then inverted to deconvolve the delta O-18 signal of the surface-dwelling foraminiferal species Globigerinoides ruber (w) and calculate the freshwater runoff volume. Our calculated African monsoon runoff suggests large increases in freshwater discharge to the eastern Mediterranean (up to similar to 8.8 times the modern pre-Aswan Nile discharge). Rapid onset of S5 deposition following the estimated increase in runoff strongly suggests a preconditioning of the eastern Mediterranean for sapropel deposition. Our study also provides insight into the stratification and warming of eastern Mediterranean surface waters during the S5 interval.