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首页> 外文期刊>Marine Geology >The effect of paleo-oceanographic changes on the sedimentary recording of hydrothermal activity in the Red Sea during the last 30,000 years
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The effect of paleo-oceanographic changes on the sedimentary recording of hydrothermal activity in the Red Sea during the last 30,000 years

机译：近三万年来古海洋变化对红海热液活动沉积记录的影响

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The restricted exchange of water with the Indian Ocean makes the Red Sea extremely sensitive to global oceanographic changes, such as sea-level variations linked with Quaternary climate change. The 120 m global sea level lowering during the last glacial maximum caused great reduction in water exchange with the open ocean. At that time, salinities reached 50 per thousand, and were beyond the tolerance of planktonic foraminifera. Some topographic depressions located on the Red Sea axial zone are the centre of hydrothermal activity. They are filled with hot brines and contain metalliferous sediments. We studied three sediment cores in the axial part of the Red Sea, one from the metal-rich Suakin Deep depression, and two cores sampled outside any deep, at two different depths. The sediment of the core located in the anoxic brine-filled Suakin Deep contained no benthic foraminifera, indicating the deep was filled by a brine pool during the recovered period of marine isotopic stages 1, 2, and 3. The distribution of benthic foraminifera in the two other cores indicates that Red Sea waters were saltier during stage 2 and 3 than today, and that at 2000 m depth, Red Sea waters were anoxic during stage 2 and dysoxic during stage 3. Profiles of Fe, Mn, and Zn indicate that the sedimentary flux of metals was higher during stage 1 than during stage 2 in hydrothermal brine-filled deeps. In contrast, the sedimentary flux of metal in cores outside the anoxic depressions was higher during stage 2. The shape of the metal profiles can be attributed to hydrological changes that induced variations of redox conditions in water column during isotopic stage 1, 2, and 3. During interglacial periods, metals dissolved in anoxic brines precipitated at the redox boundary that corresponded to the brine- seawater interface, so that metals precipitated only in the deeps. During glacial period, the deep water was anoxic. and the redox boundary was located above the brine-seawater interface. Therefore, the hydrothermal metals could diffuse into the anoxic deep Red Sea water and be precipitated over a large area. This interpretation suggests that the observed variations of metal concentrations are not only related to fluctuations of the hydrothermal fluid discharge, but also to the varying redox conditions in the deep Red Sea water.
机译：与印度洋的有限水交换使红海对全球海洋变化极为敏感，例如与第四纪气候变化有关的海平面变化。在最后一次冰川最大时期，全球海平面下降了120 m，导致与远洋的水交换大大减少。当时的盐度达到了千分之五十，已经超出了浮游有孔虫的容忍度。位于红海轴向带的一些地形凹陷是热液活动的中心。它们充满热盐水，并含有含金属的沉积物。我们研究了红海轴向部分的三个沉积岩心，其中一个来自富含金属的Suakin深凹陷，另外两个岩心则在任何深处以两个不同的深度进行了采样。位于缺氧盐水中的苏阿肯深层的岩心沉积物不含底栖有孔虫，表明在海洋同位素第1、2和3期的恢复期，该深层被盐水池充满。另外两个岩心表明，第2阶段和第3阶段的红海水比今天的咸，并且在2000 m深度处，第2阶段的红海水是缺氧的，第3阶段是缺氧的。Fe，Mn和Zn的剖面表明在充满热液盐水的深层中，第一阶段的金属沉积通量比第二阶段的高。相反，在第2阶段中，缺氧凹陷外部岩心中的金属沉积通量较高。金属剖面的形状可归因于水文变化，从而导致同位素第1、2和3阶段水柱中氧化还原条件的变化。在间冰期，溶解在缺氧盐水中的金属在对应于盐水-海水界面的氧化还原边界处沉淀，因此金属仅在深处沉淀。在冰川期，深水是缺氧的。氧化还原边界位于盐水-海水界面上方。因此，热液金属可以扩散到缺氧的深红海水中并在大范围内沉淀。这种解释表明，所观察到的金属浓度变化不仅与热液流体排放量的波动有关，而且与深红海水中变化的氧化还原条件有关。

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