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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 >Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events
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Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events

机译：Chemocline崩溃在Kivu湖作为氮循环期间的类似物

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One of the outstanding issues in the study of nutrient dynamics during Oceanic Anoxic Events (OAEs) is the preservation of N-15-depleted nitrogen isotope signals, which are not observed in analogous modern environments. The favored mechanism for delta N-15 values below 0 parts per thousand is utilization of excess ammonium derived from underlying anoxic waters by primary producers. However, there are few modern examples available for testing this hypothesis, due to the overall well-oxygenated state of modern oceans. Here, we present sedimentary delta C-13(org) and delta(15) N-bulk data, as well as pigment biomarker ratios, from the sediments of Lake Kivu, a meromictic lake in East Africa. This system serves as a potential analogue for the development of strongly depleted delta(15) N-bulk in OAE black shales. We focus on intervals of organic carbon enrichment (sapropels) that are interpreted to have been the result of lake water column mixing events. Sediment delta C-13(org) and delta(15) N-bulk decrease by up to 6 and 4 parts per thousand respectively near the base of sapropel layers. These negative excursions provide evidence for the mixing of C-13-depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need, derived from the deeper anoxic basin of the lake. Support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status. Further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers. (C) 2020 Elsevier B.V. All rights reserved.
机译：在海洋缺氧事件（OAES）期间研究营养动力学研究中的一个突出问题是保存N-15耗尽的氮同位素信号，其在类似的现代环境中未观察到。 ΔN-15值低于0份0‰的最有利机制是通过初级生产者利用过量源自亚氧基水域的过量铵。然而，由于现代海洋的整体富含氧气状态，很少有用于测试这一假设的现代化例子。在此，我们呈现沉积Delta C-13（ORG）和Delta（15）N-批量数据，以及来自Kivu Lake Kivu沉积物的颜料生物标志物比例，位于东非的Meromictic湖泊。该系统用作在OAE Black Hales的强烈耗尽的Delta（15）N-散装的发展的潜在模拟。我们专注于被解释为湖水柱混合事件的结果的有机碳浓缩（Sapropel）的间隔。沉积物Delta C-13（Org）和Delta（15）N-块分别在Sapropel层的基部附近分别降低6至4份每千份。这些负偏移提供了源自湖泊更深的缺氧盆地的C-13耗尽的溶解无机碳和铵的溶解无机碳和铵的证据。光合色素生物标志物还提供了对该模型的支持，其在光营养生态学中显示出与水柱混合一致的显着波动和营养状态的变化。在通过光脱硫硫化物氧化剂制备的菌肤氯苯基衍生物存在下发现Sapropel沉积期间的浅发的进一步证据。 （c）2020 Elsevier B.v.保留所有权利。

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