Simulating the biogeochemical effects of volcanic CO2 degassing on the oxygen-state of the deep ocean during the Cenomanian/Turonian Anoxic Event (OAE2)
Simulating the biogeochemical effects of volcanic CO2 degassing on the oxygen-state of the deep ocean during the Cenomanian/Turonian Anoxic Event (OAE2)
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DOI：
10.1016/j.epsl.2011.03.018
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发表时间：
2011-05-15
影响因子：
5.3
通讯作者：
Kuhnt, W.
中科院分区：
文献类型：
--
作者：
Floegel, S.;Wallmann, K.;Kuhnt, W.
白垩纪缺氧事件可能是由大量火山CO2脱气引发的，因为大火成岩省（LIPS）位于海底。在这里，我们提出了一个全面的模拟研究，以破译海洋生物地球化学的后果，增强火山CO2排放。一个地球化学箱模式已开发的瞬态模式运行与时间相关的火山CO2强迫。箱型模型考虑大陆风化过程、海洋输出生产、水柱中的降解过程、沉降到海底的颗粒雨、溶解物种在海底的底栖通量以及海洋沉积物中颗粒的埋藏。海洋由27个盒子代表。为了估计箱之间的水平和垂直通量，运行一个耦合的海洋-大气环流模式（AOGCM），以获得晚白垩世边界条件下的全球海洋的环流模式。AOGCM模式预测了在高pCO（2）值下，晚白垩世海洋存在强的温盐环流和强烈的通风。通过适当选择参数值，如大陆输入的磷，该模型产生海洋缺氧在低到中纬度和海洋三角洲C-13的变化，是符合地质数据，如完善的三角洲C-13曲线。在高pCO（2）条件下，河流磷通量增加，而在环境底层沃茨中低氧条件下，海洋沉积物中磷的埋藏效率降低，这两个因素支持了缺氧的扩散。在这里，我们认为，一个额外的机制可能有助于缺氧，增加海洋浮游生物的C：P比，这是由高pCO（2）值引起的。根据我们的AOGCM模型结果，只有在高pCO（2）条件下允许输出到深海的海洋有机颗粒的C：P比增加，强烈通风的白垩纪海洋才会变成缺氧。意识到成岩作用等不确定性，本模拟研究意味着Redfield比率的潜在变化可能是通过增强CO2排放来实现海洋缺氧的强反馈机制。富C海洋有机质的形成也可以解释在以高pCO（2）值为特征的其他地质时期全球缺氧的频繁发生。(C)2011爱思唯尔有限公司版权所有。
Cretaceous anoxic events may have been triggered by massive volcanic CO2 degassing as large igneous provinces (LIPS) were emplaced on the seafloor. Here, we present a comprehensive modeling study to decipher the marine biogeochemical consequences of enhanced volcanic CO2 emissions. A biogeochemical box model has been developed for transient model runs with time-dependent volcanic CO2 forcing. The box model considers continental weathering processes, marine export production, degradation processes in the water column, the rain of particles to the seafloor, benthic fluxes of dissolved species across the seabed, and burial of particulates in marine sediments. The ocean is represented by twenty-seven boxes. To estimate horizontal and vertical fluxes between boxes, a coupled ocean-atmosphere general circulation model (AOGCM) is run to derive the circulation patterns of the global ocean under Late Cretaceous boundary conditions. The AOGCM modeling predicts a strong thermohaline circulation and intense ventilation in the Late Cretaceous oceans under high pCO(2) values. With an appropriate choice of parameter values such as the continental input of phosphorus, the model produces ocean anoxia at low to mid latitudes and changes in marine delta C-13 that are consistent with geological data such as the well established delta C-13 curve. The spread of anoxia is supported by an increase in riverine phosphorus fluxes under high pCO(2) and a decrease in phosphorus burial efficiency in marine sediments under low oxygen conditions in ambient bottom waters. Here, we suggest that an additional mechanism might contribute to anoxia, an increase in the C:P ratio of marine plankton which is induced by high pCO(2) values. According to our AOGCM model results, an intensively ventilated Cretaceous ocean turns anoxic only if the C:P ratio of marine organic particles exported into the deep ocean is allowed to increase under high pCO(2) conditions. Being aware of the uncertainties such as diagenesis, this modeling study implies that potential changes in Redfield ratios might be a strong feedback mechanism to attain ocean anoxia via enhanced CO2 emissions. The formation of C-enriched marine organic matter may also explain the frequent occurrence of global anoxia during other geological periods characterized by high pCO(2) values. (C) 2011 Elsevier B.V. All rights reserved.