Changing inputs of continental and submarine weathering sources of Sr to the oceans during OAE 2
Changing inputs of continental and submarine weathering sources of Sr to the oceans during OAE 2
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DOI：
10.46427/gold2020.1889
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发表时间：
2021-03
影响因子：
5
通讯作者：
L. Yobo;A. Brandon;C. Holmden;K. Lau;J. Eldrett
中科院分区：
文献类型：
--
作者：
L. Yobo;A. Brandon;C. Holmden;K. Lau;J. Eldrett
海洋缺氧事件（OAE）的特征是全球范围内海洋沉积物有机质含量的增加，并伴随着沉积物有机和无机δ13C值的正偏移。为了维持解释C同位素偏移所需的增加的C输出和埋藏，在海洋缺氧事件期间经常调用增加的海洋营养物质供应。本研究探讨了这些事件中潜在的营养物来源，并对跨越塞诺曼-土伦界的海洋缺氧事件2进行了研究。一个或多个大火成岩省（lip）的大规模喷发被认为是OAE 2的触发因素。在OAE 2期间，与火山向大气中排放二氧化碳有关的全球变暖与大陆风化速率的增加有关，并由此扩大了对海洋的营养供应。LIP火山喷发地点的海水与热玄武岩的相互作用可以进一步将亚铁和其他还原金属输送到海水中，从而提高地表水的生产力，增加深水的氧气需求。在OAE 2期间，海洋缺氧扩大的大陆和海底风化驱动因素的相对重要性难以厘清。本文利用美国德克萨斯州Eagle Ford组Iona-1岩芯泥灰岩序列中保存的海水87Sr/86Sr比值的高分辨率记录，利用海洋Sr旋回的盒子模型来约束OAE 2期间大陆风化和海洋热液Sr通量变化的时间和相对量级。结果表明，海水87Sr/86Sr比值与Os同位素证据同步变化，表明大规模LIP火山活动开始的时间比传统意义上标志OAE 2开始的C同位素正偏移早60 kyr。本研究提供的较高时间分辨率的海水Sr同位素记录保证了对OAE 2期间大陆风化和热液Sr输入海洋变化的详细定量分析。利用海洋Sr盒模型，发现大陆风化Sr通量增加~ 1.8倍，捕获了Iona-1岩心记录的海水87Sr/86Sr的变化。大陆风化通量的增加小于OAE 2期间海水Ca同位素变化研究估计的3倍的增加，这表明热液强迫在海洋缺氧事件的发展中可能发挥了比以前认为的更大的作用
Abstract Ocean anoxic events (OAE) are characterized by increased organic content of marine sediment on a global scale with accompanying positive excursions in sedimentary organic and inorganic δ13C values. To sustain the increased C exports and burial required to explain the C isotope excursion, increased supplies of nutrients to the oceans are often invoked during ocean anoxic events. The potential source of nutrients in these events is investigated in this study for Oceanic Anoxic Event 2, which spans the Cenomanian-Turonian boundary. Massive eruptions of one or more Large Igneous Provinces (LIPs) are the proposed trigger for OAE 2. The global warming associated with volcanogenic loading of carbon dioxide to the atmosphere has been associated with increased continental weathering rates during OAE 2, and by extension, enhanced nutrient supplies to the oceans. Seawater interactions with hot basalts at LIP eruption sites can further deliver ferrous iron and other reduced metals to seawater that can stimulate increased productivity in surface waters and increased oxygen demand in deep waters. The relative importance of continental and submarine weathering drivers of expanding ocean anoxia during OAE 2 are difficult to disentangle. In this paper, a box model of the marine Sr cycle is used to constrain the timing and relative magnitudes of changes in the continental weathering and hydrothermal Sr fluxes to the oceans during OAE 2 using a new high-resolution record of seawater 87Sr/86Sr ratios preserved in a marl-limestone succession from the Iona-1 core collected from the Eagle Ford Formation in Texas. The results show that seawater 87Sr/86Sr ratios change synchronously with Os isotope evidence for the onset of massive LIP volcanism 60 kyr before the positive C isotope excursion that traditionally marks the onset of OAE 2. The higher temporal resolution of the seawater Sr isotope record presented in this study warrants a detailed quantitative analysis of the changes in continental weathering and hydrothermal Sr inputs to the oceans during OAE 2. Using an ocean Sr box model, it is found that increasing the continental weathering Sr flux by ∼1.8-times captures the change in seawater 87Sr/86Sr recorded in the Iona-1 core. The increase in the continental weathering flux is smaller than the threefold increase estimated by studies of seawater Ca isotope changes during OAE 2, suggesting that hydrothermal forcing may have played a larger role in the development of ocean anoxic events than previously considered