Beyond anoxia: exploring sedimentary thallium isotopes in paleo-redox reconstructions from a new core top collection
Beyond anoxia: exploring sedimentary thallium isotopes in paleo-redox reconstructions from a new core top collection
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DOI：
10.1016/j.gca.2022.07.022
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发表时间：
2022-07
影响因子：
5
通讯作者：
Yi Wang;Wanyi Lu;K. Costa;S. Nielsen
中科院分区：
文献类型：
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作者：
Yi Wang;Wanyi Lu;K. Costa;S. Nielsen
海水的铊同位素组成 (ε205Tl) 由于与氧化锰埋藏密切相关，已被确定为全球海洋氧化还原条件的有前景的替代指标。目前，过去海水Tl同位素重建的首选档案来自可能受到盆地限制的缺氧（未检测到氧气）和/或含硫（未检测到氧气且存在游离硫化物）环境。在这里，我们对自生沉积岩 ε205Tl 进行了全面的现代校准，其岩心顶部覆盖了广泛的底水氧化和沉积物成分。我们表明，在沉积物-水界面处/附近的还原性孔隙水中定量去除 Tl（例如，Mn 还原）可以使沉积物跟踪水柱 ε205Tl。即使底层水不缺氧，在高出口生产率和/或高沉降速率下浅氧渗透深度仍可能导致氧气快速消耗和减少孔隙水的积累，有利于完全去除铊。因此，Tl同位素氧化还原代理的应用可以极大地扩展到缺氧条件之外，进入具有开放海洋连接和高质量累积率的地方，以进行高分辨率时间重建。我们提出了一个决策树，使用 Mn、Ba 和 U 的沉积物富集因子来确定沉积物档案是否可能记录海水 ε205Tl。我们还提供了对定量铊去除环境中自生铊埋藏通量的估计，该通量大约是先前发表的全球海洋铊质量平衡估计中“缺氧/缺氧”汇大小的两倍。
The thallium isotopic composition (ε205Tl) of seawater has been identified as a promising proxy for global oceanic redox conditions due to its close association with Mn oxide burial. Currently the preferred archives for past seawater Tl isotope reconstructions are from anoxic (no oxygen detected) and/or sulfidic (no oxygen detected and free sulfide present) environments that may suffer from basin restriction. Here we conduct a comprehensive modern calibration of authigenic sedimentary ε205Tl with core tops covering a wide range of bottom water oxygenation and sediment compositions. We show that quantitative Tl removal in the reducing porewaters (e.g., Mn reduction) at/near the sediment–water interface could allow the sediments to track the water column ε205Tl. Even if the bottom water is not anoxic, a shallow oxygen penetration depth under high export productivity and/or high sedimentation rates may still allow rapid oxygen consumption and buildup of reducing porewaters conducive for complete Tl removal. Thus, applications of the Tl isotope redox proxy can be greatly expanded beyond the anoxic conditions into places with open-ocean connections and high mass accumulation rates for high-resolution temporal reconstructions. We present a decision tree using the sediment enrichment factors of Mn, Ba, and U to determine whether sediment archives are likely to record the seawater ε205Tl. We additionally provide an estimate of authigenic Tl burial fluxes in environments with quantitative Tl removal, which is roughly double the size of the ‘euxinic/anoxic’ sink in previously published global marine Tl mass balance estimates.