Marine sedimentary uranium to barium ratios as a potential quantitative proxy for Pleistocene bottom water oxygen concentrations
Marine sedimentary uranium to barium ratios as a potential quantitative proxy for Pleistocene bottom water oxygen concentrations
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海洋沉积物铀与钡的比率作为更新世底层水氧浓度的潜在定量指标
DOI：
10.1016/j.gca.2022.12.022
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发表时间：
2023
影响因子：
5
通讯作者：
Oppo, Delia W.
中科院分区：
文献类型：
--
作者：
Costa, Kassandra M.;Nielsen, Sune G.;Wang, Yi;Lu, Wanyi;Hines, Sophia K.V.;Jacobel, Allison W.;Oppo, Delia W.
氧气对海洋生态系统至关重要，它通过呼吸作用与深海中的碳储存联系在一起。重建氧气浓度在过去一直受到限制，缺乏定量，而不是定性，代理，但几个新的（半）定量氧气代理最近已经开发出来。在这项研究中，我们探讨了通过将大量沉积铀（U）归一化为钡（Ba）来将其加入该列表的可能性。首先，U/Ba和底层水的氧浓度进行了比较，在全球范围内，使用核心顶部数据库，在远洋环境大于200米的水深。然后，U/Ba和底层水氧之间的关系进行了检查在较小的空间尺度上：在每个海洋盆地和区域内的东赤道太平洋，阿拉伯海，西赤道大西洋。在这个区域范围内，二次影响的行为，U和Ba可能是更空间均匀的，经验分段线性校准开发，随后进行测试的downcore记录。铀/钡基氧重建一般同意来自以前发表的烯酮保存和底栖有孔虫表面孔隙度记录。还确定了U/Ba作为氧的替代物的效用的几个限制。该代用指标应仅适用于含有孔隙水硫酸盐的最上层沉积层段，以尽量减少重晶石成岩作用，并应监测磷含量，以了解磷灰石对铀含量的潜在影响。U/Ba在记录平均冰期和间冰期的氧浓度方面比在气候转变期间更成功，在气候转变期间，时间和幅度可能对烧毁和平滑更敏感。校准的保守误差导致U/Ba在具有相对高的氧浓度的区域中的最大效用（例如，>50 μmol/kg）和较大的氧气变异性（±10 s μmol/kg）。即使有这些警告，U/Ba只是可能能够记录50 μmol/kg以上变化的两个定量氧代用指标之一，在奋进重建过去的整个海洋氧浓度范围时，值得进一步研究其在不同环境设置中的功能。
Oxygen is essential for marine ecosystems, and it is linked by respiration to carbon storage in the deep ocean. Reconstructing oxygen concentrations in the past has been limited by the absence of quantitative, rather than qualitative, proxies, but several new (semi-) quantitative oxygen proxies have recently been developed. In this study we explore the possibility of adding bulk sedimentary uranium (U) to this list by normalizing it to barium (Ba). First, U/Ba and bottom water oxygen concentrations are compared on a global scale, using a core top database, in pelagic environments greater than 200 m water depth. Then, the relationships between U/Ba and bottom water oxygen are examined on smaller spatial scales: within each ocean basin and regionally within the Eastern Equatorial Pacific, the Arabian Sea, and Western Equatorial Atlantic. At this regional scale, where secondary influences on the behavior of both U and Ba may be more spatially uniform, empirical piecewise linear calibrations are developed and subsequently tested on downcore records. U/Ba-based oxygen reconstructions generally agree with those derived from previously published alkenone preservation and benthic foraminiferal surface porosity records. Several limitations to the utility of U/Ba as a proxy for oxygen have also been identified. The proxy should only be applied in the uppermost sedimentary intervals that contain porewater sulfate to minimize barite diagenesis, and phosphorus contents should be monitored for the potential influence of apatite on uranium content. U/Ba is more successful at recording oxygen concentrations during mean glacial and interglacial periods than during climate transitions, when the timing and amplitude may be more sensitive to burndown and smoothing. Conservative errors on the calibrations result in the greatest utility of U/Ba in regions with relatively high oxygen concentrations (e.g., >50 μmol/kg) and large oxygen variability (±10 s of μmol/kg). Even with these caveats, U/Ba is only one of two quantitative oxygen proxies potentially capable of recording variability above 50 μmol/kg, and further investigation into its functionality in different environmental settings is worthwhile in the endeavor to reconstruct the full marine range of oxygen concentrations in the past.
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