Proximity to Undersaturation and the Influences on G. bulloides Area‐Density in Southern Indian Ocean Marine Sediments
Proximity to Undersaturation and the Influences on G. bulloides Area‐Density in Southern Indian Ocean Marine Sediments
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DOI：
10.1029/2021pa004249
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发表时间：
2021-05
影响因子：
3.5
通讯作者：
N. Umling;B. Saad;E. Sikes;N. Goodkin
中科院分区：
文献类型：
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作者：
N. Umling;B. Saad;E. Sikes;N. Goodkin
有孔虫外壳厚度和钙化强度的面积密度代理有可能提供有关过去海洋二氧化碳含量的信息，并且具有样本要求小、分析技术简单以及能够将分析的有孔虫重新用于其他古代理的优点。使用从印度洋东南部（1.8-3.8 公里水深）收集的一系列多岩芯顶部，我们评估了利用沉积岩芯中的 Globigerina bulloides 面积密度值来估计表面海洋碳酸盐参数的可靠性。由于海洋沉积物中的有孔虫很少被认为是“原始”（或“玻璃状”），因此我们对贝壳的面积密度测量进行了分组，以指定成岩作用的各个阶段。在面密度值低至 ~0.122 × 104 µg/μm2 时，视觉变化迹象很明显，与“原始”端元的偏差从面密度值 ~0.087 × 104 µg/μm2 开始。我们发现，面积密度的增加在较厚的贝壳（>0.122 × 104 µg/μm2）中覆盖了表面海洋碳酸盐特征，但可以解释与海洋沉积埋藏和成岩作用相关的小幅增加，从而使该代理能够及时应用。通过估计给定样品中保存良好的贝壳（<0.122 × 104 µg/μm2；%wp）的百分比，重建给定样品中的面密度值的分布有可能提供有关总体样品保存的有价值的信息。除了评估海洋沉积物样本对表层海洋重建的适用性之外，我们的 %wp 指标还有可能用作溶斜线变异性的代理。
The area density proxy of foraminiferal shell thickness and calcification intensity has the potential to provide information about past ocean CO2 content and has the benefit of small sample requirements, simple analytical techniques, and the ability to re‐use the analyzed foraminifera for other paleo‐proxies. Using a series of multicore core‐tops collected from the southeastern Indian Ocean (1.8–3.8 km water depth), we evaluate the reliability of utilizing area density values of Globigerina bulloides from sediment cores to estimate surface ocean carbonate parameters. Because foraminifera in marine sediments can rarely be considered “pristine” (or “glassy”), we grouped area density measurements of shells to designate various stages of diagenesis. Visual signs of alteration were apparent at area density values as low as ∼0.122 × 104 µg/µm2, with deviations from the “pristine” endmember beginning at area density values of ∼0.087 × 104 µg/µm2. We find that increases in area density overprint the surface ocean carbonate signature in thicker (>0.122 × 104 µg/µm2 shells), but small increases associated with marine sedimentary burial and diagenesis can be accounted for, allowing this proxy to be applied back in time. Reconstructing the distribution of area density values in a given sample has the potential to provide valuable information on overall sample preservation by estimating the percent of well‐preserved shells (<0.122 × 104 µg/µm2; %wp) in a given sample. Our %wp metric has the potential for use as a proxy for lysocline variability in addition to assessing the suitability of marine sediment samples for surface ocean reconstructions.