The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)
The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)
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DOI：
10.5194/bg-17-2825-2020
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发表时间：
2020-05-27
期刊：
影响因子：
4.9
通讯作者：
Humphreys, Matthew P.
中科院分区：
文献类型：
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作者：
Donald, Hannah K.;Foster, Gavin L.;Humphreys, Matthew P.
高纬度海洋是大气和海洋之间碳和热交换的关键区域。因此，它们是现代海洋学和古气候研究的焦点。然而，大多数可以提供长期前景的古气候代用指标都是基于钙质生物，如有孔虫，而在南大洋南纬50度以南和北太平洋北纬40度以北的深海沉积物中，这种生物很少或完全不存在。因此，需要为在这些高纬度地区发现的蛋白石基生物（如硅藻）制定替代物，这些生物在这些地区回收的生物沉积物中占主导地位。本文介绍了硅藻蛋白石中硼（B）含量和同位素组成（δ B-11）的分析方法。我们首次将其应用于评估海水pH值，δ B-11和B浓度（[B]）之间的关系，在硅藻海链藻的硅藻壳中，培养在一个范围内的二氧化碳分压（pCO（2））和pH值。与现有数据一致，我们发现培养的硅藻硅藻壳的[B]随着pH的增加而增加（Mejia等人，2013年）。δ B-11显示出相对明确的负趋势，随着pH值的增加，完全不同于任何其他生物矿物先前测量。这种关系不仅具有影响的幅度同位素分馏过程中发生的硼纳入蛋白石，但也使我们能够探索潜在的硼为基础的代理古pH值和古CO2重建高纬度海洋沉积物，到目前为止，逃避研究由于缺乏合适的碳酸盐材料。
The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50 degrees S in the Southern Ocean and north of 40 degrees N in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) found at these high latitudes, which dominate the biogenic sediments recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (delta B-11) of diatom opal. We apply it for the first time to evaluate the relationship between seawater pH, delta B-11 and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO(2)) and pH values. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejia et al., 2013). delta B-11 shows a relatively well defined negative trend with increasing pH, completely distinct from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 re-construction in high-latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.