Development of a Deep‐Water Carbonate Ion Concentration Proxy Based on Preservation of Planktonic Foraminifera Shells Quantified by X‐Ray CT Scanning

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Paleoceanography and Paleoclimatology Pub Date : 2023-08-01 DOI:10.1029/2022PA004601

S. Iwasaki, K. Kimoto, M. Kučera

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引用次数: 0

Abstract

The quantitative and objective characterization of dissolution intensity in fossil planktonic foraminiferal shells could be used to reconstruct past changes in bottom water carbonate ion concentration. Among proxies measuring the degree of dissolution of planktonic foraminiferal shells, X‐ray micro‐Computed Tomography (CT) based characterization of apparent shell density appears to have good potential to facilitate quantitative reconstruction of carbonate chemistry. However, unlike the well‐established benthic foraminiferal B/Ca ratio‐based proxy, only a regional calibration of the CT‐based proxy exists based on a limited number of data points covering mainly low‐saturation state waters. Here we determined by CT‐based proxy the shell dissolution intensity of planktonic foraminifera Globigerina bulloides, Globorotalia inflata, Globigerinoides ruber, and Trilobatus sacculifer from a collection of core top samples in the Southern Atlantic covering higher saturation states and assessed the reliability of CT‐based proxy. We observed that the CT‐based proxy is generally controlled by deep‐water Δ[ CO32– ${{\mathrm{C}\mathrm{O}}_{3}}^{2\mbox{--}}$ ] like the B/Ca proxy, but its effective range of Δ[ CO32– ${{\mathrm{C}\mathrm{O}}_{3}}^{2\mbox{--}}$ ] is between −20 and 10 µmolkg−1. In this range, the CT‐based proxy appears directly and strongly related to deep‐water Δ[ CO32– ${{\mathrm{C}\mathrm{O}}_{3}}^{2\mbox{--}}$ ], whereas we note that in some settings, there appears to be a secondary influence on B/Ca which we suggest may be due to elevated alkalinity from carbonate dissolution in sediments. On the other hand, the CT‐based proxy is affected by supralysoclinal dissolution in areas with high productivity. Like the B/Ca proxy, the CT‐based proxy requires species‐specific calibration, but the effect of species‐specific shell difference in susceptibility to dissolution on the proxy is small.

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基于浮游有孔虫壳保存的深水碳酸盐离子浓度代用物的研制(X射线CT扫描)

浮游有孔虫化石壳溶蚀强度的定量和客观表征可以用来重建过去底水碳酸盐离子浓度的变化。在测量浮游有孔虫壳溶解程度的替代指标中，基于表观壳密度表征的X射线微计算机断层扫描(CT)似乎具有促进碳酸盐化学定量重建的良好潜力。然而，与基于底栖有孔虫B/Ca比率的替代方法不同，基于CT的替代方法的区域校准仅基于有限数量的数据点，主要覆盖低饱和状态水域。本文采用CT代入法测定了南大西洋岩心顶部覆盖较高饱和状态的浮游有孔虫Globigerina bulloides、Globorotalia inflata、Globigerinoides rubber和Trilobatus sacullifer的壳溶解强度，并评估了CT代入法的可靠性。我们观察到，基于CT的代理与B/Ca代理一样，一般由深水Δ[CO32 - ${{\ mathm {C}\ mathm {O}}_{3}}^{2\mbox{—}}$]控制，但其有效范围Δ[CO32 - ${{\ mathm {C}\ mathm {O}}}_{3}}^{2\mbox{—}}$]在−20 ~ 10µmolkg−1之间。在这个范围内，基于CT的代理似乎与深水Δ[CO32 - ${{\ mathm {C}\ mathm {O}}_{3}}^{2\mbox{—}}$]直接密切相关，而我们注意到，在某些情况下，似乎对B/Ca有次要影响，我们认为这可能是由于沉积物中碳酸盐溶解引起的碱度升高。另一方面，在生产力高的地区，基于CT的代理受到社会临床上溶解的影响。与B/Ca替代方法一样，基于CT的替代方法也需要物种特异性的校准，但物种特异性壳体对溶解敏感性的差异对替代方法的影响很小。

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来源期刊

Paleoceanography and Paleoclimatology Earth and Planetary Sciences-Atmospheric Science

CiteScore

6.20

自引率

11.40%

发文量

107

期刊介绍： Paleoceanography and Paleoclimatology (PALO) publishes papers dealing with records of past environments, biota and climate. Understanding of the Earth system as it was in the past requires the employment of a wide range of approaches including marine and lacustrine sedimentology and speleothems; ice sheet formation and flow; stable isotope, trace element, and organic geochemistry; paleontology and molecular paleontology; evolutionary processes; mineralization in organisms; understanding tree-ring formation; seismic stratigraphy; physical, chemical, and biological oceanography; geochemical, climate and earth system modeling, and many others. The scope of this journal is regional to global, rather than local, and includes studies of any geologic age (Precambrian to Quaternary, including modern analogs). Within this framework, papers on the following topics are to be included: chronology, stratigraphy (where relevant to correlation of paleoceanographic events), paleoreconstructions, paleoceanographic modeling, paleocirculation (deep, intermediate, and shallow), paleoclimatology (e.g., paleowinds and cryosphere history), global sediment and geochemical cycles, anoxia, sea level changes and effects, relations between biotic evolution and paleoceanography, biotic crises, paleobiology (e.g., ecology of “microfossils” used in paleoceanography), techniques and approaches in paleoceanographic inferences, and modern paleoceanographic analogs, and quantitative and integrative analysis of coupled ocean-atmosphere-biosphere processes. Paleoceanographic and Paleoclimate studies enable us to use the past in order to gain information on possible future climatic and biotic developments: the past is the key to the future, just as much and maybe more than the present is the key to the past.