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Evaluating shallow-water carbonates as archives for seawater zinc isotope compositions: implications for palaeoceanographic studies.

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Title: Evaluating shallow-water carbonates as archives for seawater zinc isotope compositions: implications for palaeoceanographic studies.
Authors: Zhang, Chengyu1 (AUTHOR), Cao, Mengchun1 (AUTHOR) cmc@nju.edu.cn, Li, Na1 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Feb2026, Vol. 414, p1-14. 14p.
Subjects: Paleoceanography, Marine productivity, Marine phytoplankton, Sediments, Zinc compounds, Sedimentation & deposition, Seawater composition, Marine sediments
Geographic Terms: South China Sea
Abstract: Zinc (Zn) is an essential micronutrient for marine phytoplankton and exhibits a strong linear correlation with the major nutrient silicon in modern oceans. In recent years, Zn isotopes (δ66Zn) in marine carbonates have been increasingly used as proxies for reconstructing past marine productivity. However, improved understanding of the modern marine Zn cycle suggests that this potential link may be obscured by multiple biotic and abiotic factors. Additionally, the diverse mineralogical types and broad δ66Zn ranges reported for carbonate archives have raised ongoing debates about the reliability of marine carbonates in recording seawater zinc isotopic composition. Here, we present new δ66Zn data from 39 bulk carbonate sediment samples collected from two shallow-water push cores (Jiuzhang Atoll) in the South China Sea. The samples yield relatively consistent δ66Zn values across depth profiles, averaging +0.28 ± 0.11 ‰ (2SD), suggesting that shallow-water carbonates may serve as promising archives for palaeoceanographic reconstructions. However, comprehensive comparison with other recent carbonates—considering both Zn isotopic compositions and concentrations—suggests that the original seawater δ66Zn signatures recorded in ancient carbonate rocks were likely modified by depositional and diagenetic processes. These processes include mixing between inorganic primary calcite and biogenic carbonates, and the redox conditions of pore waters during deposition. Furthermore, the low Zn concentrations in modern primary carbonates—only about 3 % of those in ancient carbonate rocks—highlight their high susceptibility to diagenetic alteration. In addition, the wide spatial variability of modern surface seawater δ66Zn complicates the establishment of a consistent isotopic offset for calibrating ancient carbonates. Together, our findings call for caution when employing carbonate-hosted Zn isotopes as proxies for past ocean productivity, particularly given the unresolved uncertainties regarding the relationship between seawater δ66Zn and marine primary production. [ABSTRACT FROM AUTHOR]
Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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DbLabel: Engineering Source
An: 191078034
AccessLevel: 6
PubType: Academic Journal
PubTypeId: academicJournal
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Items – Name: Title
  Label: Title
  Group: Ti
  Data: Evaluating shallow-water carbonates as archives for seawater zinc isotope compositions: implications for palaeoceanographic studies.
– Name: Author
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  Data: <searchLink fieldCode="AR" term="%22Zhang%2C+Chengyu%22">Zhang, Chengyu</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Cao%2C+Mengchun%22">Cao, Mengchun</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> cmc@nju.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Li%2C+Na%22">Li, Na</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Feb2026, Vol. 414, p1-14. 14p.
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  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Paleoceanography%22">Paleoceanography</searchLink><br /><searchLink fieldCode="DE" term="%22Marine+productivity%22">Marine productivity</searchLink><br /><searchLink fieldCode="DE" term="%22Marine+phytoplankton%22">Marine phytoplankton</searchLink><br /><searchLink fieldCode="DE" term="%22Sediments%22">Sediments</searchLink><br /><searchLink fieldCode="DE" term="%22Zinc+compounds%22">Zinc compounds</searchLink><br /><searchLink fieldCode="DE" term="%22Sedimentation+%26+deposition%22">Sedimentation & deposition</searchLink><br /><searchLink fieldCode="DE" term="%22Seawater+composition%22">Seawater composition</searchLink><br /><searchLink fieldCode="DE" term="%22Marine+sediments%22">Marine sediments</searchLink>
– Name: SubjectGeographic
  Label: Geographic Terms
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22South+China+Sea%22">South China Sea</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Zinc (Zn) is an essential micronutrient for marine phytoplankton and exhibits a strong linear correlation with the major nutrient silicon in modern oceans. In recent years, Zn isotopes (δ66Zn) in marine carbonates have been increasingly used as proxies for reconstructing past marine productivity. However, improved understanding of the modern marine Zn cycle suggests that this potential link may be obscured by multiple biotic and abiotic factors. Additionally, the diverse mineralogical types and broad δ66Zn ranges reported for carbonate archives have raised ongoing debates about the reliability of marine carbonates in recording seawater zinc isotopic composition. Here, we present new δ66Zn data from 39 bulk carbonate sediment samples collected from two shallow-water push cores (Jiuzhang Atoll) in the South China Sea. The samples yield relatively consistent δ66Zn values across depth profiles, averaging +0.28 ± 0.11 ‰ (2SD), suggesting that shallow-water carbonates may serve as promising archives for palaeoceanographic reconstructions. However, comprehensive comparison with other recent carbonates—considering both Zn isotopic compositions and concentrations—suggests that the original seawater δ66Zn signatures recorded in ancient carbonate rocks were likely modified by depositional and diagenetic processes. These processes include mixing between inorganic primary calcite and biogenic carbonates, and the redox conditions of pore waters during deposition. Furthermore, the low Zn concentrations in modern primary carbonates—only about 3 % of those in ancient carbonate rocks—highlight their high susceptibility to diagenetic alteration. In addition, the wide spatial variability of modern surface seawater δ66Zn complicates the establishment of a consistent isotopic offset for calibrating ancient carbonates. Together, our findings call for caution when employing carbonate-hosted Zn isotopes as proxies for past ocean productivity, particularly given the unresolved uncertainties regarding the relationship between seawater δ66Zn and marine primary production. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1016/j.gca.2025.12.012
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      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 14
        StartPage: 1
    Subjects:
      – SubjectFull: Paleoceanography
        Type: general
      – SubjectFull: Marine productivity
        Type: general
      – SubjectFull: Marine phytoplankton
        Type: general
      – SubjectFull: Sediments
        Type: general
      – SubjectFull: Zinc compounds
        Type: general
      – SubjectFull: Sedimentation & deposition
        Type: general
      – SubjectFull: Seawater composition
        Type: general
      – SubjectFull: Marine sediments
        Type: general
      – SubjectFull: South China Sea
        Type: general
    Titles:
      – TitleFull: Evaluating shallow-water carbonates as archives for seawater zinc isotope compositions: implications for palaeoceanographic studies.
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            NameFull: Zhang, Chengyu
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            NameFull: Cao, Mengchun
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            NameFull: Li, Na
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            – D: 01
              M: 02
              Text: Feb2026
              Type: published
              Y: 2026
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              Value: 414
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