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Bioactive trace metals and their isotopes as paleoproductivity proxies: An assessment using GEOTRACES-era data
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  • Tristan Horner,
  • Susan Little,
  • Tim Conway,
  • Jesse Farmer,
  • Jennifer Hertzberg,
  • Alastair Lough,
  • Jennifer McKay,
  • Allyson Tessin,
  • Stephen Galer,
  • Sam Jaccard,
  • Francois Lacan,
  • Adina Paytan,
  • Kathrin Wuttig,
  • Clara Bolton,
  • Eva Calvo,
  • Damien Cardinal,
  • Thibault de Garidel-Thoron,
  • Susanne Fietz,
  • Katharine Hendry,
  • Franco Marcantonio,
  • Patrick Rafter,
  • Haojia Ren,
  • Christopher Somes,
  • Jill Sutton,
  • Adi Torfstein,
  • Gisela Winckler,
  • David Janssen
Tristan Horner
Woods Hole Oceanographic Institution, Woods Hole Oceanographic Institution

Corresponding Author:[email protected]

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Susan Little
University College London, University College London
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Tim Conway
University of South Florida, University of South Florida
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Jesse Farmer
Princeton University, Princeton University
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Jennifer Hertzberg
Old Dominion University, Old Dominion University
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Alastair Lough
University of Leeds, University of Leeds
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Jennifer McKay
Oregon State University, Oregon State University
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Allyson Tessin
Kent State University, Kent State University
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Stephen Galer
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Sam Jaccard
University of Lausanne, University of Lausanne
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Francois Lacan
University of Toulouse, University of Toulouse
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Adina Paytan
University of California Santa Cruz, University of California Santa Cruz
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Kathrin Wuttig
University of Tasmania, University of Tasmania
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Clara Bolton
European Centre for Research and Teaching in Environmental Geoscience, European Centre for Research and Teaching in Environmental Geoscience
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Eva Calvo
Institute of Marine Sciences, Barcelona, Institute of Marine Sciences, Barcelona
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Damien Cardinal
Sorbonne University, Sorbonne University
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Thibault de Garidel-Thoron
European Centre for Research and Teaching in Environmental Geoscience, European Centre for Research and Teaching in Environmental Geoscience
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Susanne Fietz
Stellenbosch University, Stellenbosch University
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Katharine Hendry
University of Bristol, University of Bristol
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Franco Marcantonio
Texas A&M University, Texas A&M University
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Patrick Rafter
University of California Irvine, University of California Irvine
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Haojia Ren
National Taiwan University, National Taiwan University
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Christopher Somes
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
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Jill Sutton
University of Western Brittany, University of Western Brittany
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Adi Torfstein
Hebrew University of Jerusalem, Hebrew University of Jerusalem
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Gisela Winckler
Lamont-Doherty Earth Observatory, Lamont-Doherty Earth Observatory
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David Janssen
Universitat Bern,University of Bern
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Abstract

Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. How the biological pump operated in the past is therefore important for understanding past atmospheric carbon dioxide concentrations and Earth’s climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including: iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the elements that are least sensitive to productivity may be used to trace other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth’s climate history.
Nov 2021Published in Global Biogeochemical Cycles volume 35 issue 11. 10.1029/2020GB006814