Bioactive trace metals and their isotopes as paleoproductivity proxies: An assessment using GEOTRACES‐era data

Type Article
Acceptance Date 2021 IN PRESS
Language English
Author(s) Horner T.J.ORCID1, 2, Little S.H.ORCID3, Conway T.M.4, Farmer J.R.5, 6, Hertzberg J.E.ORCID7, Janssen D.J.ORCID8, Lough A.J.M.9, McKay J.10, Tessin A.ORCID11, Galer S.J.G.6, Jaccard S.L.ORCID8, Lacan F.ORCID12, Paytan A.ORCID13, Wuttig K.ORCID14, Members Geotraces–pages Biological ProductiORCID
Contributor(s) Sutton Jill
Affiliation(s) 1 : NIRVANA Labs
2 : Department of Marine Chemistry & Geochemistry Woods Hole Oceanographic Institution Woods Hole MA ,USA
3 : Department of Earth Sciences University College London London, GBR
4 : College of Marine Science University of South Florida FL, USA
5 : Department of Geosciences Princeton University Princeton NJ ,USA
6 : Max‐Planck Institute for Chemistry Mainz ,DEU
7 : Department of Ocean Earth & Atmospheric Sciences Old Dominion University Norfolk VA ,USA
8 : Institute of Geological Sciences and Oeschger Center for Climate Change Research University of Bern Bern ,CHE
9 : University of Southampton National Oceanography Centre Southampton ,GBR
10 : College of Earth, Ocean, and Atmospheric Sciences Oregon State University Corvallis OR, USA
11 : Department of Geology Kent State University Kent OH ,USA
12 : LEGOS University of Toulouse CNRS CNES, IRD, UPS Toulouse ,FRA
13 : Institute of Marine Sciences University of California Santa Cruz Santa Cruz CA ,USA
14 : Antarctic Climate and Ecosystems Cooperative Research Centre University of Tasmania Hobart ,AUS
Source Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)) In Press
DOI 10.1029/2020GB006814
Keyword(s) biological pump, marine chemistry, biogeochemical cycles, micronutrients, phytoplankton, paleoceanography
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.

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Horner T.J., Little S.H., Conway T.M., Farmer J.R., Hertzberg J.E., Janssen D.J., Lough A.J.M., McKay J., Tessin A., Galer S.J.G., Jaccard S.L., Lacan F., Paytan A., Wuttig K., Members Geotraces–pages Biological Producti Bioactive trace metals and their isotopes as paleoproductivity proxies: An assessment using GEOTRACES‐era data. Global Biogeochemical Cycles IN PRESS. Publisher's official version : https://doi.org/10.1029/2020GB006814 , Open Access version : https://archimer.ifremer.fr/doc/00702/81406/