%AHorner, T. [NIRVANA Labs Woods Hole Oceanographic Institution Woods Hole MA USA, Department of Marine Chemistry &, Geochemistry Woods Hole Oceanographic Institution Woods Hole MA USA]%ALittle, S. [Department of Earth Sciences University College London London UK]%AConway, T. [College of Marine Science University of South Florida FL USA]%AFarmer, J. [Department of Geosciences Princeton University Princeton NJ USA, Max‐Planck Institute for Chemistry Mainz Germany]%AHertzberg, J. [Department of Ocean Earth &, Atmospheric Sciences Old Dominion University Norfolk VA USA, Now at: International Ocean Discovery Program Texas A&,M University College Station TX USA]%AJanssen, D. [Institute of Geological Sciences and Oeschger Centre for Climate Change Research University of Bern Bern Switzerland]%ALough, A. [University of Southampton National Oceanography Centre Southampton England, Now at: School of Geography University of Leeds Leeds England]%AMcKay, J. [College of Earth, Ocean, and Atmospheric Sciences Oregon State University Corvallis OR USA]%ATessin, A. [Department of Geology Kent State University Kent OH USA]%AGaler, S. [Max‐Planck Institute for Chemistry Mainz Germany]%AJaccard, S. [Institute of Earth Sciences Université de Lausanne Lausanne Switzerland]%ALacan, F. [LEGOS University of Toulouse CNRS CNES, IRD, UPS Toulouse France]%APaytan, A. [Institute of Marine Sciences University of California Santa Cruz Santa Cruz CA USA]%AWuttig, K. [Antarctic Climate and Ecosystems Cooperative Research Centre University of Tasmania Hobart TAS Australia, Now at: Federal Maritime and Hydrographic Agency (BSH) Hamburg Germany]%Anull%BJournal Name: Global Biogeochemical Cycles; Journal Volume: 35; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-08-28 01:39:51 %D2021%IDOI PREFIX: 10.1029 %JJournal Name: Global Biogeochemical Cycles; Journal Volume: 35; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-08-28 01:39:51 %K %MOSTI ID: 10360338 %PMedium: X %TBioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data %XAbstract

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. Constraining how the biological pump operated in the past is 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 trace metals that are least sensitive to productivity may be used to track 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.

%0Journal Article