Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data

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