GEOTRACES is an international endeavor to elucidate the biogeochemical cycles of trace elements and their isotopes in the ocean. Inherently, this interdisciplinary program provides ample opportunities for students to develop professional, academic, and seagoing skills. This perspective recalls first-hand experiences gained from five years in the GEOTRACES community, spanning undergraduate and graduate research, including international engagement in Germany and seagoing oceanography in the South Pacific and Southern Ocean. Description of these opportunities reveals the framework that makes the GEOTRACES program a success and the culture that will ensure its ongoing legacy.
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Dissolved iron (dFe) is an essential micronutrient for phytoplankton, with vanishingly low oceanic dissolved concentrations (pico- to nanomoles per kg) known to limit growth—and thus influence primary productivity and carbon cycling—over much of the surface ocean. However, because of the considerable challenges associated with contamination-free sample collection and accurate analysis of such low dFe concentrations, the first reliable dFe measurements came only in the 1980s. Further, by 2003, despite several decades of research, there were only ~25 full-depth oceanic dFe profiles worldwide, with dust considered to be the main oceanic dFe source. Since 2008, facilitated by the extensive field campaign and rigorous intercalibration of the international GEOTRACES program, there has been an “explosion” in the availability of oceanic dFe data, with hundreds of profiles now available. Concurrently, there has been a paradigm shift to a view of the marine Fe cycle where multiple sources contribute, and some forms of dFe can be transported great distances through the intermediate and deep ocean. Here, we showcase the GEOTRACES dFe datasets across the different ocean basins, synthesize our current multi-source view of the oceanic Fe cycle, spotlight sediments as an important dFe source, and look to future directions for constraining oceanic dFe boundary exchange.
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This special issue of Oceanography celebrates the transformational findings of the international GEOTRACES program in chemical oceanography, 20 years after drafting of the GEOTRACES Science Plan in 2004 (GEOTRACES Planning Group, 2006). With the section cruise phase of the program ending soon, and a planned pivot toward smaller-scale process studies, this is an opportune time to look back at the achievements of GEOTRACES during the last two decades and to highlight some of the advances in our understanding of the processes that determine the oceanic distributions of trace elements and isotopes (TEIs).
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The micronutrient iron plays a major role in setting the magnitude and distribution of primary production across the global ocean. As such, an understanding of the sources, sinks, and internal cycling processes that drive the oceanic distribution of iron is key to unlocking iron's role in the global carbon cycle and climate, both today and in the geologic past. Iron isotopic analyses of seawater have emerged as a transformative tool for diagnosing iron sources to the ocean and tracing biogeochemical processes. In this review, we summarize the end-member isotope signatures of different iron source fluxes and highlight the novel insights into iron provenance gained using this tracer. We also review ways in which iron isotope fractionation might be used to understand internal oceanic cycling of iron, including speciation changes, biological uptake, and particle scavenging. We conclude with an overview of future research needed to expand the utilization of this cutting-edge tracer.more » « less