20 years of an international collaborative research in marine geochemistry: the GEOTRACES program

For the past 20 years, the GEOTRACES program (www.geotraces.org) has produced transformative insights into the cycling of trace elements and isotopes (TEIs) in the ocean. Be they bioactive elements essential for sea life (e.g., Fe, Ni, Cu, Zn…); contaminants (e.g., Pb, Hg); or tracers of processes like particle settling velocity (e.g. Th, Pa), source of matter (e.g. Nd, Pb isotopes) or deep vertical diffusion (e.g., Ra, Ac), TEI marine concentrations range from the nanomol to the attomole per litre, making their measurements particularly challenging. Thus, GEOTRACES encouraged international partnership while instilling a strong spirit of collaboration among scientists from more than 35 nations for more than two decades. Rigorous intercalibration efforts, standard definitions and capacity building are the cornerstone of the program to ensure that basin-scale analyses made by any researcher worldwide can be compared without doubt. The resulting high-quality data sets are synthesized and released every 4 years as intermediate data products (IDP), the fourth one being expected in 2025. Accessible to all, at no cost, these data sets resulted in the production of an online electronic atlas (www.egeotraces.org) including data from all ocean basins. GEOTRACES scientific missions and strategies are annually discussed within the « Scientific Steering Committee », the data quality assessed by the « Standard and Intercalibration Committee » while the data base building is managed by the « Data Management Committee ». The whole coordination and animation of these rich and diverse activities are ensured by the « International Project Office », hosted in Toulouse (France), which also largely contributes to the outreach and educational efforts of the program (www.geotraces.org/gted/).

The talk will briefly describe this collaborative structure and illustrate its success with breakthroughs in the understanding of the oceanic cycling of key elements, such as the paradigm shift to a view of the marine Fe cycle where multiple sources contribute, including continental margins and hydrothermal plumes, so far strongly underestimated. The contribution of radionuclides, natural chronometers of processes, will also be underlined.