Riverine fluxes of high field strength elements Zr, Hf, Nb, Ta into the oceans and their impact on the Hf isotopic composition of seawater

• Applicant: Dr. Katja Schmidt
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273947145

Although there are only little data available, rivers are commonly assumed to be the major source of the particle-reactive elements Zr, Hf, Nb, and Ta to the oceans. However, a systematic investigation of the transport of these elements from the continents to the oceans and a proper understanding of the impact of different geological and environmental conditions on their geochemical behavior are lacking. The large black box along the pathway from land to sea are the estuaries where the mixture of freshwater with seawater profoundly affects the riverine flux of particle-reactive elements into the ocean. This study addresses the distribution of Zr, Hf, Nb and Ta, and the Hf isotopic composition in boreal and temperate river water and in glacial melt water rivers in Greenland, taking into account the association of such elements with the different physical trace element pools in freshwater, i.e. the particulate (>0.2µm), the nanoparticle/colloid (0.2µm to 1 KDa), and the truly dissolved (<1KD) pools. The net riverine flux of these elements to seawater and its impact on the Hf isotopic composition of the oceans will be investigated by mixing experiments between the freshwater and seawater endmembers. The complex method work includes filtration and ultrafiltration steps and subsequent preconcentration steps. The outcome of this study will significantly enhance our understanding on the transport and fate of Zr, Hf, Nb, and Ta in freshwater and their pathways from the continents into the ocean at different geological and environmental conditions. The results for the Hf isotopes will help to better address the role of continental weathering and runoff conditions in controlling the Hf isotopic composition of seawater.

• DFG Programme: Research Grants