Supply, eastward transport, and temporal variability of trace elements in the zonal current system of the tropical West Pacific - an integrated innovative study using Nd isotopes, rare earth elements, and ocean dynamics

• Applicant: Dr. Melanie Behrens
• Subject Area: Oceanography
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396302194

The study is aimed at testing the potentially crucial role of the tropical Pacific zonal current system in providing trace elements (TE) (incl. micronutrients) from the West Pacific source area to the iron-limited East Pacific, with a particular focus on recently discovered mid-depth jets (>1000 m water depth). The main aim is to resolve their origin, spatial extent, and geochemical composition to evaluate their potential role in fuelling productivity in the East Pacific. Integrated into previous and ongoing geochemical and physical oceanographic studies of the South, West, and equatorial Pacific (own projects and those of my partners), the study will also address the temporal variability of TE supply and eastward transport. The tropical West Pacific is thought to be an important source area of micronutrients and other TEs to eastward flowing zonal currents that transport them to the iron-limited East Pacific, and thus sustain primary productivity and hence ecosystems and fisheries in this area. It is therefore imperative to understand the TE supply to the West Pacific, the origin and structure of the currents transporting them, and their possible inter-annual variability. Particularly, it is currently not known, whether TE supply occurs only to the surface and subsurface currents or also to the mid-depth jets, and whether all island margins in the West are equally important TE sources. Moreover, it is not yet clear, whether the mid-depth jets originate in the West as discrete jets transporting TEs to the East, or whether they are fed by recirculation from other currents, in which case they would take in a less important role in the eastward transport of TEs including micronutrients. Neodymium (Nd) isotopes and rare earth elements (REE) are ideally suited to identify the source and trace the transport of TEs in the tropical Pacific due to their non-bioactive nature and their distinct West and East Pacific signatures. In close collaboration with my German and French partners, experienced geochemists and physical oceanographers, I propose to combine new, high-resolution and existing Nd isotope and REE data from the tropical West Pacific with extensive physical oceanographic data from the same cruises and with additional trace metal data (Fe, Zn, Cu, Cd, Mn, Al) that are published or will soon become available. This multidisciplinary approach will provide insight into element (incl. micronutrient) sources, supply, transport, and dynamics in the tropical Pacific. The proposed study and concerted effort in data interpretation with German and French experts represents the most comprehensive approach to understand the physical and chemical oceanography of the tropical West Pacific to date and is expected to uniquely address the above-mentioned open questions.

• DFG Programme: Research Grants
• International Connection: France
• Co-Investigator: Professorin Dr. Katharina Pahnke-May
• Cooperation Partners: Dr. Sophie Cravatte; Dr. Alexandre Ganachaud; Professorin Dr. Catherine Jeandel; Professor Dr. Frédéric Marin