A researcher from Massachusetts Institute of Technology proposes to carry out coordinated studies of lead (Pb), iron (Fe), zinc (Zn), and their stable isotopes to assess the anthropogenic impact on ocean chemistry and improve our understanding of the role of trace metals in regulating ocean biogeochemical cycles. The specific goals of this project are the following: (1) determine links between trace element variability, dust flux, oceanographic and biological changes; (2) ascertain the spatial evolution of the upper North Atlantic Deep Water Pb maximum in the western North Atlantic; (3) evaluate whether the oxygen-minimum Fe-maximum develops westward via advective mixing from Fe fluxes from reducing sediments off NW Africa, or from in-situ re-mineralization of luxury-uptake dust Fe by plankton; (4) determine whether Pb isotope ratios can be used to establish the time scale of Pb transport into the eastern deep Atlantic; and (5) assess the first open-ocean measurements of Fe isotope ratios in the Atlantic and determine whether we can distinguish dust Fe from re-mineralized biological Fe and consider whether upper ocean Zn isotope ratios reflect progressive biological Rayleigh fractionation. To attain the outlined goals, the scientist will continue the Bermuda and Hawaii Pb and Fe time-series using the moored water sampler on selected BTM and MOSEAN deployments, the single-unit MITESS/ATE deployments on BATS and HOT cruises, and complete the analysis of Pb profiles collected during the summer 2005 Endeavor 408 cruise in the western tropical Atlantic. In addition, sea-going fieldwork will be carried out to establish the spatial variability of the tropical Atlantic Fe maximum associated with the shallow oxygen minimum, and to find unique mid-19th century Pb isotope ratios in the oldest east Atlantic deep water. Lastly, for the Fe and Zn isotope work, seawater Fe isotopes from surface and mid-depth waters, a seawater Zn isotope profile from the North Pacific, and a study of the progressive biological fractionation of Zn isotopes in the Peruvian upwelling region will be done.
As regards broader impacts, one graduate student will be supported by this project. However, it is anticipated that undergraduate students will also be included in the work and be trained along with the graduate student on how to obtain high quality trace metal and isotopic data using state of the art instrumentation.
