Project: Collaborative Research: US GEOTRACES GP17-OCE and GP17-ANT: Pb Isotopes

NSF Award Abstract:
Although most of the chemical element lead (Pb) found in the ocean is derived from human emissions to the atmosphere, natural sources of Pb may be important in remote locations such as the Southern Ocean. Natural sources of Pb are derived from the Earth’s crust and are delivered to the ocean by glacial erosion and aerosol inputs. Lead is produced by radioactive decay and has three stable isotopes that are derived from the decay of uranium and thorium. Thus, distinct lead isotope ratios are seen in deposits from source rocks of different ages. These isotope ratios make it possible to distinguish whether pollutant lead in the ocean is derived from American, Australian, European, and Chinese sources. Isotope measurements of Pb provide information about temporal changes in the global transport of pollutants by atmospheric aerosols and the distribution of contaminants and other elements by ocean circulation and particulate transport. In this project, water samples will be collected from the South Pacific sector of the Southern Ocean to help establish the origins of anthropogenic lead in this ocean region, distinguish it from natural lead from the Antarctic continent, and understand the dispersal of Pb by ocean circulation. The project will support one graduate student and one early career postdoctoral scholar.

The proposed work will be carried out as part of the GEOTRACES trace element and isotope sampling expedition to the South Pacific and Pacific sector of the Southern Ocean. The measurement of Pb isotopes during these expeditions will provide the ability to trace the source, fate, and transport of other particle-reactive metals in the ocean. Water column, sediment core top and aerosol samples will be analyzed for the full suite of Pb isotopes (204, 206, 207, 208) to provide insights into the extent of anthropogenic Pb contamination in the water column, the relative contribution of different lead isotopes from the South American continent, significance of hydrothermal Pb input from Pacific-Antarctic Ridge and whether sediment Pb isotopes reflect variation in the atmospheric circulation pattern. This work will allow evaluation of various anthropogenic and natural processes that determine the global distributions and processes of Pb.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.