Award: OCE-1518110

In this project, we determined the chemical composition of marine particles collected from the ocean. The marine particles were collected in two sizes, 1­-51 um and >51 um, along the U.S. GEOTRACES Eastern Pacific Zonal Transect (EPZT), which sampled from the coast of Peru to Tahiti, roughly along 12°S. This transect crossed two chemically significant zones: the large, Peruvian oxygen deficient zone in the eastern half of the cruise, and the hydrothermal plume emanating from the East Pacific Rise in the western half of the cruise. The smaller particles (1-51 um) that we collected generally remain suspended in seawater, where they can interact with dissolved constituents, whereas the larger particles generally sink, and are thus a vector by which elements can be transferred to depth. The two size fractions interact with each other by aggregation and disaggregation, which are part of a suite of particle dynamics processes. We measured major biologically ­produced carrier phases (e.g. particulate organic carbon and the biominerals, calcium carbonate and biogenic silica) and a suite of trace elements (e.g. iron, aluminum, manganese, cadmium, copper, cobalt, titanium), some of which are required as micronutrients for life, and others that act as tracers of oceanographic processes, in the size-­fractionated particles collected from the US EPZT section. Along with collaboration with researchers from other institutions, we used these data to assess the relative importance of particle concentration, composition, and size distribution on the cycling and removal of trace elements and their isotopes (TEIs). This was a rich dataset that has already led to 10 publications that have been accepted by, submitted to, or soon to be submitted to peer reviewed journals. Results of this work contributed to the overall goal of the GEOTRACES program, whose mission is to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean. Results from this work provided critical information about particle dynamics to other science communities (such as global biogeochemists, environmental engineers) interested in the role of marine particles in sequestering carbon from the atmosphere through a process known as the biological carbon pump. Some of our findings about iron cycling in the ocean, especially that iron can be oxidized in the water column even in the absence of oxygen, should be of interest to microbiologists and geobiologists who are studying similar reactions in terrestrial environments. Two young female post­doctoral scientists were supported by this project. Besides the analytical and scientific training they received on this grant, both were also given opportunities to lead components of the project, providing leadership training that they will need to be successful, independent scientists. An undergraduate and a graduate student at UCSC were also involved in this project. Last Modified: 05/30/2017 Submitted by: Phoebe J Lam