UC Santa Cruz

Marine particles are an essential component of the marine biological pump (BP). The BP transfers particulate organic matter (POM) produced by phytoplankton at the surface into the ocean interior and exerts a primary control on the atmospheric CO2 level (Volk & Hoffert, 1985). This classic view of POM transport vertically has dominated our view of particle cycling in the ocean. It has long been known, however, that marine particles are complicated matrixes consisting of phases beyond POM (e.g., Lam et al., 2015), and the transport of particles can be both horizontal and vertical (e.g., Honjo et al., 2010). A limited number of particle concentration and composition measurements globally, however, remain one of the main barriers to understanding the biogeochemical cycling of marine particles and their associated elements and isotopes. This dissertation examines the sources, sinks, and transport of marine particles in recent U.S. GEOTRACES cruises in three ocean basins: the Western Arctic, the South Pacific, and the North Atlantic. Measurements of particle composition and metal chemical speciation are used to investigate the importance of lateral transport of particles and diel cycles of particulate manganese (Mn) in the Western Arctic Ocean, respectively. Enhancements in Mn oxides in the halocline and high lithogenic particles in the deep ocean point to the significance of lateral transport throughout the water column, while the contrasting difference in particulate Mn average oxidation states during the day and at night suggests rapid redox variations of Mn in the surface Western Arctic Ocean. The Western Arctic Ocean is characterized by the lowest particle flux of the three cruises. Our data with higher spatial and depth resolution show that there are ballast minerals present in particles in the Western Arctic Ocean, unlike what was observed by Honjo et al. (2010) using a handful of ice-tethered sediment traps. The low export fluxes found in the Western Arctic Ocean result from this basin having the smallest particle sizes, lowest particle concentrations and most viscous water. Overall, this dissertation contributes to the growing body of literature on the distribution and biogeochemistry of marine particles in the global ocean.