| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013 The sinking flux of particles is an important removal mechanism of carbon from the surface ocean as part of the biological pump and can play a role in cycling of other chemical species. This work dealt with improving methods of measuring particle export and measuring export on different scales to assess its spatial variability. First, the assumption of 238U linearity with salinity, used in the 238U–234Th method, was reevaluated using a large sample set over a wide salinity range. Next, neutrally buoyant and surface-tethered sediment traps were compared during a three-year time series in the subtropical Atlantic. This study suggested that previously observed imbalances between carbon stocks and fluxes in this region are not due to undersampling by traps. To assess regional variability of particle export, surface and water-column measurements of 234Th were combined for the first time to measure fluxes on ~20 km scales. Attempts to relate surface properties to particle export were complicated by the temporal decoupling of production and export. Finally, particle export from 234Th was measured on transects of the Atlantic Ocean to evaluate basin-scale export variability. High-resolution sampling through the water-column allowed for the identification of unique 234Th features in the intermediate water column. I was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program (Grant NNX10AO72H). Specific projects were funded by grants from the National Science Foundation, including Carbon Flux Through the Twilight Zone – New Tools to Measure Change (OCE-0628416), WAPflux – New Tools to Study the Fates of Phytoplankton Production in the West Antarctic Peninsula (ANT-0838866), and GEOTRACES Atlantic Section: Trace Element Sources and Sinks Elucidated by Short- Lived Radium and Thorium Isotopes ...
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