Abstracts Category : Other

Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

by Sarah Z Rosengard

Particulate organic carbon (POC) in the ocean and mobilized by rivers on landtransfers ~0.1% of global primary productivity to the deep ocean sediments. This smallfraction regulates the long-term carbon cycle by removing carbon dioxide from theatmosphere for centuries to millennia. This thesis investigates mechanisms of POCtransfer to the deep ocean by analyzing particles collected in transit through two globallysignificant carbon reservoirs: the Southern Ocean and the Amazon River Basin. Theseendeavors test the hypothesis that organic matter composition controls the recycling andtransfer efficiency of POC to the deep ocean, and illustrate new applications for rampedpyrolysis/oxidation (RPO), a growing method of POC characterization by thermalstability. By coupling RPO to stable and radiocarbon isotope analyses of riverine POC, Iquantify three thermally distinct soil organic carbon pools mobilized by the AmazonRiver, and evaluate the degradability and fate of these different pools during transport tothe coastal Atlantic Ocean. More directly, RPO analyses of marine samples suggest thatPOC transfer in the water column is in fact selective. Observations of consistentbiomolecular changes that accompany transport of phytoplankton-derived organic matterto depth across the Southern Ocean support the argument for preferential degradation ofspecific POC pools in the water column. Combining discussions of POC recycling andtransfer across both marine and terrestrial systems offer new perspectives of thermalstability as a proxy for diagenetic stability and POC degradation state. The challenges ofinterpreting RPO data in these two environments set the stage for applying the techniqueto more controlled experiments that trace POC from source to long-term sink.