Novel Analytical Strategies for Tracing the Organic Carbon Cycle in Marine and Riverine Particles

Sarah Rosengard, Ph.D., 2017
Valier Galy, Advisor

Particulate organic carbon (POC) in the ocean and mobilized by rivers on land transfers ~0.1% of global primary productivity to the deep ocean sediments, regulating long-term climate by removing carbon dioxide from the atmosphere for centuries to millennia. This thesis investigates mechanisms of POC transfer to the deep ocean by analyzing particles collected in transit through the Southern Ocean and the Amazon River Basin. These endeavors explore the relationship between organic matter composition and POC transfer efficiency to the deep ocean, and illustrate new applications for ramped pyrolysis/oxidation (RPO), a growing method of POC characterization by thermal stability. By coupling RPO to carbon isotope analyses of riverine POC, I quantify three thermally distinct soil organic carbon pools mobilized by the Amazon River, and evaluate their degradability during transfer to the Atlantic Ocean. RPO analyses of the Southern Ocean samples show consistent biomolecular changes that accompany transport of phytoplankton-derived organic matter to depth, supporting the argument for preferential degradation of specific POC pools in the water column. Together, these discussions of POC recycling and transfer across marine and terrestrial systems set the stage for applying RPO to more controlled experiments that trace POC from source to long-term sink.