Abstracts Category : Other

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

by Sarah Zhou Rosengard

Particulate organic carbon (POC) in the ocean andmobilized by rivers on land transfers -0. 1% of global primaryproductivity to the deep ocean sediments. This small fractionregulates the long-term carbon cycle by removing carbon dioxidefrom the atmosphere for centuries to millennia. This thesisinvestigates mechanisms of POC transfer to the deep ocean byanalyzing particles collected in transit through two globallysignificant carbon reservoirs: the Southern Ocean and the AmazonRiver Basin. These endeavors test the hypothesis that organicmatter composition controls the recycling and transfer efficiencyof POC to the deep ocean, and illustrate new applications forramped pyrolysis/oxidation (RPO), a growing method of POCcharacterization by thermal stability. By coupling RPO to stableand radiocarbon isotope analyses of riverine POC, I quantify threethermally distinct soil organic carbon pools mobilized by theAmazon River, and evaluate the degradability and fate of thesedifferent pools during transport to the coastal Atlantic Ocean.More directly, RPO analyses of marine samples suggest that POCtransfer in the water column is in fact selective. Observations ofconsistent biomolecular changes that accompany transport ofphytoplankton-derived organic matter to depth across the SouthernOcean support the argument for preferential degradation of specificPOC pools in the water column. Combining discussions of POCrecycling and transfer across both marine and terrestrial systemsoffer new perspectives of thermal stability as a proxy fordiagenetic stability and POC degradation state. The challenges ofinterpreting RPO data in these two environments set the stage forapplying the technique to more controlled experiments that tracePOC from source to long-term sink.Advisors/Committee Members: Valier Galy, Phoebe Lam (advisor).