| Summary: | Thesis: Ph. D., Joint Program in Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. Cataloged from PDF version of thesis. Includes bibliographical references. While aerobic respiration is typically invoked as the dominant mass-balance sink for organic matter in the upper ocean, many other biological and abiotic processes can degrade particulate and dissolved substrates on globally significant scales. The relative strengths of these other remineralization processes - including mechanical mechanisms such as dissolution and disaggregation of sinking particles, and abiotic processes such as photooxidation - remain poorly constrained. In this thesis, I examine the biogeochemical significance of various alternative pathways of organic matter remineralization using a combination of field experiments, modeling approaches, geochemical analyses, and a new, high-throughput lipidomics method for identification of lipid biomarkers. I first assess the relative importance of particle-attached microbial respiration compared to other processes that can degrade sinking marine particles. A hybrid methodological approach - comparison of substrate-specific respiration rates from across the North Atlantic basin with Monte Carlo-style sensitivity analyses of a simple mechanistic model - suggested sinking particle material was transferred to the water column by various biological and mechanical processes nearly 3.5 times as fast as it was directly respired, questioning the conventional assumption that direct respiration dominates remineralization. I next present and demonstrate a new lipidomics method and open-source software package for discovery and identification of molecular biomarkers for organic matter degradation in large, high-mass-accuracy HPLC-ESI-MS datasets. I use the software to unambiguously identify more than 1,100 unique lipids, oxidized lipids, and oxylipins in data from cultures of the marine diatom ...
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