The Remineralization of Marine Organic Matter by Diverse Biological and Abiotic Processes

James Collins, Ph.D., 2017
Benjamin Van Mooy, Advisor

Aerobic respiration is typically invoked as the dominant mass-balance sink for organic matter in the upper ocean, yet many other biological and abiotic processes can degrade particulate and dissolved substrates on globally significant scales. In this thesis, I query some of these alternative pathways of remineralization. I first assess the relative importance of particle-attached microbial respiration compared to other processes that degrade sinking marine particles. I found that sinking particle material was transferred to the water column 3.5 times as fast as it was directly respired, questioning the assumption that direct respiration dominates remineralization. I next present a new lipidomics method and open-source software package for identification of molecular biomarkers in large, high-mass-accuracy HPLC-ESI-MS datasets. I use the software to identify > 1,100 unique lipids and oxylipins in a marine diatom. Finally, I present the results of photooxidation experiments conducted in waters of the West Antarctic Peninsula, which receive elevated doses of ultraviolet radiation as a consequence of anthropogenic ozone depletion. The mean daily rate of lipid photooxidation in the water column (equivalent to 32 ± 7 µg C m^-3d^-1) represented between 2 and 8 % of the total bacterial production observed in surface waters following sea ice retreat.