Dissolved Organic Matter in Marine Environments: A Study of the Origin, Lability and Molecular Composition

• Main Author: Jaggi, Aprami
• Other Authors: Larter, Stephen R., Oldenburg, Thomas B. P., Snowdon, Lloyd R., Huang, Haiping, Hollander, David, Roberts, Edward P. L.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Graduate Studies 2018
• Subjects: Dissolved Organic Matter; Marine Ecosystems; Biogeochemistry; Geochemistry; Arctic; Arctic Ocean
• Online Access: http://hdl.handle.net/1880/106479; https://doi.org/10.11575/PRISM/31770

As one of the Earth’s largest active carbon pools, accounting for around 90% of the organic carbon in the oceans, dissolved organic matter (DOM) plays a fundamental role in carbon storage and other biogeochemical processes. It exists as a highly functionalized and complex mixture of organic compounds which are diverse in their source, reactivity, and history, with about 95% of aquatic DOM mixture remaining un-identified on a molecular level. This thesis uses ultra-high resolution mass spectrometry to characterize the origin, composition, and lability of DOM in the aquatic system. In this thesis, water and sediment samples were collected from sampling sites in the Arctic Ocean, as well as the northern and southern slope of the Gulf of Mexico, to discern the compositional differences in DOM that occur geographically. The DOM of waters sampled across the different ecosystems show a homogenized composition with little variability in their compound class distribution, consisting primarily of NOx, N2Ox, N3Ox, and Ox classes, with a mass range between m/z 170–960. Along the water column, surface water DOM samples show the most variation in their relative intensity and abundance of multi-oxygenated species, owing to their susceptibility to photo-oxidation, in contrast to the more refractory and homogenized DOM in the bathypelagic ocean. Unlike the homogenized water DOM composition near the ocean floor, the water extractable organics from sediments underneath (top 15 cm of sediment) show significant variability in both the relative intensity and abundance of compound classes, geographically. Juxtaposed to the oxygen rich water DOM, the sediment water extractable organic matter (WEOM) are enriched in nitrogen containing species (N1-6O1-17) with smaller carbon number values. The changes in DOM from the water surface towards the sediment are attributed to the differences in solar irradiation exposure, availability of oxygen, and resident microbes. The nitrogen containing classes in sediment WEOM show compositional trends ...