Cycling of Bioavailable Carboxyl-Rich Alicyclic Molecules and Carbohydrates in Baffin Bay

• Main Author: McKee, Kayla
• Other Authors: Walker, Brett
• Format: Thesis
• Language: English
• Published: Université d'Ottawa / University of Ottawa
• Subjects: Dissolved Organic Matter; Arctic Ocean; Proton Nuclear Magnetic Resonance Spectroscopy; Carboxyl-Rich Alicyclic Molecules; Arctic; Baffin Bay; Baffin
• Online Access: http://hdl.handle.net/10393/45146; https://doi.org/10.20381/ruor-29352

At ~662 gigatonnes of carbon (GtC), marine dissolved organic matter (DOM) is the largest reduced pool of actively cycling carbon and nitrogen in the oceans1. Operationally defined as smaller than 0.1µm in size, this carbon reservoir comprises all non-living organic matter smaller than a bacterial cell and comprises organic colloids and molecules spanning as a continuum of sizes ranging from marine viruses and large macromolecules (e.g. DNA, enzymes) to small organic molecules (e.g. polymers and monomers)2. With deep apparent 14C-ages ranging between 4900-6400 ybp 3,4, marine DOM is anomalously old given timescales of global ocean ventilation (1000-1500 years). The great age of DOM has remained one of the most elusive lines of scientific inquiry in Chemical Oceanography for decades. The size and molecular composition of DOM has been shown to be a key variable in determining its biological reactivity (e.g. cycling rate) and long-term persistence in the deep ocean5,6. Despite the importance of DOM in the marine carbon and nitrogen cycles, we lack a detailed understanding of the molecular composition of DOM. Due to the high concentration of salts in seawater relative to DOM, it is difficult to analyze the molecular composition of seawater with conventional chemical- or size- fractionation methods without introducing bias (i.e. isolating only hydrophobic and/or high molecular weight DOM). In fact, it is commonly reported that >80% of DOM remains uncharacterized at the molecular level (e.g. not readily identifiable as an individual known biomolecule)5. Nuclear magnetic resonance (NMR) spectroscopy has been used as a tool for several decades to describe the composition of marine DOM isolates7. For example, 13C-NMR of major high molecular weight DOM functional groups at the molecular-level demonstrated that DOM is largely made up of reactive polysaccharides with low aromaticity compared to terrestrial DOM8. To date, all marine DOM NMR measurements have been made on size-fractionated DOM or chemically-fractionated ...