Optical Properties of Marine and Picocyanobacteria-derived Dissolved Organic Matter in the Atlantic, Pacific and during Long-term Incubation Experiments
Lahm, Madeline Amelia
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Marine dissolved organic matter (DOM) is a large, dynamic, and complex pool of carbon, comparable in size to the carbon dioxide pool in the atmosphere, yet it is arguably the least understood component of the global carbon cycle. DOM deriving from picocyanobacterial cells via situationally unique mechanisms, such as viral lysis and metazoan grazing, complicate the picture as the resident pool present reflects sequestration processes that occur at time scales ranging from days to hundreds of thousands of years. Recently virus induced cell lysis released from the globally distributed picocyanobacteria, such as Synechococcus and Prochlorococcus, have been shown to release optically active DOM known as Chromophoric DOM (CDOM) that closely matches the “humic-like” appearance of marine CDOM raising questions about our understanding of this carbon pool given the reliance on spectral measures to assess its composition. Hence, this thesis is seeking to understand CDOM released by lysed picocyanobacteria and to investigate the molecular chemical composition of picocyanobacteria-derived DOM in general. A special focus will be to confirm the refractory nature of chromophores released by lysed picocyanobacteria (Synechococcus) given the reliance on optical properties of recalcitrant DOM being used in the investigation of timescales of carbon storage and biological processing of carbon. As we consider the outcomes of the current global carbon inventory with a sizable error in flux, linking products of microbial processes to chromophore structures and spectrometry is a capstone in understanding the global carbon cycle for decades of research. This study offers a direct comparison of fluorescence signatures from the Bermuda Atlantic Time-Series (BATS) and the Hawai'i Ocean Time-series (HOT), observes optical and nutrient profiles tracking long-term incubation experiments of oligotrophic microbial communities amended with Synechococcus-derived DOM, and explores new techniques in DOM solid-phase extraction (SPE). This work is part of a National Science Foundation project - The Fate of Lysis Products of Picocyanobacteria Contributes to Marine Humic-like Chromophoric Dissolved Organic Matter – linking the accumulating evidence of picocyanobacterial-derived DOM to our understanding of marine organic carbon. Furthermore, we seek to understand how picocyanobacteria-derived DOM is degraded and what role changing heterotrophic microbial communities plays. This research is important to the concept of a microbial carbon pump that supplies a constrained and constant source of DOM which has important implications for the marine carbon cycle and its role in global climate.