Graduate Thesis Or Dissertation
 

Quantifying Carbon Production in Marine Ecosystems Using Expressions of Phytoplankton Physiology

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s4655q156

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  • Phytoplankton initiate the marine carbon cycle by fixing carbon dioxide into biologically available compounds. These abundant single celled organisms mediate carbon flux from the atmosphere to the deep ocean and are the base of the marine food web, supplying new carbon to higher trophic levels. Phytoplankton are highly diverse and exhibit a wide range of physiologies and responses to the dynamic nature of the marine environment. This dissertation investigated properties and behaviors expressed by phytoplankton under a wide range of conditions. Laboratory-based culture studies were used to inform analyses of broad scale in situ optical and imaging data. To examine the timescales of phytoplankton responses, I studied growth and metabolism of two model species Dunaliella tertiolecta and Thalassiosira pseudonana during a simulated transition from stratified mid-summer conditions to deeply mixing conditions. Both species were able to quickly photoacclimate, but the diatom responded nearly twice as fast as the green alga. Similarly fast growth responses were observed in measurements retrieved from autonomous floats in the North Atlantic ocean. In particular, I quantified rapid accumulation of new carbon below the mixed layer following multiple episodic deep mixing events occurring between April and October in 2015-2018. New carbon production ranged from 21.1 to 294 mg C m-2 d-1, at times surpassing the amount of new production occurring in the surface mixed layer. This new carbon produced in the dim sub-mixed layer and induced by episodic deep mixing represents a significant contribution to the biological carbon pump. In chapter three, I examined mixoplankton physiology. These cells combine photoautotrophy with phagotrophy and are hypothesized to have unique and important roles in controlling marine carbon fluxes. Amphidinium carterae, a dinoflagellate, and Isochrysis galbana, a prymnesiophyte, were supplied a range of light and organic carbon. Both mixoplankton exhibited cannibalism and exuded dissolved organic carbon. Results from this work showed that carbon produced through consumption of existing organic matter is vastly underreported in these organisms and has important consequences for food web processes. I next sought an optical signature of mixoplankton distributions and activity that could be obtained by remote sensing. In the fourth chapter, a comprehensive review of the literature on mixoplankton physiology was conducted to assess shared physiological properties expressed by mixoplankton across a variety of growth conditions. These data were used to guide an analysis of two large-scale field studies across multiple ocean basins. I found that chlorophyll normalized to the slope of the particle size distribution (Chl γ-1) significantly correlated with mixoplankton biovolume contribution to the phytoplankton community. Chl γ-1 and mixoplankton biovolume patterns suggested that mixoplankton strongly impact carbon flux during periods of transient resource supply, such as the peak of annual phytoplankton biomass accumulation in the spring in the North Atlantic Ocean. This collection of research contributed new understanding of when, where, and how much carbon is being produced through primary and secondary production in the global oceans.
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  • Intellectual Property (patent, etc.)
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  • 2021-12-14 to 2023-01-14

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