Variability and Controls of Production, Partitioning, and Utilization of Organic Matter in the North Pacific Subtropical Gyre
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2016-05
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University of Hawaii at Manoa
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Oceans account for approximately half of global primary production, and oligotrophic gyres account for a large fraction of this production. Understanding of time-varying changes to ocean ecosystems largely derives from time-series observations. Since 1988, the Hawaii Ocean Timeseries (HOT) program has conducted near-monthly sampling at Station ALOHA (22° 45’N, 158° 00’W), providing information on the magnitude and pathways of carbon cycling in the North Pacific Subtropical Gyre (NPSG). These observations have identified microbial production and consumption of organic matter as major processes catalyzing upper ocean carbon fluxes. In this dissertation, I quantified rates of dissolved and particulate organic carbon production over daily to annual time scales in this ecosystem. Measured rates of primary production (PP) demonstrated significant depth-dependence, unlike rates of dissolved organic carbon (DOC) production. On average, depth-integrated (0–75 m) rates of DOC production were equivalent to 18 ± 10% of total (particulate and dissolved) productivity. My findings indicate that in this oligotrophic ecosystem, rates of dissolved and particulate production appear temporally decoupled over daily to monthly time scales. In addition, over a ~2-year period, I quantified rates of bacterial production (BP) at near-monthly time scales, to evaluate potential coupling between photosynthetic production of organic matter and its consumption by heterotrophic bacteria. There was no temporal correlation between rates of bacterial growth and primary production across daily to seasonal time scales, with BP lagging rates of PP by 1 to 2 months. Moreover, in the well-lit (<45 m) upper ocean, there was a significant relationship between seawater temperatures and bacterial production. In the lower euphotic zone (>75 m), there was no significant relationship between temperature and bacterial production. My results suggest photosynthetic production varies seasonally with changes in light, while bacterial production appears more sensitive to variations in upper ocean temperature. I also experimentally evaluated the effects of abrupt changes to the seawater carbonate system on rates of primary and bacterial production at Station ALOHA. These experiments revealed that abrupt changes in the partial pressure of seawater CO2 (pCO2) had little effect on rates of primary and bacterial production in this persistently oligotrophic ecosystem.
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Primary productivity (Biology), Carbon cycle (Biogeochemistry), Heterotrophic bacteria, North Pacific Subtropical Gyre, Time-series analysis
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Oceanography
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