Browsing by Subject "ocean"

Now showing 1 - 3 of 3
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    Accumulation of recalcitrant dissolved organic matter in aerobic aquatic systems
    (2021-02-09) Cotner, James; Anderson, NJ; Osburn, Christopher; cotne002@umn.edu; Cotner, James; Cotner Lab
    An oxygenated atmosphere led to many changes to life on Earth but it also provided a negative feedback to organic matter accumulation over billions of years by increasing decomposition rates. Nonetheless, dissolved organic carbon (DOC) is a huge carbon pool (>750 Pg) and it can accumulate to high concentrations (20-100 mg C L-1) in some freshwater aquatic systems, yet it is not clear why. Here, we examine DOC in several arctic lakes with varying concentrations and identify processes that alter its composition to make it recalcitrant to further degradation processes. Aging of DOC (from radiocarbon Δ14C ratios) corresponded with changes in its concentration, degradation rates, δ13C-DOC isotope ratios and optical quality, all suggesting that photochemical and microbial degradation processes contributed to decreased DOC reactivity over time. The degradation of young DOC was strongly stimulated by inorganic phosphorus, but older DOC was not, suggesting an important role for nutrients in regulating organic carbon degradation rates and pool sizes. Photochemical processing coupled with decreased habitat and microbial diversity in hydrologically isolated systems may enable recalcitrant DOC to accumulate with important implications for the Earth's carbon and oxygen cycles.
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    Inorganic carbon cycling in Lake Superior and responses to anthropogenic carbon dioxide
    (2024-10) Sandborn, Daniel
    The rapid increase of Earth’s atmospheric concentration of carbon dioxide drives myriad changes to marine chemistry and ecology, yet its influence in inland waters is relatively unknown. This research advances the understanding of inorganic carbon cycling in Lake Superior, the largest fresh water body on Earth by surface area, and describes how its carbon biogeochemistry responds to perturbations on seasonal to interannual scales. Improved instrumentation for measuring inorganic carbon parameters in freshwater environments was developed and deployed. These tools enabled analysis of the first multi-year underway time series describing drivers of Lake Superior’s inorganic carbon cycle, demonstrating a sustained rise in surface water carbon dioxide partial pressure (pCO2) at approximately the same rate as the atmospheric increase. Machine learning modeling produced an observation-based model of Lake Superior pCO2 and air-sea CO2 flux spanning the lake surface over 2019-2023, over which period Superior demonstrated periods of sustained net CO2 influx and efflux which nearly balanced on annual scales. This result brought Superior’s carbon budget closer to closure. Finally, aragonite saturation state was proposed as a useful variable to synthesize inorganic carbon cycling trends with calcifying species presence in inland waters in the face of the potential for lake acidification. The findings of these research projects advance the understanding of Lake Superior’s shifting carbon cycle in light of atmospheric CO2 invasion and acidification, with ecologic outcomes dependent on humanity’s choices in the coming decades.
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    Planetary Sea: Oceanography and the Making of the World Ocean
    (2016-07) Lehman, Jessica
    How has the concept of a world ocean emerged in a world of difference? This question reveals the crucial problematic of planetary environmental politics, which attempt to contend with global-scale environmental crises caused by the human species, at the risk of ignoring geographical specificity and different ways of knowing and experiencing life on Earth. By tracing the emergence of the world ocean concept in international oceanographic science, my research explores key practices and paradigms that characterize this tension. Drawing on expert interviews as well as archival materials from the US, UK, and South Africa, I study the world-making practices of three projects in physical oceanography: the International Geophysical Year (1957-58), the World Ocean Circulation Experiment (1990-2002), and the Global Ocean Observing System (current). Finally, I suggest the ocean archive as an alternate role for the ocean in planetary thought.