Gauglitz Julia M.

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Gauglitz
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Julia M.
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  • Article
    Optical dignatures of dissolved organic matter transformation in the global ocean
    (Frontiers Media, 2016-01-07) Nelson, Norman B. ; Gauglitz, Julia M.
    Characterization of dissolved organic matter (DOM) in terms of its composition and optical properties, with an eye toward ultimately understanding its deep ocean dynamics, is the currently active frontier in DOM research. We used UV-visible absorption spectroscopy and fluorescence excitation-emission matrix (EEM) spectroscopy to characterize DOM in the open ocean along sections of the U.S. CO2/CLIVAR Repeat Hydrography Project located in all the major ocean basins outside the Arctic. Despite large differences in fluorescence intensity between ocean basins, some variability patterns were similar throughout the global ocean, suggesting similar processes controlling the composition of the DOM. We find that commercially available single channel CDOM sensors are sensitive to the fluorescence of humic materials in the deep ocean and thermocline but not to the UVA-fluorescing and absorbing materials that characterize freshly produced CDOM in surface waters, revealing fundamental diversity in the DOM profile. In surface waters, UVA fluorescence and absorption signatures indicate the presence of freshly produced material and the process of bleaching removal, but in the upper mesopelagic and in the main thermocline these optical signatures are replaced by those of humic materials, with distribution patterns correlated to apparent oxygen utilization (AOU) and other signatures of remineralization. Empirical orthogonal function analysis (EOF) of the EEM data suggests the presence of two (unidentified) processes which convert “fresh” DOM to humic materials: one located in the surface ocean (shallower than 500 m) and one located in the main thermocline. These inferred humification processes represent less than 5% of the overall variability in oceanic humic DOM fluorescence, which appears to be dominated by terrestrial input and solar bleaching of humic materials.
  • Article
    Publisher Correction : Pelagic barite precipitation at micromolar ambient sulfate
    (Nature Publishing Group, 2018-01-18) Horner, Tristan J. ; Pryer, Helena V. ; Nielsen, Sune G. ; Crockford, Peter W. ; Gauglitz, Julia M. ; Wing, Boswell A. ; Ricketts, Richard D.
    Correction to: Nature Communications https://doi.org/10.1038/s41467-017-01229-5, Article published online 07 November 2017
  • Article
    Pelagic barite precipitation at micromolar ambient sulfate
    (Nature Publishing Group, 2017-11-07) Horner, Tristan J. ; Pryer, Helena V. ; Nielsen, Sune G. ; Crockford, Peter W. ; Gauglitz, Julia M. ; Wing, Boswell A. ; Ricketts, Richard D.
    Geochemical analyses of sedimentary barites (barium sulfates) in the geological record have yielded fundamental insights into the chemistry of the Archean environment and evolutionary origin of microbial metabolisms. However, the question of how barites were able to precipitate from a contemporary ocean that contained only trace amounts of sulfate remains controversial. Here we report dissolved and particulate multi-element and barium-isotopic data from Lake Superior that evidence pelagic barite precipitation at micromolar ambient sulfate. These pelagic barites likely precipitate within particle-associated microenvironments supplied with additional barium and sulfate ions derived from heterotrophic remineralization of organic matter. If active during the Archean, pelagic precipitation and subsequent sedimentation may account for the genesis of enigmatic barite deposits. Indeed, barium-isotopic analyses of barites from the Paleoarchean Dresser Formation are consistent with a pelagic mechanism of precipitation, which altogether offers a new paradigm for interpreting the temporal occurrence of barites in the geological record.
  • Article
    Quantifying oxygen management and temperature and light dependencies of nitrogen fixation by Crocosphaera watsonii
    (American Society for Microbiology, 2019-12-11) Inomura, Keisuke ; Deutsch, Curtis A. ; Wilson, Samuel T. ; Masuda, Takako ; Lawrenz, Evelyn ; Bučinská, Lenka ; Sobotka, Roman ; Gauglitz, Julia M. ; Saito, Mak A. ; Prášil, Ondřej ; Follows, Michael J.
    Crocosphaera is a major dinitrogen (N2)-fixing microorganism, providing bioavailable nitrogen (N) to marine ecosystems. The N2-fixing enzyme nitrogenase is deactivated by oxygen (O2), which is abundant in marine environments. Using a cellular scale model of Crocosphaera sp. and laboratory data, we quantify the role of three O2 management strategies by Crocosphaera sp.: size adjustment, reduced O2 diffusivity, and respiratory protection. Our model predicts that Crocosphaera cells increase their size under high O2. Using transmission electron microscopy, we show that starch granules and thylakoid membranes are located near the cytoplasmic membranes, forming a barrier for O2. The model indicates a critical role for respiration in protecting the rate of N2 fixation. Moreover, the rise in respiration rates and the decline in ambient O2 with temperature strengthen this mechanism in warmer water, providing a physiological rationale for the observed niche of Crocosphaera at temperatures exceeding 20°C. Our new measurements of the sensitivity to light intensity show that the rate of N2 fixation reaches saturation at a lower light intensity (∼100 μmol m−2 s−1) than photosynthesis and that both are similarly inhibited by light intensities of >500 μmol m−2 s−1. This suggests an explanation for the maximum population of Crocosphaera occurring slightly below the ocean surface.