Sharpless Charles M.

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Sharpless
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Charles M.
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  • Article
    Production of two highly abundant 2-methyl-branched fatty acids by blooms of the globally significant marine cyanobacteria Trichodesmium erythraeum
    (American Chemical Society, 2021-08-26) Gosselin, Kelsey M. ; Nelson, Robert K. ; Spivak, Amanda C. ; Sylva, Sean P. ; Van Mooy, Benjamin A. S. ; Aeppli, Christoph ; Sharpless, Charles M. ; O’Neil, Gregory W. ; Arrington, Eleanor C. ; Reddy, Christopher M. ; Valentine, David L.
    The bloom-forming cyanobacteria Trichodesmium contribute up to 30% to the total fixed nitrogen in the global oceans and thereby drive substantial productivity. On an expedition in the Gulf of Mexico, we observed and sampled surface slicks, some of which included dense blooms of Trichodesmium erythraeum. These bloom samples contained abundant and atypical free fatty acids, identified here as 2-methyldecanoic acid and 2-methyldodecanoic acid. The high abundance and unusual branching pattern of these compounds suggest that they may play a specific role in this globally important organism.
  • Article
    Oxygen isotopes (delta O-18) trace photochemical hydrocarbon oxidation at the sea surface
    (American Geophysical Union, 2019-05-31) Ward, Collin P. ; Sharpless, Charles M. ; Valentine, David L. ; Aeppli, Christoph ; Sutherland, Kevin M. ; Wankel, Scott D. ; Reddy, Christopher M.
    Although photochemical oxidation is an environmental process that drives organic carbon (OC) cycling, its quantitative detection remains analytically challenging. Here, we use samples from the Deepwater Horizon oil spill to test the hypothesis that the stable oxygen isotope composition of oil (δ18OOil) is a sensitive marker for photochemical oxidation. In less than one‐week, δ18OOil increased from −0.6 to 7.2‰, a shift representing ~25% of the δ18OOC dynamic range observed in nature. By accounting for different oxygen sources (H2O or O2) and kinetic isotopic fractionation of photochemically incorporated O2, which was −9‰ for a wide range of OC sources, a mass balance was established for the surface oil's elemental oxygen content and δ18O. This δ18O‐based approach provides novel insights into the sources and pathways of hydrocarbon photo‐oxidation, thereby improving our understanding of the fate and transport of petroleum hydrocarbons in sunlit waters, and our capacity to respond effectively to future spills.