Sutherland Kevin M.

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Last Name
Sutherland
First Name
Kevin M.
ORCID
0000-0002-4617-3375

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Subject: Photochemical oxidation ×

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Revised microbial and photochemical triple-oxygen isotope effects improve marine gross oxygen production estimates

2022-10-12 , Sutherland, Kevin M. , Johnston, David T. , Hemingway, Jordon D. , Wankel, Scott D. , Ward, Collin P.

AbstractThe biogeochemical fluxes that cycle oxygen (O2) play a critical role in regulating Earth’s climate and habitability. Triple-oxygen isotope (TOI) compositions of marine dissolved O2 are considered a robust tool for tracing oxygen cycling and quantifying gross photosynthetic O2 production. This method assumes that photosynthesis, microbial respiration, and gas exchange with the atmosphere are the primary influences on dissolved O2 content, and that they have predictable, fixed isotope effects. Despite its widespread use, there are major elements of this approach that remain uncharacterized, including the TOI dynamics of respiration by marine heterotrophic bacteria and abiotic O2 sinks such as the photochemical oxidation of dissolved organic carbon (DOC). Here, we report the TOI fractionation for O2 utilization by two model marine heterotrophs and by abiotic photo-oxidation of representative terrestrial and coastal marine DOC. We demonstrate that TOI slopes associated with these processes span a significant range of the mass-dependent domain (λ = 0.499 to 0.521). A sensitivity analysis reveals that even under moderate productivity and photo-oxidation scenarios, true gross oxygen production may deviate from previous estimates by more than 20% in either direction. By considering a broader suite of oxygen cycle reactions, our findings challenge current gross oxygen production estimates and highlight several paths forward to better understanding the marine oxygen and carbon cycles.

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Oxygen isotopes (delta O-18) trace photochemical hydrocarbon oxidation at the sea surface

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.

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