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Abstract Marine microbes produce extracellular reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H2O2) as a result of regulated and nonregulated physiological and metabolic reactions. ROS production can be a sink and cryptic recycling flux of dissolved oxygen that may rival other key fluxes in the global oxygen cycle; however, the low abundance and high turnover rate of ROS makes this figure difficult to constrain. One key step in determining the disparity between the gross production of ROS and the net sink of dissolved oxygen lies in understanding the degradation pathways of H2O2in the marine water column. In this study, we use isotope‐labeling techniques to determine the redox fate of H2O2in a range of marine environments off the West Coast of California. We find that H2O2reduction is greater than or equal to H2O2oxidation at most sampled depths, with notable exceptions in some surface and intermediate water depths. The observation that H2O2oxidation can exceed reduction in the dark ocean indicates the presence of an oxidizing decay pathway that is not among the known suite of microbially mediated enzymatic pathways (i.e., catalase and peroxidase), pointing to an abiotic and/or a nonenzymatic decay pathway at intermediate water depths. These results highlight the complexity and heterogeneity of ROS decay pathways in natural waters and their unconstrained regulation of oxygen levels within the ocean.
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Examining superoxide dynamics in irradiated natural waters
Abstract Superoxide () is a reactive oxygen species (ROS) that is primarily produced by the one‐electron transfer of photooxidized chromophoric dissolved organic matter (CDOM) to O2in sunlit natural waters. Here we examine the environmental and chemical parameters (pH, ionic strength, buffer, and halides) that may influence photochemical production rates and decay pathways in natural water. Using the enzyme superoxide dismutase and H2O2measurements, we present results from an irradiated freshwater CDOM source indicating that reductive decay pathways (P/PSOD) dominate with increased pH and NaCl additions and maximal photoproduction rates () increase with carbonate compared to borate buffer. Over 2 h of irradiation, a significant decline in was seen for all samples along with a minor increase in oxidative pathways. These results imply shifts in decay pathways and production rates that seem to vary across natural waters and as a function of irradiation history.
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- Award ID(s):
- 1924763
- PAR ID:
- 10399437
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 68
- Issue:
- 4
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 878-890
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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