title: Blending remote sensing data products to estimate photochemical production of hydrogen peroxide and superoxide in the surface ocean.
abstract: Hydrogen peroxide (H₂O₂) and its precursor, superoxide (O₂(-)), are well-studied photochemical products that are pivotal in regulating redox transformations of trace metals and organic matter in the surface ocean. In attempts to understand the magnitude of both H₂O₂ and O₂(-) photoproduction on a global scale, we implemented a model to calculate photochemical fluxes of these products from remotely sensed ocean color and modeled solar irradiances. We generated monthly climatologies for open ocean H₂O₂ photoproduction rates using an average apparent quantum yield (AQY) spectrum determined from laboratory irradiations of oligotrophic water collected in the Gulf of Alaska. Because the formation of H₂O₂ depends on secondary thermal reactions involving O₂(-), we also implemented a temperature correction for the H₂O₂ AQY using remotely sensed sea surface temperature and an Arrhenius relationship for H₂O₂ photoproduction. Daily photoproduction rates of H₂O₂ ranged from <1 to over 100 nM per day, amounting to ∼30 μM per year in highly productive regions. When production rates were calculated without the temperature correction, maximum daily rates were underestimated by 15-25%, highlighting the importance of including the temperature modification for H₂O₂ in these models. By making assumptions about the relationship between H₂O₂ and O₂(-) photoproduction rates and O₂(-) decay kinetics, we present a method for calculating midday O₂(-) steady-state concentrations ([O₂(-)]ss) in the open ocean. Estimated [O₂(-)]ss ranged from 0.1-5 nM assuming biomolecular dismutation was the only sink for O₂(-), but were reduced to 0.1-290 pM when catalytic pathways were included. While the approach presented here provides the first global scale estimates of marine [O₂(-)]ss from remote sensing, the potential of this model to quantify O₂(-) photoproduction rates and [O₂(-)]ss will not be fully realized until the mechanisms controlling O₂(-) photoproduction and decay are better understood.
authors.affiliation: Department of Marine Sciences, University of Georgia, Athens, GA 30602, USA. bmiller@uga.edu.
authors.forename: Leanne C
authors.initials: LC
authors.lastname: Powers
authors.forename: William L
authors.initials: WL
authors.lastname: Miller
mesh_terms: D004784:Environmental Monitoring; D006861:Hydrogen Peroxide / Q000032:analysis*; D007700:Kinetics; D009792:Oceans and Seas; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D058998:Remote Sensing Technology; D012623:Seawater / Q000737:chemistry*; D013481:Superoxides / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000032:analysis / Q000706:statistics & numerical data*
chemical_list: D013481:Superoxides; D006861:Hydrogen Peroxide