Depth-resolved photochemical production of hydrogen peroxide in the global ocean using remotely sensed ocean color

Abstract

Hydrogen peroxide (H2O2) is an important reactive oxygen species (ROS) in natural waters, affecting water quality via participation in metal redox reactions and causing oxidative stress for marine ecosystems. While attempts have been made to better understand H2O2 dynamics in the global ocean, the relative importance of various H2O2 sources and losses remains uncertain. Our model improves previous estimates of photochemical H2O2 production rates by using remotely sensed ocean color to characterize the ultraviolet (UV) radiation field in surface water along with quantitative chemical data for the photochemical efficiency of H2O2 formation. Wavelength- and temperature-dependent efficiency (i.e., apparent quantum yield, AQY) spectra previously reported for a variety of seawater sources, including coastal and oligotrophic stations in Antarctica, the Pacific Ocean at Station ALOHA, the Gulf of Mexico, and several sites along the eastern coast of the United States were compiled to obtain a “marine-average” AQY spectrum. To evaluate our predictions of H2O2 photoproduction in surface waters using this single AQY spectrum, we compared modeled rates to new measured rates from Gulf Stream, coastal, and nearshore river-outflow stations in the South Atlantic Bight, GA, United States; obtaining comparative differences of 33% or less. In our global model, the “marine-average” AQY spectrum was used with modeled solar irradiance, together with satellite-derived surface seawater temperature and UV optical properties, including diffuse attenuation coefficients and dissolved organic matter absorption coefficients estimated with remote sensing-based algorithms. The final product of the model, a monthly climatology of depth-resolved H2O2 photoproduction rates in the surface mixed layer, is reported for the first time and provides an integrated global estimate of ∼21.1 Tmol yr−1 for photochemical H2O2 production. This work has important implications for photo-redox reactions in seawater and improves our understanding of the role of solar irradiation on ROS cycling and the overall oxidation state in the oceans.

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions

“…While 1 O 2 production was confirmed in this system with FFA ([ 1 O 2 ] ss = 2 pM) and may have contributed to the degradation of 6PPDQ, it is apparent that there is a second unknown reaction contributing to 6PPDQ attenuation in these microcosms. Previous work has reported that semiquinones, produced by the one-electron reduction of quinones, may catalyze metal-independent reduction of hydrogen peroxide to generate a hydroxyl radical. − While this work focuses on photochemical pathways, future work should investigate the potential interplay between 6PPDQ redox properties and environmental photoproduction of hydrogen peroxide . To further test the hypothesis that the production of 1 O 2 in sunlit waters by dissolved organic matter may contribute to its degradation in the environment, we conducted additional experiments employing either furfuryl alcohol (FFA, 5 mM) or sodium azide (NaN 3 , 1 mM) as a 1 O 2 scavenger in SRFA microcosms.…”

“…31−33 While this work focuses on photochemical pathways, future work should investigate the potential interplay between 6PPDQ redox properties and environmental photoproduction of hydrogen peroxide. 34 To further test the hypothesis that the production of 1 O 2 in sunlit waters by dissolved organic matter may contribute to its degradation in the environment, we conducted additional experiments employing either furfuryl alcohol (FFA, 5 mM) or sodium azide (NaN 3 , 1 mM) as a 1 O 2 scavenger in SRFA microcosms. The attenuation rate of 6PPDQ in the presence of 1 O 2 scavengers was observed to decrease more than in the presence of the • OH scavenger isopropanol (IPA, 17.5 mM) (Figure 3c).…”

Reactive oxygen species and chromophoric dissolved organic matter drive the aquatic photochemical pathways and photoproducts of 6PPD-Quinone under simulated high-latitude conditions

“…[31][32][33] While this work focuses on photochemical pathways, future work should investigate the potential interplay between 6PPDQ redox properties and environmental photo-production of hydrogen peroxide. 34 To further test the hypothesis that the production of 1 O2 in sunlit waters by dissolved organic matter may contribute to its degradation in the environment, we conducted additional experiments employing either furfuryl alcohol (FFA, 5 mM) or sodium azide (NaN3, 1 mM) as a 1 O2 scavenger in SRFA microcosms. The attenuation rate of 6PPDQ in the presence of 1 O2 scavengers was observed to decrease more than in the presence of the •OH scavenger isopropanol (IPA, 17.5 mM) (Figure 3c).…”

Global Ocean dimethylsulfide photolysis rates quantified with a spectrally and vertically resolved model

“…Unlike previous assessments of photochemical processes, which used a fixed AQY spectrum globally (Fichot and Miller 2010;Zhu and Kieber 2020;Zhu et al 2022), spectrally and vertically resolved DMS photolysis assessments require an additional submodel that accounts for AQY variability. Here, we used two alternative parameterizations developed using insitu datasets that encompass the wide ranges of variability of AQY and its predictors (Supplementary Table S1).…”