Hydrogen peroxide and superoxide photoproduction in diverse marine waters: A simple proxy for estimating direct CO₂ photochemical fluxes

Abstract

The photoproduction of H 2 O 2 and CO 2 exhibits a well-defined relationship with an average CO 2 : H 2 O 2 molar ratio of 6.6 ± 1.8 as determined in a variety of marine waters ranging from a dark tidal creek to clear offshore stations near the Gulf Stream. Even when corrected for photobleaching, accumulation of both H 2 O 2 and CO 2 was not linear beyond 12 h of constant irradiation, with interval rates indicating that production efficiency for both products decreased with increasing photon dose. Direct measurements of O 2 À photoproduction, together with its dark thermal decay to H 2 O 2 , indicate that O 2 À may be the better proxy for photochemical dissolved organic matter oxidation to CO 2. Given the very short irradiation times needed to determine O 2 À production rates (~2-5 min), determination of O 2 À photoproduction may provide robust estimates for initial CO 2 photoproduction rates even in blue water, allowing greatly improved estimates for the global significance of dissolved organic carbon photooxidation.

Using liquid chromatography‐isotope ratio mass spectrometry to measure the δ13C of dissolved inorganic carbon photochemically produced from dissolved organic carbon

“…Therefore, CDOM absorption spectra, measured at each time point during the irradiation, were used to correct all DIC rates for the loss of CDOM with an average % fading value for wavelengths in the UV (280–400 nm). As in previous studies (Powers and Miller 2015 a,b ), the drop in DIC photoproduction rates with continued irradiation cannot be quantitatively explained by the loss in CDOM alone (DIC production rates corrected for fading, Table ). Following Eq.…”

Apparent quantum yield of photochemical dissolved organic carbon mineralization in lakes

“…Hence, with increasing experimental duration, the initial photochemical DIC production may be underestimated. Therefore, choosing the duration of the irradiation represents a trade‐off of being long enough to yield reliably detectable photochemical DIC production but as short as possible to remain within the initial linear increase in DIC concentrations (Miller ; Powers and Miller ). Since we irradiated low‐CDOM water samples longer than high‐CDOM water samples during AQY determination this might result in linear trends due to differences in irradiation time rather than water properties such as, for example, water color.…”

“…in DIC concentrations (Miller 1998;Powers and Miller 2015a). Since we irradiated low-CDOM water samples longer than high-CDOM water samples during AQY determination this might result in linear trends due to differences in irradiation time rather than water properties such as, for example, water color.…”

Apparent Quantum Efficiency Spectra for Superoxide Photoproduction and Its Formation of Hydrogen Peroxide in Natural Waters

“…One last critical issue for any accurate AQY calculation made using a single time point measurement is the assumption that photochemical production is linear to the point at which the sample is sacrificed and measured. As noted previously, H 2 O 2 photochemical efficiency decreases with prolonged exposure ( Kieber et al, 2014;Powers and Miller, 2015a). Therefore, to ensure H 2 O 2 photoproduction was always a linear function of photon dose during our AQY experiments, we performed broadband irradiation of SRE water and plotted the resulting data against Q a (λ) integrated from 280 to 600 nm (mol photons absorbed) at each time point over the course of the irradiation (Figure 2).…”