Controls on the photochemical production of hydrogen peroxide in arctic surface waters

Abstract

Photochemical production of hydrogen peroxide (H2O2) from chromophoric/colored dissolved organic matter (CDOM) is a major source of H2O2 in natural waters. In a rapidly warming Arctic, H2O2 may increase due to thawing permafrost soils that are expected to export more CDOM to sunlit surface waters. At the same time, arctic surface waters are increasingly ice-free and thus exposed to sunlight for greater lengths of time during the summer. Thus, it has been hypothesized that photochemical production of H2O2 and H2O2 concentrations may increase in arctic surface waters. Testing this hypothesis requires determination of whether H2O2 production by CDOM is limited by CDOM concentration (substrate-limited) or by sunlight (light-limited). In waters with high concentrations of CDOM, H2O2 production may be limited by the sunlight reaching the water. In waters with low concentrations of CDOM, H2O2 production may be limited by CDOM concentration. This study quantified the substrate and light limitation of H2O2 production in surface waters of the Alaskan Arctic in summer 2022 and 2023. In each water, concentrations of CDOM were measured along with the apparent quantum yield of H2O2 (𝝓𝝓H2O2,λ) produced from CDOM. The 𝝓𝝓H2O2,λ increased with increasing aromatic content of the CDOM. Photochemical production rates for all waters in this study were strongly limited by sunlight and limited by CDOM concentration. Photochemical production of H2O2 increased linearly with increasing sunlight and non-linearly with increasing CDOM. Thus, increasing sunlight exposure of arctic lakes (due to less ice cover) will increase H2O2 production and likely increase H2O2 concentrations. Likewise, increasing CDOM concentrations in arctic lakes due to export of CDOM from thawing permafrost soils will likely also increase H2O2 production in lake waters where H2O2 production is limited by CDOM.