Hydroxyl Radical Photoproduction in the Sea and Its Potential Impact on Marine Processes

TLDR

The study measured photochemical production rates and steady‑state concentrations of hydroxyl radicals in sunlight‑irradiated seawater. Hydroxyl radical production ranged from 110 nM h⁻¹ in coastal surface water to 10 nM h⁻¹ in the open ocean, driven mainly by UV‑B (280–320 nm) photolysis of dissolved organic matter, with upwelling regions also contributing via nitrite/nitrate photolysis; deep‑sea DOM is degraded 6–15 times faster by ⋅OH, potentially explaining discrepancies in dissolved organic carbon measurements.

Abstract

Photochemical production rates and steady-state concentrations of hydroxyl radicals (⋅OH) were measured in sunlight-irradiated seawater. Values ranged from 110 nanomolar per hour and 12 × 10 -18 molar in coastal surface water to 10 nanomolar per hour and 1.1 × 10 -18 molar in open ocean surface water. The wavelengths responsible for this production are in the ultraviolet B region (280 to 320 nanometers) of the solar spectrum. Dissolved organic matter (DOM) appears to be the main source for ⋅OH over most of the oceans, but in upwelling areas nitrite and nitrate photolysis may also be important. DOM in the deep sea is degraded more readily by ⋅OH (and its daughter radicals), by a factor of 6 to 15, than is DOM in open-ocean surface water. This finding may in part bear on major discrepancies among current methods for measuring dissolved organic carbon in seawater.