Photochemical production of hydrogen peroxide in Antarctic Waters

Photochemical production rates of hydrogen peroxide (H₂O₂) were determined in Antarctic waters during two research cruises. The first cruise was from mid-October to mid-November, 1993, in the confluence of the Weddell and Scotia Seas, and the second cruise was in December, 1994, along the coast of the Antarctic Peninsula. During these cruises, midday sea-surface production rates ranged from 2.1 to 9.6 nM h^?1, with an average rate of 4.5 nM h^?1. Production rates were consistently smaller than rates determined at lower latitudes (>9 nM h^?1), primarily due to the colder temperatures and lower ultraviolet irradiances in polar waters. In situ production rates were determined with a free-floating drifter that was deployed for 12–14 h. Production rates, averaged over the deployment time, were highest at or near the surface (ca. 2.4–3.5 nM h^?1) and decreased rapidly with depth to 0.1–0.7 nM h^?1 at 10–20 m. The decrease in production rates with depth generally paralleled the decrease in ultraviolet irradiance in the water column. Production rates of hydrogen peroxide in Antarctic seawater were largely controlled by the ultraviolet irradiance in the water column, although there was some evidence for production in the blue region of the solar spectrum. A laboratory study was conducted to determine the wavelength dependence of the apparent quantum yield for the photochemical formation of hydrogen peroxide in Antarctic waters. Apparent quantum yields determined at 0°C decreased from 0.74×10^?3 mol einstein^?1 at 290 nm to 1.0×10^?5 mol einstein^?1 410 nm. At 20°C, apparent quantum yields for the photochemical production of hydrogen peroxide were within a factor of two of apparent quantum yields determined in temperate waters at 20–25°C. Sunlight-normalized H₂O₂ production rates were determined as a function of wavelength using noontime irradiance data from Palmer Station, Antarctica. A decrease in stratospheric ozone from 336 to 151 Dobson units resulted in a predicted 19–42% increase in the photoproduction of H₂O₂ at the sea surface in Antarctic waters. The magnitude of this increase depends on the concentration and absorbance characteristics of dissolved organic matter in the photic zone, as well as on other factors such as cloudiness and decreasing solar zenith angle that tend to lower photochemical rates offsetting increases due to stratospheric ozone depletion.