Light absorption by soluble chemical species in Arctic and Antarctic snow

Abstract

Using a liquid core waveguide spectrophotometer we have quantified the very low light absorption of dissolved chromophores (light absorbing trace species) in filtered samples of melted polar snows. Light absorption coefficients at 280 nm span the ranges of 0.005–0.029 m−1 and 0.002–0.027 m−1 for samples from Summit, Greenland, and Dome C, Antarctica, respectively. Absorption coefficients decrease with increasing wavelength and also decrease with depth in the snowpack. At both sites, NO3− and H2O2 together account for approximately half of the summed light absorption coefficients for wavelengths of 280 nm and above; the remaining ∼50% of light absorption is due to unknown, probably organic, chromophores. Rates of sunlight absorption by soluble chromophores in surface snows are approximately (1–4) × 1011 and (0.5–9) × 1011 photons cm−3 s−1 during summer at Summit and Dome C, respectively. Approximately 50–90% of this sunlight absorption is due to unknown chromophores, while the remainder is due to hydrogen peroxide and nitrate. Although we do not know quantum yields for the photochemical reactions of the unknown chromophores, their large contribution to the rate of sunlight absorption suggests that they play an important role in the photochemistry of polar snowpacks. In addition, at Summit it appears that up to 60% of the unknown chromophores are emitted from the snow into the boundary layer during the day and redeposited at night. This flux might affect the composition and chemistry of both the snowpack and boundary layer.