UVA variability overrules UVB ozone depletion effects on the photoreduction of iron in the Southern Ocean

Rijkenberg, Micha J.A., Gerringa, Loes J.A., Neale, Patrick J., Timmermans, Klaas R., Buma, Anita G.J. and de Baar, Hein J.W. (2004) UVA variability overrules UVB ozone depletion effects on the photoreduction of iron in the Southern Ocean. Geophysical Research Letters, 31 (24), L24310. (doi:10.1029/2004GL020829).

Abstract

A spectral weighting function describing the wavelength dependency of the photoproduction of Fe( II) in Antarctic seawater was established. The strong wavelength-dependent photoproduction of Fe( II) from amorphous ferric hydroxides can be described as an exponential function: epsilon(lambda) = 3.57 . 10(3) . e (-0.02)((lambda-300)). Solar spectra recorded during the 2000 Antarctic ozone depletion season were used to demonstrate that daily and seasonal variability of the ultraviolet A ( UVA: 315-400 nm) and the visible part of the light spectrum (VIS: 400-700 nm) dominates Fe( II) production rates in surface waters ( respectively > 60% and about 30%) and in the water column. Although ultraviolet B ( UVB: 280-315 nm) is the most effective wavelength region for Fe( II) photoproduction, the impact of UVB was small due to the relatively low flux of UVB into the ocean surface waters. However, the impact of UVB did indeed increase significantly from 3.54 to 6.15 % during the austral ozone minimum.

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