Control of biological exposure to UV radiation in the Arctic Ocean: Comparison of the roles of ozone and riverine dissolved organic matter

Reports of severe stratospheric ozone depletion over the Arctic have height ened concern about the potential impact of rising ultraviolet-B (UV-B) radi ation on north polar aquatic ecosystems. Our optical measurements and model ling results indicate that the ozone-related UV-B influence on food web pro cesses in the Arctic Ocean is likely to be small relative to the effects ca used by variation in the concentrations of natural UV-absorbing compounds, known as chromophoric dissolved organic matter (CDOM), that enter the Arcti c basin via its large river inflows. The aim of our present study was to de velop and apply a simple bio-optical index that takes into account the comb ined effects of attenuation by atmospheric ozone and water column CDOM, and photobiological weighting for high-latitude environments such as the Arcti c Ocean. To this end, we computed values for a biologically effective UV do se rate parameter ("weighted transparency" or T*) based on underwater UV me asurements in high-latitude lakes and rivers that discharge into the Arctic Ocean; measured incident UV radiation at Barrow, Alaska: and published bio logical weighting curves for UV-induced DNA damage and UV photoinhibition o f photosynthesis. The results underscore how strongly the Arctic Ocean is i nfluenced by riverine inputs: shifts in CDOM loading (e.g., through climate change, land-use practices, or changes in ocean circulation) can cause var iations in biological UV exposure of much greater magnitude than ozone-rela ted effects.