Ocean Science

Light Sunburn

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Science  13 Jun 2003:
Vol. 300, Issue 5626, pp. 1625
DOI: 10.1126/science.300.5626.1625a

Springtime depletion of stratospheric ozone over Antarctica (the ozone hole) allows more ultraviolet B radiation to reach the sea surface, which decreases phytoplankton productivity. In localized studies, estimates of the impact on oceanic photosynthesis have varied, with daily losses ranging from <1 to 12% in comparison to the phytoplankton carbon fixation measured during normal ozone concentrations. Most regional estimates of ozone-related productivity losses have been based either on spatial extrapolations of these local values or on calculations that assume a spatially uniform ozone concentration (an idealized hole).

In order to avoid these assumptions of homogeneity, Arrigo et al. use numerical modeling and accurate maps of ozone abundance to assess the large-scale effects of stratospheric ozone depletion on oceanic primary production. They take into account the complicating effects of vertical mixing, spatial and temporal variations in ozone abundance, sea ice cover, cloudiness, wind speed, ocean mixed layer depth, and phytoplankton chlorophyll a. They conclude that ultraviolet radiation-induced losses of surface phytoplankton production are substantial under all ozone conditions, mostly due to ultraviolet A, but that the loss of primary production resulting from enhanced fluxes of ultraviolet B (integrated to 0.1% light depth) was less than 0.25%. The loss of primary production is minimized by the strong attenuation of ultraviolet radiation within the water column and by sea ice, which is at its peak extent during the months when ozone is lowest.—HJS

J. Geophys. Res. 108, 3154 (2003).

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