Major role of ultraviolet-B in controlling bacterioplankton growth in the surface layer of the ocean

There is evidence that the potentially harmful solar ultraviolet-B (UV-B, 280-320 mm) radiation penetrates much deeper into the ocean's water column than previously thought^1,2. UV-B radiation is also responsible for photochemical degradation of refractory macromolecules into biologically labile organic compounds^3,4. It thus seems reasonable to assume that UV-B radiation might influence the cycling of organic matter in the sea, which is believed to be largely mediated by bacterioplankton⁵. Here we report that bacterioplankton activity in the surface layers of the oceans is suppressed by solar radiation by about 40% in the top 5 m of the water column in nearshore waters, whereas in oligotrophic open oceans suppression might be detectable to a depth of >10 m. Bacterioplankton from near-surface (0.5 m depth) waters of a highly stratified water column were as sensitive to surface UV-B radiation as subpycnocline bacteria, indicating no adaptative mechanisms against surface solar radiation in near-surface bacterioplankton consortia. Surface solar radiation levels also photochemically degrade bacterial extracellular enzymes. Thus elevated UV-B radiation due to the destruction of the stratospheric ozone layer might lead to reduced bacterial activity and accompanying increased concentration of labile dissolved organic matter in the surface layers of the ocean as bacterial uptake of this is retarded.