Oceans Oceans cover more than 70% of Earth's surface and produce fish which provides about 18% of the protein consumed worldwide. Radiation that falls upon the oceans' surfaces is absorbed by the water and converted into heat energy. In clear water, uv radiation at 315 nm is attenuated at a rate of about 14%/m. So at a depth of 5m the intensity has decreased by about half. Oceans are a source and a sink for methyl bromide (CH3Br), an effective ozone-depleting compound. It is uncertain as to whether they are more efficient as a sink or source. Photo: www.arttoday.com
Lakes and Rivers Lakes and rivers are also important components of the hydrosphere. As we know, ozone reduction in middle and higher latitudes has been much greater than at equatorial latitudes. Because of other factors, however, much less uv radiation reaches the ground in the higher latitudes. Organisms at these latitudes have adapted to the relatively low levels of uv radiation; consequently, any increase they experience is important. Photo: www.arttoday.com
The northern (boreal) lakes are particularly susceptible to even small increases in uvb radiation. In these lakes, dissolved organic compounds are generally effective in limiting uvb radiation to just a few millimeters. As we saw, clear water attenuates uvb radiation at a much slower rate. Too much uvb radiation helps destroy these compounds, allowing greater penetration of the uvb into the depths of the lake. The results include downward migration of zooplankton and large reductions in chlorophyll production. Both of these conditions seriously affect the boreal lake food chain.
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