LONG-TERM CHANGES IN ELEMENTAL DEPOSITION AT THE EARTHS SURFACE

The rate of deposition of elements at a point on the earth's surface can change, quite dramatically, even on relatively short time-scales, as a function of weather patterns. On a global scale volcanoes (and more rarely large meteors) can overwhelm steadier sources of trace elements. In recent centuries human activities have increased emissions to the atmosphere to a point where they are above those of natural sources for some of the rarer elements. On a longer time-scale climate change can also alter the deposition of elements, although such changes are often slower than those brought about through anthropogenic emissions. Changes in climate can also alter the distribution of deposition, but there are few studies estimating such changes. This paper uses estimates of the balance of natural and anthropogenic sources of a range of elements to examine the likely variation in deposition at the earth's surface. It particularly focuses on those elements regarded as toxic, whose concentrations seem likely to go on increasing in industrial areas.