Are changes in atmospheric cleansing responsible for observed variations of impurity concentrations in ice cores?

Abstract

A simple model tests the effect on ice-core impurity concentrations of climate-induced changes in the physical conditions of the atmosphere influencing transport and deposition processes, while keeping source areas and production rates constant. The model results show that the increased glacial concentrations observed for most impurities can be explained entirely by changes in transport and deposition. No increase in source emission is necessary, however possible, to explain the ten-fold increase in impurity concentrations during the Last Glacial Maximum. This shows that the effect of dynamic changes in the atmosphere can be large and has to be taken into account before translating deposition records into emission records. The total impurity content in the global atmosphere during the glacial period was higher if dynamic changes in the atmosphere rather than source-emission changes were responsible for the variations observed in polar areas. This implies that a climate-forcing mechanism is to be found in the dynamics of the atmosphere, since the radiative properties of the atmosphere depend on the total content of impurities in the atmosphere. The effect on the climate can probably be compared with, although opposite in sign to, the present-day anthropogenic greenhouse forcing.