IMPURITY INFLUENCE ON NORMAL GRAIN-GROWTH IN THE GISP2 ICE CORE, GREENLAND

Intercept analysis of approximately bi-yearly vertical thin sections f rom the upper part of the GISP2 ice core, central Greenland, shows tha t grain-size ranges increase with increasing age. This demonstrates th at something in the ice affects grain-growth rates, and that grain-siz e cannot be used directly in paleothermometry as has been proposed. Co rrelation of grain-growth rates to chemical and isotopic data indicate s slower growth in ice with higher impurity concentrations, and especi ally slow growth in ''forest-fire'' layers containing abundant ammoniu m; however, the impurity/grain-growth relations are quite noisy. Littl e correlation is found between growth rate and isotopic composition of ice.