CHANGES IN NATURAL LEAD, COPPER, ZINC AND CADMIUM CONCENTRATIONS IN CENTRAL GREENLAND ICE FROM 8250 TO 149,100 YEARS AGO - THEIR ASSOCIATION WITH CLIMATIC CHANGES AND RESULTANT VARIATIONS OF DOMINANT SOURCE CONTRIBUTIONS

We present here the first reliable time series of Ph, Cu, Zn and Cd in Greenland ice for the last climatic cycle. They were obtained by anal ysing various sections of the 3028.8 m GRIP deep ice core drilled at S ummit, central Greenland. Our results show that climatic changes have led to large variations in the concentrations of natural Pb, Cu, Zn an d Cd in the high-latitude troposphere of the Northern Hemisphere, Betw een the interglacial and glacial periods, concentrations have varied b y factors of similar to 320 for Pb, 100 for Cu, 36 for Zn and 13 for C d. Based on a good correlation between each heavy metal and Al, Pb and Cu are found to have mainly originated from soil and rock dust for bo th glacial and interglacial periods, On the other hand, continental bi ogenic emissions were the main source of Cd and to a lesser extent Zn in the Arctic troposphere during the warm Eemian and the Pre-Boreal to Holocene transition, whereas wind-blown dust was the predominant sour ce for these two metals during the cold glacial climatic stages, This characteristic change of relative Cd and Zn contributions from differe nt sources in contrast to that for Pb and Cu is well documented in the ice from the last deglaciation period (15,000 to 8250 yrs ago), After the Younger Dryas event ended, a remarkable increase of Cd/Al and Zn/ Al ratios occurred from 13,000 to 9300 yrs ago, which is consistent wi th the progressive expansion of vegetation following the retreat of th e North American and North Eurasian ice sheets. The subsequent decreas e of these ratios to Holocene values can be explained by the stabiliza tion of atmospheric circulation in the northern high-latitude regions, which became similar to that for the Holocene due to further reductio n of the Laurentide ice sheet, Finally, the observed variations of the metal/Al ratios suggest changes in the soil and rock dust source regi ons in parallel with climatic changes which have altered the mean comp osition of the crustal particles transported to the Arctic.