THE CO2 CONCENTRATION OF AIR TRAPPED IN GREENLAND ICE-SHEET PROJECT-2ICE FORMED DURING PERIODS OF RAPID CLIMATE-CHANGE

The CO2 content of air occluded in Greenland Ice Sheet Project 2 (GISP 2) ice formed over two separate intervals of rapidly changing climate, centered at approximately 46 and 63 kyr B.P., is as much as 90 ppm mo re during warm periods (interstadials) than during cold periods (stadi als). These CO2 variations are superimposed on changes in annual layer thickness and delta(18) O of the ice and do not show the 200- to 700- year offsets which would be expected for concurrent variations in the atmosphere and the ice. The CO2 concentrations during the stadials are similar to the atmospheric values recorded by Antarctic ice of the sa me age, so processes occurring in the ice after bubble enclosure must be enriching the air trapped in GISP2 ice formed during the interstadi als. This conclusion is supported by Ca content and electrical conduct ivity measurements of the ice, which show that adequate carbonate is p resent to produce these enrichments and that CO2 content is high only when the electrical conductivity (a proxy for H+ concentration) is hig h. High-resolution mapping of one 4-cm section of ice shows a 200-ppm increase in the CO2 content of the trapped air, from approximately 275 to 475 ppm. Analyses of the total inorganic carbon of ice from both t he LGM and Holocene show that most of the Ca in the ice is from CaCO3 and that the delta(13)CO(2) approaches that of soil and marine carbona tes. These results show that the CO2 record preserved in ice can be al tered by in situ decarbonation reactions and that only ice containing either abundant carbonate or essentially no carbonate contains a relia ble record of paleoatmospheric CO2.