CH4 AND DELTA-O-18 OF O-2 RECORDS FROM ANTARCTIC AND GREENLAND ICE - A CLUE FOR STRATIGRAPHIC DISTURBANCE IN THE BOTTOM PART OF THE GREENLAND ICE CORE PROJECT AND THE GREENLAND ICE-SHEET PROJECT-2 ICE CORES

The suggestion of climatic instability during the last interglacial pe riod (Eem), based on the bottom 10% of the Greenland Ice core Project (GRIP) isotopic profile, has been questioned because the bottom record from the neighboring Greenland Ice Sheet Project 2 (GISP2) core (28 k m away) is strikingly different over the same interval and because rec ords of the delta(18)O of atmospheric O-2 from both cores showed unexp ected rapid fluctuations. Here we present detailed methane records fro m the Vostok (Antarctica), GRIP, and GISP2 cores over the relevant int ervals. The GRIP and GISP2 data show rapid and large changes in methan e concentration, which are correlative with variations of the delta(18 )O of the ice, while the Vostok record shows no such variations. This discrepancy reinforces the suggestion that the bottom sections of the Greenland records are disturbed. By combining the methane data with me asurements of delta(18)O of O-2 in the same samples, we attempt to con strain the nature of the stratigraphic disturbance and the age of the analyzed ice samples. Our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice c ores and that some of the apparent climate instabilities in the GRIP c ore would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penult imate glaciation.