ICE CORE AGE DATING AND PALEOTHERMOMETER CALIBRATION BASED ON ISOTOPEAND TEMPERATURE PROFILES FROM DEEP BOREHOLES AT VOSTOK STATION (EAST ANTARCTICA)

An interpretation of the deuterium profile measured along the Vostok ( East Antarctica) ice core down to 2755 m has been attempted on the bas is of the borehole temperature analysis. An inverse problem is solved to infer a local ''geophysical metronome,'' the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of Mi lankovich periods. By correlating the smoothed isotopic temperature re cord to the metronome, a chronostratigraphy of the Vostok ice core is derived with an accuracy of +/-3.0-4.5 kyr. The developed timescale pr edicts an age of 241 kyr at a depth of 2760 m, The ratio delta D/delta T-i between deuterium content and cloud temperature fluctuations (at the top of the inversion layer) is examined by fitting simulated and m easured borehole temperature profiles. The conventional estimate of th e deuterium-temperature slope corresponding to the present-day spatial ratio (9 per mil/degrees C) is confirmed in general. However, the mis match between modeled and measured borehole temperatures decreases not iceably if we allow surface temperature, responsible for the thermal s tate of the ice sheet, to undergo more intensive precession oscillatio ns than those of the inversion temperature traced by isotope record. W ith this assumption, we obtain the long-term temporal deuterium-temper ature slope to be 5.8-6.5 per mil/degrees C which implies that the gla cial-interglacial temperature increase over central Antarctica was abo ut 15 degrees C in the surface temperature and 10 degrees C in the inv ersion temperature. Past variations of the accumulation rate and the c orresponding changes in the ice-sheet surface elevation are simultaneo usly simulated.