A COMPARISON OF THE VOSTOK ICE DEUTERIUM RECORD AND SERIES FROM SOUTHERN-OCEAN CORE MD-88-770 OVER THE LAST 2 GLACIAL-INTERGLACIAL CYCLES

Taking advantage of the fact that the Vostok deuterium (delta D) recor d now covers almost two entire climatic cycles, we have applied the or bital tuning approach to derive an age-depth relation for the Vostok i ce core, which is consistent with the SPECMAP marine time scale. A sec ond age-depth relation for Vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from Souther n Ocean core MD 88-770. Both methods lead to a close correspondence be tween Vostok and MD 88-770 time series. However, the coherence between the correlated delta D and insolation is much lower than between the orbitally tuned delta D and insolation. This reflects the lower accura cy of the correlation method with respect to direct orbital tuning. We compared the ice and marine records, set in a common temporal framewo rk, in the time and frequency domains. Our results indicate that chang es in the Antarctic air temperature quite clearly lead variations in g lobal ice volume in the obliquity and precession frequency bands. More over, the average phase we estimated between the filtered delta D and insolation signals at precessional frequencies indicates that variatio ns in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the sum mer in northern low latitudes or winter in southern low latitudes, The relatively large lag found between Vostok delta D variations and obli quity-driven changes in insolation suggests that variations in the loc al radiative balance are not the only mechanism responsible for the va riability in surface temperature at those frequencies. Finally, in con trast to the cross-spectral analysis method used in previous studies, the method we use here to estimate the phases can reveal errors in cro ss-correlations with orbitally tuned chronologies.