A 135,000-Year Vostok-Specmap Common Temporal Framework

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The object of the present study is to introduce a means of comparing the Vostok and marine chronologies. Our strategy has been to use the delta(18)O of atmospheric O-2 (denoted delta(18)O(atm)) from the Vostok ice core as a proxy for the delta(18)O of seawater (denoted delta(18)O(sw)). Our underlying premise in using delta(18)O(atm) as a proxy for delta(18)O(sw) is that past variations in delta(18)O(sw) (an indicator of continental ice volume) have been transmitted to the atmospheric O-2 reservoir by photosynthesizing organisms in the surface waters of the world's oceans. We compare our record of delta(18)O(atm) to the delta(18)O(sw) record which has been developed from studies of the isotopic composition of biogenic calcite (delta(18)O(foram)) in deep-sea cores. We have tied our delta(18)O(atm) record from Vostok to the SPECMAP timescale throughout the last 135 kyr by correlating delta(18)O(atm) with a delta(18)O(sw) record from V19-30. Results of the correlation indicate that 77% of the variance is shared between these two records. We observed differences between the delta(18)O(atm) and the delta(18)O(sw) records during the coldest periods, which indicate that there have been subtle changes in the factors which regulate delta(18)O(atm) other than delta(18)O(sw). Our use of delta(18)O(atm) as a proxy for delta(18)O(sw) must therefore be considered tentative, especially during these periods. By correlating delta(18)O(atm) with delta(18)O(sw), we provide a common temporal framework for comparing phase relationships between atmospheric records (from ice cores) and oceanographic records constructed from deep-sea cores. Our correlated age-depth relation for the Vostok core should not be considered an absolute Vostok timescale. We consider it to be the preferred timescale for comparing Vostok climate records with marine climate records which have been placed on the SPECMAP timescale. We have examined the fidelity of this common temporal framework by comparing sea surface temperature (SST) records from sediment cores with an Antarctic temperature record from the Vostok ice core. We have demonstrated that when the southern ocean SST and Antarctic temperature records are compared on this common temporal framework, they show a high degree of similarity. We interpret this result as supporting our use of the common temporal framework for comparing other climate records from the Vostok ice core with any climate record that has been correlated into the SPECMAP chronology.


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