USE OF TEPHROCHRONOLOGY IN THE EVALUATION OF ACCUMULATION RATES ON NELSON ICE CAP, SOUTH SHETLAND ISLANDS, ANTARCTICA

A volcanic ash layer was observed in the 3 ice cores on the Nelson Ice Cap, Antarctica. A comparison of major elemental composition of glass shards from the 3 tephra layers with average whole-rock compositions of 1967-1970 eruptions on the Deception Island and of glass shards fro m other suspected Deception Island eruptions collected from Antarctic ice and firn indicate that the most reasonable source for the tephra i n the Nelson Ice Cap cores is the 1970 eruption on the Deception Islan d. From the depth of the volcanic ash layer and measured density profi le of the cores, the net accumulation rate at the summit, Core GW, is 1200 g . cm(-2) . a(-1) during the past 20 years, and the net accumula tion rates are 700 g . cm(-2) . a(-1) and 6 g . cm(-2) . a(-1) at site s N30 and N50, respectively. In the eastern part of the Nelson Ice Cap , the accumulation rate may be higher than that in the northern part, because no volcanic ash in ice cores was observed at similar depths co llected from this region.