A CONTINUOUS 770-YEAR RECORD OF VOLCANIC ACTIVITY FROM EAST ANTARCTICA

A 100-m ice core from site G 15 (accumulation rate 0.1 m water yr1, mean annual temperature -38-degrees-C) on the Mizuho plateau, Dronning Maud Land, East Antarctica, has been analysed using the dielectric profiling (DEP) technique. The capacitance and conductance of the core were measured at ac frequencies (20 Hz-300 kHz). The high-frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity. The Tambora (1815) eruption can be identified with the aid of an approximate chronology based on the firm densification rate, other historic eruptions can then be recognised. Beyond about 300-years historical observations are very few, however if a constant overall accumulation rate is assumed, a well-known eruption of 1259 A.D. can be found near the bottom of the core. Other peaks in the conductivity profile can then be assigned dates accurate to within a few years. Using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy. The estimated acid deposisition fluxes realtive to the Tambora (1815) eruption, of Agung (1963) is 27%, Krakatoa (1883), 25%, the signal of 1601, 28%, and that of 1259, 53%.