TEPHRA LAYERS AND ICE CHEMISTRY IN THE BYRD-STATION ICE CORE, ANTARCTICA (VOLCANOLOGY, GLACIOLOGY)

Volcanic ash layers in an ice core from Byrd Station (80(DEGREES)01' S, 119(DEGREES)31' W), West Antarctica were examined in order to establish the sources of volcanism that have contributed to the soluble and insoluble impurity concentrations of Antarctic ice. The composition, grain size distribution and particle morphology of the tephra and the chemical composition of the ice associated with the layers were studied in order to achieve this objective. The nature of the eruptions and their probable atmospheric and climatic impact were also evaluated from these studies.; The compositional similarity between glass shards in the ash layers and rock analyses from Mt. Takahe, a volcano currently located about 450 km NNW of Byrd Station, support the conclusion that Mt. Takahe is the most likely source of the tephra layers. The median grain size of most of the tephra is finer and the sorting is poorer than expected (considering the distance from the source), based on previous studies of the areal distribution of volcanic ash deposits.; These characteristics of the grain size distribution and the morphology and surface chemistry of ash particles studied by scanning electron microscopy provide useful information about the type of the volcanic eruptions that produced the tephra layers. The coarse ash layers were most likely formed during subaerial, central vent eruptions, while the fine ash layers were formed from hydrovolcanic eruptions.; Studies of the chemical composition of ice associated with the tephra layers suggest that the chemical composition of the snow and the atmosphere in Antarctica near Byrd Station were affected very little by these eruptions. This is because much of the fine ash fell out prematurely as aggregate particles, that scavenged gas-derived aerosols in the eruption plume. This minimized the atmospheric residence time of the volcanic emissions and therefore the eruptions probably had a negligible effect on local and global climate.