An Oxygen Isotope Investigation of the Origin of the Basal Zone of the Matanuska Glacier, Alaska

Abstract

An analysis of the oxygen isotope content of ice of the englacial and basal zones of the Matanuska Glacier at its terminus reveals the origin of the ice and entrained debris. The decrease with depth in the $$\delta O^{18}$$ values of ice of the diffused facies of the englacial zone and the dispersed facies of the basal zone is consistent with previous studies and indicates this ice originates in the accumulation area. Characteristics of the ice and debris of the dispersed facies indicate a subglacial source for most of the debris. The sharp increase of more than 4‰ in the $$\delta O^{18}$$ values of ice of the lower, stratified facies of the basal zone and its young radiocarbon age indicate this facies formed by subglacial freezing of isotopically enriched meltwater, probably surface-derived, to the glacier sole. The bubble-poor, fine-grained ice, thickness, stratification, rounded pebbles, and undisturbed sedimentary structures in this facies support this conclusion. The location, extent, and rates of subglacial ice formation and sediment entrainment vary. The Matanuska Glacier is therefore thermally complex, with zones of ice at the glacier sole that are at or below the pressure-melting point.