New frontiers in glacier ice dating: Measurement of natural 32Si by AMS

Abstract

Cosmogenic 32Si with a half-life of ca. 140 years is an excellent candidate to provide time information in the range 100-1000 years. Accelerator mass spectrometry (AMS) could greatly enhance its applicability as a natural clock due to the small sample size required for measurement. In this paper we describe the requirements for AMS measurement of natural samples, and we demonstrate the first 32Si AMS measurement for rainwater and glacial ice and snow. The results indicate that with AMS measurement of ca. 1 kg of water, a period of seven half-lives (ca.1000 years) can be covered. The 32Si result on Fox Glacier ice (New Zealand, 43°S) indicates an ice residence time on the bottom of the glacier of more than 800 years.