Progress in AMS measurement of natural 32Si for glacier ice dating

AMS measurement of ³²Si can allow for ice core dating over the last thousand years. Technique developments are reported. Necessary negative-ion yields of 20–30% can now be consistently achieved, and permit an overall efficiency from ice sample to detector of ～1%. A ³⁰Si-spike technique has overcome the problem of extremely low intrinsic silicon concentration, with the added benefit of allowing determination of ppb-level silicon via isotope dilution. Improvements have also been made to the ionization detector in the gas-filled magnet that separates the accelerated ³²Si ions from the intense flux of ³²S ions. Preliminary ³²Si AMS results of snow and ice samples from Mt. Cook National Park, New Zealand, are reproducible, and with ³²Si concentrations 1.2–7.2 mBq/m³ comparable to results from mid-latitude snow samples measured previously via the radiometric technique, demonstrating the feasibility of the method. With these developments, the potential of ³²Si as ice core dating tool is close to being realized, and attempts to determine chronologies for both alpine and Antarctic glaciers are underway.