Dating the Initiation of Polar Ice Sheet Formation

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Major ice sheets are one of the best climate archives on Earth, but there are at present no reliable methods for determining when these ice sheets last began to form. Such information is of great importance to verifying climate models and to other studies which make use of fossil material preserved close to the bottom of the ice (e.g., ancient DNA). Although the ice itself may not be datable, any mineral grains incorporated during initial ice build up can, in principle, be dated using luminescence techniques.In the course of the project a new luminescence method for dating the last time polar ice sheets began to form will be developed. Firstly, the suitability of recently-investigated luminescence signals from individual sand-sized grains of feldspar will be tested on ice core material. To determine the rate of energy storage from internal radioactive potassium (40K) of the individual grains both scanning electron microscopy (SEM) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) will be applied on the individual grains. Additionally, a new laser based spectrometry system (now under development to automatically analyse K/Na ratios in the grains) will be tested in the second phase on the project. Based on the luminescence data and the information on the internal dose rate, age estimates for the ice formation can be derived. The project will provide previously unavailable input and verification data to global climate models, and a chronological framework for the fossil record in basal ice.