Cosmogenic Nuclides in Erratics below the Greenland Ice Sheet at GISP ll Site

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This award supports an investigation of cosmogenic nuclide accumulation in rocks beneath the ice at the GISP2 site on Greenland. Two sources of material will be studied: 1) the chloritic boulder above the bedrock and 2) the granitic/dioritic boulder directly below. The overall goal of this work is to demonstrate the utility of cosmogenic nuclides to dating materials beneath the ice sheet. If the last ice-free period was long, on the order of tens of thousands of years, the samples would have been exposed to cosmic radiation long enough to accumulate measurable amounts of cosmogenic nuclides. In this case, measured concentrations of these nuclides should yield information about the time when the Greenland ice sheet began to build up: essentially the age of the present Greenland ice sheet. If the duration of exposure is not long, then only qualitative information about the age of the ice sheet will be produced. The age of the present Greenland ice sheet is an important parameter for climate and ice dynamics models as well as being an important constraint for models paleoenvironmental evolution.