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[1] Absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations, the compression and expansion of the atmosphere due to cooling and warming, and changes in katabatic winds near large ice masses. These atmospheric processes can result in changes in production rates of cosmogenic nuclides which, when integrated over long exposure durations may result in 0% to >5% adjustments in site production rates depending on location. Combining a CCM3 model with imbedded ice sheets for 20 ka, we show that production rates changes (relative to today) are greatest at high elevations (6-7% at 5 km altitude) due to atmospheric compression from decreased temperature. Production rates at specific times for sites near ice sheet margins can be reduced more than 10% due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling. Nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions. Atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations.

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[1] The Ferrar Glacier extends from the Taylor Dome, through the Royal Society Range, to the Ross Sea. Its pathway is strongly influenced by large-scale topographic features. Ice thins and flows over these features, like water over a dam. Recently acquired evidence demonstrates that the profile of the Ferrar Glacier has been relatively static for the last $4 million years. This long record of stability is in sharp contrast to numerous other features in Antarctica and motivates an exploration of the stability with a numerical model. Large variations in ice thickness along the Ferrar profile make necessary a thermomechanically coupled model which includes higher-order stress terms. Such a model is presented here and then is used to investigate (1) glacial ice flow patterns, (2) stress fields, and (3) sensitivity to climate forcing. In all three cases, the Ferrar Glacier is shown to be generally insensitive to the changes and to have stability consistent with cosmogenic nuclide evidence. The modeling is novel in that the Ferrar Glacier is a member of a class of glaciers which has never before been modeled. Ice flow results indicate that curious flow patterns arise in the glacier, producing very old ice ($100,000 years) near the surface up glacier of thinning points. This flow pattern is demonstrated to be of consequence when interpreting the inheritance of cosmogenic nuclides in two ways. First, the velocity field is used to determine the maximum time a cobble found on the glacier surface could have been exposed to cosmic radiation. Second, the flow entrains supraglacial material from the glacier's surface, shielding it from cosmic rays for a period, and then deposits the material at the surface down glacier. Both flow effects are discussed in relation to cosmogenic nuclide inheritance and are quantified. The sensitivity of the results to past climates and glacier surfaces is also considered.