9321261 Alley This award is for support for a three year program to continue the physical properties measurements and dating of the Greenland Ice Sheet Project Two (GISP2) ice core, reconstruct accumulation rates, and jointly interpret the accumulation rate, contaminant and isotopic records. Dating of the GISP2 ice core has relied most heavily on visible strata, although other indicators have been critical. Flow discontinuities in the deeper part of the GISP2 core could invalidate the climate record obtained there. It is thus critical to know at what depth the climate record becomes suspect. Fortunately, flow discontinuities have a physical signature that may be detected by study of the size, shape, and arrangement of grains and their c axes using optical and sonic techniques. Physical data are also important in ice flow modeling for dating of the deep ice core and for understanding any past and future changes in the ice sheet. ***
