The accumulation pattern across Siple Dome, West Antarctica, inferred fromradar-detected internal layers

The spatial distribution of accumulation across Siple Dome, West Antarctica , is determined from analysis of the shapes of internal layers detected by radio-echo sounding (RES) measurements. A range of assumed accumulation pat terns is used in an ice-now model to calculate a set of internal layer patt erns. Inverse techniques are used to determine which assumed accumulation p attern produces a calculated internal layer pat tern that best matches the shape of internal layers from RES measurements. Ail of the observed interna l layer shapes at Siple Dome can be matched using a spatially asymmetric ac cumulation pattern which has been steady over time. Relative to the divide, the best-fitting accumulation pattern predicts 40% less accumulation 30 km from the divide on the south flank of Siple Dome and 15-40% more accumulat ion 30 km from the divide on the north flank. The data also allow the possi bility for a small time variation of the pattern north of the divide. The m ismatch between the calculated and the observed layer shapes is slightly re duced when the accumulation rate north of the divide is higher in the past (> 5 kyr BP) than at present. Sensitivity tests show that the predicted cha nge in the spatial accumulation pattern required to cause the slight Siple Dome divide migration (inferred from previous studies) would be detectable in the internal layer pattern if it persisted for > 2 kyr. Our analysis rev eals no evidence that such a change has occurred, and the possible change i n accumulation distribution allowed by the data is in the opposite sense. T herefore, it is unlikely that the Siple Dome divide migration has been caus ed by a temporal change in the spatial pattern of accumulation. This conclu sion suggests the migration may be caused by elevation changes in Ice Strea ms C and D at the boundaries of Siple Dome.