Recent intra-annual snow accumulation at South Pole: Implications for ice core interpretation

Spatial and temporal variability in snow accumulation can have a significant impact on interpretation of ice cores, particularly for chemical species that show a strong seasonal dependence either in atmospheric loading or in the atmosphere-to-snow transfer process. Using a unique, 7.25-year record of recent, year-round monthly snow accumulation at South Pole, we compute the number of years of averaging required to statistically ensure that an ice core record would have equivalent representation of snow from each month of the calendar year. For current South Pole meteorological conditions, averaging times of the order of 300 years are required to ensure equal representation of each month, with May being the least well-represented month. To ensure equal representation of 3-month seasons still requires averaging times of the order of 130 years. Through correlations of variability in monthly accumulation with potential snow transport by wind, we estimated a similar averaging time for Summit, Greenland. For studies of longterm, inter-annual changes in the atmospheric concentration of species that are reversibly deposited to snow such as hydrogen peroxide (H2O2), it is imperative that comparisons are made over intervals with equivalent representation of high versus low concentration periods. This is critical for H2O2 because it has a very high annual variability in the surface snow, driven by photochemical and temperature cycles.