The effects of meltwater percolation on the seasonal isotopic signals in an Arctic snowpack

Abstract We investigate the evolution of snow temperature, water content, density and stable water isotopes of δ18O at four Arctic snow-pit sites during early-season melt, in order to understand the effects of melt on snowpack stratigraphies and seasonal isotopic signals. We relate isotopic changes observed at these sites to temperature reconstructions derived from a 33 year firn-core record drilled on the same icefield. Decreases in seasonal isotopic amplitudes observed at all but one snow-pit site coincide with the percolation of more enriched meltwater into the snowpack, suggesting that meltwater percolation is the dominant process causing isotopic redistribution in Arctic snowpacks during the melt season. The decrease in isotopic range was accompanied by increases in mean δ18O values at all snow-pit sites. Positive degree-day (PDD) calculations are used to relate the amount of melt observed at the low-elevation snow-pit sites to the firn-core site. Results based on PDD values suggest an average overestimation of 1.1°C in average annual temperature reconstructions from the firn-core site from 1967 to 2006, with the possibility of errors in excess of 3°C during high-melt years.