Isotope thermometry in melt‐affected ice cores

Abstract

A statistically significant relationship is observed between stable water isotopes (δ18O) and melt amounts in a melt‐affected firn core (SSummit) taken from the Prince of Wales Icefield, Ellesmere Island, Canada. By contrast, a low‐melt firn core taken from a higher‐elevation, higher‐latitude location on the same icefield shows no relationship between these variables. We interpret this as evidence for meltwater‐induced isotopic enrichment at SSummit. A percent melt–based correction slope is applied to isotopic values from SSummit. Uncorrected and corrected temperature records derived from the raw and corrected δ18O values are compared to bias‐corrected temperature data from the NCEP Reanalysis. Improvements are observed in the isotopic reconstruction of SSummit annual precipitation‐weighted temperatures when we correct for meltwater enrichment, with a reduction from +0.6°C to 0.0°C in the mean annual error and a decrease in root‐mean‐square error from 1.8°C to 1.6°C. The correction factor appears to overcorrect isotopic modification during high melt years such as 1999, during which SSummit experienced nearly 70% more melt than the average from 1975 to 2000. Excluding 1999 data from the correction analysis results in a slight reduction in mean absolute error from 1.4°C to 1.3°C. These results suggest that melt‐induced isotopic modification cannot be corrected in very high melt years.