Atmospheric circulation variability associated with shallow-core seasonal isotopic extremes near Summit, Greenland

Seasonal back-diffused delta(18)O time series, reconstructed for nine shallow firn cores from the Greenland Summit for 1959-1987, are evaluated in terms of (1) their spatial and temporal variability and (2) their association to the atmospheric circulation. Rotated principal component analysis evaluates spatial and temporal patterns of organization in the back-diffused delta(18)O ice core time series. Mean sea level pressure and 500-hPa height fields are obtained for winter and summer seasons that fall in the isotopically warmest rind coldest thirds of the seasonal data. The winter back-diffused delta(18)O data indicate that some degree of longitudinal separation takes place between isotopic records from western and eastern Greenland in agreement with coastal station climatic data. Temporal variability is linked with statistical significance to the variability of the atmospheric circulation over the Denmark Strait, as well as over the Norwegian and Barents Seas. The North Atlantic Oscillation (NAO) and the mean Icelandic low in the Denmark Strait affect isotopic variability over the cores west of the ice divide, just as they have been shown to prominently affect west coast air temperature records, Isotopic variability at some ice cores east of the divide is influenced by pressure variability over the Norwegian and Barents Seas,, although statistical significance is lower. The NAO appears insignificant in summer isotopic variability, as the circulation in that season is very much localized and dominated by either ridging (warm cases) or troughs (cold cases) over eastern Greenland and the Arctic Ocean. Results suggest that long-term winter delta(18)O variability can potentially be linked to climate variation over Europe, especially from the Mediterranean basin northward to about 55 degrees N and as far east as central Siberia.