Variations in melt-layer frequency in the GISP2 ice core: implications for Holocene summer temperatures in central Greenland

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Abstract
The rare melt features in the GISP2, central Greenland deep ice core have decreased in frequency over the most recent 7000 years. Calibration of this change in melt frequency against modern spatial variation of melt frequency and temperature in central Greenland, and against modern temporal variability of temperatures in central Greenland, indicates that mean mid-summer temperatures have cooled over the most recent 7000 years, probably by slightly more than l°C if variability of summer temperatures has not changed. Comparison to GRIP isotopic records from central Greenland and to the melt record from the Agassiz Ice Cap, Arctic Canada, suggests some seasonal and regional coherence for this cooling signal, as well as for a cold event about 8000-8500 BP.