Excess methane data from the Greenland Ice Sheet Project Two (GISP2) and North Greenland Eemian Ice Drilling (NEEM) ice cores, 1400-2400 meter depth

This dataset includes new measurements of in-situ, non-atmospheric methane release during the melt-refreeze analysis of ice samples for atmospheric methane measurement, also known as excess methane (CH4xs). All measurements were made at the Oregon State University Ice Core Laboratory and followed the methods of Lee et al., 2020 and Mitchell et al., 2013. Measurements were made using ice from the Greenland Ice Sheet Project Two (GISP2) and North Greenland Eemian Ice Drilling (NEEM) ice cores in 2018, 2019, and 2021. In total, 70 new measurements were made on NEEM ice and 406 measurements on GISP2 ice. The Ca2+ content of the ice was calculated using the published Ca2+ concentration records, and the mass and depth ranges of each sample. For GISP2, the year the measurement was made is included. Mitchell, L., Brook, E., Lee, J. E., Buizert, C. & Sowers, T. Constraints on the late Holocene anthropogenic contribution to the atmospheric methane budget. Science 342, 964-966 (2013). Lee, J. E. et al. Excess methane in Greenland ice cores associated with high dust concentrations. Geochimica et cosmochimica acta 270, 409-430 (2020).