The ECM data has been temperature corrected to a standard temperature of -14 °C, according to an Arrhenius relationship using an activation energy of 0.23 eV. Subsequently, the measured current has been converted to ice acidity using the relationship suggested by Hammer (1980). For more information on the calibration procedure see Rasmussen et al, 2013.Due to the manual approach of the applied ECM technique depth assignment is only accurate to within 1-2 cm. Data in areas of breaks have been removed from the resulting data sets, and data has been downsampled to 1 cm resolution. The ECM data was obtained in the field during the NEEM field seasons 2008-2011, and given for the interval 8.26-2533.84m. Upper part of the interval (8.26-98.46 m) is measured on NEEM 2008 S1 core, which was the NEEM pilot core.