ECM data of the DYE-3 cores obtained with the technique described by Hammer (1980). People involved in the measurements include Henrik B. Clausen, Dorthe Dahl-Jensen, Niels Gundestrup and Steffen B. Hansen, Jakob Schwander, and J.P. Steffensen. Data were originally recorded on paper in high resolution but was digitized by hand in 1 cm resolution by laboratory assistant Anita Boas. The data set includes data from the DYE-3 main core and from two shallow cores, known as 4B and 18C, drilled upstream of the main drilling site. Main core: Drilled to bedrock 1979-1981 during the GISP program. Position: 65.18N, 43.83W, 2480 m a.s.l.. Core 4B: Drilled to 174 m 8 km upstream from DYE-3. Exact position not available. Core 18C: Drilled to 110 m 36 km upstream from DYE-3. Position 65.03N 44.39W. The data are given as H^+ ion concentration versus depth (measured from the undisturbed surface at the year where drilling started), but the absolute calibration must be considered tentative. For more information on the measurements and calibration, see Hammer 1980. Please cite the Hammer (1980), Neftel et al. (1985), and Rasmussen et al. (2023) when using this data file.