The NorthGRIP ice-core logging procedure: Description and evaluation

Abstract

The ice-core logging procedure used to log the North Greenland Icecore Project (NorthGRIP) ice cores is described. The existence of two deep ice cores, NorthGRIP 1 and 2, drilled 25 m apart, allows an independent evaluation of the procedure. The logged depths of the NorthGRIP 1 and 2 cores deviate from the length of the unwound drill cable corrected for elongation of the cable when hanging in the hole, by 1.5‰ and <0.5‰ at depths of 1371 and 2931 m, respectively. Differences between logged depths of identified layers found in both cores are studied in the depth interval where they overlap. Layers are identified by electrical conductivity measurements and dielectric profiling. The difference between the logged depths of layers identified in both cores increases to 0.5 m close to the bottom of the NorthGRIP 1 core, which is <0.5 mm m-1 ice core. The comparison between the two cores shows that the NorthGRIP logging procedure is accurate and reproducible. Further, our results show that the temperature conditions and handling of the core during logging are important for obtaining a precise depth.