Extension of the stable oxygen isotope and density profile of the NGRIP ice core

The firn core array of the North Greenland Traverse (NGT) provides unique climatic information for North Greenland until the mid 1990ies. In order to extend this climate record into more recent time, some of the drill sites were revisited and extension cores were drilled. The record consists of a firn core from 0 to 17m m depth with a diameter of 75 cm. Density was measured by micro-focus Computer Tomography with a resolution of 0.1mm and subsequently smoothed with a Gaussian filter with sigma 2cm. Stable oxygen isotopes (δ18O) were measured on discrete samples using Cavity Ring-Down spectroscopy with an L2120-i and L2130-i by Picarro Instruments. The δ18O concentration with depth is provided with a precision of better than 0.1 per mil. Using raw, un-calibrated dielectrical profiling (DEP) data from the field (NEEM Set-up), volcanic tie points were derived. Together with the smoothed density data and the isotopic composition the record was dated by layer counting. The annual mean values of δ18O were obtained based on this dating. Based on the density measurements and the dating, the annual accumulation rate in water equivalent depth was derived.