A search in north Greenland for a new ice-core drill site

Abstract

A new deep ice-core drilling site has been identified in north Greenland at 75.12 ° N, 42 .30 ° W, 316 km north-northwest (NNW) of the GRIP drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m. The North GRIP (NG RIP) site is identified so that ice of Eemian age (115- 130 ka BP, calendar years before present ) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input. The surface accumulation rate drops from 0.23 mice equivalent year 1 at GRIP to 0.19 mice equivalent year- 1 50 km from GRIP. Over the following 300 km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100- 250 km from GRIP. The NGRIP site is located 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year 1 • The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traceq between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP ). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710 - 2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core ite.