A search in North Greenland for a new ice-core drill site
Journal of Glaciology, Vol. 43, No. 144, p. 300-306, 1997
D. Dahl-Jensen, N.S. Gundestrup, S.J. Johnsen
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen.
National Survey and Cadastre, Rentemestervej 8, DK-2400 Copenhagen NV, Denmark.
S.P. Gogineni, C.T. Allen, T.S. Chuah
University of Kansas for Research, Ins., Radar Systems and Remote Sensing Laboratory, 2291 Irving Hill Road, Lawrence, Kansas 66045-2969, USA.
H. Miller, S. Kipfstuhl
Alfred Wegener Institute, Columbusstrasse, D-27568 Bremerhaven, Germany.
University of Washington, Geophysics Programs, Box 351650, Seattle, Washington 98195, USA.
A new deep ice-core drilling site has been identified in north Greenland at 75,12 deg N, 42,30 deg 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 (NGRIP) site is identified so that ice of Eemian age (115-130 ka BP, calendar years before present) is located as for 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 elevation, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as motel input. The surface accumulation rate drops from 0,23 m ice equivalentper year at GRIP to 0,19 m ice equivalent per year 50 km from GRIP. Over the following 300 km the accumulation is relatively constant, before it starts decreasing 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 per year. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced 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 site.