Visual stratigraphy of the North Greenland Ice Core Project (NorthGRIP) ice core during the last glacial period

Journal of Geophysical Research, Vol 110, D02108, doi:10.1029/2004JD005134, 2005

A. Svensson, S.W. Nielsen, S.J. Johnsen and J.P. Steffensen
Geofysisk Afdeling, Niels Bohr Institutet, Københavns Universitet
S. Kipfstuhl and U. Ruth
Department of Geophysics/Glaciology, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
M. Bigler and R. Röthlisberger
Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland

A continuous high-resolution record of digital images has been obtained from the NorthGRIP ice core (75.1°N, 42.3°W) in the depth interval from 1330 m to the bedrock at 3085 m. The ice core stratigraphy is clearly visible throughout the glacial period with the most frequent and brightest visible layers appearing during the coldest events. Down to a depth of 2600 m the horizontal layering is very regular; below this depth, small irregularities in the layering start to appear, and below 2800 m the visual stratigraphy becomes more uncertain, perhaps because of penetration into climatically warmer ice. Comparison of the visual stratigraphy with high-resolution continuous records of chemical impurities and dust reveals a high degree of correlation, which indicates that the visible layers are caused by these impurities. A new approach is used to automatically determine annual layer thicknesses from the visual stratigraphy record by carrying out a frequency analysis of the most prominent visible layers in the profile. The result gives strong support for the NorthGRIP time scale model.