Properties of GRIP ice crystals from around Greenland interstadial 3 

Annals of Glaciology, Vol. 35, p. 531-537, 2002 

K.M. Hansen, A. Svensson and J.P. Steffensen
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet
Y. Wang
Alfred-Wegener-Institut für Polar- und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany.

ABSTRACT.
Ice crystal textures (sizes and shapes) and fabrics (c-axis orientations) have been determined in 3 meters of vertical thin sections from the GRIP ice core. The samples cover ice from before, during, and after Greenland interstadial 3 (IS3) that occurred about 25 kyr BP. The texture of 60k crystals has been obtained from stacked digital images by semi-automated methods, and the fabric of 5k selected crystals have been measured on the Automatic Ice Fabric Analyzer at AWI, Bremerhaven. The area distribution function of the crystals is close to a log normal distribution, and the mean area is found to be 3.36 mm² in ice from IS3, and 3.04 mm² in ice from colder periods before and after IS3. The overall c-axis orientations show a strong single maximum with vertical orientation. Those results agree well with earlier GRIP fabric studies obtained by manual methods. From comparisons of crystal areas with the concentrations of dust, Ca²⁺, SO₄^2-, Cl^- and NO₃^- in the ice we determine NO₃^- to be the one correlating the best with crystal areas. Crystals within clearly visible cloudy bands are significantly smaller than the surrounding crystals, and their c-axis orientations are less well confined than the average.