Glaciochemical dating of an ice core from upper Grenzgletscher (4200 m a.s.l.)

One crucial condition for the interpretation of ice-core records is the est ablishment of an accurate time-scale. This task is especially difficult fbr glacier sites in a complex topography such as the Alps, due to the often i rregular deposition of fresh precipitation. In this work, dating techniques were applied to an Alpine ice core from upper Grenzgletscher; Monte Rosa m assif (4200 m a.s.l.), representing about two-thirds of the total glacier t hickness. They are leased on (i) the radioactive decay of the isotope Pb-21 0, (ii) seasonally varying signals such as the concentrations of NH4+ and t he isotopic ratio delta O-18, and (iii) stratigraphic markers from Saharan dust falls, atmospheric nuclear weapon tests and the reactor accident in Ch ernobyl. From the combined application of these dating methods, a time peri od of 1937-94 covered by the ice core was derived. Dating uncertainty is <1 year for the period 1970-94 and +/-2 years for the period 1937-69. The obs erved thinning of the annual layers as a function of depth could be well de scribed by a simple kinematic glacier flow model.