Impact of subsurface crevassing on the depth-age relationship of high-alpine ice cores extracted at Col du Dôme between 1994 and 2012
Abstract. Three seasonally-resolved ice-core records covering the 20th century were extracted in 1994, 2004 and 2012 at a nearly identical location at the Col du Dôme (4250 m above sea level, m asl, Mont Blanc, French Alps) drill site. Here we complete and combine chemical records of major ions and radiometric measurements of 3H and 210Pb obtained on these three cores together with a 3D ice flow model of the Col du Dôme glacier, to investigate in detail the origin of the discontinuities observed in the depth-age relation of the ice cores drilled in 2004 and 2012. Taking advantage of the granitic bedrock at Col du Dôme, which makes the 210Pb ice-core records sensitive to the presence of upstream crevasses, and the fact that the depth-age disturbances are observed at depths for which absolute time markers were available, we draw an overall picture of a dynamic crevasse formation which can explain the non-disturbed depth-age relation of the ice core drilled in 1994 as well as the perturbations observed in those drilled in 2004 and 2012. Since crevasses are common at high alpine glacier sites, our study points out the mandatory need of rigorous investigations of the depth-age scale before using high alpine sites to interpret atmospheric changes.
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