HR: 1340h
AN: PP33C-1593    [Abstracts]
TI: Mapping Layer Sequence and Folds of Pre-Holocene Ice at the Pakitsoq "Horizontal Ice Coring"-Site, West Greenland.
AU: * Reeh, N
EM: nr@oersted.dtu.dk
AF: Niels Reeh, Andreas Ahlstrøm, Ørsted-DTU, Technical University of Denmark, Ørsted Plads Building 348, Kgs. Lyngby, 2800 Denmark
AU: Severinghaus, J
EM: jseveringhaus@ucsd.edu
AF: J. Severinghaus, V. Petrenko, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093 United States
AU: Ahlstrom, A
EM: aa@oersted.dtu.dk
AF: Niels Reeh, Andreas Ahlstrøm, Ørsted-DTU, Technical University of Denmark, Ørsted Plads Building 348, Kgs. Lyngby, 2800 Denmark
AU: Brook, E
EM: brook@geo.oregonstate.edu
AF: E. Brook, Oregon State University, Department of Geosciences, 104 Wilkinson Hall, Cornvallis, OR 97330 United States
AU: Petrenko, V
EM: vpetrenko@ucsd.edu
AF: J. Severinghaus, V. Petrenko, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093 United States
AB: Since 1985, the δ¹⁸O content of the surface ice has been studied at several ice-margin locations in Greenland. A provisional chronology for the ice margin records was established by correlating characteristic δ¹⁸O-features in the ice margin records with similar features in dated Greenland deep ice core records. This demonstrated that, at many ice-margin locations, a several hundred metre wide band of ice pre-dating the present warm interglacial occurs adjacent to the ice edge. A main concern with utilizing this aincient ice for studies of the past has been the fear of likely disturbances of the layer sequence by folds and faults. Recent trace element analyses of ice samples from the ice-sheet margin at Pakitsoq, 50 km northeast of Ilulissat/Jakobshavn, West Greenland have unambiguously demonstrated the occurrence of ice from the transition from the Last Glacial Maximum to the Holocene including ice from the Bølling-Allerød and Younger Dryas intervals. Thus large amounts of well-dated old ice with intact content of trace constituents are available at the Pakitsoq ice-margin. However, analysis of the trace constituents as well as visual inspection also demonstrated the occurrence of a large-scale fold in ice representing the Allerød/Younger Dryas/Pre-Boreal climate oscillation. Moreover, observations of ice ablation and dynamics clearly showed that the Pakitsoq ice-margin sector is presently far from a balanced state, stressing the need for developing a model for the evolution of the ice margin in order to support future ice-mining activities. Here, we report on the development of such a model based on mapping of the large-scale structures on the ice margin by using GPS, ground-penetrating radar (GPR), and trace element geo-chemical analysis (mainly δ¹⁸O-analysis of ice samples). Samples for δ¹⁸O-analysis were collected each year in the period 2001 - 2005 in several profiles across the large scale fold in order to document the time evolution. Altogether more than 3500 samples were collected. Photographs taken from helicopter provided an overview of the fold. Poles were drilled into the ice in a network for measuring ablation rate (ice melt) and ice velocity and deformation. The results of the different mapping methods is combined with observations of ice flow and deformation to set up a model for the three-dimensional structural evolution of the ice margin.
DE: 0724 Ice cores (4932)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005