HR: 1340h
AN: PP33B-1273    [Abstracts]
TI: Constraining Glacial Chronologies Using Beryllium-10 Depth Profiles
AU: * Goehring, B M
EM: goehring@ldeo.columbia.edu
AF: Dept. of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: * Goehring, B M
EM: goehring@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Schaefer, J M
EM: schaefer@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Kelly, M A
EM: meredith@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AB: Establishing a chronology of glacial advances and retreat in the Polar Regions is critical to understanding hemispheric and inter-hemispheric climate change. To date, this has proved to be a difficult task as radiocarbon dateable material is either absent or rare in ice-contact and/or ice-distal features. Progress is being made via the application of surface exposure dating to boulders resting on moraines. However, a major problem with the boulder dating method is the issue of varying amounts of inheritance, resulting in scatter in boulder ages from a single moraine. We propose an alternative method to constrain glacial advances and retreat by sampling surface and sub-surface samples from deltas and other ice-contact features. Beryllium-10 (¹⁰Be) concentrations were measured in an amalgamation of surface cobbles and four subsurface sand/gravel samples down to a depth of ~~1.5 m from each profile. A non-linear least squares regression of the ¹⁰Be concentrations and shielding depth yield model exposure ages and quantify the inherited component of the ¹⁰Be accumulated during pre-exposure and/or transport. Five depth profiles were sampled in east Greenland, three from an ice-contact glaciomarine delta in southern Kjove Land and one each from a raised marine beach and glaciolacustrine delta in southern Milne Land. Initial results indicate that profile exposure ages from the ice- contact delta are in agreement within uncertainties with radiocarbon age and boulder exposure ages, while the other features are slightly younger than radiocarbon ages. In the case presented, all ages are considered minimum ages, as no corrections have been made for erosion and/or glacio-isostatic rebound. In cases where boulder exposure ages show a high degree of scatter and/or inheritance, profile ages may provide a more accurate deglacial age since the sediments are well mixed with respect to pre-exposure, and inheritance can be quantified and accounted for in the model exposure age.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 1105 Quaternary geochronology
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting