HR: 0800h
AN: GP21B-0503    [Abstracts]
TI: Polar ice magnetization: Comparison of results from NorthGRIP (Greenland) and Vostok (Antarctica) ice cores
AU: * Lanci, L
EM: luca.lanci@uniurb.it
AF: Istituto di Scienze della Terra, Urbino University, Campus Scientifico, Urbino, PU 61029, Italy
AU: Kent, D V
EM: dvk@ldeo.columbia.edu
AF: Department of Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, United States
AU: Kent, D V
EM: dvk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Route 9W, Palisades, NY 10964, United States
AB: Low temperature measurements of isothermal remanent magnetization (IRM) in Greenland ice spanning the last glacial and Holocene have shown that ice samples contain a measurable concentration of magnetic minerals which are part of the atmospheric aerosol. Assuming that the source materials do not change much with time, the concentration of magnetic minerals should be proportional to the measured concentration of dust in ice. We have indeed found a consistent linear relationship with the contents of dust. However, the linear relationship between low temperature ice magnetization vs. dust concentration has an offset, which when extrapolated to zero dust concentration would seemingly indicate that a significantly large magnetization corresponds to a null amount of dust in ice. Thermal relaxation experiments have shown that magnetic grains of nanometric size carry virtually all the uncorrelated magnetization. Magnetic measurements in Antarctic ice cores confirm the existence of a similar nanometric-size magnetic fraction, which also appear uncorrelated with measured aerosol concentration. The magnitude of the uncorrelated magnetization from Vostok is similar to that measured in NorthGRIP ice. Measurements of IRM at 250K suggest that the SP magnetic particles are in the size range of about 7-17 nm, which is compatible with the expected size of particles produced by ablation and subsequent condensation of meteorites in the atmosphere. The concentration of extraterrestrial material in NorthGRIP ice was estimated from the magnetic relaxation data based on a crude estimate of chondritic Ms. The resulting concentration of 0.78±0.22 ppb for Greenland is in good agreement with the outcome based on published iridium concentrations; a virtually identical concentration of 0.53±0.18 ppb has been measured in Vostok ice core.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1540 Rock and mineral magnetism
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting