HR: 1330h
AN: V42D-0390    [PDF]
TI: Flux and size fractionation of IDP-borne $^{3}$He from Antarctic ice core samples
AU: * Brook, E J
EM: brook@vancouver.wsu.edu
AF: Geology Department Washington State University, 14204 NE Salmon Creek Ave, vancouver, WA 98686 United States
AU: Kurz, M D
EM:
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Curtice, J
EM:
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AB: Previous measurements of helium isotopes in particles from polar ice yielded extraterrestrial $^{3}$He fluxes similar to results from marine sediments (Brook et al., 2000, GRL, 27, 3145-3148). The agreement is surprising since the area-time product (sample mass divided by mass accumulation rate) for these samples is relatively small. We now report new helium measurements from larger samples of the Vostok Ice Core (Antarctica) and results of a series of size fraction experiments designed to determine the dominant particle size transporting $^{3}$He in Interplanetary Dust Particles (IDP's) to earth. The mean $^{3}$He flux from 8 longitudinally cut replicate ice samples (821-1201 g each) from the 112-115 m interval (~3.8-4 ka) at Vostok is 1.1$\pm$0.3 x 10$^{-12}$ cm$^{3}$ STP cm$^{-2}$ ka$^{-1}$. These samples have a mean area-time product of ~ 0.05 m$^{2}$a, which is ~ 5 times that of the previous ice measurements. The inferred $^{3}$He fluxes are similar to values previously reported from late Quaternary ice samples and marine sediments, further demonstrating the potential of ice cores as archives of $^{3}$He accretion. We also separated dust from one 1.5 kg sample of Vostok ice into 5 size fractions, $>$63, 20-63, 10-20, 5-10, and 0.45-5 microns, using sieves and filters. Models predict that most $^{3}$He in IDP's is carried in relatively large particles, in the ~ 5-35 micron range. However, the new data shows that over 76% of the $^{3}$He is found in the 5-10 micron size interval, and only 18% of the $^{3}$He in size classes larger than this. Implications for reconstructing the IDP $^{3}$He flux will be discussed.
DE: 1040 Isotopic composition/chemistry
DE: 1827 Glaciology (1863)
DE: 2129 Interplanetary dust
DE: 6213 Dust
DE: 6215 Extraterrestrial materials
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting