HR: 1340h
AN: PP33B-0926    [Abstracts]
TI: Ambiguities in Interpreting the Beryllium-10 Record From Marine Sediments
AU: * McHargue, L R
EM: mchargue@physics.Arizona.EDU
AF: University of Arizona, Department of Geosciences P.O. Box 210077 , Tucson, AZ 85721-0077 United States
AU: Donahue, D J
EM: djd@physics.Arizona.EDU
AF: University of Arizona, Department of Physics P.O. Box 210081, Tucson, AZ 85721-0081 United States
AB: Beryllium-10 from Blake Outer Ridge (BOR) late Pleistocene marine sediments at Leg 72, site 1061 B.P. was measured in order to obtain a record of the cosmic-ray flux incident upon the Earth. The variations in the concentration of $^{10}$Be per gram of sediment in BOR sediments and that of the oxygen isotope record of the North Atlantic are strikingly similar highlighting the effects of climate on the deposition of $^{10}$Be in marine sediments. In particular, an abrupt change in the oxygen isotope record from Marine Isotope Stage (MIS) 6 to MIS 5 also is observed in $^{10}$Be record (as normalized to gram of sediment) as a result of an abrupt change in the sedimentation rate. In addition, the long-term trends of $^{9}$Be and $^{10}$Be concentrations, both source dependent, are inversely correlated and thus the $^{10}$Be/$^{9}$Be normalization is ambiguous at best. The effects of climate on $^{10}$Be deposition was best removed by normalization of $^{10}$Be to the mass of the authigenic fraction of the sediment from which it was contained. The $^{10}$Be content of the sediments at site 1061 was correlated to another site on the Blake Outer Ridge, CH88-10P, and to a site in the Gulf of California Leg 64, site 480. $^{10}$Be normalized to the authigenic mass at these sites show that the $^{10}$Be concentrations within the sea are bounded within a specific range consistent with the expected secular variations of the Earth's dipole field.
DE: 4825 Geochemistry
DE: 4860 Radioactivity and radioisotopes
DE: 4267 Paleoceanography
DE: 1521 Paleointensity
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting