A comparative study of accumulation rates derived by He and Th isotope analysis of marine sediments
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We present a detailed down-core analysis of helium isotope ratios and concentrations for bulk sediments from the central Equatorial Pacific that span the last two glacial-interglacial cycles. Measured 3 He 4 He ratios range from 1.0 10 -5 to 2.1 10 -4 , or 7.4 to 149 times the atmospheric ratio. The 3 He from interplanetary dust particles (IDPs) constitutes virtually all of the 3 He measured within the sediment. Because carbonate accumulation rates are high in the Equatorial Pacific, the measured 3 He concentrations are lower than have been measured elsewhere, and range from 4.7 10 -13 to 3.0 10 -12 cm 3 STP g -1 . If the cosmic dust 3 He-flux is constant with time, sediment mass accumulation rates can be determined from the 3 He concentration in sediments. The excess 230 Th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in-situ decay of 234 U in seawater. To first order, initial excess 230 Th activities correlate with 3 He concentrations within this core. Based on the 230 Th results, we estimate the 3 He-flux to the Earth's surface as (9.6 2.0) 10 -16 cm 3 STP cm -2 a -1 . If this flux has remained constant over extended periods of time, it can be used to determine sediment accumulation rates beyond the 230 Th range (300,000 yr). 1995.
Earth and Planetary Science Letters
author list (cited authors)
Marcantonio, F., Kumar, N., Stute, M., Anderson, R. F., Seidl, M. A., Schlosser, P., & Mix, A.
complete list of authors
Marcantonio, Franco||Kumar, Niraj||Stute, Martin||Anderson, Robert F||Seidl, Michele A||Schlosser, Peter||Mix, Alan