A comparative study of accumulation rates derived by He and Th isotope analysis of marine sediments

Details A comparative study of accumulation rates derived by He and Th isotope analysis of marine sediments A comparative study of accumulation rates derived by He and Th isotope analysis of marine sediments

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.133..549m&link_type=abstract

Earth and Planetary Science Letters, vol. 133, Issue 3-4, pp.549-555

Physics

30

Scientific paper

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 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).

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