Extraterrestrial He-3 in Paleocene sediments from Shatsky Rise: Constraints on sedimentation rate variability
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We attempt to constrain the variability of the flux of extraterrestrial 3 He in the Paleocene by studying sediments from Shatsky Rise (Ocean Drilling Program, ODP Leg 198) that have tight orbital age control. 3 He concentrations in Shatsky Rise sediments vary periodically at high frequency by about a factor of 6 over the 800-ka record analyzed. Virtually all of the sedimentary 3 He (> 99.98%) is of extraterrestrial origin. The total helium in the sediments can be explained as a binary mixture of terrestrial and extraterrestrial components. We calculate an average 3 He/ 4 He ratio for the extraterrestrial endmember of 2.41 0.29 10 - 4 , which is, remarkably, equal to that measured in present-day interplanetary dust particles. We determine a constant extraterrestrial 3 He flux of 5.9 0.9 10 - 13 cm 3 STP . cm - 2 ka - 1 for our 800-ka Paleocene record at ~ 58 Ma. This value is identical within error to those for the late Paleocene in sediments from the northern Pacific and the Weddell Sea. Bulk sediment MARs (derived using a constant extraterrestrial 3 He flux) respond to climate-forced carbonate preservation cycles and changes in eolian flux over the late Paleocene. This is the first direct evidence for significant changes in dust accumulation in response to eccentricity forcing during a greenhouse climate interval. 2009 Elsevier B.V. All rights reserved.
