Temporal variation of ³He/⁴He ratio recorded in deep‐sea sediment cores

Abstract

He isotopic composition was measured for 72 deep‐sea sediments from 16 sites in the Pacific and Atlantic oceans and the Japan Sea. 3He content ranges from less than 10−12 cm3 STP/g to about 6 × 10−11 cm3 STP/g and 3He/4He from about 10−8 to 1.67 × 10−4. The He isotopic data lie fairly well on a mixing curve in a 3He/4He‐3He diagram, where the end‐members of the mixing curve are extraterrestrial He in interplanetary dust particles (IDP's) and terrestrial He in ocean sediments. This confirms the view that there are significant amounts of extraterrestrial He in ocean sediments from global fallout of IDP's into deep‐sea sediments. 3He flux estimated for two long cores gives a value of about (1.5 ± 1.0) × 10−15 cm3 STP/cm2 yr over a time span of 40 m.y., which corresponds to an annual fallout rate of IDP's (size < 10 μm) of about 400 t. In one of the cores, we observe a “3He‐spike” which is associated with anomalously high Ir content (1.86 ± 0.56 ppb). This may be due to meteorite debris.

A record of the extraterrestrial 3He flux through the Late Cretaceous

“…A third approach is concerned not with large impactors themselves, but with interplanetary dust that is released by the cometary or asteroid events which produce large impacts. This dust accumulates on Earth and can be detected directly (Maurette et al, 1991;Robin et al, 1992;Taylor et al, 1998;Meier et al, 2010), or more generally, using its geochemical fingerprint in the sedimentary record (Takayanagi and Ozima, 1987;Farley, 2001;Dalai et al, 2006). Here we present data that extends the existing 3 He-based record of the interplanetary dust flux Mukhopadhyay et al, 2001) through the Late Cretaceous Period.…”

Helium isotopes in ferromanganese crusts from the central Pacific Ocean

“…0.05 R a ) in detrital minerals delivered as aeolian dust (e.g. Ozima et al, 1984;Takayanagi and Ozima, 1987;Patterson et al, 1999). Although this is the simplest interpretation for the bulk of the Fe-Mn crust He isotope data, there are several other potential sources of helium (Farley, 2001).…”

Chemical Tracers of Particle Transport

“…As the cosmic dust is enriched in 3 He by ca. eight orders of magnitude compared to terrigenous matter, IDPs are the principal contributor to the total 3 He concentration in pelagic marine sediments (Farley, 1995;Farley and Patterson, 1995;Marcantonio et al, 1996Marcantonio et al, , 1995Takayanagi and Ozima, 1987).…”