Flux and size fractionation of He-3 in interplanetary dust from Antarctic ice core samples

Abstract

Accretion of extraterrestrial material to earth is of interest for a variety of reasons, including as a possible driver of long or short-term climate change, and as a record of solar system events preserved in the geological record. 3He is highly enriched in extraterrestrial material, and provides a useful tracer of its input into sedimentary archives. Previous work showed that polar ice could be a suitable archive for studying variations in extraterrestrial input. Additional measurements reported here confirm that the late Quaternary 3He flux derived from Antarctic ice samples is similar to 3He fluxes determined from marine sediments. The mean flux from nine replicate ~ 1 kg ice samples from the Vostok ice core site (112-115 m depth, age of ~ 3800 years) is 1.25 ± 0.37 x 10-12 cm3 STP cm-2 ka-1 (mean ± 2se). The large range for the 9 replicates is probably due to the small number of interplanetary dust particles (IDPs) present, and illustrates that large ice samples are required for precise constraints on temporal variations in the 3He flux. Size fraction experiments show that the majority of the 3He flux is delivered by particles in the 5-10 micron size range, consistent with the hypothesis that helium in IDPs is primarily solar helium implanted in particle surfaces.