The accretion rate of extraterrestrial 3He based on oceanic 230Th flux and the relation to Os isotope variation over the past 200,000 years in an Indian Ocean core
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In the eastern equatorial Indian Ocean, the flux of extraterrestrial 3 He, a proxy of interplanetary dust particles (IDPs), has been relatively constant over the past 200 ka. The flux is equal to (1.1 0.4) x 10 -12 cm 3 STP cm -2 ka -1 , a value obtained using the xs 230 Th profiling method. Variations in mass accumulation rates (MARs) derived assuming a constant extraterrestrial 3 He flux have a 40-ka periodicity similar to that observed in the 18 O-derived MARs. This frequency is similar to that of the Earth's obliquity. Measured 187 Os/ 188 Os ratios are less radiogenic than present-day seawater (0.49-0.98), reflecting the mixing of Os derived from extraterrestrial, terrigenous and hydrogenous sources. When coupled with He data measured on the same samples. Os isotope data yield important information about the terrigenous component supplied to the eastern equatorial Indian Ocean. The amount of Os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics. Once corrected for the extraterrestrial component of Os, Os isotope signatures, in conjunction with the 4 He concentrations, suggest a supply of terrigenous material from Indonesian ultramafic and Himalayan crustal sources that clearly varies through time.
