Extraterrestrial3 He in marine polymetallic nodules: A potential method for measuring growth rate of nodules

Abstract

The comparative measurements of helium isotope compositions between marine polymetallic nodules and their surrounding sediments, their magnetic fractions and bulk from C-C Zone of the East Pacific Basin are reported. The4He content and3He/4He ratio of polymetallic nodules and their surrounding sediments are extremely high; the3He,4 He concentrations and most3He/4He ratios of magnetic fractions in nodules and sediments are apparently higher than those in bulk. The helium isotope data points of nodules and sediments are all distributed along or closely to the mixing curve of the interplanetary dust particles (IDPs) and the terrigenous sediments in the chart of3He-3He/4He. In the same sampling site, the3He/4He ratios of nodules and their surrounding sediments are very similar, and the changes of both ratios are synchronous. It shows that the high3He/4He ratios in nodules and sediments may all result from IDPs. So, if the flux of extraterrestrial3He into the nodules and sediments is constant, the growth rate of polymetallic nodules and the sedimentation rate of sediments can be independently calculated according to the concentra-tion of extraterrestrial3He in nodules and sediments.