Recycled selenium in hot spot–influenced lavas records ocean-atmosphere oxygenation

Oxygenation of Earth’s oceans and atmosphere through time has consequences for subducted surface signatures that are now stored in the mantle. Here, we report significant mass-dependent selenium isotope variations in modern hot spot–influenced oceanic lavas. These variations are correlated with tracers of mantle source enrichment, which can only be explained by incorporation of abyssal pelagic sediments subducted from a redox-stratified mid-Proterozoic ocean. Selenium geochemical signatures of these sediments have mostly been preserved during long-term recycling and may therefore complement the global surface sediment record as ancient oxygen archives. Combined deep mantle and surface perspectives, together with emerging models for atmospheric oxygen based on selenium systematics, further imply a significantly oxygenated ocean-atmosphere system throughout the mid-Proterozoic.

HIGH-PURE ZINC FOR GROWING Zn82Se SCINTILLATION CRYSTALS

A process has been developed to produce high-purity granular zinc for growing Zn82Se scintillation crystals de-signed to study the neutrinoless double beta decay (0ν2β) of the selenium isotope 82Se in the CUPID-0 experiment. The chemical and isotopic compositions of high-purity zinc were studied and its radioactive purity was evaluated. At a level less than mBqkg-1 in the background spectrum of high-purity zinc, measured by a germanium detector, no peaks were observed for natural radionuclides 40K, 60Со, 137Cs and the uranium-thorium decay chain. An in-creased activity of such nuclides as 54Mn, 56Со, 57Со, 58Co, and 65Zn, formed mainly due to cosmogenous effects, was noted.

Precise measurement of selenium isotopes by HG-MC-ICPMS using a 76–78 double-spike

A novel 76Se–78Se double spike allows for rapid and precise selenium isotope measurements in geological samples.