Depositional Flux of Cosmogenic 10Be in Southern India

Abstract

The sun and the other exploding stars in our galaxy are a regular source of cosmic rays. These rays contain particles- mostly protons (~90%), alpha particles and small fraction of bigger nuclei. These particles, which are of both galactic and solar origin, have high energy such that they are able to penetrate the heliosphere (in case of the galactic cosmic rays) and the geomagnetic field of the earth, and then reach earth’s atmosphere, where they generate a cascade of secondary particles. These secondary cosmic rays are able to knock out few nucleons from the nuclei of atmospheric gases, leaving behind a lighter nucleus. These newly formed nuclides are the cosmogenic nuclides. The isotope 10Be is one such radionuclide formed by this spallation process and it has a half -life of 1.39*106 years. The 10Be produced in the atmosphere, named meteoric 10Be, binds to aerosols and reaches the surface of Earth through both wet and dry deposition., where they adsorb strongly onto to soil, sediment, ice pits, speleothems etc. The meteoric 10Be serves as a valuable geochemical tracer for plenty of earth science applications across various natural environments, like assessing erosion, surface stability, quantifying denudation rates etc. The prerequisite for such applications is the depositional fluxes of 10Be to the diverse geographical settings. Except in regions with low rainfall, the wet deposition exceeds dry deposition. Though some studies have suggested that its flux correlates with precipitation, others have shown the dilution of 10Be with higher levels of precipitation. The present work tries to investigate the existence of any such relation between the flux of meteoric 10Be and precipitation along a rainfall gradient region in India. The 10Be concentration in soil increases with annual rainfall in places receiving <1500 mm y-1 and decreases with rainfall in regions having > 1500 mm y-1 annual rainfall. The flux values in these regions also shows a similar pattern of deposition and its value ranges from 0.32*106 to 3.13*106 atoms/cm2/year.