Full solar spectrum measurements of absorption of light in a sample of the Beacon Sandstone containing the Antarctic cryptoendolithic microbial community

Abstract

AbstractWe report measures of absorption (negative log10 of the transmissivity) of a collimated beam through a 2.27 mm surface layer of Beacon Sandstone that harbours a cryptoendolithic microbial community. Consistent with the findings of previous work in the visible light range with these rocks, and in analogous sediments, blue wavelengths are more strongly attenuated than red. At wavelengths from 2400–1200 nm the absorption of the dry rock layer is roughly constant at 3.1 except in the water bands at 2000 nm and 1600 nm. From 1200–300 nm the absorption increases from 3.1 to 6.4, below 300–190 nm (the lowest wavelength measured) the absorption exceeds 6.4. When the rock is saturated with water the absorption uniformly decreases by about 0.1–0.2 over the 700–400 nm region but decreases sharply for lower wavelengths, with the decrease equal to 0.5 at 300 nm. Thus, the relative protection against UV is attenuated when the rock is wet. Even with this decreased absorption the UV absorption is still greater than that for the visible. The absorption at wavelengths less than 300 nm was too large to measure (> 6.4) for both the wet and dry rocks.