Rock Varnish: Nature's Shield

Barerock surfaces in dry to semiarid places of the world oftenhost a black-brown accretion rich in Mn and Fe known as rock varnish.The varnish surface presents an ideal environment for microbial development.A burgeoning interdisciplinary arena of scholarship focuses on thebiogeochemical fingerprints of life in severe settings. Given thata large number of researchers hypothesize that varnish formation isa key process by microorganisms, the high altitude Ladakh remainsa largely unexplored research setting. Thus, as one of the world'sharshest dry deserts, we selected Ladakh as the focus for this investigationinto the nature of organic biomarkers found in subaerial rock varnishin this severe climate. Microbial fingerprinting using organic biomarkersand isotopic analyses in conjunction with electron microscopy revealsthe presence of organic metabolites such as fatty acids, alkyl benzenes,oxime, amide, and fatty acids that we interpret as resulting frommineral-microbial interactions. We hypothesize that a newlydiscovered change in surface wettability characteristics from hydrophilic(in host rock) to hydrophobic (in varnish) might be important in facilitatingthe development of microbial processes that could be related to varnishformation.