Abstract

The subseafloor basaltic aquifer is known to be home to microbial communities, at least in young ocean crust.  Based on its predicted size, modeled using temperature gradients and 120°C as a cutoff for microbial life, it is predicted to host a biomass equal to or larger than that found in subseafloor sediments.  However, to date, these predictions remain unconstrained, with no real data available.  The goal of our C-DEBI project was to develop a method for quantifying cell biomass in subseafloor basement samples and, if possible, to scan the same samples with deep-UV scanning technology to determine the spatial heterogeneity of microbial samples.  Through two visits to the lab of Fumio Inagaki at Japan Agency for Marine-Earth Science Technology (JAMSTEC) in Kochi Japan, and with training from Yuki Morono, we were able to develop a method and successfully quantify microbes in subseafloor basaltic samples from the Louisville Seamount Chain (IODP Expedition 330, 65-75 Ma rocks) and the Juan de Fuca Ridge flank (3 Ma rocks).  Through our international collaboration, we now know that biomass in these basement environments are generally low (<104 cells cm^-3) and this will allow us to model global biomass distributions in subseafloor basement. Deep-UV analysis of rocks was attempted, but results remained difficult to interpret.  Therefore, this analysis remains a future goal.