BIOALTERATION OF SEAFLOOR BASALT AND SULFIDES: USING SYNCHROTRON X-RAY RADIATION TO INVESTIGATE KEY MICROBE-MINERAL INTERACTIONS

A very diverse microbial community has been shown to colonize both the basalt and hydrothermal metal sulfides at the seafloor to a greater degree that it inhabits the overlying seawater. Upon introduction to seawater, both substrates have undergone extensive alteration reactions (mainly via redox and hydration) at rock-seawater interfaces. The rock-hosed (or endolithic) microbes are suspected of catalyzing these energy-yielding though kinetically-inhibited alteration reactions and of using the energy from these reactions (e.g. electrons) for primary production. Even though our understanding of seafloor microbe-mineral interactions is growing by leaps and bounds daily, answers to key questions remain elusive. What exactly are the products of alteration reactions? What microbial groups are capable of what reactions? What can these reactions tell us about how the deep rock-hosted biosphere is affecting global geochemical cycles? We addressed the first question by applying synchrotron x-ray radiation to a basalt and an iron sulfide (both with known starting composition) reacted in situ at the seafloor. Using micron-scale x-ray fluorescence, absorption and diffraction, we are beginning to untangle the complicated interactions between microbes and minerals that occur on seafloor basalts and iron sulfides and to determine the time frame in which interactions occur. Understanding how the endolithic microbes interact with their substrates may help us understand if they affecting global geochemical cycling of Fe, Mn, S, C and other important elements.