Reduced (oxygen-poor) forms of iron (and possibly manganese) deep in the Earth and contained in volcanic rocks provide a rich source of energy for the growth of a very interesting group of rust-forming (iron-oxidizing) bacteria. Loihi Seamount is a hydrothermally active seamount in the mid-Pacific ocean where waters containing high concentrations of reduced iron exit the Earth's crust and where massive amounts of volcanic rock come in contact with sea water. Here abundant iron-oxidizing bacteria, in the darkness of the deep sea, carpet the rock surfaces, forming rust coatings on massive areas of the seamount's surface. The bacteria form microbial mats and crusts on exposed rock surfaces and greatly accelerate the alteration of these rocks and affect water chemistry. In turn, the rust (iron oxide) impacts other microorganisms and affects elemental cycling on the planet. Processes such as these are probably widespread in deep dark environments where water circulates below the surface of land and the oceanic crust. The primary focus of our FeMO project and this cruise is to understand who the important iron-oxidizing bacteria in the environment are, how fast they form iron oxide deposits, how they do it biochemically, and how this process affects ocean chemistry and ecosystem function.

 

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