Award: OCE-1123871

In this project we studied the shallow-water hydrothermal vent sites at Milos Island (Greece) to better understand the extent of autotrophic carbon fixation and its chemical and isotopic signature along environmental (redox/thermal) gradients. This was a 12-day long expedition (May 18 to 30, 2012) to sample vent fluids, gases and retrieve sediment cores at Paleochori Bay by using SCUBA diving at 8-10 m depth. In addition to the submarine vent sites, two subaerial locations of venting were identified at 36o 40' 28"N - 24o 31' 14" E and 36o 40' 25" N - 24o 30' 44" E. Both the subaerial and submarine sites are located on the same fracture zone that likely controls the hydrothermal circulation of evolved meteoritic water and seawater within the magmatic zone of Milos Island. To this end, the geochemistry of the fluids and gases emitted from subaerial sites provide important information towards identifying the linkage between the subaerial and submarine magmatic activity and provide insights on the metabolic functions (e.g. H2 oxidation, Fe(III) reduction, C and S cycling) of the subsurface microbial community. The group from Geophysical Laboratory, Carnegie Institution of Washington was responsible for processing the fluid and gas samples. At the site, we performed gas chromatography to determine the concentration of dissolved gases (methane, C2-C6 alkanes, H2, CO2, H2S) collected by gas-tight syringes. Samples returned to the Geophysical Lab were analyzed to determine dissolved concentrations of: dissolved inorganic carbon (DIC), organic acids and a range of major anions/cations species (e.g. SO42-, PO42-, NO3-, Cl-, Na+, K+, Ca2+, Mg2+) including trace elements and metals. Fluids were analyzed for metal and trace element concentrations at the MC-ICP-MS facility of Prof. Michael Bizimis at the University of South Carolina. In this project, we shared our samples with Dr. Bizimis and encouraged him to proceed with any further analysis that may suit his research program. We also determined the d13C composition of dissolved inorganic carbon at the stable isotope facility of the Geophysical Lab. Data have been released to the public through our Data Depository (http://people.gl.ciw.edu/dfoustoukos/Site/Data_Repository.html). Furthermore, sediments and minerals collected from the submarine and subaerial vents are to be analyzed and studied as part of Joe MaloneyÆs M.Sc. Thesis. This is a collaborative project with Dr. Julia Nord, who is the academic advisor of Maloney at George Mason University. An important contribution to the discipline is the isolation and?characterization of a novel thermophilic Fe(III)-reducing microorganisms; that overall have been very scarcely described in microbial communities from either deep-sea or shallow-water hydrothermal vent sites. Fe(III)-reducing bacteria play a key role on the cycling of Fe between the oceanic crust and the overlying hydrosphere. This microorganism has been isolated and phylogenetically/physiologically characterized by Dr. Perez-Rodriguez (GL Postdoctoral Fellow) and Matthew Rawls (undergraduate student, George Mason University). This appears to be a thermophilic Fe(III) reducing species of Deltaproteobacteria named strain MAG-PB1. This strain was isolated from a marine sediment core located at 8 meters water depth and with a pore fluids temperature of 26oC. However, this anaerobic Fe(III) reducing bacterium attains optimum growth temperature of 65oC, which highlights the adaptation of these organisms to the strong thermal gradients of the hydrothermal fluids circulating in the shallow-water sedimentary seafloor. The organism was phylogenetically characterized revealing a ~ 97% similarity in the 16S rRNA gene to the closest relative Deferrisoma camini. D. camini is a thermophilic, anaerobic, Fe(III) reducing bacterium isolated from a deep-sea hydrothermal vent chimney at the Eastern Lau Spreading Centre, in the Pacific Ocean. Interestingly, the MAG-PB1 is directly linked to a micr...