Lost City; hydrothermal systems; serpentinization; carbonate precipitation; volatiles; organic geochemistry; stable isotopes; radiocarbon; compound-specific isotopes; lipid biomarkers; carbon; nitrogen; microbial activity; deep biosphere
Lang Susan Q., Früh-Green Gretchen L., Bernasconi Stefano M., Lilley Marvin D., Proskurowski Giora, Reeves Eoghan P. (2012), Letter: H2/CH4 ratios cannot reliably distinguish abiotic vs. biotic methane in natural hydrothermal systems, in Proc. Natl. Acad. Sci. USA
Lang Susan Q., Früh-Green Gretchen L., Bernasconi Stefano M., Lilley Marvin D., Proskurowski G., Méhay Sabine, Butterfield David A. (2012), Microbial Growth on Abiotic Carbon and Hydrogen in a Serpentinite-Hosted System, in Geochimimica et Cosmochim Acta
, 92, 82-99.
Lang Susan Q., Bernasconi Stefano M., Früh-Green Gretchen L. (2012), Stable Isotope Analysis of Organic Carbon in Small (μg) Samples and Dissolved Organic Matter Using a GasBench Preparation Device, in Rapid Communications in Mass Spectrometry
, 26(1), 9-16.
This project is a continuation of SNF project No. 200021-121840 (2008-2010) and builds on results of organic geochemical and stable isotope studies of geochemical and microbial processes associated with the formation of high alkaline fluids in two modern serpentinite-carbonate systems: the active marine Lost City hydrothermal system (MAR, 30°N), and modern high alkaline, Ca-OH springs associated with present-day serpentinization in the Voltri Massif (Liguria, N. Italy). Lost City is unlike all other hydrothermal known to date and is characterized by metal- and CO2-poor, high pH (9-11) fluids with elevated hydrogen and methane contents resulting from serpentinization processes at depth. Microbiological studies indicate that the alkaline 40-90°C fluids at Lost City support sulfur-oxidizing, sulfate-reducing, and methane-cycling microorganisms living within distinct domains of the hydrothermal chimneys and in the subsurface. An important finding of the integration of published genomic data and our preliminary results of molecular and isotopic characterization of the archaeal lipids is that the dominant phylotype of archaea in this system, the Lost City Methanosarcinales, can adapt to strong chemical gradients within a biofilm and may be capable of both methanogenesis and methanotrophy. The origin of carbon for methanogenesis and carbon cycling during fluid-rock-microbe interaction remain a conundrum in this CO2-limited system. In addition, genomic studies have identified a wide range of nitrogen fixation genes, suggesting that the Lost City Methanosarcinales may also have the ability to fix nitrogen from N2. In this follow-up study, we specifically address questions of the origin of formate and acetate in the Lost City fluids and their role as a methanogenic substrate. We also propose to conduct nitrogen isotope studies of organic nitrogen within the chimneys to test for active nitrogen fixation and to characterize the amino acids to elucidate nitrogen-cycling. A further aspect of our proposed study is to thermodynamically model metabolic reactions available for chemolithoautotrophy to compare the energy available for methanogenesis, methanotrophy, and sulfate reduction under alkaline conditions. Thus, our study will address the following questions: •Is the carbon source to the Lost City microbial communities mantle-derived (CH4, ?CO2, formate, acetate) or seawater-derived (DIC, carbonate chimneys)? •Is the abiological formation of formate a ubiquitous occurrence under conditions of serpentinization? •Is nitrogen fixation occurring at Lost City and/or Liguria? •Are amino acids abiologically formed during serpentinization processes? •What is the nature and fate of nitrogen cycling in highly alkaline serpentinizing environments? Is the biomass in Lost City chimneys fresh or degraded? •What are the most energetically favorable metabolic reactions available for chemolithoautotrophy under conditions similar to those at Lost City and Liguria?By comparing high pH serpentinite-carbonate systems in modern marine environments with those in modern meteoric environments, we will be able to evaluate the importance of abiotic versus biotic processes in the origin of organic compounds associated with serpentinization and to address the question as to whether Lost City is a good geological and bio-geochemical analogue for present-day serpentinization processes on land and in ancient marine systems.