Project

Discipline

Lost City; hydrothermal systems; serpentinization; carbonate precipitation; volatiles; organic geochemistry; stable isotopes; radiocarbon; compound-specific isotopes; lipid biomarkers; carbon; nitrogen; microbial activity; deep biosphere

Lead
Lay summary
This project is an organic geochemical and stable isotope study of modern serpentinite-carbonate systems, focused on understanding geochemical and microbial processes associated with the formation of high alkaline fluids during serpentinization. We compare two modern serpentinite-carbonate systems: the active marine Lost City hydrothermal system (MAR 30°N) and the land based alkaline springs in the Voltri Massif (Liguria, N. Italy). Our study builds on an immense set of data from the peridotite-hosted Lost City hydrothermal system, produced in collaboration with an international team of scientists over the past nine years. Lost City is unlike all other hydrothermal known to date and is characterized by metal- and CO2-poor, high pH fluids (9-11) with elevated hydrogen and methane contents resulting from serpentinization processes at depth. Similar processes occur in the ophiolites of Liguria, Italy, where fluids originating from deep aquifers circulate through variably serpentinized peridotites, resulting in Mg-rich to Ca- or Na-rich, high pH (10 - 12) waters, with elevated hydrogen and methane concentrations. We specifically aim to link inorganic reactions in the ultramafic basement rocks (i.e. serpentinization reactions) to microbial activity by characterizing the cycling of carbon and nitrogen in these high pH systems. Elucidating the sources of carbon to these systems is of particular interest as small organic compounds are hypothesized to form abiologically under conditions similar to those found in the subsurface of these two sites. Field and laboratory studies are designed to (1) determine if the high concentrations of the small organic acid, formate, found at Lost City is abiologically formed and if it is a common feature of serpentinization processes; (2) identify the primary carbon sources to microbial communities and determine if these compounds are the result of serpentinization reactions (CH4, formate); (3) determine if amino acids also form abiologically at Lost City and/or Liguria; (4) investigate the role of nitrogen fixation at these locations; and (5) identify the most energetically favourable metabolic reactions available for chemolithoautotrophy in these environments.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

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.