serpentinization; carbonate precipitation; volatiles; organic geochemistry; radiocarbon; compound-specific isotopes; lipid biomarkers; carbon; sulfur; microbial activity; Lost City Hydrothermal System
Mehay S., Frueh-Green G. L., Lang S. Q., Bernasconi S. M., Brazelton W. J., Schrenk M. O., Schaeffer P., Adam P. (2013), Record of archaeal activity at the serpentinite-hosted Lost City Hydrothermal Field, in GEOBIOLOGY
, 11(6), 570-592.
Schwarzenbach Esther M., Lang Susan Q., Früh-Green Gretchen L., Lilley Marvin D., Bemasconi Stefano M., Méhay Sabine (2013), Sources and cycling of carbon in continental, serpentinite-hosted alkaline springs in the Voltri Massif, Italy, in LITHOS
, 177, 226-244.
Bach W., Früh-Green G.L. (2010), Alteration of the Oceanic Lithosphere and Implications for Seafloor Processes, in Elements
, 6(3), 173-178.
We propose a comparative 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. The proposed study builds on an immense set of data from the peridotite-hosted Lost City hydrothermal system (MAR, 30°N), produced in collaboration with an international team of scientists over the past seven 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. We specifically address a number of important open questions about the links between the inorganic reactions in the ultramafic basement rocks (i.e. serpentinizing reactions), cycling of carbon and sulfur, and microbial activity in these high pH systems. We are requesting funds to support Dr. Sabine Méhay as a post-doctoral researcher for two years. The overall goal of our project is to quantify C and S pools in active serpentinite-carbonate systems and to constrain their changes over time. To achieve this goal we propose a comparative organic geochemical and C-and S-isotope study of Lost City with modern high alkaline Ca-OH springs and carbonate deposits associated with present-day serpentinization processes in Liguria (Italy). The field and laboratory studies proposed here are specifically aimed to (1) characterize the organic matter at a molecular and isotopic level; (2) constrain the origin and cycling of C and S in modern marine and meteoric systems; and (3) make quantitative volume estimates of the amount of organic carbon and CO2 that is sequestered in these environments.The structure and carbon isotope compositions of lipids from living organisms are well preserved in organic matter within the hydrothermal deposits, and can be precisely identified using state of the art analytical procedures. This work will provide important data concerning the nature, function and distribution of the micro-organisms and help to evaluate possible links between abiotic and biotic reactions in the cycling of carbon and sulfur in these systems. In addition, the evolution of different mineral precipitates during serpentinization and their influence on microbial activity will be investigated. Specific questions to be addressed with organic geochemistry and compound-specific isotope analyses include: •What organic compounds are characteristic of high alkaline environments associated with serpentinite-carbonate alteration processes? How do marine systems differ from meteoric systems?•What is the source of C and S at Lost City and Liguria (seawater, organic or mantle origin)? How are they cycled through the system, and how do the C and S budgets change with mineral-fluid and microbe-fluid interactions over time?•What controls the isotopic compositions of these species? Can we determine signatures/parameters that can be used to distinguish biogenic from abiogenic processes in modern and ancient rocks formed in similar environments?•Is Lost City a good geological and bio-geochemical analogue for present-day serpentinization processes on land and in ancient marine systems (e.g., ophiolites)?