Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p13b1392l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P13B-1392
Physics
[0424] Biogeosciences / Biosignatures And Proxies, [0454] Biogeosciences / Isotopic Composition And Chemistry, [0456] Biogeosciences / Life In Extreme Environments
Scientific paper
Evaporite deposits observed on Mars represent potential environments where microbial life may have existed, possibly for extended time periods due to the maintenance of liquid water at lower temperatures and pressures. As such, microbial communities living in saline, alkaline, evaporitic systems on Earth represent analogues that can be used to identify and assess the potential for preservation of biosignatures associated with extremophilic microbial metabolisms. The saline, alkaline lakes (pH > 10) of the Cariboo Plateau, B.C., Canada have a wide range of geochemical conditions, and many are host to extensive microbial mats. This study investigated the active microbial mat communities and associated sedimentary deposits in three of these lakes, Probe Lake, Deer Lake and Goodenough Lake, to characterize biosignature patterns of microbial activity in inorganic and organic carbon pools using both concentration and stable isotope based approaches. Extensive photosynthetic activity resulted in pCO2 below equilibrium during most sampling periods over 4 years. δ13C values of dissolved inorganic carbon (DIC) in surface waters enriched by up to +6.0 ‰ above values expected for equilibrium with atmospheric CO2 were observed. Further, offsets between DIC and bulk organic matter of the microbial mats of 20 - 25 ‰ were characteristic of photosynthesis producing 13C-depleted organic matter. These biosignatures of microbial activity were preserved in precipitated carbonates that generally had δ13C values within 1 - 2 ‰ of the concurrent DIC. This was interpreted as being due to rapid precipitation of carbonates within the microbial mats due to the high pH conditions and the influence of photosynthetic activity on carbonate saturation levels. However, variations in the relative photosynthetic versus heterotrophic carbon inputs and outputs led to some observed seasonal and annual variations in carbonate and DIC δ13C values. While isotopic evidence of heterotrophic metabolism influencing carbonate δ13C values was observed within the microbial mats, downcore assessment of the δ13C values of carbonate and organic matter demonstrated that surface water isotopic biosignatures were preserved in sediments underlying the lakes. This preservation occurred notwithstanding the existence of heterotrophic processing including sulphate reduction and methanogenesis within the sediments. The fact that a recognizable biosignature pattern in isotopic compositions was produced within these microbial systems and was further preserved in underlying sediments indicates that evaporitic, saline, alkaline systems hold potential for the preservation of biosignatures on Mars.
Brady A. L.
Leoni Lorenzo
Lim Darlene S. S.
Slater Greg F.
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