NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Stable light isotope biogeochemistry of hydrothermal systemsThe stable isotopic composition of the elements O, H, S and C in minerals and other chemical species can indicate the existence, extent, conditions and the processes (including biological activity) of hydrothermal systems. Hydrothermal alteration of the 18O/16O and D/H values of minerals can be used to detect fossil systems and delineate their areal extent. Water-rock interactions create isotopic signatures which indicate fluid composition, temperature, water-rock ratios, etc. The 18O/16O values of silica and carbonate deposits tend to increase with declining temperature and thus help to map thermal gradients. Measurements of D/H values can help to decipher the origin(s) of hydrothermal fluids. The 34S/32S and 13C/12C values of fluids and minerals reflect the origin of the S and C as well as oxygen fugacities and key redox processes. For example, a wide range of 34S/32S values which are consistent with equilibration below 100 degrees C between sulfide and sulfate can be attributed to sulfur metabolizing bacteria. Depending on its magnitude, the difference in the 13C/12C value of CO2 and carbonates versus organic carbon might be attributed either to equilibrium at hydrothermal temperatures or, if the difference exceeds 1% (10/1000), to organic biosynthesis. Along the thermal gradients of thermal spring outflows, the 13C/12C value of carbonates and 13C-depleted microbial organic carbon increases, principally due to the outgassing of relatively 13C-depleted CO2.
Document ID
20040173290
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Des Marais, D. J.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
August 22, 2013
Publication Date
January 1, 1996
Publication Information
Publication: Ciba Foundation symposium
Volume: 202
ISSN: 0300-5208
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other
Keywords
Review, Tutorial
Review
NASA Discipline Exobiology
NASA Center ARC

Available Downloads

There are no available downloads for this record.
No Preview Available