Distinguishing Biotic from Abiotic Phosphate Oxygen Isotopic Signatures

Details Distinguishing Biotic from Abiotic Phosphate Oxygen Isotopic Signatures Distinguishing Biotic from Abiotic Phosphate Oxygen Isotopic Signatures

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.v43c..04b&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #V43C-04

Biology

5200 Planetary Sciences: Astrobiology, 5225 Early Environment Of Earth, 1041 Stable Isotope Geochemistry (0454, 4870)

Scientific paper

On earth, phosphate has a strong biological oxygen isotope signature due to its concentration and intense cycling by living organisms as an essential nutrient. Phosphate does not undergo oxygen isotope exchange with water at low temperature without enzymatic catalysis, making the oxygen isotope ratio (18O/16O) of phosphate, δ18OP, an attractive biosignature in the search for early and extraterrestrial life. Recent laboratory and field studies have demonstrated that the δ18OP value of dissolved inorganic phosphate (PO4) records specific microbial activity and enzymatic reaction pathways in both laboratory cultures and natural waters/sediments (Blake et al., 2005; Colman et al 2005; Liang and Blake, 2005). Phosphate oxygen isotope biosignatures may be distinguished from abiotic signatures by: (1) evaluating the degree of temperature-dependent PO4-water oxygen isotope exchange in aqueous systems and deviation from equilibrium; and (2) evolution from an abiotic P reservoir signature towards a biotic P reservoir signature. Important abiotic processes potentially affecting phosphate δ18OP values include dissolution/precipitation, adsorption/desorption, recrystallization of PO4 mineral phases, diagenesis and metamorphism. For most of these processes, the recording, retention and alteration of δ18OP biosignatures have not been evaluated. Deep-sea hydrothermal vent fields are an ideal system in which to study the preservation and alteration of δ18OP biosignatures, as well as potential look-alikes produced by heat-promoted PO4 -water oxygen isotope exchange. Results from recent studies of δ18OP biosignatures in hydrothermal deposits near 9 and 21 degrees N. EPR and at Loihi seamount will be presented.

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