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Isotopic biosignatures in carbonate‐rich, cyanobacteria‐dominated microbial mats of the C ariboo P lateau, B.C.
Author(s) -
Brady A. L.,
Druschel G.,
Leoni L.,
Lim D. S. S.,
Slater G. F.
Publication year - 2013
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12050
Subject(s) - heterotroph , microbial mat , carbonate , autotroph , environmental chemistry , organic matter , carbon dioxide , phototroph , cyanobacteria , anoxic waters , chemistry , photosynthesis , dissolved organic carbon , geology , bacteria , biochemistry , paleontology , organic chemistry
Photosynthetic activity in carbonate‐rich benthic microbial mats located in saline, alkaline lakes on the C ariboo P lateau, B.C. resulted in p CO 2 below equilibrium and δ 13 C DIC values up to +6.0‰ above predicted carbon dioxide ( CO 2 ) equilibrium values, representing a biosignature of photosynthesis. Mat‐associated δ 13 C carb values ranged from ~4 to 8‰ within any individual lake, with observations of both enrichments (up to 3.8‰) and depletions (up to 11.6‰) relative to the concurrent dissolved inorganic carbon ( DIC ). Seasonal and annual variations in δ 13 C values reflected the balance between photosynthetic 13 C ‐enrichment and heterotrophic inputs of 13 C ‐depleted DIC . Mat microelectrode profiles identified oxic zones where δ 13 C carb was within 0.2‰ of surface DIC overlying anoxic zones associated with sulphate reduction where δ 13 C carb was depleted by up to 5‰ relative to surface DIC reflecting inputs of 13 C ‐depleted DIC . δ 13 C values of sulphate reducing bacteria biomarker phospholipid fatty acids ( PLFA ) were depleted relative to the bulk organic matter by ~4‰, consistent with heterotrophic synthesis, while the majority of PLFA had larger offsets consistent with autotrophy. Mean δ 13 C org values ranged from −18.7 ± 0.1 to −25.3 ± 1.0‰ with mean Δ 13 C inorg‐org values ranging from 21.1 to 24.2‰, consistent with non‐ CO 2 ‐limited photosynthesis, suggesting that P recambrian δ 13 C org values of ~−26‰ do not necessitate higher atmospheric CO 2 concentrations. Rather, it is likely that the high DIC and carbonate content of these systems provide a non‐limiting carbon source allowing for expression of large photosynthetic offsets, in contrast to the smaller offsets observed in saline, organic‐rich and hot spring microbial mats.

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