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Spatial variability in photosynthetic and heterotrophic activity drives localized δ^(13)C_(org) fluctuations and carbonate precipitation in hypersaline microbial mats

Houghton, J. and Fike, D. and Druschel, G. and Orphan, V. and Hoehler, T. M. and Des Marais, D. J. (2014) Spatial variability in photosynthetic and heterotrophic activity drives localized δ^(13)C_(org) fluctuations and carbonate precipitation in hypersaline microbial mats. Geobiology, 12 (6). pp. 557-574. ISSN 1472-4677. https://resolver.caltech.edu/CaltechAUTHORS:20141201-092909674

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Abstract

Modern laminated photosynthetic microbial mats are ideal environments to study how microbial activity creates and modifies carbon and sulfur isotopic signatures prior to lithification. Laminated microbial mats from a hypersaline lagoon (Guerrero Negro, Baja California, Mexico) maintained in a flume in a greenhouse at NASA Ames Research Center were sampled for δ^(13)C of organic material and carbonate to assess the impact of carbon fixation (e.g., photosynthesis) and decomposition (e.g., bacterial respiration) on δ^(13)C signatures. In the photic zone, the δ^(13)C_(org) signature records a complex relationship between the activities of cyanobacteria under variable conditions of CO_2 limitation with a significant contribution from green sulfur bacteria using the reductive TCA cycle for carbon fixation. Carbonate is present in some layers of the mat, associated with high concentrations of bacteriochlorophyll e (characteristic of green sulfur bacteria) and exhibits δ^(13)C signatures similar to DIC in the overlying water column (−2.0‰), with small but variable decreases consistent with localized heterotrophic activity from sulfate-reducing bacteria (SRB). Model results indicate respiration rates in the upper 12 mm of the mat alter in situ pH and HCO_3^- concentrations to create both phototrophic CO_2 limitation and carbonate supersaturation, leading to local precipitation of carbonate minerals. The measured activity of SRB with depth suggests they variably contribute to decomposition in the mat dependent on organic substrate concentrations. Millimeter-scale variability in the δ^(13)C_(org) signature beneath the photic zone in the mat is a result of shifting dominance between cyanobacteria and green sulfur bacteria with the aggregate signature overprinted by heterotrophic reworking by SRB and methanogens. These observations highlight the impact of sedimentary microbial processes on δ^(13)C_(org) signatures; these processes need to be considered when attempting to relate observed isotopic signatures in ancient sedimentary strata to conditions in the overlying water column at the time of deposition and associated inferences about carbon cycling.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1111/gbi.12113DOIArticle
http://onlinelibrary.wiley.com/doi/10.1111/gbi.12113/abstractPublisherArticle
ORCID:
AuthorORCID
Fike, D.0000-0003-2848-0328
Orphan, V.0000-0002-5374-6178
Alternate Title:Spatial variability in photosynthetic and heterotrophic activity drives localized δ13Corg fluctuations and carbonate precipitation in hypersaline microbial mats
Additional Information:© 2014 John Wiley & Sons Ltd. Received 18 March 2014; accepted 30 August 2014. Article first published online: 13 OCT 2014. We would like to thank NASA AMES NAI team, particularly Mike Kubo, Linda Jahnke, and Abigail Green-Saxena for discussion and assistance in the laboratory and field, and Exportadora del Sal, S. A. for access to the field site. Funding for this work was supported by NSF EAR-1124389 as well as a Packard Fellowship and a Hansewissenschaftskolleg Fellowship to D.A.F., NSF EAR-1123391 to V.J.O, and NSF EAR-1304352 and EAR-1261423 to G.D.
Funders:
Funding AgencyGrant Number
NSFEAR-1124389
David and Lucile Packard FoundationUNSPECIFIED
Hansewissenschaftskolleg FellowshipUNSPECIFIED
NSFEAR-1123391
NSFEAR-1304352
NSFEAR-1261423
Issue or Number:6
Record Number:CaltechAUTHORS:20141201-092909674
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20141201-092909674
Official Citation:Houghton, J., Fike, D., Druschel, G., Orphan, V., Hoehler, T. M. and Des Marais, D. J. (2014), Spatial variability in photosynthetic and heterotrophic activity drives localized δ13Corg fluctuations and carbonate precipitation in hypersaline microbial mats. Geobiology, 12: 557–574. doi: 10.1111/gbi.12113
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52204
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:01 Dec 2014 18:00
Last Modified:13 Dec 2019 00:43

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