Modern carbonate microbialites from an asbestos open pit pond, Yukon, Canada

Our plain-English summary of Modern carbonate microbialites from an asbestos open pit pond, Yukon, Canada, by I.M. Power, S. Wilson, G.M. Dipple, et al (Geobiology, 2011).

The study

• Authors: I.M. Power, S. Wilson, G.M. Dipple, G. Southam
• Journal: Geobiology
• Published: 2011;9(2):180-95
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Microbialites were discovered in an open pit pond at an abandoned asbestos mine near Clinton Creek, Yukon, Canada. These microbialites are extremely young and presumably began forming soon after the mine closed in 1978. Detailed characterization of the periphyton and microbialites using light and scanning electron microscopy was coupled with mineralogical and isotopic analyses to investigate the mechanisms by which these microbialites formed. The microbialites are columnar in form (cm scale), have an internal spherulitic fabric (mm scale), and are mostly made of aragonite, which is supersaturated in the subsaline pond water. Initial precipitation is seen as acicular aragonite crystals nucleating onto microbial biomass and detrital particles. Continued precipitation entombs benthic diatoms (e.g. Brachysira vitrea), filamentous algae (e.g. Oedogonium sp.), dinoflagellates, and cyanobacteria. The presence of phototrophs at spherulite centers strongly suggests that these microbes play an important initial role in aragonite precipitation. Substantial growth of individual spherulites occurs abiotically through periodic precipitation of aragonite that forms concentric laminations around spherulite centers while pauses in spherulite growth allow for colonization by microbes. Aragonite associated with biomass (δ(13)C = -4.6‰ VPDB) showed a (13)C-enrichment of 0.8‰ relative to aragonite exhibiting no biomass (δ(13)C = -5.4‰ VPDB), which suggests a modest removal of isotopically light dissolved inorganic carbon by phototrophs. The combination of a low sedimentation rate, high calcification rate, and low microbial growth rate appears to result in the formation of these microbialites. The formation of microbialites at an historic mine site demonstrates that an anthropogenically constructed environment can foster microbial carbonate formation.

© 2011 Blackwell Publishing Ltd.

In plain English

This was a geology and microbiology study. It did not study people or health. The authors examined microbialites, hardened structures that form with the involvement of microbes, in a flooded open pit at the abandoned Clinton Creek chrysotile asbestos mine in Yukon, Canada. The mine closed in 1978. In August 2007 about 20 microbialites were seen around the pond's edge. Two were collected, along with pond water and the microbial film (periphyton) on submerged rocks. The columns were up to about 15 cm tall and mostly aragonite, a calcium carbonate mineral, with minor clinochrysotile. Chrysotile fibers lay on their surfaces. Diatoms, algae, dinoflagellates and cyanobacteria were trapped at the centers of small mineral spheres, whose outer layers were nearly free of them. Aragonite near biomass was enriched in carbon-13 by 0.8 per mil relative to aragonite without biomass. The authors concluded that low sedimentation, high mineral precipitation and low microbial growth together produced these structures. They noted that microbes at the sphere centers do not by themselves confirm the microbes' role.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field sampling and laboratory study (light and electron microscopy, X-ray diffraction, water chemistry, stable isotope analysis) of microbialites; not a study of human health
• Who was studied: Microbialites in the Porcupine open pit pond at the abandoned Clinton Creek asbestos mine, 77 km northwest of Dawson City, Yukon, Canada. About 20 were seen in August 2007 and two were collected, plus periphyton and pond water samples.
• Exposure: No human exposure was studied. The site is a former chrysotile asbestos mine that operated for 11 years before closing in 1978. Asbestos fibers were observed in the pond setting.
• Main results:
  • The microbialites were mostly aragonite, with minor clinochrysotile, magnesium-rich calcite, quartz and possibly vermiculite
  • Microbialite surfaces were covered in debris including chrysotile fibers. Mats of asbestos fibers were seen draping over rock surfaces around the pond.
  • The pond water was supersaturated with respect to aragonite, calcite, dolomite and magnesite, with mean saturation indices of 0.60, 0.74, 3.36 and 0.91 respectively
  • Microbial remnants and detrital particles were at the centers of the mineral spheres (spherulites). The aragonite growing outward from those centers was almost entirely free of them.
  • Darker, biomass-containing areas of the microbialite slab (n = 17) had a mean carbon-13 value of minus 4.6 per mil. Milky white areas (n = 19) had a mean of minus 5.4 per mil. The darker areas were on average 0.8 per mil enriched in carbon-13.
  • The tallest microbialite, about 15 cm, gave an estimated maximum accretion rate of 5.2 mm per year, assuming 29 years of formation
• The authors' conclusion: The authors concluded that a balance of low sedimentation rate, high calcification rate and low microbial growth rate at this site leads to microbialites with an internal spherulitic fabric
• Limitations the authors state:
  • The presence of phototrophs at spherulite centers does not confirm their role in carbonate precipitation
  • Better preservation of diatoms and dinoflagellate cysts makes it difficult to tell which microbes are most responsible for precipitation
  • The micromilled isotope samples were likely mixtures of biologically mediated and abiotic carbonate
  • The pond's depth was not measured

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), Acicular.

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