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Abstract Most Earth surface carbonates precipitate out of isotopic equilibrium with their host solution, complicating the use of stable isotopes in paleoenvironment reconstructions. Disequilibrium can arise from exchange reactions in the DIC‐H2O system as well as during crystal growth reactions in the DIC‐CaCO3system. Existing models account for kinetic isotope effects (KIEs) in these systems separately but the models have yet to be combined in a general framework. Here, an open‐system box model is developed for describing disequilibrium carbon, oxygen, and clumped (Δ47, Δ48, and Δ49) isotope effects in the CaCO3‐DIC‐H2O system. The model is used to simulate calcite precipitation experiments in which the fluxes and isotopic compositions of CO2and CaCO3were constrained. Using a literature compilation of equilibrium and kinetic fractionation factors, modeledδ18O and Δ47values of calcite are in good agreement with the experimental data covering a wide range in crystal growth rate and solution pH. This relatively straightforward example provides a foundation for adapting the model to other situations involving CO2absorption (e.g., corals, foraminifera, and high‐pH travertines) or degassing (e.g., speleothems, low‐pH travertines, and cryogenic carbonates) and/or mixing with other dissolved inorganic carbon sources.
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Flaming as part of aseptic technique increases CO 2 (g) and decreases pH in freshwater culture media
Abstract Aseptic technique has historically served as a fundamental practice in microbiology, helping to maintain culture purity and integrity. This technique has been widely encouraged and employed for use with cultures of heterotrophic bacteria as well as freshwater and marine algae. Yet, recent observations have suggested that these approaches may bring their own influences. We observed variations in growth among replicate experimental cyanobacterial cultures upon flaming of the culture tube opening during sample transfer and collection. Investigation revealed the pH of culture media had decreased from the initial pH established during media preparation. Flaming of sterile culture media alone confirmed a significant decrease, by as much as 1.7 pH units, and correlated with increased flaming events over time. We hypothesized that the causative factor was the introduction of carbon dioxide (CO2) into the media. To test this hypothesis, qualitative and quantitative analyses were used to determine the primary driver of pH decline. We further assessed the direct effects of flaming and subsequent pH changes onMicrocystis aeruginosacultures, showing flame‐driven pH changes and/or the introduction of CO2influenced experimental results. Our observations provide a cautionary tale of how classic and well‐accepted approaches may have unintended consequences, suggesting new approaches may be necessary in research areas assessing pH or carbon‐related effects on microbial communities.
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- Award ID(s):
- 1840715
- PAR ID:
- 10458047
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- Volume:
- 18
- Issue:
- 5
- ISSN:
- 1541-5856
- Page Range / eLocation ID:
- p. 211-219
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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