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Rock metamorphism releases substantial CO2 over geologic timescales (>1 My), potentially driving long-term planetary climate trends. The nature of carbonate sediments and crustal thermal regimes exert a strong control on the efficiency of metamorphic CO2 release; thus, it is likely that metamorphic CO2 degassing has not been constant throughout time. The Proterozoic Earth was characterized by a high proportion of dolomite-bearing mixed carbonate-silicate rocks and hotter crustal regimes, both of which would be expected to enhance metamorphic decarbonation. Thermodynamic phase equilibria modeling predicts that the metamorphic carbon flux was likely ~1.7 times greater in the Mesoproterozoic Era compared to the modern Earth. Analytical and numerical approaches (the carbon cycle model PreCOSCIOUS) are used to estimate the impact this would have on Proterozoic carbon cycling and global atmospheric compositions. This enhanced metamorphic CO2 release alone could increase pCO2 by a factor of four or more when compared to modern degassing rates, contributing to a stronger greenhouse effect and warmer global temperatures during the expansion of life on the early Earth.
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Timescales for the Spray-Mediated Gas Exchange of Carbon Dioxide
The air–sea exchange of carbon dioxide (CO2) on a global scale is a key factor in understanding climate change and predicting its effects. The magnitude of sea spray’s contribution to this flux is currently highly uncertain. Constraining CO2’s diffusion in sea spray droplets is important for reducing error margins in global estimates of oceanic CO2 uptake and release. The timescale for CO2 gas diffusion within sea spray is known to be shorter than the timescales for the droplets’ physical changes to take place while aloft. However, the rate of aqueous carbonate reactions relative to these timescales has not been assessed. This study investigates the timescales of droplet physical changes to those of chemical transformations across the H2CO3/HCO3−/CO32− sequence. We found that physical timescales are rate limiting and that evaporation drives carbonate species into gaseous CO2, promoting the production and evasion of CO2 from sea spray droplets. This has important implications for carbon cycling and feedback in the surface ocean.
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- Award ID(s):
- 2218781
- PAR ID:
- 10538085
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Journal of Marine Science and Engineering
- Volume:
- 12
- Issue:
- 7
- ISSN:
- 2077-1312
- Page Range / eLocation ID:
- 1128
- Subject(s) / Keyword(s):
- sea spray gas exchange carbonate chemistry CO2 flux evaporation hypersalinity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/jmse12071128
