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The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon (C and C) by the admixture of large amounts of fossil-fuel derived CO₂, which contains no CO₂ and is depleted in CO₂ relative to CO₂ in the atmosphere and carbon in the upper ocean and the terrestrial biosphere . It was discovered by and is named for the Austrian chemist Hans Suess, who noted the influence of this effect on the accuracy of radiocarbon dating. More recently, the Suess effect has been used in studies of climate change. The term originally referred only to dilution of atmospheric CO₂ relative to CO₂. The concept was later extended to dilution of CO₂ and to other reservoirs of carbon such as the oceans and soils, again relative to C.

Although the ratio of atmospheric CO₂ to CO₂ decreased over the industrial era (prior to atmospheric testing of nuclear weapons, commencing about 1950), because of the increase, due to fossil fuel emissions, in the amount of atmospheric CO₂ over this period, roughly 1850 to 1950, the amount of atmospheric CO₂ actually increased over this period.

Carbon isotopes

Carbon has three naturally occurring isotopes. About 99% of carbon on Earth is carbon-12 (C), about 1% is carbon-13 (C), and a trace amount is carbon-14 (C). The C and C isotopes are stable, while C decays radioactively to nitrogen-14 (N) with a half-life of 5730 years. C on Earth is produced nearly exclusively by the interaction of cosmic radiation with the upper atmosphere. A C atom is created when a thermal neutron displaces a proton in N. Minuscule amounts of C are produced by other radioactive processes; a large amount was produced in the atmosphere during nuclear testing before the Limited Test Ban Treaty. Natural C production and hence atmospheric concentration varies only slightly over time.

Plants take up C by fixing atmospheric carbon through photosynthesis. Animals then take C into their bodies when they consume plants (or consume other animals that consume plants). Thus, living plants and animals have nearly the same ratio of C to C as the atmospheric CO₂. Once organisms die they stop exchanging carbon with the atmosphere and thus no longer take up new C. This effect is the basis of radiocarbon dating, with the proviso that mass-dependent fractionation and the decrease in C due to radioactive decay and are accounted for.

Photosynthetically fixed carbon in terrestrial plants is depleted in C compared to atmospheric CO₂. This fractionation of carbon isotopes is caused by kinetic isotope effects and mass dependence of CO₂ diffusivity. The overall effect is slight in C4 plants but much greater in C3 plants which form the bulk of terrestrial biomass worldwide. Depletion in CAM plants vary between the values observed for C3 and C4 plants. In addition, most fossil fuels originate from C3 biological material produced tens to hundreds of millions of years ago. C4 plants did not become common until about 6 to 8 million years ago, and although CAM photosynthesis is present in modern relatives of the Lepidodendrales of the Carboniferous lowland forests, even if these plants also had CAM photosynthesis they were not a major component of the total biomass.

Fossil fuels such as coal and oil are made primarily of plant material that was deposited millions of years ago. This period of time equates to thousands of half-lives of C, so essentially all of the C in fossil fuels has decayed. Fossil fuels also are depleted in C relative to the atmosphere, because they were originally formed from living organisms. Therefore, the carbon from fossil fuels that is returned to the atmosphere through combustion is depleted in both C and C compared to atmospheric carbon dioxide.

See also

• Environmental isotopes
• Bomb pulse

References

1. Tans, P.P.; de Jong, A.F.M.; Mook, W. G. (30 August 1979). "Natural atmospheric C variation and the Suess effect". Nature. 280 (5725): 826–828. Bibcode:1979Natur.280..826T. doi:10.1038/280826a0. S2CID 4323299.
2. "CARD: What is the Suess effect?". Canadian Archaeological Radioactive Database. Archived from the original on 2007-09-29. Retrieved 2007-10-19.
3. Keeling, C. D. (1979). "The Suess effect: Carbon-Carbon interrelations". Environment International. 2 (4–6): 229–300. Bibcode:1979EnInt...2..229K. doi:10.1016/0160-4120(79)90005-9.
4. Schwartz, S. E.; Hua, Q.; Andrews, D. E.; Keeling, R. F.; Lehman, S. J.; Turnbull, J. C.; Reimer, P, J.; Miller, J. B.; Meijer, H. A. J. (2024). "Discussion: Presentation of Atmospheric CO₂ Data". Radiocarbon. xx (xx): 1–14. doi:10.1017/RDC.2024.27.{{cite journal}}: CS1 maint: multiple names: authors list (link)
5. Farquhar, G. D.; Ehleringer, J. R.; Hubick, K. T. (1989). "Carbon Isotope Discrimination and Photosynthesis". Annu. Rev. Plant Physiol. Plant Mol. Biol. 40: 503–537. doi:10.1146/annurev.pp.40.060189.002443.
6. Bozhinova, D.; van der Molen, M. K.; van der Velde, I. R.; Krol, M. C.; van der Laan, S.; Meijer, H. A. J.; Peters, W. (17 July 2014). "Simulating the integrated summertime Δ14CO2 signature from anthropogenic emissions over Western Europe". Atmos. Chem. Phys. 14 (14): 7273–7290. doi:10.5194/acp-14-7273-2014.

Further reading

• Cabaneiro, A.; Fernandez, I. (October 2015). "Disclosing biome sensitivity to atmospheric changes: Stable C isotope ecophysiological dependences during photosynthetic CO₂ uptake in Maritime pine and Scots pine ecosystems from southwestern Europe". Environmental Technology & Innovation. 4: 52–61. Bibcode:2015EnvTI...4...52C. doi:10.1016/j.eti.2015.04.007. (a 25-year-long dendrochronological study (1978–2002) using stable C isotope ratio mass spectrometry in growth rings of perennial trees from the Southern Atlantic Europe that explores the Suess Effect-ecosystem relationships to examine the biome sensitivity to C-CO₂ atmospheric changes)
• Suess, H. E. (September 1955). "Radiocarbon Concentration in Modern Wood". Science. 122 (3166): 415–417. Bibcode:1955Sci...122..415S. doi:10.1126/science.122.3166.415-a. S2CID 177102578. (in Northern hemisphere)
• Lerman, J. C.; Mook, Wim; Vogel, J. C. (1970). Olsson, Ingrid U. (ed.). Radiocarbon Variations and Absolute Chronology: Proceedings of the Twelfth Nobel Symposium held at the Institute of Physics at Uppsala University. New York: Wiley. pp. 275–301. LCCN 73115769. (in the Southern Hemisphere)

External links

• An anomalous Suess effect above Europe
• Magnitude and Origin of the Anthropogenic CO₂ Increase and C Suess Effect in the Nordic Seas Since 1981
• Are arable soils of urban areas influenced by the atmospheric Suess-Effect?
• The need to correct for the Suess effect in the application of δC in sediment of autotrophic Lake Tanganyika, as a productivity proxy in the Anthropocene

• Geochemistry
• Greenhouse gas emissions
• Radiocarbon dating