Suess-effect

Fossil fuel emissions alter the isotopic composition of atmospheric carbon, since they contain no C and are depleted in C. Releasing radiocarbon-free CO2 to the atmosphere dilutes the atmospheric C content, 3delding lower C/C ratios ("the Suess effect"). From 1850 to 1954 the C/C ratio in the atmosphere decreased by 2.0 to 2.5% (Fig. 11-23) (Suess, 1965 Stuiver and Quay, 1981). Then, this downward trend in C was disrupted by a series of atmospheric nuclear tests. Many large fission explosions set off by the United States with high emission of neutrons took place in 1958 in the atmosphere and the Soviet Union held extensive tests during... 

Fig. 11-23 Comparison between the Peng ct fl/. (1983) model-derived Suess effect curve (solid line) and the observed trend (points) for atmospheric CO2...

Using the actual C02 production history, Oeschger et al., [26] calculated for the Suess effect in 1950 a value of -2.0 percent. This is essentially in agreement with the measurements [44], though 14C fluctuations due to 14C production rate variation make a precise determination of the Suess effect difficult. 

Gruber N, et al. (1999) Spatiotemporal patterns of carbon-13 in the global surface oceans and the oceanic Suess effect. Global Biogeochem Cycles 13 307-335 Gussone N, et al. (2005) Calcium isotope fractionation in calcite and aragonite. Geochim Cosmochim Acta 69 4485 494... 

Note that this approach assumes Fl4C = 1.0 and is constant prior to 1950. Actually the 14C/12C of atmospheric C02 did vary with time prior to 1900, mostly reflecting changes in the rate of 14C production in the upper atmosphere. During the Holocene, these variations were less than 10%, and they are documented in the calibration data sets based on 14C measured in known-age wood. Between 1900 and 1950, Eatm declined due to the addition of 14C-free C02 derived from fossil fuels, known as the Suess effect. Modeling of turnover times should use the actual atmospheric 14C inputs to photosynthesis, although it is not as important before 1959 as after. 

The ratio of a sample is measured in relation to a standard to improve the accuracy and precision of accelerator mass spectrometry measurements (Elmore and Phillips, 1987). Multiplying the ratio by 1000 results in the delta (del) values having units of parts per thousand, also know as per mil (%o). For standards, it is necessary to use wood from trees harvested before about 1850 pre-industrial, to avoid the Suess effects. The standard value for pre-industrialized atmospheric CO2 is 13.56 dpm g-1 or 14C/C equals 1.176 x 10-12 (Broecker and Peng, 1982). A correction term involving the effects of isotopic fractionation (IF) are also subtracted out of this equation. Isotopes are fractionated due to physical and chemical reactions (more details in the following section), thereby making the abundance of carbon isotopes (12C, 13C, and 14C) different in plants (Faure, 1986). The National Bureau of Standards currently provides an oxalic acid 14C standard that is used for this correction however, there have been many problems associated with development of this standard (Craig, 1954, 1961 Stuiver and Polach, 1977). 

Suess effects the dilution effect on 14C from inputs of fossil fuel combustion are clear after about 1850 in the early stages of the Industrial Revolution. 

Variability in the Amount of Carbon in Reservoirs. In addition to variations in the production and distribution of radiocarbon over time and within portions of various carbon reservoirs, variations may result in situations where carbon not in equilibrium with the contemporary standard values is added or removed from any reservoir. Two instances of this are well documented since they occurred within the last century as a result of human intervention. The first is known as the industrial or Suess effect and is caused by the combustion of fossil fuels beginning about 1890, resulting in a depletion of atmospheric activities by about 3% (76). A more recent occurrence has been called the atomic bomb or Libby effect. The detonation of nuclear devices in the atmosphere beginning in 1945 produced large amounts of artificial increasing the radiocarbon concentrations in the atmosphere by more than 100% in the Northern Hemisphere (77). Because of equilibration with the oceans, the levels have been diminishing steadily since the atmospheric testing was terminated by the major nuclear powers except France and the People s Repub-... 

In addition, the output of CO2 from fossil fuels—which contain no C—has tended to dilute the natural level [Suess effect (Suess, 1955)], and recent injections of nuclear bomb-produced— artificial— C have enhanced the C level in the opposite direction. 

Bacastow RB, Keeling CD, Lueker TJ, Wahlen M, Mook WG (1996) The d C Suess effect in the world surface oceans and its implications for oceanic uptake of CO2 analysis of observations at Bermuda. Global Biogeochem Cycles 10 335-346... 

Finally, evidence of increased fossil fuel emission into the atmosphere can be seen in the general decrease in A " C from 1850 to 1955 in shallow corals from the Atlantic and Pacific Oceans. This phenomenon, referred to as the Suess Effect, is mainly the result of " C-free CO2 produced from combusted fossil fuel entering the atmosphere, the oceans and eventually, the coral skeleton (post-1950, coral A " C values skyrocketed as a result of produced by thermonuclear bombs effectively swamping out the Suess effect). 

During the last 50 years, two factors have disturbed the natural equilibrium of carbon-14. The first factor relates to industrial development and the combustion of a significant quantity of fossil fuel. Due to its age, fossil carbon is essentially free of carbon-14 and thus its introduction into the atmosphere has significantly diluted atmospheric carbon-14. This so-called "Suess effect" has reduced the level of modern carbon-14. 

---