Radiocarbon fluctuation

Sternberg, R. S., Damon, P. E., Radiocarbon bating, Sensitivity of Radiocarbon Fluctuations and Inventory to Geomagnetic and Reservoir Parameters, p. 691-717, 1979. 

One of the most interesting of the geophysics results from radiocarbon dates is the history of the sun. Apparently, it is registered in fluctuations of the cosmic ray intensity. These are fluctuations of rather short duration in terms of the radiocarbon lifetime, perhaps a century or so, and apparently they are caused by variations in the solar wind due to long-term changes in the solar emissions. This idea has been developed in some detail recently by Dr. Lai and his collaborators. It promises to give us a way of watching the history of the sun over tens of thousands of years. This fine structure on the curve of calibration was discovered by Dr. Suess and others. 

The atmospheric 14C/C ratio during the last 50,000 y was sufficiently constant to make radiocarbon a remarkably reliable dating tool. Evidence for fluctuations of the 14C/C ratio could be found by high precision measurements on samples of known age. These fluctuations can be attributed to variations of processes in the solar system (solar activity) and on earth (fluctuations of C02 distribution among the atmospheric, oceanic, and biospheric reservoirs). Both fluctuations of solar activity and of the atmospheric C02 content may have contributed to past climatic changes. 

Fluctuation of Atmospheric Radiocarbon and the Radiocarbon Time Scale... 

The basic assumption of constant atmospheric X4C activity in radiocarbon dating is not strictly valid. We now have a record of the fluctuation of atmospheric 14C variations for the last 8,400 years B.P. obtained by measurement of the isotopes of carbon in dendrochron-ologically dated wood. Prior to contamination of atmospheric 14C activity by fossil fuel combustion and nuclear technology in the 20th century, the first-order secular variation can be closely approximated by a sine curve with a period of 10,600 years and an amplitude of ... 

In spite of prior difficulties, problems associated with 14C impurities have been overcome, and recently reported ambient HO measurements (84) have given HO concentrations with impressively short collection times of 100 s per HO datum. Current implementation of the radiocarbon technique has been described in detail (85), and repetitive measurements at a clean-air site in eastern Washington state have yielded midday HO concentrations of (5.6 0.1) x 106 molecules per cubic centimeter with impressively high precision (86). Instrumental sensitivity fluctuations were estimated to have an upper bound of 16%, and the detection limit was 105 cm"3 (86). 

Kitagawa H. and van der Plicht J. (1998) Atmospheric radiocarbon calibration to 45,0(X) yr BP Late Glacial fluctuations and cosmogenic isotope production. Science 279, 1187-1190. 

In radiocarbon dating, a reasonable assumption is that the ratio of carbon-14 to carbon-12 in the atmosphere has been relatively constant for the past 50,000 yr. However, because variations in solar activity control the amount of carbon-14 produced in the atmosphere, that ratio can fluctuate. We can correct for this effect by using other kinds of data. Recently scientists have compared carbon-14 data with data from tree rings, corals, lake sediments, ice cores, and other natural sources to correct variations in the carbon-14 clock back to 26,000 yr. 

If it can be assumed that the rate of production has not varied over time, and thus that a dynamic equilibrium has formed, and if it is possible to extract clean sample carbon, unaltered apart from the decline in and to measure its current concentration, it is possible using eqn [1] to calculate the elapsed time since the death of the organism. In practice, the process is far more complicated than this brief description indicates. Principally, one of the basic assumptions, that the rate of formation is constant, is known to be incorrect. The rate has, in fact, varied over time in response to a number of effects, principally fluctuations in the cosmic-ray flux with changes in the geomagnetic field and in solar activity. Because of this, no radiocarbon measurement equates directly with a calendar date, and all such measurements must be calibrated before use. 

The examples mentioned so far point to considerable flexibility of the auxin transport system. This view is also supported by the observation of oscillations of electric potential moving down Avena coleoptiles after illumination or after the supply of auxin (Newman 1959, 1963), by the report of fluctuations of lAA movement in segments of oat coleoptiles after blue light illumination (Thornton and Thimann 1967), and in individual plant parts, by the demonstration of even more pronounced oscillations of the export rate of radiocarbon from auxin-depleted segments of oat and corn coleoptiles, supplied with labeled lAA (Hertel and Flory 1968). It is further supported by previously mentioned (see Sect. 3.3.3.4) experiments of Shen-Miller (1973a), where rhythmic fluctuations of the lAA transport intensity in intact coleoptiles of oat and corn were observed, moreover the rhythmicity was out of phase between the upper and lower halves of geostimulated coleoptiles (Shen-Miller 1973b, p 169). 

The ratio is fairly uniform within each atmospheric hemisphere. There is a small-amplitude annual oscillation of the order of 0.4 % in the preindustrial era (Kromer et al. 2001) with Imiger-term fluctuations due both to changing production rates and changes in the carbon cycle itself (particularly ocean circulation and ventilation). The Southern Hemisphere is typically depleted in radiocarbon compared to the Northern Hemisphere by about 0.5 %. 

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