Cosmic ray intensity variations

The advent of new techniques to collect undisturbed sediment cores, with well preserved sediment - water interface has brought into sharper focus the various deep sea sedimentary processes, their rates and their effects on the preserved records. As mentioned earlier, recent studies have shown that the record contained in sediments is not a direct reflection of the delivery pattern of a substance to the ocean floor as has so far been assumed the record is modified as a result of several complex physical, chemical and biological processes. Therefore, information on the temporal variations in the tracer input to oceans, if sought, has to be deciphered from the sediment-residuum. In the following we consider one specific example of retrieval of information from the sediment pile the application of deep sea sediments to obtain historical records of cosmic ray intensity variations. 

Figure 9. Calculated attenuation factors for various values of T (period in the sinusoidal cosmic ray intensity variations) and A (the total rate constant). See section on deep-sea sediments and historical records for discussion.

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 amplitude attenuation factor, 1 + (tu/Ai)2 for nuclides satisfying relation [14], for various values of Ax and T are presented in figure 9. It is obvious from figure 9 that the attenuation is minimal when Ai > u>, i.e., when the removal residence time of the nuclide from sea water is less than the period in the variation of cosmic ray intensity. 

The generation process for radiocarbon in the atmosphere makes C02 which enters the biosphere because of the long lifetime the mixing is essentially perfect. We assumed the rate of production to be constant which turns out to be somewhat incorrect. Variations of about 10 percent can be seen back in time to early Egyptian periods and before. The earth s magnetic field was apparently weaker then as the cosmic rays delivered to the surface and the atmosphere were more intense. 

Figure 35 Reconstructed variations in mean temperature of shallow low-latimde seawater during the Phanerozoic based on the data in Figure 34. Note the good agreement of the cooling episodes with the extended latitudinal dispersion of ice rafted dehris (shaded histograms). In the subsequent publication, Shaviv and Veizer (2003) showed that the proposed temperamre variations correlated with the intensity of cosmic-ray flux reaching the Earth. The pco2 (PAL— present-day atmospheric level) is that for the Geocarb model of Berner (1994).

Radionuchdes produced from cosmic-energy interactions are usually formed high in the atmosphere where cosmic radiation is most intense. The spatial variabihty of these radionuclides is partly due to variation in the dux of cosmic radiation, which varies spatially with altitude and latitude and temporally with changes in cosmic-ray production rates. For example, the latitudinal production rate between the poles and the equator varies by about a factor of 4, and production rates of some radionuclides have varied by about 10% over the past 10 million yr. There are only a few radionuclides that are formed in sufficient quantities and are long-lived enough to contribute to the... 

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