(2000a) concluded that variations in solar activity were the primary cause of the larger atmospheric 14C fluctuations for the period 11,000 to 14,500 years before present, although many researchers believe that carbon cycle changes tied to deep ocean circulation are a significant cause of atmospheric 14C fluctuations in this time interval (Edwards et al., 1993 Mikolajewicz, 1996 Stocker and Wright, 1996 Hughen et al., 2000 Muscheler et al., 2000 Delaygue et al., 2003). For the past 11,000 years, fluctuations in the atmospheric 14C have been largely produced by changes in the solar magnetic field (de Vries, 1958, de Vries, 1959 Stuiver, 1961 Stuiver and Quay, 1980). Produced by cosmic rays in the upper atmosphere (Lal and Peters, 1962 Suess 1968 Lal, 1988), 14CO 2 rapidly mixes throughout the troposphere and exchanges with the reactive carbon reservoirs of the oceans and biosphere, where it decays (Suess, 1955 Craig, 1957 de Vries, 1958, de Vries, 1959). The records of the 14C content of the atmosphere and oceans contain a remarkable array of information about Earth history (Arnold and Libby, 1949 Libby, 1955 Suess, 1970 Damon et al., 1978 Stuiver, 1982 Stuiver and Pearson, 1986 Damon, 1988 Bard, 1998). Our radiocarbon calibration program is publicly accessible at: along with full documentation of the samples, data, and our statistical calibration model. We developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years, taking full account of combined errors in input ages and calibration uncertainties. This paper presents high precision paired 230Th/ 234U/ 238U and 14C age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12,000 to 50,000 years before present. Four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12,000 calendar years before present. As a result of these two variables, a radiocarbon age is not equivalent to a calendar age. The production of 14 C in the atmosphere varies through time due to changes in the Earth's geomagnetic field intensity and in its concentration, which is regulated by the carbon cycle. Today, it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates. Recent advances in Accelerator Mass Spectrometry (AMS) and sample preparation techniques have reduced the sample-size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes. ![]() ![]() Radiocarbon dating is the most widely used dating technique in the world.
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