Conventional vs ams radiocarbon dating
From the laminated sediments we selected terrestrial-origin macrofossils such as leaves, branches and insects for AMS 14C measurements.(see Appendix B) The samples are processed using a strong acid-alkali-acid (AAA) treatment for both samples and reference blank materials.One of the products of the continuing cycles of the seasons can be found on the bottoms of some lakes.Each spring, tiny plants bloom in Lake Suigetsu, a small body of water in Japan.The tree-ring calibration range, our calibration agrees well with the European sediments (3) and generally with marine calibrations obtained by combined U/Th and 14C dating of corals (4,5). with 1-p bars = Lake Suigetsu, , ~ and O correspond to U-series based 14C calibration on corals." The results from just one source could possibly be readily contested, but in this case the scientists have correlated the results from multiple sources including that of Lake Gosciaz (Poland), German oak and pine tree ring chronologies and also calibrations from coral data.Many in the scientific community are proposing the result of the above study as a "calibration" to radiometric C14 data, see Appendix A.Detailed comparison with short piston cores shows that the sampling does not cause significant loss of varves - typically 0-2 cm to a maximum of 3 cm, corresponding to ca. 20,000 cal BP) were estimated by varve counting of a single core, the ages quoted should be considered as minimum ages, the error increasing with depth.Based on the results of some duplicated countings of selected subsamples and independent counting of different subsamples collected from the same horizon, we estimate that the counting error is less than 1.5%, corresponding to 150 yr for 10,000 varve years.
The sedimentation or annual varve thickness is relatively uniform (typically 1.2 mm yr-1 during the Holocene and 0.62 mm yr-1 during the Glacial).
Most information on the past 30,000 years or so is from sites or specimens that have been dated using radiocarbon (14C).
However, the radiocarbon age scale that would be calculated from first principles (based on the decay rate of the 14C isotope, assuming that 14C was at the same level of abundance as it is at present) is not always reliable, because there have been fluctuations in the rate of production in 14C at the top of the atmosphere.
At the bottom of Lake Suigetsu, thin layers of microscopic algae have been piling up for many years.
The alternating layers of dark and light count the years like tree rings.