| Summary: | Changes in the concentration of cosmogenic nuclides measured in natural archives are related mainly to changes in the cosmic-ray-induced production rate in the atmosphere, but also to the subsequent transport and deposition processes which depend on the geochemical properties of the nuclides. A comparison of 10 Be and 36 Cl data from ice cores from Greenland ice cores and 14 C data from tree rings and other archives provides the following information for the isotope stages 2 and 3: 1. Changes in the cosmogenic-nuclide production rate on time scales longer than approximately 2 kyr agree well with paleomagnetic data derived from deep-sea sediments. In particular, the geomagnetic excursions leading to weak fields around 40kyr BP (Laschamp) and 32 kyr BP (Mono Lake) can be clearly seen. 2. Production variations on shorter time scales contain information on solar variability. As an example, the 205 yr DeVries cycle already known from the analysis of 14 C tree ring data during the Holocene is also present in the 10 Be data of the time period 25-55 kyr BP. 3. A comparison of Δ 14 C calculated using 10 Be data with the measured Δ 14 C record, points to a reduction of the global deep-water formation during the Younger Dryas cold event. 4. Using information available on the production rates of cosmogenic nuclides in the past derived from paleomagnetic data, the paleoprecipitation rate can be calculated. This is crucial for establishing precise time scales.
|
|---|