Berlin 2005 – wissenschaftliches Programm
EP 6.1: Hauptvortrag
Samstag, 5. März 2005, 14:00–14:45, TU BH349
History of cosmic rays, solar variability and climate forcing derived from cosmogenic radionuclides. — •Jürg Beer — EAWAG, Überlandstrasse 133, Postfach 611, CH-8600 Duebendorf
Cosmogenic radionuclides are produced continuously by the interaction of cosmic rays with the atoms of the Earth*s atmosphere. Their production rate reflects changes in the intensity of the GCR flux penetrating into the atmosphere. The GCR flux is subject to changes caused by e.g. nearby supernova explosions, heliomagnetic, and geomagnetic modulation. After production cosmogenic radionuclides behave differently depending on their geochemical properties. 14C forms 14CO2 and starts exchanging between atmosphere, biosphere and ocean. A small part of it gets built into tree rings where it is stored for many millennia. 10Be, on the other hand, becomes attached to aerosols and is removed from the atmosphere mainly by dry deposition within 1-2 years. Some of it gets incorporated into snowflakes and, subsequently, is stored in polar ice sheets which are formed layer by layer.
As a consequence measurements of cosmogenic radionuclides in well dated polar ice cores and tree rings offer the unique opportunity to derive information about changes in the cosmic ray intensity over the past 50 000-100 000 years. Although the interpretation of the measured signal in terms of the different production and transport processes is not straight forward, the data obtained so far are consistent with independent reconstructions of the geomagnetic dipole moment and reveal new insights into the long-tern history of solar variability and its potential influence on climate change. The last decades are characterized by high solar activity and there is growing evidence that solar forcing plays an important role in the pre-industrial period.