Constraints on long-term changes in solar activity from the range of variability of cosmogenic radionuclide records
08 Sep 2011
1Department of Earth and Ecosystem Sciences, Division of Geology, Lund University, Sölvegatan 12, SE-22362 Lund, Sweden
2Uni Bjerknes Centre, Bjerknes Centre for Climate Research, Allegaten 70, NO-5007 Bergen, Norway
3Australian Nuclear Science and Technology Organisation (ANSTO)
Abstract. There is a variety of different cosmogenic radionuclide-based reconstructions of solar activity variations for the past. Especially the longer-term changes and the absolute levels of past solar activity are uncertain as it is illustrated by the differences between these reconstructions. On the one hand there are differences between 10Be and 14C records that are commonly used as proxies for the varying solar modulation of galactic cosmic rays. On the other hand estimates of past changes in the geomagnetic shielding also include relatively large uncertainties. Here, we concentrate on variations in cosmogenic radionuclide records on time scales of 50 to 500 yr. We show that these are to a large extent independent of the geomagnetic field intensity. The range of variability of cosmogenic radionuclide records allows us to set constraints about long-term changes in solar activity. These records indicate that present solar activity levels were reached or exceeded regularly in the past.