HR: 09:15h
AN: U41B-06 INVITED     [Abstracts]
TI: The Holocene Total Solar Irradiance Based on $^{10}$Be Extracted From Ice Core
AU: * Vonmoos, M
EM: maura.vonmoos@eawag.ch
AF: EAWAG, Ueberlandstr. 133, D�bendorf, 8600 Switzerland
AU: Beer, J
EM: beer@eawag.ch
AF: EAWAG, Ueberlandstr. 133, D�bendorf, 8600 Switzerland
AU: Mende, W
EM: mende@bbaw.de
AF: ISSI, Hallerstr.6, Bern, 3012 Switzerland
AU: Muscheler, R
EM: raimund.muscheler@geol.lu.se
AF: Lund University, S”lvegatan 12, Lund, 22362 Sweden
AB: The sun is by far the most important energy source for the Earth's climate system. Although its magnetic variability has been revealed by various observations of solar parameters, the solar irradiance was considered for a long time as constant and misleadingly named `solar constant'. Since satellite based radiometers have shown that the solar irradiance varies with the 11-year sunspot cycle, increasing interest has been directed towards the sun's significance as a variable natural climate forcing factor. However, the measurements reveal that the total solar irradiance (TSI) changes over a solar cycle by only approx. 0.1 % what has questioned the relevance of the solar forcing. On the other hand, historical observations of the sun such as the 400 years long sunspot record clearly point to solar magnetic variability larger than observed during the satellite based monitoring period. A longer record of past TSI is needed to determine the full spectra of past variability in the sun's impact on our climate. Cosmogenic radionuclides like $^{10}$Be and $^{14}$C stored in ice cores and tree rings, respectively, provide the only indirect information on the sun's long-term behavior on millennial time scales and thus on the sun's total potential of variability. We present a new method to reconstruct past TSI from $^{10}$Be measurements from the GRIP ice core, which provides an improved basis for the detailed calculation of the effect of solar forcing on the Earth's climate. $^{10}$Be is produced by the interaction of galactic cosmic rays with the Earth's atmosphere. The heliomagnetic and geomagnetic fields modulate the cosmic ray intensity and therefore the production rate. Taking the geomagnetic modulation into account we reconstructed quantitatively the solar activity in terms of the heliospheric modulation parameter $\Phi$ and subsequently the TSI for the past $\sim$9300 years. Based partly on physical models, this method differs widely from previously applied linear regression approaches to reconstruct TSI from cosmogenic radionuclides. The results reveal a longtime solar variability significantly larger than observed so far by direct measurements and point out that the current high activity of the sun is not exceptional regarding the entire Holocene.
DE: 3344 Paleoclimatology
DE: 1650 Solar variability
SC: Union [U]
MN: 2004 AGU Fall Meeting