Modeling cosmogenic radionuclides 10Be and 7Be during the Maunder Minimum using the ECHAM5-HAM General Circulation Model U. Heikkilä1, J. Beer1, and J. Feichter2 1EAWAG, Dübendorf, Switzerland 2Max-Planck Institute for Meteorology, Hamburg, Germany
Abstract. All existing 10Be records from Greenland and Antarctica show increasing
concentrations during the Maunder Minimum period (MM), 1645–1715, when solar
activity was very low and the climate was colder (little ice age). In detail,
however, the 10Be records deviate from each other. We investigate to
what extent climatic changes influence the 10Be measured in ice by
modeling this period using the ECHAM5-HAM general circulation model.
Production calculations show that during the MM the mean global 10Be
production was higher by 32% than at present due to lower solar activity.
Our modeling shows that the zonally averaged modeled 10Be deposition
flux deviates by only ~8% from the average increase of 32%, indicating
that climatic effects are much smaller than the production change. Due to
increased stratospheric production, the 10Be content in the downward
fluxes is larger during MM, leading to larger 10Be deposition fluxes in
the subtropics, where stratosphere-troposphere exchange (STE) is strongest.
In polar regions the effect is small. In Greenland the deposition change
depends on latitude and altitude. In Antarctica the change is larger in the
east than in the west. We use the 10Be/7Be ratio to study changes in
STE. We find larger change between 20° N–40° N during
spring, pointing to a stronger STE in the Northern Hemisphere during MM. In
the Southern Hemisphere the change is small. These findings indicate that
climate changes do influence the 10Be deposition fluxes, but not enough
to significantly disturb the production signal. Climate-induced changes
remain small, especially in polar regions.
Citation: Heikkilä, U., Beer, J., and Feichter, J.: Modeling cosmogenic radionuclides 10Be and 7Be during the Maunder Minimum using the ECHAM5-HAM General Circulation Model, Atmos. Chem. Phys., 8, 2797-2809, doi:10.5194/acp-8-2797-2008, 2008.