Modeling cosmogenic radionuclides <sup>10</sup>Be and <sup>7</sup>Be during the Maunder Minimum using the ECHAM5-HAM General Circulation Model

Abstract

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.

Influence of model resolution on the atmospheric transport of <sup>10</sup>Be

“…Therefore, first modelling studies of beryllium isotopes were conducted using 31 vertical levels and the model top at ca. 30 km (T42L31, Heikkilä et al, 2008b). Later it was reasoned that allowing for a better representation of stratospheric dynamics would improve the beryllium transport in the model (T42L39, model top at 80 km Heikkilä et al, 2009).…”

“…The beryllium isotopes ( 10 Be and 7 Be) have been implemented into the model including their production rate following Masarik and Beer (2009) interpolated to the monthly varying solar activity parameter , transport and deposition and, in the case of 7 Be, its radioactive decay. Details of the implementation of all these processes are given in Heikkilä et al (2008b). The model was forced with observed sea-surface temperatures and seaice cover (AMIP2).…”

Solar Influence on Global and Regional Climates

“…10 Be is a spallation product of galactic cosmic rays hitting atmospheric O, N and Ar atoms; 14 C is produced by thermal neutrons, generated by cosmic rays, interacting with N. About two-thirds of the 10 Be are formed in the stratosphere and about one-third in the troposphere from where precipitation times into the reservoirs are typically 1 year and 1 week, respectively. The deposition into any one reservoir is influenced, to some extent, by climate conditions (e.g., Vonmoos et al 2006;Field et al 2006;Aldahan et al 2008;Heikkila et al 2008). On the other hand, the 14 C generated by GCRs takes part in the carbon cycle and is exchanged with the two major reservoirs, the oceans and the biomass.…”

A history of solar activity over millennia

“…Recent efforts in employing modern atmospheric 3D circulation models for simulations of 10 Be transport and deposition, including realistic air-mass transport and dry-vs-wet deposition Heikkilä et al 2008Heikkilä et al , 2009), look more promising. An example of 10 Be deposition computed on the world grid using the NASA GISS model ) is shown in Fig.…”

“…13. Precision of the models allows one to distinguish local effects, e.g., for Greenland (Heikkilä et al 2008). A simulation performed by combining a detailed 10 Be-production model with an air-dynamics model can result in an absolute model relating production and deposition of the radionuclide.…”