Meridional transport and deposition of atmospheric Be-10

Be-10 concentrations measured in ice cores exhibit larger temporal variability than expected based on theoretical production calculations. To investigate whether this is due to atmospheric transport a general circulation model study is performed with the Be-10 production divided into stratospheric, tropospheric tropical, tropospheric subtropical and tropospheric polar sources. A control run with present day Be-10 production rate is compared with a run during a geomagnetic minimum. The present Be-10 production rate is 4-5 times higher at high latitudes than in the tropics whereas during a period of no geomagnetic dipole field it is constant at all latitudes. The Be-10 deposition fluxes, however, show a very similar latitudinal distribution in both the present day and the geomagnetic minimum run indicating that Be-10 is well mixed in the atmosphere before its deposition. This is also confirmed by the fact that the contribution of Be-10 produced in the stratosphere is dominant (55%-70%) and relatively constant at all latitudes. The contribution of stratospheric Be-10 is approximately 70% in Greenland and 60% in Antarctica reflecting the weaker stratosphere-troposphere air exchange in the Southern Hemisphere.