Factors influencing Be-7 accumulation on rock varnish

Rocks coated with desert varnish were translocated from Scottsdale, Arizona , and Panamint Valley, California, to a fenced-in plot near Biosphere 2 whe re they were allowed to accumulate a new crop of the 53 day half life, cosm ic ray-produced Be-7. Those exposed to precipitation accumulated several ti mes more of this isotope than those shielded from precipitation. No signifi cant difference in Be-7 accumulation was observed between a set which was U V irradiated (in an attempt to kill resident bacteria) and a set which rece ived no UV irradiation. This experiment suggests that 62 +/- 10 percent of the beryllium accumulated on the varnish was supplied by precipitation and 38 10 percent by some combination of dew, dust, and aerosols. If bacteria a re, as has been proposed, responsible for varnish growth, then either our U V irradiation was inadequate to squelch their activity or the Be-7 we measu red had not yet been built into the varnish.