The geochemical cycle of 9Be: A reconnaissance

An initial survey has been made of the geochemistry of 9Be in natural waters with a view to utilizing the isotope with the cosmogenic species 10Be (tsub(1/2)=1.5m.y.) in geochronological studies of sedimentary accumulation. The mobility of 9Be in continental waters is a strong function of pH with acid streams (pH<6) being strongly enriched as compared to alkaline carbonate rivers. Large-scale scavenging of beryllium occurs in the estuaries of rivers containing more than about 200 pM of the element. In alkaline systems of lower concentration the element appears to behave conservatively. The net flux of beryllium to the ocean is estimated as that equivalent to an average effective river concentration of about 150 pM. Beryllium is strongly enriched in ridge crest hydrothermal solutions over ambient seawater. The flux is approximately 70% of that from the continents. The deep water concentrations of 9Be vary by only 20% between the North Atlantic and North Pacific demonstrating that the 'chemical saltation' produced by scavenging from the deep water column and release from the sediments predominates over simple advective concentration along flow lines. Isotopic homogenization of 10Be and 9Be is probably achieved in the ocean. The situation in continental waters appears much less promising. (orig.)