CL-36 IN THE LAURENTIAN GREAT-LAKES BASIN

We have measured the relative concentration of Cl-36 in the five major lakes of the Laurentian Great Lakes by AMS techniques at the Chalk River TASCC facility. The ratio of Cl-36 to stable chloride decreases from 1300 CLU (1 CLU is a ratio of Cl-36/Cl of 1 x 10(-15)) in Lake Superior to 300 CLU in Lake Ontario. However, the salt content increases rapidly from Superior to Ontario so that the concentration of Cl-36 increases from a low of 3.3 +/- 0.3 x 10(7) in Lake Superior to a high of 11.7 +/- 1.7 x 10(7) atoms/l in Lake Ontario. The results are compared to a model that includes the contribution of Cl-36 from the bomb tests in the 1950s as determined from ice-core data taken in Greenland. It is found that there is too little Cl-36 in Lake Superior to be consistent with current ideas on Cl-36 in precipitation.