TROPOSPHERIC 14C VALUES IN THE PACIFIC NORTHWEST AND THE ARCTIC BASIN DURING 1964 JAMES A, YOUNG, NILS E. ERICKSON, and ARTHUR W. FAIRHALL University of Washington, Seattle, Washington ABSTRACT Samples of atmospheric CO, were collected by using a molecular sieve and counted for their ‘“C content. Taking 0.95 of the National Bureau of Standards oxalic acid standard as the pre-1945 level of ‘4C in the atmosphere, the results are expressed as percent above normal. Dur- ing the summer of 1963, tropospheric levels reached about 115% above normal, followed by a rapid drop to about 88% above normal in the early fail of 1963, a level which was maintained until May 1964, when a new summerrise was noted. The sudden drop in C specific activity is attributed to exchange of atmospheric CO, with dissolved CO, in the ocean. Increases in the tropospheric 'C concentration is attributable to injection of CO, of high specific activity from the stratosphere. Samples of CO, taken during the passage of storm fronts give evidence of this injection, as well as evidence of exchange with oceanic CQ,. INTRODUCTION Samples of atmospheric CO, of from 2 to 8 liters are collected periodically for ‘*C analysis from several locations in the state of Washington and the Arctic basin. The collection system consists ofa Linde type 4-A molecular sieve designed for field use. The first successful use of a molecular-sieve material for sam- pling of atmospheric CO, for '4C was apparently made by Fergusson.' Previous investigators attempting to use this material for similar studies experienced difficulty because the untreated sieve material has 422