By means of selective absorption in situ, Cesium-137 was measured in November and December 1968 in two depth profiles (near 39°N, 69°W) and in ten widely scattered surface samples in the North Atlantic Ocean. The surface concentrations of Cs-137 are compatible with the surface concentrations of Sr-90 obtained by other workers in the same latitudinal range....
Kupferman, Stuart L.. 1971. "Cesium-137 in the North Atlantic measured by selective absorption in situ." Journal of Marine Research 29, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1198