FURTHER APPLICATION OF BOMB C-14 AS A TRACER IN THE ATMOSPHERE AND OCEAN

Bomb C-14 from nuclear tests in the atmosphere has proved to be a part icularly useful tool in the study of the carbon cycle. We provide here a ca. 30-yr time series of C-14 concentrations in the atmosphere betw een 28 degrees N and 71 degrees N and in the ocean surface between 45 degrees S and 45 degrees N. More recently (since 1990), a north-south profile also has been obtained for C-14 in the surface waters of the A tlantic Ocean. The measurements were performed using the conventional technique of beta counting of large samples (4 to 5 liter CO2) in CO2 proportional counters. These data show that the C-14 concentration in the atmosphere is leveling off with a time constant of 0.055 yr(-1), a nd is now approaching that of the ocean surface at lower latitudes. Ad ditional tracer studies have been concerned especially with the penetr ation of bomb C-14 into the deep ocean. The Norwegian and Greenland se as are of interest as a sink for atmospheric CO2 and also a source of water for the deep Atlantic Ocean. During the last five years, several C-14 depth profiles have been measured from the Fram Strait (79 degre es N) to south of Iceland (62 degrees N), using the AMS technique avai lable at the University of Arizona AMS Facility. We considered it impo rtant to repeat and compare a few of the profiles with those produced by the GEOSECS expedition in 1972 and the TTO expedition in 1981. The profiles show that water descending to the deep Atlantic Ocean is orig inating mainly from intermediate and surface depths in the Nordic Seas . However, the ventilation rate of the Norwegian Sea deepwater is too slow to be an important component in the transfer of water over the Gr eenland-Scotland Ridge.