The determination of air-sea exchange and oceanic mixing rates using7Be during the Bomex experiment

Abstract

The concentrations of 7Be and other radionuclides were measured in air, rain, and seawater in a region east of Barbados, British West Indies, in the summers of 1968 and 1969 during the Barbados Oceanographic and Meteorological Experiment. The radionuclide inventories in the sea varied rapidly owing to the horizontal motion of seawater through the sampling region. The salinity also varied considerably, presumably as a result of Amazon River water carried into the sampling region by the Guiana current, which flows northwestward along the coast of South America. The 103Ru to 95Zr ratio in the top 15 m of the sea indicated that large amounts of these radionuclides from the French nuclear test series at 23°S beginning July 7, 1968, were transported into the sampling region, probably by the Guiana current, on August 15, 1968, and also in June but not in May of 1969. The deposition Of 7Be on the sea surface by rainfall in the sampling region in August 1968 and May through July 1969 was only 13 and 26%, respectively, of that necessary to maintain the measured inventories. it is possible, however, that the inventories resulted from wet deposition outside the sampling region, such as in the intertropical convergence zone, followed by advective transport of the water into the sampling region. The calculated average deposition velocity Of 7Be was 1.0 cm/s, and the calculated average yearly 7Be flux across the sea surface was 1.6×10−2 atom cm−2 s−1. The calculated vertical eddy diffusion coefficient in the sea decreased from greater than 7 cm2/s at the surface to 0.25–0.85 cm2/s at 30–40 m.