No abstract

Surface and subsurface samples of seawater collected in the Atlantic, Arctic, Indian, Pacific, and Antarctic oceans have been analyzed for 228Ra. The results agree with those obtained by Moore (1969) and show that near‐shore surface waters normally contain much higher 228Ra concentrations than surface waters collected in the open sea, that surface waters normally contain much higher 228Ra concentrations than intermediate and deep waters, but that nearbottom waters are somewhat enriched in 228Ra. Surface waters of the North Atlantic and Indian oceans contain significantly higher concentrations of 228Ra than those of the Pacific and Antarctic oceans. Vertical profiles of 228Ra activities have been used to calculate values of the constant for vertical eddy diffusion Kz of about 0.3 cm2/sec in the Arctic Ocean in the zone between the cold water mass that originates in the Bering Sea and the underlying warmer but more saline water mass that originates in the Atlantic. Values of Kz of about 0.5 to about 7 cm2/sec have been calculated for the upper 200 meters of the Atlantic and Pacific and of about 5–100 cm2/sec for the bottom water masses of the Atlantic and Pacific. The. meridional gradient of 228Ra in the surface waters south of Australia and New Zealand has been used to calculate a value of the constant for horizontal eddy diffusion perpendicular to the wind‐driven circulation KY of about 107–108 cm2/sec.

No abstract

The average stratospheric residence half-time of particulate radioactive debris, as represented by strontium-90 and manganese-54, was approximately 10 months during the two years following the last atmospheric tests of high yield nuclear weapons. During this interval, the carbon-14 which was produced artificially by nuclear weapons tests showed a stratospheric residence half-time which increamed with time, but averaged about 18 months. It is suggested that the stratospheric residence half-time of particulate debris did not increase significantly during 1963 until early 1966 because in the upper stratosphere, above 20 km, the rate of particle settling of the debris exceeded the rate of upward diffusion, and as a result, this debris remained highly concentrated in the lower stratosphere throughout this period. It is also suggested that the relatively more rapid meridional movement of particulate debris, compared to the movement of carbon-14, into the stratosphere of the Southern Hemisphere during the second half of 1963 resulted to some extent from the partial separation of the particulate debris from the carbon-I4 in the equatorial stratosphere as a result of particle settling. 9t c c FIG. 2. Sampling corridor with Stardust and AEC balloon program flight tracks. TeiUus XVIII (1966), 2