abyssal currents originate: the North Atlantic Ocean, and the Weddell 

 Sea in the Antarctic region of the South Atlantic. The rates at which 

 such water masses form, the nature of their subsequent sub-surface 

 flow within the different oceans, and whether other sources exist, are 

 questions which remain to be studied. 



The vertical and horizontal boundaries of chemical constituents in 

 the sea are eroded by diffusion. Although we have a crude idea of the 

 average effective speed of diffusion processs, in a turbulent environment 

 such as the ocean, we know little of its vertical, horizontal, or time- 

 dependent variations, or of the source of energy that drives the turbulence. 

 The recent introduction of fission and nuclear products such as radio- 

 strontium and cesium, tritium, and man-produced carbon-14, as fallout 

 to the surface waters of the ocean, provides a unique means of tagging 

 which can be used to measure the rates of downward mixing from the 

 surface to intermediate depths, and so of determining quantitatively 

 the rates of turbulent diffusion and downwelling in various oceanic 

 situations. 



A complication with the use of radioisotopic tracers is that all are 

 involved, to varying extents, with the downward flux and regeneration 

 of biological particles within the water column. In order to obtain esti- 

 mates of these fluxes, it is necessary that complete information be ob- 

 tained on the corresponding stable isotopes. For example, the in-situ 

 production of C^* by the decay of biological particles is correlated with 

 the in-situ production of CO,, which can be estimated from measure- 

 ment of dissolved total COo, alkalinity and pH, or any two species within ^ y 

 the oceanic carbonate system. By measuring the concentrations of the 

 natural radioactive isotopes radium-226, silicon-32, and cosmic-ray pro- 

 duced carbon-14 in the deep and bottom waters of the ocean, it should 

 be possible to improve our knowledge of advection and turbulent diffusion. 

 These convenient nuclear clocks can be used to determine the "age" of 

 water masses in typical situations, in much the same way that carbon-14 

 is used to measure the age of solid objects. 



Sampling Plan 



The GEOSECS project is designed to give the first detailed informa- 

 tion of distribution patterns, by measuring simultaneously and 

 mapping the distribution of the important oceanic tracers and proper- 

 ties along continuous north-south sections of the three major oceans in 

 the world. The survey tracks follow, as far as is now known, the ap- 

 proximate trajectories of the bottom water currents. The United States 

 project will carry out the major survey work along these tracks in the 

 Atlantic, Indian, and Pacific Oceans, and in subantarctic waters. Ad- 

 ditional projects now being planned by West Germany, Japan, and other 

 nations will add supplementary sections. 



The U.S. project calls for the occupation of 120 oceanographic sta- 

 tions along the main survey tracks. At each station, vertical profiles 

 of 50 samples will be taken. At alternate stations, very large samples 

 will be taken at 18 to 20 depths for measurements of trace constituents 

 and low concentration radioisotopes. The vertical spacing of all these 

 samples will be guided by continuous recording, on station, of temperature. 



