SECT. 2] SOLUBLES 311 



existed between the introduction of salt particles into the atmosphere and their 

 return to the sea. In each sampling area, cimiulus clouds were developing at the 

 top of a nearly mixed layer of air which extended down to the sea surface. 



Through the use of averages of data from the Hawaii area of the Pacific, and 

 making certain assumptions about the relative humidity at the top of the 

 boundary layer of the sea and the salinity of rains, Eriksson (1959, pp. 399-400) 

 has estimated an average rate of fallout of salt from the whole atmosphere of 

 about 10^ metric tons per year. Somewhat more realistic estimates by Blanchard 

 {in litt.), using mean winds from a world climatic atlas, the data of Fig. 7 and 

 reasonable assumptions about relative humidity and the salinity of rains, 

 produced a value of about 2 x 10^ tons per year. 



These are the best estimates which have been made indicating the probable 

 rate of production at the sea surface of salt particles which remain airborne at 

 least long enough to be transported up to local cumulus cloud-base altitudes. 

 The maximum value (2 x 10^ tons) is the quantity of salt contained in about 

 the upper one-tenth of a millimeter of the sea surface. There is little doubt, 

 however, that far more salt and water is ejected into the surface air by bursting 

 bubbles remaining airborne only a relatively short time before falling back 

 into the sea. A study of the droplets within a few meters of the sea surface is 

 required before one can attempt a direct evaluation of their role in evaporation. 

 From the above estimates it is clear that the rate of production of salt particles 

 (droplets) at the surface must exceed that derived from the salt at cloud levels 

 by a thousand times or more to contribute significantly to the total evaporation 

 from the seas. 



It should be reported that droplet production has also been observed by 

 Mason (1957) from the shattered surface films of bursting bubbles. The salt 

 content of the largest of these droplets was estimated to be 2 x 10~i4 g, about 

 one fiftieth of the weight of the smallest particle considered here. From Junge's 

 numerous impactor measurements (Junge, 1957) it is reasonably concluded that 

 particles ^2xl0~i4g contain less than 1% of the airborne chlorides, and 

 contribute little to the exchange of solubles between sea and air. These film 

 droplets may be meteorologically important, however, if they are produced in 

 great numbers. 



At the present time the major significance of the exchange of sea-salt particles 

 between the seas and the atmosphere seems to lie in their role as nuclei for the 

 formation of large cloud droplets and of raindrops (Woodcock and Blanchard, 

 1955), in contributing to the "cyclic salts" of geochemistry (Eriksson, 1959), 

 and in the transfer of charge (Blanchard, 1960). This exchange is a further 

 example of the interrelation of many oceanic and atmospheric properties and 

 problems. Exploration and expansion of this exciting area of study and under- 

 standing has just begun. 



References 



Blanchard, D. C, 1958. Electrically charged drops from bubbles in sea water and their 

 meteorological significance. J. Met., 15, 383-396. 



