ZoBell — 180 — Marine Microbiology 



Sweden to New York. He found an average of from 0.7 to 18 pollen grains 

 per cubic meter of air at different stations. These figures for air over the 

 ocean may be contrasted with the average of 18,000 pollen grains per 

 cubic meter of air near Stockholm. In general, the number of pollen 

 grains in marine air was related to the distance from land, the direction 

 and velocity of the wind, and the flowering time of plants. Pollens of 

 trees, shrubs, grains, and grasses were found several hundred miles from 

 the nearest land. 



Meier and Lindbergh (1935) found pollens, as well as fungus spores, 

 diatoms, and insect wings, in Arctic air several hundred miles from land 

 and at an elevation exceeding 3000 feet. 



Pollen surveys over the ocean at different elevations made by air-lines 

 and other agencies show that, while pollens are widely distributed, their 

 abundance drops off sharply with distance from land and in the face of 

 marine air currents. 



Aerial transport of marine bacteria: — There is ample evidence that 

 bacteria, mold spores, and pollens from the land are carried around the 

 world by the wind. Marine microorganisms likewise may be widely dis- 

 seminated by the movements of the atmosphere, although there are few 

 data on the transportation of marine bacteria inland. 



From an onshore wind having a velocity of 5 to 1 2 miles per hour fol- 

 lowing a rainstorm, ZoBell and Mathews (1936) recovered appreciable 

 numbers of marine bacteria from air on a mountain 80 miles inland. Some 

 marine bacteria probably fall with precipitation, but at inland stations 

 their presence is masked by the preponderance of terrestrial forms. 



Microorganisms are introduced into the air over the land by atmos- 

 pheric disturbances of various kinds, by the movements of animals, and 

 by other agencies. Bacteria are being carried continually from the sea 

 into the air, along with droplets of water. The transfer is most intense 

 along rugged coasts when waves are dashed against rocks or along 

 gently sloping shores where the incoming swell breaks into foam. The 

 transfer is most extensive in the open sea where strong winds often blow 

 spray from crests of waves. Large droplets fall back into the sea almost 

 at once but small ones may be lifted to great elevations by advection and 

 convection currents, and carried away by the wind to regions far re- 

 moved from the place of origin. The almost universal distribution of 

 sea salt in the air makes this manifest. 



Table xxxvii. — Rate of fall of water droplets through air and the minimum distance they 

 would he carried by a steady lo mile per hour wind before they fell loo meters in the absence of 

 turbulence: — 



According to evidence summarized by ZoBell (1942c), droplets of 

 water exceeding i.o mm. in diameter may be conveyed several thousand 

 feet above sea level by convection currents, by orographic uplift, and by 

 vertical motion caused by converging winds (see Fig. 12). In the absence 



