422 BOUNDARIES OF THE SEA 



of carbon dioxide in the air between warm and cold regions and 

 estimated the pressure heads needed in sea water for this trans- 

 port. Considering the more rapid mixing of cold surface waters the 

 pressure head over polar waters should be divided by four. This will 

 give an average of 0.2 X 10-^ atm instead of 0.8 X 10-^ 



If 5 X 10-^ cm sec-' is accepted as a rough value for the trans- 

 port velocity between sea surface and subsurface water, this can 

 be applied to some gaseous constituents which take part in the 

 biological circulation in the sea. Sulfur in organic matter must be 

 released as hydrogen sulfide. It is generally assumed that this hy- 

 drogen sulfide is oxidized in sea water to sulfate. However, hydro- 

 gen sulfide is a rather volatile gas, so escape to the atmosphere is 

 quite likely to occur. Such an escape, if it took place, is of rather 

 great geochemical significance. Assume now that none of the hy- 

 drogen sulfide is oxidized in sea water but is readily oxidized in the 

 atmosphere, presumably to sulfur dioxide. W^ith a transport velocity 

 of 5 X 10—'' cm ■ sec~' and a yearly rate of biological production of 

 75 ng-cm.-', a figure computed from estimated rates of assimilation 

 and the sulfur content in plankton, we ask what the steady state 

 equilibrium in subsurface water is under such circumstances. The 

 answer is 0.5 fxg. liter~\ a concentration so low that it cannot be 

 detected by present analytical methods in oceanography. 



Similar calculations can be made for nitrogen, if it is assumed 

 that all nitrogen is released as ammonia in the biological cycle. 

 With a yearly rate of production of 1800 jug-cm-- and the transport 

 velocity used above, the concentration in subsurface waters should 

 be about 12^igditer~i or 12 mg-m-^. Redfield and Keys (1938) 

 analyzed waters from the Gulf of ]\Iaine and found values between 

 10 and 60 mg-m-^. It is therefore quite possible that some of the 

 ammonia released in the biological cycle in the sea goes into the 

 atmosphere, especially in areas of high seasonal production. If 

 this is applied to the North Sea area, it will perhaps account for 

 some of the ammonia found in precipitation in western Europe. 

 Over large areas of the sea this transport may be unimportant. 



It is seen that the concept of a vertical transport velocity in the 

 surface waters of the oceans is useful and simple to apply. Even if 

 we know a likely average, it would also be most useful to know the 



