OCEAN CURRENTS 147 



Melting Ice. 

 According to Pettersson, melting- ice plays an important 

 part in causing" océan currents, not only in the displacement 

 of large water masses in the Southern Hémisphère, but also 

 in the formation of important océan currents, of which the 

 East Greenland Current may be taken as a type.* 



Atmospheric Pressure and Océan Currents. 



Atmospheric pressure is an important factor in the causa- 

 tion of océan currents, and it works in two ways — partly by 

 local variations in pressure and partly through wind. The 

 océan is really a gigantic water barometer. When the 

 barometer rises over a given water area, it is équivalent to an 

 extra pressure on the water surface, which consequently sinks. 

 Pressure gradients are consequently formed as the resuit of a 

 variation of atmospheric pressure. 



During the monsoon period gradients are caused in the 

 transitional period from high to low atmospheric pressure. 

 The extra pressure on the water when the barometer is high 

 causes a flow of water to areas of lower atmospheric pressure. 

 With a low barometer off the Shetlands and a high one off the 

 Continental coast, the North Sea water is forced in two or 

 three days to the north. When the barometer falls over the 

 Baltic and rises over the northern part of the North Sea, water ■ 

 is forced in through the Belt into the Baltic. Knudsen says 

 that the strength of the current at the entrance to the Baltic is 

 directly proportional to the variations in atmospheric pressure 

 in the North and Baltic Seas. If v be the velocity of the 

 stream, then 



V =éjl^ + c {B-B'), 

 a ^ 



when p is the rainfall, e the evaporation, a the section of the 

 exit (08 square kilomètre), c a constant (estimated by Knudsen 



* Geographical Journal, vol. xxiv,, p. 285, and vol. xxv., p. 279, . 



