CHAPTER X 

 SEA CURRENTS AND ICE 



Section 129. Certain Peculiarities of Sea Currents 



Sea currents are divided into permanent currents, periodic currents and temporary currents. 

 The permanent and periodic currents (if tidal currents are excluded) determine the general circu- 

 lation of the oceans and seas. Temporary currents only alter or distort this circulation. 



Among the factors causing the permanent currents are unequal distribution and variations of 

 temperature and salinity and prevailing winds . The coastal flow is also a factor in the creation of 

 permanent currents in small basins. Temporary currents arise in connection with temporary 

 alterations of atmospheric pressure, temporary winds, etc. 



Whatever the reasons causing the permanent currents, they are only slightly different from 

 each other in respect to the character of their movements, i.e. , in respect to the vertical distri- 

 bution of speed and direction. They are more substantially different in respect to temperature and 

 here they are conditionally divided into warm, cold, and neutral currents. 



The temperature of a warm current is higher than the water temperature created by local 

 conditions; the temperature of a cold current, lower. From this it follows that the temperature of 

 a warm current is lowered as it progresses, while that of a cold current is raised. One and the 

 same current in different geographical coordinates may be warm, cold, or neutral. 



The deep Atlantic current is a warm current in the Arctic Basin where its temperature does 

 not exceed 3°. The Peru current, running north along the Pacific coast of South America and hav- 

 ing a temperature of about 22° at the equator, is a cold current. 



But warm currents, as a general rule, carry their water from ocean regions where evapora- 

 tion exceeds precipitation. As a result, the water of the warm current is not only warmer but 

 usually more saline than the local water. This factor is very sharply felt in such currents. Cold 

 currents, on the other hand, flow from regions where the water is freshened by precipitation, 

 coastal flow, and melting of ice. Typical examples of such currents are the East Greenland and 

 Labrador currents. Due to this, the density of surface water is very little different for warm and 

 cold currents. However, the density of surface strata of warm currents increases as the tempera- 

 ture is lowered while the density of surface strata of cold currents decreases as the temperature is 

 raised. In such currents as the East Greenland and Labrador the decrease in density of upper 

 layers assists in melting the ice carried into or formed in the sea, as well as the icebergs. 



Great importance is attached to the gradual raising of density of upper layers of warm cur- 

 rents bringing about convective mixing and thereby involving the entire water mass of such a cur- 

 ent in an exchange of heat with the atmosphere. The latter phenomenon is especially noticeable in 

 the winter. As has already been noted in the chapter "Melting of Ice," the importance of the West 

 Spitzbergen and Norwegian currents and of currents from the Pacific Ocean is not only due to the 



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