220 WATER MASSES AND CURRENTS OF THE OCEANS 



long. 25°40'W, but otherwise remains of icebergs are rarely reported from 

 localities north of 35°S in the Atlantic Ocean, north of 45°S in the Indian 

 Ocean, and north of 50°S in the Pacific Ocean. 



Ice and Icebergs in the Arctic. The Polar Sea with its adjacent 

 seas, the western portion of the Norwegian Sea, Baffin Bay, and the 

 western portion of the Labrador Sea are covered by sea ice during the 

 greater part of the year, whereas, under the influence of the warm Atlan- 

 tic water the west coast of Norway is always ice-free except for occasional 

 freezing over of the inner parts of fjords. 



The arctic pack ice that covers most areas is more broken and piled 

 up than the antarctic pack ice. Large, flat ice floes are rare, but fields 

 of hummocked ice and pressure ridges rising up to 5 or 6 m above the 

 general level of the ice are frequently found. The broken-up and rugged 

 appearance of the arctic pack ice is ascribed to the action of the wind in 

 connection with the restricted freedom of motion of the ice due to land 

 barriers on all sides. 



The wind drift of the ice has been discussed by Nansen and by S verdrup, 

 who found that the direction of the drift deviated, on an average, 28° 

 and 33°, respectively, from the direction of the wind, instead of 45° as 

 required by Ekman's theory of wind currents. The discrepancy is due 

 to the resistance against motion offered by the ice itself. Because this 

 resistance is greatest at the end of the winter, when the ice is most 

 closely packed, the deviation of the ice drift from the wind direction is 

 smallest at that time of the year. Similarly the wind factor — that is, 

 the ratio between the velocity of the ice drift and the wind velocity — is 

 smaller at the end of the winter than in summer, varying between 1.4 X 

 10-2 in April to 2.4 X IQ-^ in September. 



Under the influence of variable winds the ice, in all seasons of the year, 

 is torn apart in some localities where lanes of open water are formed, 

 and is packed together in others. In winter the lanes are rapidly covered 

 by young ice which in a week or less may reach a thickness of 50 cm, but 

 from the end of June to the middle of August no freezing takes place, 

 because over the entire Polar Sea the air temperature remains at zero 

 degrees or a little above zero. Where lanes are formed the ice always 

 breaks along a jagged line, and when the ice fields move apart they also 

 are displaced laterally. In summer such lanes remain ice-free, and when 

 they close, because the ice is packed together, the two sides of the lane 

 do not fit, corners meet corners, and between the corners openings of 

 different shapes remain, many of which are several hundred meters 

 long. In summer the arctic ice fields are therefore not continuous, but 

 are honeycombed to such an extent that from no point can one advance 

 as much as 10 km in any direction without striking a large opening in 

 the ice. This characteristic makes possible the use of a submarine for 

 exploration of the Polar Sea, as claimed by Sir Hubert Wilkins. 



