67 



and turbulent waters near the shore tend to remove eroded material 

 rai)idly, and extensive shoal areas rarely occur. 



The (Continental Shelf alon^ all the coasts of Alaska is wide; in the 

 Bering Sea it averages 400 miles. The Bering Sea shelf is the flattest 

 area of this size on the face of the earth, primarily because of the 

 fine silt deposited on an irregular rocky platform by glacier-fed 

 rivers, 



OCEAN CURRENTS 



The major ocean currents impinging on or passing close to the 

 continent exert strong, if subtle, effects on the estuarine zone; see 

 figure IV. 1.1. 



The best knoAvn of these is the Gulf Stream which moves northward 

 along the South Atlantic coast from Florida to Cape Hatteras, where 

 it turns east out across the Atlantic. Between Cape Hatteras and 

 Newfoundland, water from the Labrador Current moves slowly south- 

 ward between the Gulf Stream and the coast. 



The Labrador Current, a cold water mass with abundant plant 

 nutrients, makes the Grand Banks off Newfoundland one of the most 

 productive fisheries of the world. While much of the Labrador Current 

 mixes with the Gulf Stream, some of its water enters the Gulf of 

 Maine as part of the strong tidal and wave-driven flow^, and still more 

 drifts down the Middle Atlantic coast from Massachusetts to North 

 Carolina. 



The Gulf Stream is very warm water from subtropical latitudes, 

 and carries with it subtropical life forms as well as heat. Its warming 

 effect on the land can be seen in the difference in vegetation above and 

 below Cape Hatteras, as w^ell as in differences in kinds of aquatic 

 life (fig. IV.1.7). 



A major part of the Gulf Stream emerges from the warm, sub- 

 tropical Gulf of Mexico and flows around the tip of Florida. These 

 waters nurture the great shrimp fishery and warm the coasts of 

 northern Europe as well as those of the southeastern United States. 



Along the west coast of North America the eastward-flowing warm 

 current of the Pacific Ocean (the North Pacific Current) splits at 

 about the latitude of the United States-Canadian border ; the portion 

 moving south is called the California current, while that moving north 

 into the Gulf of Alaska is called the Alaska Current. 



The California Current exerts a moderating effect on continental 

 temperatures as it moves southward; the major effect, however, occurs 

 during the spring and early summer when the winds are such that in 

 some places the California Current moves away from the coast and 

 cold, nutrient-laden deep water comes to the surface near the shore. 

 Two major zones of this "upwelling" are off Santa Barbara and off 

 Cape Mendocino, near the northern part of California. During other 

 seasons a complex series of eddies and conn tercur rents develops, all 

 of which tends to make the nearshore areas very productive. 



The Alaska Current exerts a warming effect on the southern part of 

 Alaska, similar to that of the Gulf Stream in northern Europe. The 

 Bering Sea, which receives some water from the Pacific Subarctic 

 Current, is the birthplace of the cold deep currents of the northern 

 Pacific, and the waters within the Bering Sea are very cold and 

 rich in nutrients. 



None of the effects of Continental Shelf and ocean current structure 



