1 68 WATER MASSES AND CURRENTS OF THE OCEANS 



along the American east coast shows that the mean sea level increases 

 toward the north from St. Augustine, Florida, to Halifax, Nova Scotia, 

 the most conspicuous increase taking place directly north of Cape 

 Hatteras. In table 18, summarizing the results of precise leveling, the 

 sea level along the coast has been referred to that on the coast of Florida 

 and southern Georgia, values from stations less than 200 km apart having 

 been combined as averages. The distances along the coast from Florida- 

 Georgia are entered, and also the values of the slope of the sea surface. 

 These values are of the same order of magnitude as those derived from 

 oceanographic data in the Caribbean Sea, where Parr computed a slope of 

 17 X 10-8, and Sverdrup a slope of 12 X 10"^ (p. 181). 



If the upward slope along the American east coast were due to the 

 distribution of mass in the ocean, the average density of the Gulf Stream 

 water off the continental shelf would have to decrease in the direction of 

 flow and the Gulf Stream would have to flow uphill, but no such decrease 

 is found. A discrepancy therefore exists between the results of precise 

 leveling and the results of what has been called ''oceanographic leveling." 

 It is not surprising that such discrepancies appear because, as explained 

 on p. 99, oceanographic observations can give information only as to the 

 topography of the sea surface relative to some selected surface in the ocean, 

 and information as to the absolute topography of the sea surface must be 

 derived from precise leveling along the coasts. It seems possible, how- 

 ever, to reconcile the different observations by assuming that an actual 

 piling up of water is maintained in the western North Atlantic and that, 

 owing to this piling up, a current flowing southwest along the continental 

 shelf is not reflected in the distribution of mass. 



The North Atlantic Current. The North Atlantic Current 

 represents the continuation of the Gulf Stream after it leaves the region 

 to the east of the 'Hail" of the Grand Banks. Beyond this region the 

 Gulf Stream loses its characteristics as a well-defined current and divides 

 into branches that are often separated by countercurrents or eddies. 

 Some of the branches turn south, but others continue toward the east 

 across the mid- Atlantic Ridge, being flanked on the northern side by waters 

 of the Labrador Current that have been mixed with Gulf Stream water. 



The contrast between the Gulf Stream and the North Atlantic Cur- 

 rent to the north of the Azores is illustrated in fig. 41, which shows two 

 temperature profiles on the same scale. To the left in the figure are 

 shown the isotherms in a vertical section from Chesapeake Bay toward 

 Bermuda, according to observations at Atlantis stations 1231-1226. 

 The Gulf Stream is here concentrated within the narrow band in which 

 the isotherms slope steeply downward toward the right. The section 

 to the right in the figure runs north-northwest from the Azores to lat. 

 48°N and is based on the observations on board the Altair during the 

 International Gulf Stream Expedition in 1938. In this section the 



