A belt of gravity high more than 500 km in width with values ranging in 

 amplitude from to 20 mgal runs along the east coast margin (including the 

 Appalachians and the Coastal Plain) from about 30°N to 40°N. Slightly north of 

 40° it swings eastwards. Free-air anomalies over the edge of the shelf off 

 Newfoundland exceed 60 mgal Gravity values further to the north in the Labrador 

 Sea also exceed 20 mgal but these values are based on poorer data. 



The "1x1° difference" geoid clearly shows a similar marginal high with values 

 exceeding 5 m east of Newfoundland. 



In the western North Atlantic Basin the geoid shows two prominent lows. One 

 lies just seaward of the continental margin. This low runs roughly northwards from 

 Hispaniola (between 68°W and 76°W) , has a minimum slightly more negative than -10 m 

 south of 35°N, and then turns northeast with values between and 5 m. This geoid 

 low includes the area of the Hatteras Abyssal Plain. There is a similar low in the 

 gravity map with minima more negative than -40 mgal. Between 25°N and 30°N and 

 along about 73°W there is a relative gravity high. This high is associated with the 

 Bl'ake Bahama Outer Ridge, a sedimentary ridge. If we had used a -6 m contour map 

 for the geoid this relative high would have been delineated quite clearly. The 

 relative high of -5.4 m is an indication of this high over the Outer Ridge. 



The second prominent geoid low in the western North Atlantic is centered near 

 25°N 55°W and clearly correlated with low gravity values of the western North Atlantic 

 Basin. This low lies over the eastern part of the Nares Abyssal Plain and over the 

 abyssal hills to the east of it. In between the two lows the gravity values, as 

 well as the geoid heights, increase, reflecting the influence of the "Outer High" 

 seaward of the Puerto Rico Trench. This gravity and geoid high continues northwards 

 with a geoid maximum of 1.8 m over the Bermuda platform. The other two closed 

 geoid highs are over the Kelvin Sea Mount chain. 



23-30 



