Chapter I 

 THE NOKTHWESTERN NORTH ATLANTIC 



DEFINITION AND GENERAL DESCRIPTION 



The northwestern North Atlantic, as it is discussed here, is that 

 portion of the western Atlantic Ocean embraced by the normal drift 

 of Arctic ice ; and, so defined, includes the waters around and on the 

 Grand Banks, and northward, between North America and Green- 

 land to the seventieth parallel of latitude. Observations in the areas 

 closer to the sources of Arctic ice have not been undertaken by the 

 Coast Guard. Information, therefore, on the oceanography of Baffin 

 Bay and other tributaries as they affect our own investigations, has 

 been dra^vn from previously published works. 



The bathymetric features of the northwestern North Atlantic are 

 shown on tlie frontispiece (fig. 1). The depth contours have been 

 drawn from information contained on various navigational charts 

 and from several other sources, such as Ricketts and Trask (1932) ; 

 Defant (1931) ; Stocks and Wust (1935), and Soule (1936). 



Northwestward from the Newfoundland Basin to the sixty-third 

 parallel the bottom rises gradually (more than 2,000 meters below 

 the surface) to form, between Greenland and Labrador, the Labrador 

 Basin. Continuing northward the basin grades upward more 

 abruptly to depths slightly less than 700 meters in the region of 

 Davis Strait Ridge where the slope is reversed, the bottom receding 

 to form the Baffin Bay Basin with depths greater than 2,000 meters. 



The sides of the Labrador Basin present an interesting contrast. 

 Along the Greenland slope the basin rises steeply to a narrow con- 

 tinental shelf, while on the Labrador side a well-defined continental 

 edge and wide coastal margin prevails. 



Greenland's shelf from a narrow continental ledge along its south- 

 western coast broadens to the latitude of Davis Strait, where in 

 places the 400-meter contour lies 80 miles oflfshore. This forma- 

 tion (Nielsen, 1928) is divided into three principal shoals, south to 

 north — Fylla, Little Hellefiske, and Great Hellefiske Banks. The 

 entrance to Baffin Bay places the deepest part of the channel through 

 Davis Strait nearer the Baffin Land than the Greenland shore. The 

 American shelf as bounded by the 400-meter contour broadens from 

 a width of TO miles off northern Labrador to a width of 180 miles 

 off Newfoundland and thence southward, as the Grand Banks and 

 Flemish Cap, it becomes one of the broadest of continental shelves. 



The northeasterly extension of the 2,000-meter isobath (see frontis- 

 piece) between the Greenland slope and Reykjanes Ridge creates an 

 eastern appendage and a heart-shaped form to the Labrador Basin. 

 This eastern arm falls necessarily without the limits of our station 

 observations, and is, therefore, referred to only as its waters (the 

 Irminger Sea) affect our own regions under investigation. 



