178 MARION EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



melting of ice alonji' the coast or over the continental shelves. The 

 expansion and recession of reservoirs of li«>ht water ahjii"' the 

 margin of the current are especially si<inihcant in this connection. 

 The greater the quantity and the lower the specific gravity of these 

 masses, the steeper becomes the gradient and the greater the velocity 

 and volume of the flow. The principal sources that contribute this 

 coastal supply of light water are the melting ice,'' and the drainage 

 from the l;ordering land areas. Since contributions are at their 

 maxinnun in s])ring and sununer. their effect in iin])arting. therefore, 

 a seasonal variati(m to the fringing ocean current is cunndative 

 with that of the wind. Such oceanographic observations on the 

 Labrador current as are at hand have been collected mostly in sum- 

 mer, and in the region south of New^foundland. The investigations 

 of the ice patrol, which embrace 95 per cent of the total, have been 

 very scanty in February and March, but voluminous and in detail 

 from May to July, with only one survey in October. 11)128. Few 

 observations have been taken of the current north of Xewfoundland, 

 except for those collected by the C/iaNcc in the summer of ID'iC. and 

 by the Mar/'o/i expedition and the (rodf/ioah expeditions in the sum- 

 mer of 1928. The volume and strength of tlie Labrador current 

 around tlie (xrand Bank, as shown by comparing the ice patrol's data 

 of temi)erature, salinity, and dynamic topography from vear to vear 

 (see Fries 1922, p. 61; Smith 1923, p. 84; 1924, p. 109: and 1924a, p. 

 98), indicates the occurrence of seasonal variations. In normal 

 years, at least according to the foregoing observations from around 

 the Grand Bank, the cold current appears to reach a maximum 

 during sj^iing and early summer, after which it dwindles to a 

 minimum in fall and winter. The fact that little Arctic ice drifts 

 into the Atlantic during fall and early winter may also indicate that 

 the Labrador current is then interru])ted. It should be noted, 

 however, that no year-round observations have yet been made from 

 several sections distributed over the entire length of the Lal)i'ador 

 current, and until tliey are collected we can not reach final 

 conclusions. 



The Labrador current is also marked by frequent irregular pulsa- 

 tions occui'ring within the interval of a few weeks, or of a month or 

 two, all of which tends to mask the more important major cycle. 

 (See figs. 99, 100, and 101.) These secondary short-term fluctuation^ 

 may hark back to corresponding excesses or deficiencies developing in 

 the light water along the continental slo})e from time to time. For 

 examj)le, a i)eriod of warm, wet weather around Newfoundland may 

 appreciably accelerate the melting of the coastal ice and the dischai'ge 

 from the rivers, increasing the supply of light water, thus swelling 

 the mass and the velocity of the southern end of the cokl current. 

 Under such conditions any ice in that particular locality will move 

 south faster than will the ice situated farther north, although the 



'"Many stai<Miieiits have appeared in print that the cold Arctic currents avf augmented 

 by great ()iiaiititics of ice which are melted every sum'mer In the far north. The impres- 

 sion is therefore tjiven that excess masses of light water or a high level at a riverlike 

 source (in Baffin Bay for the Labrador current) constitutes the necessary head to dis- 

 charge the water downstream into the Atlantic. It is high time that the river idea be 

 discarded when considering unrestricted movements on a rotating sphere, under which 

 class belong ocean currents. The pressure gradient which impels the stream flow of water 

 lies on the right-hand side of the current in the northern hemispliere. Therefore, in order 

 for thaw water to assist the flow of the Labrador current, the ice must be distributed and 

 melt, not in Baffin Bay or the I'olar Basin, but along the shelves of Baffin Land, Labrador, 

 and Newfoundland. 



