SCIENTIFIC EESULTS 201 



The heat from the sun (hiriii<r the wanner months of the year heats 

 a «rreater mass of water than is shown in the ease cited above, because 

 the cohl current is continually brintrino- cold water from a far- 

 northern unheated source. It is assumed that the current has an 

 average rate of 7 miles per day, so that during the period of summer 

 the surface hiyers of the northern half of the melting area will have 

 been completely replaced, partly b}' Mater from west Greenland and 

 2)artly by still colder masses from the waterways of the Arctic Archi- 

 pelago. The total amount of heat received by the melting area 

 might, therefore, be conservatively increased 50 per cent more than 

 what is shown. 



The fact that nearly all of the ice tends to remain in coastal 

 Avaters from formation to dissipation also allows expression of this 

 cooling factor of the North Atlantic Ocean masses in terms of the 

 two cold currents — the east Greenland and the Labrador. The low 

 temperature of these is due chiefly to (a) back radiation to the air, 

 accompanying the dinumition of solar radiation during winter and 

 {h) the chilling effect of melting ice.^- If we could determine the 

 respective volumes of ice and Avater that are carried annually out 

 into the North Atlantic by the cold currents, we would obtain an 

 approximate quantitative estimate of the relative importance of 

 each factor. The processes of mixing between the frigid coastal 

 waters and the much more temperate oceanic masses, takes place 

 along the entire continental edge, but in some places to a greater 

 degree than others. The only sector for which quantitative infor- 

 mation is yet available is the discharge of the Labrador current as 

 it flows southwestward past the Tail of the Grand Bank into the side 

 of the Gulf Stream. 



According to the data collected by the international ice patrol, 

 the volume of this discharge at its maximum is about 62.4 aubic 

 miles per day (5,000,000 tons per second). The basis for the stated 

 value of 62.4 cubic miles is the observations collected by the ice 

 patrol, stations 195 to 211. and 21T. and 223 to 228, inclusive, Mav 

 3-30. 1922, around the Tail of the Grand Bank. (See Smith, 1923, 

 pp. 74-80.) After calculating the dynamic potentials of these 23 

 stations according to Bjerknes' formula*, a map showing the topog- 

 raphy of the sea surface was drawn. (See Smith. 1926, p. 39.) At 

 the time and place the Labrador current measured 68 miles in width 

 from its inside edge in on the Tail to latitude 41° 55', in longitude 

 50° 19', and had a mean depth of about 600 meters. Its velocity was 

 then the greatest on the surface and in its middle, least along its 



"-The chilliiifr effects of melting snow and evapoi-ating surface water are agencies which 

 also withdraw significant amounts of heat energy from' the northern waters. It Is also 

 well known tliat a great deal of evaporation takes place directly from the ice and snow, 

 the latent heat per unit volume heing about eight times that in the case of melting ice. 

 Probably 75 per cent of the total annual snow that falls on northern coastal shelves and 

 seas goes to cover the sea ice which has already spread over these regions, but the remain- 

 ing 25 per cent is believed to fall in The water and thereby directly to cool the latter. In 

 the Gulf of Maine, by Bigelow's (lOiiT. p. 696) calculations the chilling effect of melting 

 snow is ecpiivalent to that of an ice cover 2 inches in thickness. In the Arctic, with 

 roughly efjual snowfall, its effect equals only about 2 or 8 per cent that of melting ice. 

 Evaporation is most rapid with low atmospheric pressure, low humidity, high temperature, 

 both of water and of air, and with high winds — conditions which in c'ombination seldom 

 obtain in northern regions — therefore, evaporation as a chilling factor is of small impor- 

 tance there as compared with lower latitudes. Even so. however, the effect is greater than 

 that of melting snow, for in the Gulf of .Maine, according to Bigelow's calculations, cooling 

 by evaix)ration in thi' course of a year is equivalent to the cooling effect of an ice cover 2 

 feet in thickness. Thus, assuming equal evaporation in the North, the chilling effect of 

 evaporation would then etjual about 30 per cent of that of the melting of ice. 



