SCIEXTIFIC r.ESULTS 201 



The heat from the sun (hiiin<i- the wuruier months of the year heats 

 a rji'eater mass of water than is shown in the case cited above, because 

 the cokl current is continually briufiino; 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 layers of the northern half of the melting area will have 

 been completely replaced, partly by water from west Greenland and 

 partly by still colder masses from the Avaterways 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 

 waters 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 (ireenland and the Labrador. The low 

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

 accompanving the dimunition of solar radiation during winter and 

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

 respective volumes of ice and water 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 })atrol, 

 the volume of this discharge at its maxinunn 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 217, and 223 to 228. inclusive. May 

 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" formulae, 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 chlllins effects of melting snow and evapoi'atlns surface water are agencies which 

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

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

 the latent heat per unit volume being almur 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 lielieved to fall in the water and thereby directly to cool the latter, m 

 the Gulf of Maine, by Bigelow's (1027. p. 60tV) calculations the chilling effect of melting 

 snow is equivalent to that of an ice cover 2 inches in thickness, ni the Arctic, with 

 roughly equal snowfall, its effect equals only about 2 or 3 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 combination seldom 

 obtain in northern regions — therefore, evajjoration 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 evaporation in the course of a year is equivalent to the cooling effect of an ice cover 2 

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

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



