TRANSACTIONS OF SECTION E. 713 



•waters of the ocean is extremely slow {vide G. Schott's description of tlie results of 

 the German Valdivia expedition). 



In 1878 the author pointed out that a great — and probably the greatest — part 

 of the oceanic current system must be due to another cause, viz., the thermo- 

 dynamic cycle of latent heat, consisting in the formation of ice in polar regions 

 and the melting of ice in sea-water at lower latitudes.^ In ' Petermann's 

 Mitteilungen,' lUOO, Ileft I. and II., be calculated the energy generated by the 

 melting ot ice in the sea between Iceland and Jan Mayen to be about 400,000 hor.se- 

 power, which energy is employed in accelerating the movement of the waters of 

 the East Iceland polar current, which makes its way from the sea between Iceland 

 and Jan Mayen towards the Faroes, there to dip under the current of Atlantic 

 water which sets in between the Shetlands and the Fiiroes, and ultimately 

 vanislies into the Atlantic depths in the shape of a submarine waterfall over the 

 Icelaud-Fiiroe and W. Thomson bank. The energy set free on the melting of ice 

 in sea-water is expended on raising the water from the submerged part of the ice 

 to the surface, and may be likened to a waterfall where the water, instead of 

 descending, arises from below to the surface. The heat necessary for this melting 

 is supplied from undercurrents of warm Atlantic water, which exist wherever the 

 melting of ice goes on in the ocean. One part (in the case referred to about j^^) of 

 this warmer and Salter water mixes with the ice-water and forms the polar 

 surface-current, while the greater part (here about ^J) is cooled to a temperature 

 approaching the temperature of equilibrium between ice and salt water, and sinks 

 to the bottom, there to form the layer of cold water which is known to exist in all 

 oceans. The temperature and the salinity of this bottom water depend upon the 

 relation between the quantity of ice which is melted and the amount of warm 

 water supplied by the undercurrent. In the Atlantic Ocean the temperature is a 

 little below or above + 2°, whicli shows that the warm water here is in excess of 

 the ice. In the Norwegian Sea the bottom temperature is about —I'd'' C. icliich 

 is the Imcest exiatiu;/ on the (jlobe. This shows that the warm water supplied by 

 the Atlantic current is just sufficient to melt the ice which is brought down along 

 the coast of Greenland b}' the polar current. It is inferred from this that the 

 state of this part of the sea is in a very unstable equilibrium, which may account 

 for the instability of the climate of the northern countries of Europe and the gi-eat 

 variations in the extension of the ice in this sea. In the Polar Sea we meet with 

 the startling fact, discovered by Nansen, that the bottom temperature is higher 

 than in the Norwegian Sea, or above — 0'9° C. This is explained by the fiict that 

 the ice in the polar sea floats in a layer of cold water diluted by the admixture of 

 river-water from Siberia. Thereby the access to the ice of the warm and salt 

 undercurrent, which Nansen discovered at about 200 m. dejith, is more or less 

 prevented. The ice-melting in the polar sea thereby becomes less intense, the 

 surface of the sea is filled with ice-floes and pack-ice, which must be carried out 

 into the Norwegian Sea or the Atlantic in order to melt. Therefore the cooled 

 bottom layer has a higher salinity and temperature than in the adjacent Norwegian 

 Sea. 



The influence of the thermodynamic cycle of latent heat upon oceanic circula- 

 tion is characterised by the following circumstances : — 



1. The seat of the accelerating force is localised in the meeting places of the 

 ice-currents of polar origin with warm currents. The most important of these 

 places are the seas between Iceland and Jan Mayen, W. of Spitzbergen, S.E. of 

 Newfoundland, and the ice girdle encircling the Antarctic Sea. 



2. In all such places warm undercurrents are found to exist under the ice. 

 The melting process is maintained chiefly at the cost of the heat stored up in the 

 waters of the undercurrent. The sy.stem of currents and undercurrents of the 

 Norwegian Sea is represented on a chart prepared by the author. 



•3. The warm water of the undercurrent, which in the northern hemisphere is 

 denoted by the name of ' Atlantic' water (alias Gulf Stream water), is modified by 



' OfvcVK. lufL yctenfliajiK-Ahadfiiiicns Forhandl., 1878, No. 2, p. Gl, and On 

 the Properties of Water and Ice (Vegaexpeditionens iakttagelscr, Stockholm, 1883). 



