What remains to discuss is the source of the winter warming from Spitsbergen, respectively what role the Norwegian- and Spitsbergen Current played. When the Spitsbergen Current reaches the shelf of Spitsbergen (ca. 79°N), it splits in two and passes in the West and the East Spitsbergen, to sink into the Arctic Basis eventually. The incoming water is relatively warm (6 to 8°C) and salty (35.1 to 35.3%) and has a mean speed of ca. 30 cm/sec -1 . In contrast, the East Greenland Current transports very cold (0°C), low-salinity water (at the surface less than 30%) and Arctic icebergs southward. The current speed has a medium range of about 10 to 15 cm s -1 .

After having reached the Spitsbergen region, the warm current goes through a series of highly complex processes. As no ocean observing systems were in place in the late 1910s, any theoretical analysis would hardly bring any relevant results because there are too many components involved in the transformation process of the warm Atlantic water into cold Arctic Ocean water. At the sea surface, major components are air temperature, wind, waves, sea ice, ice motion and rain- or melt-water. Below the sea surface, there are only two components that are the overriding forces on ocean dynamics: seawater temperature and its degree of salinity. Density, the third major component, becomes a significant factor only at much greater depths.

While the water temperature and salinity for internal oceanic dynamics is generating forces in every ocean water around the globe, the matter is particular crucial with regard to the Spitsbergen Current. There is no other place as ‘sensitive’ as that one. Very warm and saline water arrives in a very cold environment. The principal rules functioning in this situation are simple:

• Warm water is lighter than cold water.
• Salty water is heavier than less saline water.

These two components allow uncountable variations and the sea areas around Spitsbergen have an increased range of variability.

Finally, the ‘capacity’ issue needs to be taken into account. The fact that Spitsbergen’s warming was the most pronounced during the winter is a highly significant aspect. In winter, it becomes much more obvious how important the ocean’s role is for to supply of the atmosphere with heat. And here it comes in discussion the capacity issue. In average, a sea surface layer of mere three metres holds the same heat as an entire air column of 10,000 metres. One can explain it with a ‘one-degree-image’. If 1° of heat is taken out of the upper three-metre of the sea surface layer, the entire atmosphere above warms up with one-degree. This is a relation which stresses the importance of the transfer of the warm Atlantic water into the Polar region.

One need only to review an April ice-cover chart (Annex C), which demonstrates that towards the end of the winter season the open sea area is reduced to a small percentage of about 10-20%. The section from were high winter temperatures could have only been released from an open sea area is the SW- sector of Spitsbergen, and that is the section where the West Spitsbergen Current transports the warm and saline Atlantic water towards the permanently ice-covered Arctic Basin.

The sudden warming at Spitsbergen after the winter of 1918/19 could have been caused only by one distinct force: the sea, which, in this case, needed an additional forcing mechanism, namely the warm Atlantic water. It could clearly be indicated that the sea areas around Spitsbergen in combination with the West Spitsbergen Current flowing into Arctic Basin had been the sole driving force of the sudden Arctic warming in the early 20 th century.