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influx of warm water has some effect in heating the Polar sea and thus reducing the formation of ice on its surface.

There is also another important factor which prevents the ice which covers this sea from growing very thick; that is, that the ice is constantly carried across the Polar region by the winds and the currents and is transported southwards to lower latitudes, where it melts before it reaches the age necessary to grow above a certain thickness. The thickest floes formed directly by freezing which we measured were about fourteen feet thick.

What would, however, take place if this constant outflow of ice and cold water and the constant influx of warm water were completely stopped? If, for instance, by the upheaval of the sea-bottom, a ridge of land were formed across the Atlantic Ocean from Scotland over Shetland, the Faroe Islands, and Iceland to Greenland, such as we know there probably once has been, in some quite recent geological period? The result would be that the ice would be blocked up by this land even more completely than it is now blocked up by the north side of the islands of the American Arctic Archipelago. The drift of the ice would gradually be stopped, the floes would grow thicker and thicker, partly by freezing underneath, partly by accumulation of snow on the surface, and the Polar sea would be covered with an enormous ice-mantle, such as that which so many have believed covers the Pole.

The Gulf Stream, now running northwards between Scotland and Iceland, would also be stopped by such a land ridge, and the influx of warm water into the Polar sea would no longer take place. The result of this would necessarily be that the water in this basin would be cooled down and we would probably find the same low temperature which is now limited to the upper layer through the whole depth of the sea. But whether the result would be that the water would freeze solid to the bottom, I think is rather doubtful.

It is evident that the climatic conditions would be very much altered by the changes which are here described. The surface of the Polar sea would now be more like an enormous glacier than an ice-covered ocean. On account of the radiation of heat from the surface of this snow-covered ice-mantle, the average temperature of the year would gradually sink, and the climate would become colder than it is at present. But at the same time the Atlantic Ocean to the south of the land ridge mentioned would not be cooled down by the outflow of cold water and ice from the North, and it would not constantly give off a great