Page:EB1911 - Volume 21.djvu/993

Rh and in 83° N. and 13° E. it is 1860 fathoms. The northern and eastern extension of this deep basin is not known. Commander Peary reports a depth of 1500 fathoms with no bottom at 5 sea miles from the Pole (about 89° 55′ N.) where he tried to obtain a sounding It was formerly believed that still greater depths existed west of Spitsbergen, in the so-called Swedish deep, where 2600 fathoms had been sounded, but the Nathorst expedition in 1898 found no greater depths there than about 1700 fathoms. The Norwegian Sea, farther south, is 2000 fathoms deep midway between Iceland and Norway, in about 68° N. This so-called Norwegian deep is, as before stated, separated from the North Atlantic Basin by the Wyville Thomson ridge and the Faeroe-Iceland ridge. Farther north there is a low transverse ridge extending eastwards from Jan Mayen, in about 72° N., which is about 1300 fathoms deep. North of this the sea is again deeper-1985 fathoms in 75° N. From the north-west corner of Spitsbergen a submarine ridge extends in a north-westerly direction, with depths of about 430 fathoms in 81° N. and about 4° E. How far this ridge extends is unknown, but there is a probability that it reaches Greenland, and thus separates the Swedish and the Norwegian deep from the deep depression of the North Polar Basin. Baffin Bay forms, probably, a relatively deep basin of about 1000 or 1200 fathoms, which is separated from the West Atlantic Basin by the shallow submarine ridge from Greenland to Baffin Land in about 65° or 66° N.

The deposit composing the bottom of the Arctic Sea contains in its northern part, in the North Polar Basin, extremely little matter of organic origin. It is formed mainly of mineral material, sandy clay of very fine grain, to an extent which is hardly found in any other part of the ocean with similar depths. It contains only from 1 to 4% of carbonate of lime. Farther south, in the sea between Spitsbergen and Greenland, the amount of carbonate of lime gradually increases owing to the shells of foraminifera (especially biloculinae); west of Spitsbergen the proportion rises to above 20 or even 30%, while in the direction of Greenland it is considerably lower.

The circulation of the Arctic Sea may be explained firstly by the vertical and horizontal distribution of temperature and salinity (i.e. density); secondly, by the influence of the winds, especially on the ice-covered surface. The currents in this sea may to some extent be considered as convection currents, caused by the cooling of the water near the surface, which becomes heavier, sinks, and must be replaced on the surface by warmer water coming from the south, which is also influenced by the prevailing winds. On account of the rotation of the earth the northward-running water on the surface, as well as the sinking water, will be driven in a north-easterly or easterly direction, while the southward-flowing water along the bottom, as well as the rising water, is driven south-west or westward. This very simple circulation, however, is to a great extent complicated on the one hand by the irregular configuration of the sea-bottom, especially the transverse submarine ridges—e.g. the Spitsbergen ridge, the Jan Mayen ridge, and the Scotland-Faeroe-Iceland ridge, and on the other hand by the circumstance that the upper water strata of the sea are comparatively light in spite of their low temperature. These strata, about 100 or 120 fathoms thick, are diluted by the addition of fresh water from the North European, Siberian, Canadian and Alaskan rivers, as well as by precipitation, while at the same time the evaporation from the surface of the mostly ice-covered sea is insignificant. The light surface strata will have a tendency to spread over the heavier water farther south, and thus the polar surface currents running southward along the east coasts of Greenland, Baffin Land and Labrador are formed, owing their westerly course to the rotation of the earth. These currents are certainly to a great extent helped and increased by the prevailing winds of the region. The winds get a firm hold on the rough surface of the floating ice, which, with its deep hummocks and ridges, gets a good grip of the water, transferring the movement of the surface immediately down to at least 5 or 10 fathoms.

Temperature and Salinity.—While the temperature is comparatively uniform, with small variations, the difference in salinity between the upper and lower strata is greater than in most other parts of the ocean. In the North Polar Basin the vertical distribution of temperature as well as salinity is very much the same in all places examined. Near the surface, from 0 down to 100 fathoms, the water is below the freezing point of fresh water—with a minimum of between 28·7° (−1·8° C.) and 28·6° (−1·9° C.) at a depth of about 30 fathoms—and is much diluted with fresh water (see above), the salinity gradually increasing downward from about 29 or 30 per mille near the surface to nearly 35 per mille in 100 fathoms. Below 100 fathoms the temperature as well as the salinity gradually increases, until they approach their maximum in about 160 or 200 fathoms, where the temperature varies between 32·5° (0·3° C.), north of the New Siberia Islands, and about 33·8° (1° C) north of Franz Josef Land; and the salinity is about 35·1 per mille. From this depth the temperature gradually sinks downward; 32° (0° C.) is found at about 490 fathoms in the western part of the basin—e.g. between about 84° N. 15° E. and 85° N. 58° E., while it is found in about 400 fathoms farther east—e.g. in 81° N. and 123° E. In depths between 1400 and 1600 fathoms the temperature has a second minimum between 30·6° (−0·8° C.) and 30·4° (−0·9° C.), below which depth the temperature again rises slowly, a few tenths of a degree towards the bottom. In all depths below 200 fathoms the salinity of the water remains very much the same, about 35·1 per mille, with very slight variations. This comparatively warm and saline water evidently originates from the branch of the Gulf Stream passing north across the submarine ridge from north-west Spitsbergen. The vertical distribution of temperature and salinity is very much the same,