After a storm the whole of the water in the North Sea assumes a homothermic condition, i.e.
Curve B shows the typical distribution of temperature in an enclosed sea, in this case the Sulu Basin of the Malay Sea, where from the level of the barrier to the bottom the temperature remains uniform or homothermic. Curve C shows a typical summer condition in the polar seas, where layers of sea-water at different temperatures are superimposed, the arrangement from the surface to 200 fathoms is termed FIG.
39.6° F., not even at the bottom of the great Bartlett Deep in 3439 fathoms. Such homothermic masses of water are characteristic of all deep enclosed seas.
Thus in the Malay Sea the various minor seas or basins are homothermic below the depth of the rim, at the temperature prevailing at that depth in the open ocean: in the China Sea below 875 fathoms with 36.5° F.; in the Sulu Sea (depth 2550 fathoms) below 400 fathoms with 50 5° F.; in the Celebes Sea below 820 fathoms with 38.6° F.; in the Banda Sea below 902 fathoms with 37.9° F.
In other enclosed seas which are shut off from the ocean by a very shallow sill the rule holds good that the homothermic water below the level of the sill is at the lowest temperature reached by the surface water in the coldest season of the year, provided always that the stratification of salinity is such as to permit of convection being set up. To this group belongs the Arctic Sea; the Norwegian Sea is homothermic below J50 fathoms at 29.8° F., but this cold water does not penetrate into the Arctic Basin on account of the ridge between Spitsbergen and Greenland, and there the water below 1400 fathoms has a temperature of 30 6° to 30.7° F.
The Mediterranean Sea also belongs to this group; its various deep basins are homothermic (at the winter surface temperature) below the level of their respective sills - the Balearic Basin below 190 fathoms at 55° F.; the Eastern Basin below 270 fathoms at 55.9° F; the Ionian Sea at 56.3° F.; and at 56.7° south of Cyprus.
Similarly in the Red Sea the water below 380 fathoms is homothermic at 70.7° F.
In shallow seas such as the North Sea and the British fringing seas, where tidal currents run strong, there is a general mixing together of the surface and deeper water, thus making the arrangement of vertical temperature anathermic in summer and katathermic in winter, while at the transitional periods in spring and autumn it is practically homothermic. Thus at Station E2 of the international series at the mouth of the English Channel in 49° 2 7' N., 4 42' W., the following distribution of temperature F.