In the extreme west the salinity of the surface water is about 36 3 per mille, and it increases eastwards to 37 6 east of Sardinia and 39 0 and upwards in the Levant.
In the equatorial region between these belts the salinity is markedly less, especially in the eastern part.
Our knowledge of the salinity of waters below the surface is as yet very defective, large areas being still unrepresented by a single observation.
The chief facts already established are the greater saltness of the North Atlantic compared with the South Atlantic at all.depths, and the low salinity at all depths in the eastern equatorial region, off the Gulf of Guinea.
Observations in temperature and salinity have only been taken during summer.
During summer the surface salinity of the Black Sea is from 1.70 to 2'00% down to 50 fathoms, whereas in the greater depths it attains a salinity of 2.25%.
Its salinity is comparable to that of the eastern basin of the Mediterranean, which is greater than that of the Black Sea, viz.
Water of less salinity flows outwards from the Black Sea as an upper current, and water of greater salinity from the Sea of Marmora flows into the Black Sea as an under-current.
The empirical data on which the hydrodynamical investigations are based are: (I) observed velocities and directions of oceanic currents and drifts; (2) salinity; (3) density; (4) temperature of the sea water in situ; (5) oceanic soundings.
A very large amount of local detailed observation in the various sea-areas must be the next important work to be undertaken: this means currentobservations b y direct readings of metres, by the employment of drift-bottles and numerous determinations of temperature and salinity at all seasons.
The flow culminates about March in each year, when a considerable part of the North Sea is covered with water of 35 °/oo salinity, but in Nov.
The study of marine life has in recent years become more general, and has become associated with very precise investigations into the chemical composition of sea-water, changes in chemical equilibrium, the effect of variations in salinity and temperature, the processes set up by marine bacteria, and so on.
They are connected with the ocean by narrow straits, the salinity of the water contained in them differs in a marked degree from that of the ocean, and the tidal waves are of small amplitude.
The Baltic Sea and Hudson Bay with very low salinity, the Red Sea and Persian Gulf with very high salinity.
Hence their tidal conditions are quite oceanic, though their salinity is usually rather lower than that of ocean water.
Solar radiation warms the tropical more than the polar waters, but, assuming equal salinity, this cause would not account for a difference of level of more than 20 ft.
Mohn has shown how the inequalities of what he terms the densitysurface can be found from the salinity and temperature; and he calculates that the level of the Skagerrak should be about 2 ft.
One can look on sea-water as a mixture of very dilute solutions of particular salts, each one of which after the lapse of sufficient time fills the whole space as if the other constituents did not exist, and this interdiffusion accounts easily for the uniformity of composition in the sea-water throughout the whole ocean, the only appreciable difference from point to point being the salinity or degree of concentration of the mixed solutions.
Two other facts are totally opposed to the origin of all the salinity of the oceans from the concentration of the washings of the land.
Sorensen and Martin Knudsen after a careful investigation decided to abandon the old definition of salinity as the sum of all the dissolved solids in sea-water and to substitute for it the weight of the dissolved solids in 1000 parts by weight of sea-water on the assumption that all the bromine is replaced by its equivalent of chlorine, all the carbonate converted into oxide and the organic matter burnt.
8050 Cl where S is the salinity and Cl the amount of total halogen in a sample.
Such a simple formula is only possible because the salts of sea-water are of such uniform composition throughout the whole ocean that the chlorine bears a constant ratio to the total salinity as newly defined whatever the degree of concentration.
Besides the determination of salinity by titration of the chlorides, the method of determination by the specific gravity of the sea-water is still often used.
Buchanan, which has an arbitrary scale and can be varied in weight by placing small metal rings on the stem so as to depress the scale to any desired depth in sea-water of any salinity, the specific gravity being calculated for each reading by dividing the total weight by the immersed volume; (3) the total immersion areometer, which has no scale and the weight of which can be adjusted so that the instrument can be brought so exactly to the specific gravity of the water sample that it remains immersed, neither floating nor sinking; this has the advantage of 'eliminating the effects of surface tension and in Fridtjof Nansen's pattern is capable of great precision.
Sorensen, carried out a careful investigation of the relation between the amount of chlorine, the total salinity and the specific gravity of sea-water of different strengths including an entirely new determination of the thermal expansion of sea-water.
The relations between the various conditions are set forth in the following equations where 0-o signifies the specific gravity of the sea-water in question at o° C., the standard at 4° being taken as 1000, S the salinity and Cl the chlorine, both expressed in parts by weight per mille.
The refraction of light passing through sea-water is dependent on the salinity to the extent that the index of refraction is greater as the salinity increases.
Sarasin and longer series of experiments by Tornde and Kriimmel this relation is shown to be so close that the salinity of a sample can be ascertained by determining the index of refraction.
Von Drygalski for the measurement of salinity at sea, and was found to have the same degree of accuracy as an areometer with the great advantage of being quite unaffected by the motion of the ship in a sea-way.
Any influence on transparency which may be exercised by the temperature or salinity of the water is quite insignificant.
On account of its salinity, sea-water has a smaller capacity for heat than pure water.
According to Thoulet and Chevallier the specific heat diminishes as salinity increases, so that for io per mille salinity it is o 968, for 35 per mille it is only o 932, that of pure water being taken as unity.
The thermal conductivity also diminishes as salinity increases, the conductivity for heat of sea-water of 35 per mille salinity being 4.2% less than that of pure water.
The speed is 1482.6 metres (4860 ft.) per second, in Baltic water of 8 per mille salinity and a temperature of 50° F.
The electrical conductivity of sea-water increases with the salinity; at 59° F.
4282 t +0 0074527 t20.0000-5494 t3 Cl(o 2149 - o o07117 / 2 +0.0000931 13) In the case of ocean water with a salinity of 35 per mille, this gives for saturation with atmospheric gases in cc. per litre: The reduction of the absorption of gas by rise of temperature is thus seen to be considerable.
The alkalinity of North Atlantic water of 35 per mille salinity is 26.86 cc. per litre, corresponding to a total amount of carbonic acid of 49 07 cc. According to the researches of August Krogh,' the alkalinity is greatly increased by the admixture of land water.
Ruppin's analysis of Baltic water, which has an alkalinity of 16 to 18 instead of the 5 or 6 which would be the amount proportional to the salinity, while the water of the Vistula and the Elbe with a salinity of o 1 per mille has an alkalinity of 28 or more.
Frequently the case in fjord basins; for instance, in the Gullmar Fjord at a depth of 50 fathoms with water of 34.14 per mille salinity and ' Meddelelser om Gronland (Copenhagen, 1904), p. 331.
A temperature of 40.1 ° F., the carbonic acid amounts to 51 J5 cc. per litre, and the oxygen only to 2.19 cc. Vegetable plankton in sunlight can reverse this process, assimilating the carbon of the carbonic acid and restoring the oxygen to solution, as was proved by Martin Knudsen and Ostenfeld in the case of diatoms. Little is known as yet of the distribution of carbonic acid in the oceans, but the amount present seems to increase with the salinity as shown by the four observations quoted: Water from Gulf of Finland of 3.2 per mille salinity =17.2 cc. C02 Western Baltic of 14.2 North Atlantic of .0, , 49'0 Eastern Mediter ranean of 39.o, , =53'0, , Unfortunately the very numerous determinations of carbonic acid made by J.
Distribution of Salinity.-A great deal of material exists on which to base a study of the surface salinity of the oceans, and Schott's chart published in Petermanns Mitteilungen for 1902 incorporates the earlier work and substantially confirms the first trustworthy chart of the kind compiled by J.
In each of the three oceans there are two maxima of salinity-one in the north, the other in the south tropical belt, separated by a zone of minimum salinity in the equatorial region, and giving place poleward to regions of still lower salinity.
The North Atlantic maximum is the highest with water of 37.9 per mille salinity; the maximum in the South Atlantic is 37.6; in the North Indian Ocean, 36.7; the South Indian Ocean, 36.4; the South Pacific, 36.9; and the North Pacific has the lowest maximum of all, only 35'9.
The comparatively fresh equatorial belt of water, has a salinity of 35.
O in the Indian Ocean, 34.5 in the Western and 33.5 in the Eastern Pacific. Taking each of the oceans as a whole the Atlantic has the highest general surface salinity with 35'37.
The salinity of enclosed seas naturally varies much more than that of the open ocean.
The Arctic Sea presents a great contrast between the salinity of the surface of the ice-free Norwegian Sea with 35 to 35.4 and that of the Central Polar Basin, which is dominated by river water and melted ice, and has a salinity less than 25 per mille in most parts.
The average salinity of the whole surface of the oceans may be taken as 34.5 per mille.
The vertical distribution of salinity has only recently been investigated systematically, as the earlier expeditions were not equipped with altogether trustworthy apparatus for collecting water samples at great depths.
As yet it is only possible to speak with confidence of the vertical distribution of salinity in the seas surrounding Europe, where there is a general increase of salinity with depth.