Our knowledge of the Pacific in this respect is still very imperfect, but it appears to be less salt than the other oceans at depths below 800 fathoms, as on the surface, the salinity at considerable depths being 34.6 to 34.7 in the Western part of the ocean, and about 34.4 to 34.5 in the eastern, so that, although the data are by no means satisfactory, it is impossible to assign a mass-salinity of more than 34.7 per mille for the whole body of Pacific water.
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.
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.
Hence their tidal conditions are quite oceanic, though their salinity is usually rather lower than that of ocean water.
In the North Atlantic a strong submarine current flowing outward from the Mediterranean leaves the Strait of Gibraltar with a salinity of 38 per mille, and can be traced as far as Madeira and the Bay of Biscay in depths of from 600 to 2800 fathoms, still with a salinity of 35.6 per mille, whereas off the Azores at equal depths the salinity is from 0.5 to 0.7 per mille less.
So also any exhaustive survey of the temperature and salinity of the sea at a great number of points on and below the surface reveals a complexity of conditions that may defy mathematical analysis and could not easily be predicted.
The comparatively fresh equatorial belt of water, has a salinity of 35.
The determination of salinity was formerly carried out by evaporating a weighed quantity of sea-water to dryness and weighing the residue.
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.
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.