Hydrographical Observations, North. Atlantic, 1903 and 1904 105 



300 and 800 fathoms. Salinities show a remarkably large volume of 

 water between 35 - 6 and 35'8 per mille down to 500 fathoms from the 

 Irish coast to Station 8. It would seem that the increased surface 

 salinity as the Azores are approached is due to increased evaporation, 

 and the general impression conveyed by the temperature and salinity 

 sections together is that the line is nearly perpendicular to the direc- 

 tion in which the water is moving, if it is moving at all. 



The main question raised by the remaining sections is that of the 

 effect of the extremely saline water flowing out of the Mediterranean 

 through the Straits of Gibraltar. The effective width of the strait 

 may be taken as about 1\ miles, and depth about 200 fathoms. 



Below the level of the ' sill ' the temperature on the Mediterranean 

 side (Stations 43 and 44) is uniformly 12 - 5°, and the salinity 38'6. 

 The plane of separation of the inflowing and outflowing waters lies at 

 a depth of between 50 and 100 fathoms at Station 44, and in the strait 

 itself (Stations 42 and 45) between 100 and 150 fathoms, apparently 

 nearer the first figure. Thus we have an outflowing stream some 

 70 fathoms thick and 7 miles across, consisting of water which at this 

 season is of practically the same temperature as the water outside in 

 the Atlantic, and 2 to 3 per mille Salter than it. 



It is clear that the outflowing water at first streams over the ridge 

 and falls down, mixing rapidly with the fresher waters, until it begins 

 to reach the layers of ecpial density in the lower temperatures below. 

 This apparently happens at a depth of about 600 fathoms, and from 

 this level the horizontal movements are more extensive than the 

 vertical. At the time these observations were made it would seem 

 that the influence of Mediterranean water was inappreciable west of 

 about Long. 22° W. and below 1,300 fathoms. Northwards the effect 

 is still apparent at Station 53, where there is a remarkable stratum of 

 water, salter and heavier than the water above and below it, between 

 1,000 and 1,200 fathoms. This is the only 'inversion' of specific 

 gravity which occurs in these observations, and it does not seem easy 

 to account for it. It is certainly a temporary phenomenon. Its 

 occurrence so far north, and so close to the land, is rather unexpected, 



14 



