CLYDE SEA AREA. 



65 



Observations were, however, often made nearer the entrance and farther from it. 

 The average density of the water was as follows : — 



Surface, 5 observations. 



Bottom, 5 observations. 



Mean, . . . 



. 1-02461 



1-02497 



Maximum, . 



. 1-02486 



1-02507 



Minimum, . . 



. 1-02416 



1-02470 



Average percentage of pure 









93-0 



95-7 



In vertical section, 95*2, or in normal year, 94 - 9. 



Table XXII. — Temperature Observations at Otter I. 



No. . . . 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



Date 



19.4.86 



21.6.86 



10.8.86 



11.8.86 



28.9.86 



17.11.86 



29.12.86 



4.2.87 



29.3.87 



10.5.87 



15.6.87 



7.7.87 



No. of Pts. . 



7 



7 



7 



4 



4 



6 



6 



6 



6 



3 



6 



7 



Temp. . . 



42-0 



444 



49-9 



50-4 (?) 



51-9 



50-8 



47-4 



44-7 



44-1 



45-8(?) 



47-4 



49-9 



Slope . . 



+ 1-6 



+ 1-8 



+ 2'9 



+ 24 



+ 0-9 



-1-3 



-1-7 



-1-5 



+ 0-3 



+ 05 



+ 3-2 



+ 31 



Depth . . 



38 



33 



25 



14 



15 



15 



28 



53 



33 



15 



20 



22 



The main interest of this station arises from its position on the seaward side of the 

 steep barrier which shuts off Loch Fyne from the Arran Basin. The discussion of density 

 observations showed that there is a marked upwelling of deep water about this point, and 

 temperature observations amply confirm the fact. The evidence from surface temperature 

 will be given when speaking of Loch Fyne, but the clearest proof is shown by the rise of 

 the isotherms to the surface at Otter on the temperature sections (Plates VIII. to XV.) 



The effect of the tidal current running north up the wide Central Arran Basin, and 

 finding no outlet except the narrow entrance of Loch Fyne to the north-east, seems to 

 be to drag the deep layers of water up the slope, and so give rise to a back-flow on the 

 surface, or in the still deeper layers. It is largely to this disturbance of the equilibrium 

 of the mass of water in the Arran Basin, and to the similar action of other sloping shores, 

 that I am inclined to attribute the continual mixing, which tends to maintain a homo- 

 thermic state in the deep water. The tidal reaction-currents would naturally be powerfully 

 reinforced by wind, and possibly modified to some slight extent by variations in 

 density. 



Temperature Sections of the Arran Basin. — The outstanding features of the mass 

 distribution of temperature on eighteen trips were laid down in the form of isotherms 

 upon a much exaggerated profile of the section from the Channel through the East and 

 Central branches of the Arran Basin and Loch Fyne to Cuill. These sections, 

 coloured according to the principle already described, are useful in showing the nature 



VOL. XXXVIII. PART I. (NO. 1). I 



