& 



CLYDE SEA AREA. Ill 



The range of temperature between surface and bottom layers, as would be expected 

 from the depth, is considerably less than for Shandon ; but the dates of change from 

 positive to negative slope are practically the same, coinciding with the seasonal maximum 

 and minimum, the former in September, the latter in March. 



Temperature Sections of Gareloch. — Temperature sections were drawn for each trip, 

 and are reproduced in Plate. XVI., figs. I. to XVII. 



Section I., April 13th, 1886. — The weather was practically dead calm, anticyclonic, 

 with air-temperature below the average of the month. Observations were made at all 

 stations, the average temperature of the loch being 41 0, 8, and of the superficial 5 fathoms 

 42 0, 7. The isotherm of 42° was at 6 fathoms at Row I., 4 fathoms at Row II., and at 

 2^- fathoms at Garelochhead. The other isotherms ran fairly parallel, and especially in 

 the seaward half of the loch showed a marked dip toward the mouth, such as suggests an 

 upwelling of colder deep layers about Shandon, or a less rapid heating of the water just 

 inside the bar. The upper half of the loch showed practically horizontal isotherms indi- 

 cating a tranquil condition. The observations were all made nearly at low tide. 



Section II, April 21st, 1886. — Observations being made only at Shandon and Gare- 

 lochhead, this section is confined to the upper half of the loch. The weather up to the 

 18th had been calm, on the 19th there was a north-easterly breeze, on the 20th an E.N.E. 

 gale, and on the 21st there was a breeze from north-east blowing obliquely down the 

 loch. Great temperature disturbances had taken place. The mean vertical temperature 

 at Shandon had risen from 41°"4 to 42°'0, that at Garelochhead from 41°"6 to 43°'0. The 

 great mass of the water was close to 42°, but varied irregularly. At Shandon the 

 isotherms from 44° - 5 to 42° were crowded into the superficial 1|- fathoms ; at the head 

 those from 45° to 42° were spread through the upper 5 fathoms. There thus appeared 

 to be a distinct heading up of warm surface water, the isotherms all dipping to the head 

 of the loch, where the surface water had been considerably freshened. The state of 

 matters was such as could be readily explained by the action of a southerly wind, but the 

 wind had blown only from the north-east since the calm. It is, of course, possible that 

 the easterly component drove estuary water into the Gareloch, but this does not seem 

 to be the case ; and the section stands an interesting exception to the usual action of the 

 wind. The result is very probably due to deep tidal effects ; observations were made 

 nearly at high-water. The intermediate minimum of temperature is too slight to be 

 profitably discussed. 



Section III, June 16th, 1886. — Here warming had gone on rapidly, the mean tempera- 

 ture of the loch being 48°"1, and of the superficial 5 fathoms 48°"5. The water was well 

 stratified, the isotherms dipping strongly toward the mouth, and the bar seemed to have 

 no effect on them. The isotherm of 48° was at a depth of 15 fathoms at Row II., 

 9 fathoms at Shandon, and only 2^ fathoms at Garelochhead. The higher isotherms were 

 farther apart than the lower, showing a more thorough equalisation of temperature, 

 contrary to what would be expected during warming-up. An anticyclone had prevailed 

 from June 1st to 9th, followed by a cyclone, which on the 16th caused a stiff breeze from 



