Long-term trends and changes in the hydrography of the Faroe-Shetland Channel region 487 



isohaline having been estimated as at 260 metres by rapid hydrometric measurements 

 at a position over the lower continental slope north-west of Shetland, the result of 

 repeated short-interval current meter suspensions to this depth yielded the incon- 

 siderable vector of only 0-63 centimetres per second. When the more accurate 

 salinity determinations were made it transpired that the above-estimated depth of 

 the 35°/oo isohaline at the position concerned was less by some 12 or 13 metres than 

 the probable true depth, so that sufficiently near confirmation of the basic assumption 

 underlying the volume transport computations on this northern section may be said 

 also to have been achieved. Unfortunately, the favourable conditions which had 

 prevailed to this point broke down thereafter, thus precluding further similar experi- 

 mentation at other positions on the section. 



Table I gives the results of the volume transport computations on the foregoing 

 Hnes through the above-mentioned two Faroe-Shetland Channel cross-sections in 

 contemporary pairs. The unit of cubic kilometres per hour has been chosen in 

 preference to the hitherto more usual unit of milhons of cubic metres per second, as 

 affording to fishery research biologists, in whose interest these investigations were 

 primarily carried out, a more readily grasped conception of the phenomenon of the 

 intensity of the oceanic incursion into north-west European fishery regions. 



As already indicated, the agreement between the pairs of values is remarkably 

 close in all cases except one, namely, that for the latter half of May 1951. The im- 

 mediately succeeding values, referring to the second and third weeks of June, being 

 not only in close mutual agreement, but in agreement also with the higher of the two 

 values for the preceding period, suggest that the disagreement in respect of this 

 earlier period was in fact real, and significant of a radical change in the intensity 

 of the Atlantic Current within the short interval of the two latter weeks of May 

 1951. 



For present purposes, however, the interest of Table 1 is mainly in such evidence 

 as it yields of longer than annual variations in the intensity of the Atlantic Current 

 in the Faroe-Shetland Channel. Because of the highly disproportionate seasonal, 

 and to a somewhat less extent annual distributions of the values, this evidence can 

 only be regarded on the whole as of a very tentative nature. 



The majority of the entries in Table I relate to the months of May, June and July, 

 especially the two former months. Considering these values apart, their range is 

 very considerable, namely, taking the means of paired values, from about 2-3 km^hr 

 in July 1951, and 2-4 kmVhr in May 1931, to 19-6 km^hr in June 1947, which in fact 

 all but embraces the entire range of the values of Table I. It may of course be entirely 

 fortuitous, the frequency of the values being insufficient for anything approaching 

 positive assertion, but it can at least be observed that the highest spring-summer 

 oceanic transports, as chronologically entered in Table I, occur in the years 1929, 

 1938, 1947, and 1951, that is, apparently after intervals of nine, nine, and four years 

 respectively. 



On the other hand, the lowest spring-summer values do not admit any similar 

 inference of long-term periodicity. Their main feature in Table 1 would seem to be 

 an unbroken succession of them in the six years from 1931 to 1936. 



More or less in parenthesis at this still early stage in scientific oceanographical 

 investigation, but nevertheless perhaps associated in some at present indefinable way 

 with the subsequent phenomenon, brief notice may be taken in passing of the lowest 



