Papers in Marine Hiology aad Oceanography. Suppl. lo vol. 3 of Deep-Sea Research, pp. 482-498. 



Long-term trends and changes in the hydrography of the 

 Faroe-Shetland Channel region 



By John B. Tatt 



Summary Between the years 1927 and 1952 inclusive, more or less systematic temperature and 

 salinity observations on two roughly parallel hydrographic cross-sections of the Faroe-Shetland 

 Channel have revealed certain fluctuations, both dynamic and characteristic, which exemplify the 

 phenomenon of marine climatic change. 



Except perhaps in 1947, the Atlantic Current through the Channel evidently flowed more strongly 

 in the autumn-winter than in the spring-summer seasons of the period from 1946 to 1952, and these 

 autumnal-winter intensities themselves apparently increased in magnitude to a maximum in December 



1 95 1 . 



In the fourth decade, the oceanic water-mass in the Channel was infused with extra-Mediterranean 

 water which has not appeared, save sporadically in isolated trace in the years before or since, and 

 which from small beginnings in 1930-1931 showed maximum concentration in 1933 1934 and there- 

 after waned to extinction in 1938-1939. 



Similar circumstances marked the appearance of first one, and then two, types of Arctic water-mass 

 in the bottom layers of the Channel in the latter years of the fifth and the first years of the sixth decades. 



Probably most oceanographers at least entertain the idea, and indeed, from much 

 practice in a given oceanic region, many may have formed some sort of empirical 

 conception in regard to the circulation of the oceans, to the effect that this pheno- 

 menon, besides varying seasonally and in greater or less degree annually, is subject 

 also to longer-term fluctuation which may or may not be periodic in character. Such 

 a conception, even discounting the probability of connection or connections between 

 the respective phenomena, is similar to that of climatic change in regard to which 

 much and various evidence has been adduced in recent years, e.g. glacier recession, 

 timber line advance, seasonal mean atmospheric temperature changes, etc. 



A major handicap to the adducement of oceanographic evidence of long-term 

 fluctuation in hydrospheric conditions lies in the general inadequacy to date of the 

 raw material of oceanographic observations. The collection and compilation of data 

 of the necessary reliability is not yet of long duration — a prerequisite of effective 

 research into the question of long-term fluctuation — and, moreover, has already been 

 seriously interrupted by two world wars in those regions where it was being most 

 intensively prosecuted. Nevertheless, it has been possible, for instance, to deduce 

 from the trend of mean sea surface temperature in high northern latitudes that, 

 during the past half-century or so, the Arctic region has on the whole been slowly 

 warming up. A similar tendency to the extent of at least 0-5" C up to 1951 has recently 

 been noted also in respect of the North Sea and English Channel regions. 



Still another example of longer-term change in sea conditions than the familiar 

 seasonal and annual variations is that instanced by Kemp (1938) in regard to the 

 annual maximum phosphate content of English Channel waters between the third 

 and fourth decades of the present century, with apparently correlated changes in the 

 plankton, young fish, and, ultimately, adult fish populations of the region. These 

 later mdications. from an economic standpoint alone, point a moral which is not to 



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