ATLANT. DEEP-SEA EXPED. 1910. VOL. i] PHYSICAL OCEANOGRAPHY AND METEOROLOGY 



19 



North Atlantic. The former water has an e.xtraordinarily 

 high salinity (above 38 "/oo) because the evaporation in 

 the Mediterranean is in great excess compared with the 

 dilution by river-water and rain, while the temperature is 

 only about IS"" C due to the winter-cooling of the 

 surface (in the^gean Sea). At this temperature the Atlantic 

 water would have a salinity below 36 "im. The heavy 

 water from the Mediterranean sinks in the Atlantic, while 

 strong mixing processes take place, resulting in mi.\ed 

 water with a high salinity as compared with the temperature. 

 Such variations occur, and we cannot, therefore, expect 

 to find an invariable ratio between salinity and temperature 

 in sub-surface waters. 



The figure on page 75* shows the mutual values of 

 temperature and salinity found by all observations from 

 the "Michael Sars"-Expedition, at 20 metres below the 

 surface and downwards. Various marks have been used 

 according to depth and locality. As to depth the grouping 

 has been 20—500, 501 — 1500, and below 1500 metres. 

 As to locality the following groups have been formed: 



1) observations from the English Channel and the Bay of 

 Biscay, and along the coast of Portugal (Stats. 1 — 17), 



2) from Spain southwards, off the coast of Marocco, as 

 far as 26'' N lat. (Stats. 20—40), 3) from the Canary 

 islands westwards to the Sargasso Sea and thence to the 

 Azores (Stats. 44—58), 4) from the Azores along the route 

 of the "Michael Sars" (cf. chart p. 63*) in the western 

 parth of the North Atlantic as far as Stat. 87 above the 

 central ridge (Stats. 59—87), and finally 5) from the latter 

 place north-eastwards towards Ireland (Stats. 88—96). 

 The fourth group (Stats. 59—87) composes the observations 

 from the western part of the North Atlantic, while the 

 other four embrace observations from the eastern part only. 



It is noteworthy that the marks for the sub-surface 

 observations are chiefly crowded within a relatively narrow 

 zone with an even, slightly curved direction. A distinct 

 deviation will be seen for temperatures about 10 — 11°, 

 the salinities connected with these temperatures being 

 exceptionally high in intermediate water off Spain, Por- 

 tugal and Marocco. This is a sign of the influence of 

 the Mediterranean in the sense mentioned. 



On the basis of our observations from the summer 

 of 1910 i have tried to draw a line representing the 

 average relation between temperature and salinity in the 

 "ordinary" North Atlantic waters. This line will be seen 

 in the figure on p. 75*. In the original drawing a more 

 specialized marking of the mutual values was worked 

 out. In drawing the line special attention was paid to 

 the waters of the western and central parts of the North 

 Atlantic where the influence of the Mediterranean or of 

 the Labrador current was mitigated. The conditions in 

 the upper 100 metres were mostly neglected. A study 



of the figure p. 75* will show that the marks on the 

 upper side of the line (relatively high salinities) for the 

 most part represent those regions where the influence 

 of the Mediterranean is chiefly felt. 



The average correlation between temperature and 

 salinity in the North Atlantic as found by us in 1910, 

 represented by the "normal" line, cannot be expressed 

 by a simple formula for the whole interval between 2° 

 and 20° C. A calculation by means of the method of 

 least squares has resulted in the following formula for 

 the interval between 5 and 15° C. 



S, — 34-737 + 0038 1 + 0.0029 t- 



This formula will nowhere within the interval give a 



greater deviation than 001 



from the value found 



from the curve. 



A variation of 1°C intermediately in the North Atlantic 

 will on an average be connected with a vanation of 

 salinity to such an extent that the density will vary by 

 about 01 in o,. An increase of temperature generally 

 means an increase of salinity and a decrease of density. 



The "normal" temperature-salinity curve is reproduced 

 on p. 74* in such a way that the corresponding values 

 of temperature and salinity can easily be read off. When 

 the value of salinity, found from this diagram for some 

 temperature observed, is subtracted from the observed 

 value of salinity we get a value which may be termed 

 salinity-anomaly. It is most conveniently expressed in 

 Vioo »/oo of S, and may be termed A § (— ^00 {S-S,)). 



The salinity-anomaly defined in this way is not an 

 explicit expression of the variations. A high (positive) 

 value means either a concentration of the water above 

 the normal, or a cooling below the normal, or both. A 

 low (negative) value represents either an abnormal dilu- 

 tion, or heating, or both. When the calculation of the 

 salinity-anomaly is extended to the upper water-layers we 

 find relatively high values in winter, as well as at most 

 times in regions with an excess evaporation, and we find 

 low values at or near the surface in summer on account 

 of the heating as well as after a relatively large supply 

 of fresh-water from rivers. 



In spite of this ambiguity the salinity-anomaly will, 

 however, often give valuable results in regard to the origin 

 and evolution of the water-masses, as will be shown 

 later on. As it is a combined expression of both tem- 

 perature and salinity, irrespective of the absolute values 

 of those quantities as well as of the densities, it may give 

 numencal values which are useful for revealing conditions 

 not easily found by the ordinary methods [cf. Helland- 

 Hansen, 1916). It may also be possible to study long- 

 penod temperature variations by starting from the salini- 

 ties observed and calculating "temperature anomalies" 

 (chapter VI). 



