38
CHAPTER 3 TEMPERATURE AND SALINITY DISTRIBUTIONS AND WATER-MASSES OF THE REGION
By
J . B. T a i t Marine Laboratory, Aberdeen
A. J. L e e Fisheries Laboratory, Lowestoft
U. S t e f a n s s o n Hafrannsöknastofnunin, Reykjavik and
F. H e r m a n n Danmarks Fiskeri- og Havundersøgelser, Charlottenlund
FOREWORD A general view of these diagrams reveals at once, on While the main objective of the ICES international all three surveys, an increasing complexity of the expedition of 1960 to the Iceland-Faroe Ridge region pattern of temperature and salinity distributions from was the detection, delineation, and, as far as possible, the surface downwards to at least 300 metres, where the measurement, of cold, deep water overflow across the complexity is greatest. It is only a little less so at the Ridge from the Norwegian Sea into the North 400 metres, but at 500 metres, the bathymetrics of Atlantic Ocean basin, the region has for so long been this depth defining the northern and southern “shoul known as one of conjunction and conflict between ders” of the Ridge proper, the intervention of the relatively warm oceanic waters on the one hand, and Ridge physically separates the deep oceanic and cold cold, Arctic waters on the other, that the occasion of northern water-masses, except for small overspills such a unique exercise in concentrated oceanographi from one into the other. The temperature and salinity cal observation should not be overlooked for the distribution patterns therefore at this level are com material it provides for a closer study of these con paratively straightforward and uncomplicated. flicting phenomena than has previously been possible. Figures 3:1, 3:8 and 3:15 represent surface temper An immediate reason, moreover, for such a study, ature and salinity conditions on each of the three from the ICES point of view, resides in the fact of the surveys. On all three occasions the Ridge area was significance of the region from a fisheries standpoint. completely overlaid, on the surface, by oceanic water Here, as is well known, commercial fisheries are which in fact extended northward far beyond the subject to wide and often apparently abrupt fluctu Ridge itself. Only in the northwest corner of the ations from more or less ample abundance to complete region investigated, as well as eastward beyond the absence, and the oceanographical nature of the region Ridge, and farther north between about latitudes suggests that these fluctuations may be more or less 64°30'N and 65° N, was there evidence of the near closely associated with corresponding changes in the vicinity of Arctic type waters of low temperature physico-chemical environmental milieu. ( < 6° C) and salinity of less than 34-90 °/00. High J. B. T a i t salinity oceanic water, in excess of 35-30 °/00, ocurred in patches over the Ridge and, on the first survey, HORIZONTAL TEMPERATURE AND SALINITY DISTRI beyond it. Highest salinity water, of over 35-40 °/00 BUTIONS (J. B. T a i t ) salinity, was found only over the southern end of the Taking, first, horizontal distributions and, in parti Faroe-Shetland Channel and, on the third survey cular, those of temperature and salinity, Figures 3:1- only, some 30-40 miles northwest of the Faroe Bank 3:21 give the dispositions of these parameters at the and a similar distance northwest of the Faroe Islands surface, 100, 300, 400, and 500 metres, and on the respectively. bottom, on each of the three surveys of the expedition. As between the first and second surveys, the relative 39
16° 15° 14° 10° 65° .34-80
I '----- 35-10
<35-00
!35-00_X 35-1: 35-20- > 35-30 ■ 3.5-25 64° 35-25 500m
<35-25
10001 35-0! < 9 35-25
,>35-30
.>35-30 63°
500m 35-25 35-30 e - 35-30 15-35
•M / 7 > 35-30' ■<35-30
1500
[>35-35] '>35-35 FAROE Is. -10
35-30' >35-3! .<35-31
> 35-35 ■35-30 500m
1000m
61° 35-35
500m ' .
35-40 - r 1000m > 35-40 500i 35-40- <35-40
60° 14° 10 °
Figure 3:1. First Survey: surface temperature and salinity. 40 positions of the surface 9° G and 10°C isotherms, and appear on the third survey, perhaps because the the occurrence of the 11° G isotherm just within the narrow region of its occurrence on the second survey region investigated on the second survey, argues an was not included on the third occasion. Likewise, the increasingly progressive surface oceanic influence main 35-30 °/00 isohalines of the two surveys were on northwards towards and over the Ridge, with, of the whole similarly disposed, although the third course, a concomitant regression northwards of the survey would appear to have witnessed a greater Arctic influence tending to bear southwards towards intrusion of higher salinity water, above 35-35 °/00, the Ridge. On the whole, the salinity distributions of and indeed, in two places, corresponding very nearly the first two surveys scarcely bear the same implication. to the two loci of maximum salinity surface waters on Indeed, so far as salinity is an index, the difference the first survey (> 35-35 °/00), above 35-40 °/00. These between Figures 3:1 and 3:8 almost points in the circumstances indicate still further progression of the reverse sense, namely, in favour of a slight impediment oceanic influence northwards at the expense of the to the northern progress of oceanic influence over the colder and fresher northern influence southward Ridge by southerly directed Arctic influence. The towards the Ridge. difficulty in assessing the differential significance as On the other hand, the dilutive eddy or vortex over between oceanic and Arctic influences of the surface the Rose Garden area, which was noticed on both the salinity distributions of the first two surveys arises previous surface charts, had evidently intensified in from the increased evidence of vorticity movement the third week of the exercise, reducing its nuclear over the Ridge on the second survey. On the first surface salinity to below 34-95 °/00. Concomitantly, survey there was apparently only one of those entities, surface temperatures which had been between 8°C but, as will appear later, probably a significant one, and 9° C on the first two surveys, were here reduced to in the area over the Rose Garden (Rosengarten) below 7°C. fishing area. Here, on the first survey, the general Passing to a consideration of conditions at 100 salinity of the neighbourhood of over 35-25 °/00 was, metres’ depth (Figures 3:2, 3:9, and 3:12), it may be presumably by influence from the north, reduced to noticed at once that the vortex of the Rose Garden below 35-15 °/00. O n the second survey, in this same area, similarly increasing in intensity from the first, area and in a similar vortex, the surrounding salinity through the second, to the third survey, was again of about 35-25 °/00 was reduced in the centre of the revealed at this level, with a marked change in vortex to a nuclear value of below 35-00 °/oo> indicative position, however, as between the surface and 100 it would appear of increasing influence, in this parti metres on the first survey, and as between the first and cular region at least, of colder fresher water from the the second and the second and third surveys at the north or northeast. latter level. The curious feature is further noticeable Farther south towards the narrowest part of the at the 100 metres level (Figure 3:2) on the first survey Ridge, but still on its northern boundary, a second, that the thermal vortex was apparently entirely less intense vortex appeared on the surface on the separate from the salinity entity. The 100 metres second survey, reducing the salinity there from a diagram of the first survey, however, as distinct from general distribution of over 35-25 °/00 to below the others, contains, in the trends of isotherms and 35-20 o/00. isohalines, a fairly clear indication of the direction A third of these apparently diluting vortices appe from which dilution of the northward-tending oceanic ared on the second survey on the southwestern water-mass proceeded. This was evidently more from shoulder of the Ridge, enclosing a minimum salinity the eastward than the northward, approximately along of less than 35-15 °/00 in an area of 35-25 °/00 to the latitude of 63°45'N. 35-30 °/00 salinity water. On the broad general features of the three 100- Despite these indications, however, by salinity, and metre charts, the relative positions of the main while at the same time accepting the intrusive in 35-30 °/00 isohalines undoubtedly denote at this level fluence which they evidently signify, the total or also a northwards progression of the oceanic water- aggregate interpretation of the surface temperature mass, more marked between the first and second and salinity distributions from the first to the second than between the second and third surveys. A similar survey points to the recession of the northern in inference attaches to the dispositions of the 35-35 °/00 favour of the southern, oceanic influence. and 35-40 °/00 isohalines over the region of the Faroe The difference between the surface distributions of Bank Channel. the second and third surveys is on the whole less It seems rather odd, however, to find, on the third impressive. The 10° C, 9° C, and 8° C isotherms retained survey, (Figure 3:16) an indication of oceanic water much the same positions geographically on the third so far north as almost on latitude 65 N, at longitude s u r v e y , as on the second. The 11° C isotherm did not 7°30'W. Although in essence depending upon an 41
16° 15° 14° 13° 12° 65° 34-90 34 90. 34-95- -35-00. - 35-05, 35-10 35-20
.35-25 64°
I5-20J. -34-95 35-25 =35-05 500m 35-15 35-20 '35-25 "35-30 !>500r
-3515 63° ■500m- 35-30 <8
35-30'
1000m 35-30 35-30 <35-30
1500m
<35-30 62° 62° \FAROE
35-35 f>35-35>
35-35
500 m 61°
35-35 v 35-40' 500m 60° 16° k° 13° 10 ° Figure 3:2. First Survey: temperature and salinity at 100 metres. 42 isolated observation, it must be conceded that the week and to have become further separated by inter observation in question is to some extent supported by vention of a colder tongue of northern derivation, the next nearest observation southeastward on the according to its salinity. third survey, as well as by the extreme northerly Although difficult to gauge, in the light of the above locations on the first and second surveys (Figures 3:2 complications, the total impression of the result of the and 3:9) of the 35-00 °/00 isohalines, as also by the opposition between oceanic and northern influences particular trends in this region of the lesser surface at the 300 metres’ level between the first and second isohalines of the first survey (Figure 3:1). weeks of the exercise, is one of perhaps small advantage Isothermal dispositions at 100 metres present on the in favour of the former, a deduction which would whole a less clear picture of a northward oceanic seem to derive some measure of support from the progression. This in itself is probably indicative of relative conditions at the same time in the southern increasing impediment to this progression as the total Faroe-Shetland Channel region. three weeks’ exercise proceeded. The difficulty in At the 300 metres’ level, the argument for progres interpreting the main isothermal dispositions in this sion of the oceanic as opposed to the northerly-derived, sense arises from the convolutions in water-movement southerly-directed water-masses, is on the whole which, throughout the period of the exercise and clearer on the third survey as compared with the more clearly by the evidence of salinity than temper second. As denoted by salinity, with associated temper ature distributions, were obviously taking place over atures broadly corresponding, there is a distinct the Ridge at the level of 100 metres. northwards advancement of the higher denominations These convolutions in water movement are obviously from the second to the third survey, and a concomitant the most prominent feature of Figures 3:3, 3:10 and regression of the lower isotherms and isohalines, 3:17, representing conditions at 300 metres depth. denoting retreat of the colder northern water-mass. It is obvious that, particularly on the first survey, but Probably the most interesting feature of the three in only slightly lesser degree on the succeeding surveys, charts of temperature and salinity distributions at the a turmoil of water movement was taking place on top level of 400 metres (Figures 3:4, 3:11, 3:18), is their of the Ridge. On the first survey two “pockets” of illustration of the extent to which cold northern cold (<2°C) northern water (< 34-95 °/00 salinity) waters had thus far overtopped (or more likely passed were “caught” between the advancing oceanic water round the eastern boundaries of) the highest parts of mass from the southwest over the Ridge and a closed the Faroe-Iceland Ridge on all three surveys, but circulation on the Rose Garden of oceanic water decreasingly so from the first survey to the third. On greater than 6°C in temperature and 35-15°/00 in Figure 3:4, appreciable areas of water of less than salinity. On either side of this circulation the cold 2°C and 34-95 °/00 are delineated southwards below northern waters penetrated more or less deeply into the 400 metres bathymetric. On Figure 3:11 these the oceanic water mass which nevertheless extended areas are somewhat less, while on Figure 3:18 of the considerably northward beyond the Ridge proper third survey, they scarcely exist, the 34-95 °/00 isohaline along its southeastern part. At the same time, towards having retreated considerably northwards on top of the narrowest part of the Ridge, two diluted oceanic the Ridge. incursions, one of which scarcely survived as such by Closed circulations of relatively high salinity the evidence of a nuclear salinity barely reaching (>35-15°/00) and high tem perature (> 6°C) still 35-00 °/00, became isolated in swirl formations engen appear at the 400 metres level on top of the Ridge dered no doubt by the conflict between southern and towards its southeastern end, near the narrowest part northern influences. of the Ridge; this on the first survey (Figure 3 :4) when The closed oceanic water circulation of the first also two high salinity vortices appeared well north survey over the Rose Garden re-appeared in a more wards beyond the Ridge - > 35-10 °/00 in one case and southerly position on the second survey, its place > 35-25 °/00 in the other. being taken by a colder, northern water swirl, probably Some evidence of at least the latter remains on that which had lain to the westward of it on the first Figure 3:11, but the two smaller high salinity cir survey. The second northern water circulation of the culations of the first survey on top of the Ridge appear first survey, below the oceanic complex of the Rose to have dissolved before the second survey whereon Garden area was, on the second survey, displaced appeared, however, near the narrowest part of the farther south and separated from its “fellow” by the Ridge, two new small circulations, one a cold low displaced oceanic vortex. Then, moving southeast salinity (< 34.95 °/00) complex and the other a higher ward towards the narrowest part of the Ridge, the temperature (>6°C) oceanic salinity (>35.25 °/00) two weak oceanic complexes of the first survey would vortex. On the third survey, these two entities would appear to have moved northwestward in the next almost appear to have changed places and intensified
(Continued on p. 46) 43
~^34-90 35-05, 34-95 ; 34-90
<34-90
1000m '350S-4, 35-30 (035-00; 3500
1500m
150 On
FAROE Is.
1000 m
1000 m
Figure 3:3. First Survey: temperature and salinity at 300 metres. 44
■34-90-. ^34-SSX; 3 5 -0 0 \
.34-90
•400 m ------35-0! C35-10
15-15 • 34-90 ^ f34-5)5 500m-^ 1000m HOOmJ
1500m
5 ^ 35-00 15*10 .500m
ADOm
1500m
FAROE Is.
1000m ■400m 5obU. •
Figure 3:4. First Survey: temperature and salinity at 400 metres. 45
15° 13° 12° 11° 10° 65°
500m ;
35-25
35*15 64° -35-20 64°
>35-20 35-15 ' •
34-90
63° 1500m 63°
35-00
•35-25 .35-05 34-95
6 - Z 7
1500m
62° 62° FAROE Is. > 35-30 \35-20
V_35-30‘ 35-30
-35:20 35-301 •35-25 . ,
61° 1000m 500m' 61°
500m
35-iOv 500m )0m 1000m ‘35-15
500m 60° 60° 14° 13° 12° 11° 10° 9° Figure 3:5. First Survey: temperature and salinity at 500 metres, 46 somewhat, although more probably these were new second, and Figures 3:20 and 3:21 for the third), vortices which formed on the third survey on which a and, in addition, graduated colour schemes, in red third made its appearance in approximately the same for temperature and blue for salinity, are introduced region near the Ridge’s narrowest part. to aid visual appreciation of the interaction of the Changes from one survey to the next in the Faroe oceanic and northern water-masses. Bank Channel would appear to reflect a slow gain in Figure 3:6, illustrating bottom thermal conditions oceanic influence there, probably from the southeast. on the first survey, shows the zero isotherm only just Figures 3:5,3:12 and 3:19, deal with the 500 metres encroaching on the Ridge proper over a small part level. Here the Ridge most decidedly intervenes to of its northern, 500-metres’ shoulder. The 2°C iso separate oceanic from northern waters. Only a small therm, which probably marks the southern boundary indication (by salinity) of oceanic water occurred of relatively undiluted cold deep northern water, the north of the Ridge at its southeastern extremity on the Polar Front in other words, was not only far advanced first survey at 500 metres depth. At this level north over the top of the Ridge, but in two places completely of the Ridge practically all of the waters sampled crossed the Ridge into depths of 600 to 800 metres on registered less than 2°C in temperature, and from its southwestern slope. The same isotherm also just under 34-90 °/00 salinity to over 34-95 °/00. On the protruded far beyond the western end of the Faroe south and west sides of the Ridge in Figure 3 :5 are to Bank Channel which indeed marked the limit ap be seen mainly oceanic characters of temperature and proximately of sub-zero temperature water from the salinity except along its southern boundary where a depths of the Faroe-Shetland Channel. narrow strip under 3°C to below 2°C, and less than Despite the far advance of the “Polar Front” 35 00 °/00 salinity, the only unmistakable evidence of isotherm of 2°C over and across the Faroe-Iceland cold deep water overflow, is to be found. Ridge, high temperature ( > 6° C) oceanic water There is somewhat greater evidence, mainly by evidently secured a substantial circulatory base towards salinity, of oceanic water on the north side of the the northern end of the Ridge, and again, southwards Ridge at 500 metres on the second survey, while, south towards the Ridge’s narrowest part, the 2°C isotherm of the Ridge, the cold water overflow would appear to was pushed back halfway across the Ridge by a have been less on the second than on the first survey. “pocket” of oceanic water in vorticial circulation. No temperatures of less than 2°C or salinities less Conversely, as it were, a cold northern water circula than 35 00 °/00 were recorded at this level on the tion disputed the advance of the “oceanic front” over second survey. the bottom in the deep indentation of the 500-metres On the third survey, the evidence for oceanic water bathymetric contour on the south side of the Ridge. north of the Ridge at the depth in question was slight, Similar, if less intense, cold water enclaves on the but on its south side in one small location cold northern much deeper sea bed to the northwest of the Faroe overflow water was signalised by a temperature of Bank may be taken to have derived from the deep under 1°C and salinity below 34-95 °/00. effluent from the Faroe Bank Channel rather than Turning to the Faroe Bank Channel region at 500 from Ridge overflow which in any case tends to move metres, the evidence is all of oceanic water on all westward under geostrophic forces on overspill from three surveys, with, however, on the second survey in the Ridge. particular, (Figure 3:12), an obvious tendency at the Turning to the haline character of the bottom water southern end of this Channel for cold, less saline on and on either side the Ridge on the first survey, waters from the Faroe-Shetland Channel to seek Figure 3:7 reveals, as might be expected from the entry into the Faroe Bank Channel. On the third bottom thermal distribution of Figure 3:6, the ap survey (Figure 3:19), what would appear to be a parently tenuous hold on top of the Ridge, except in relic of this cold intrusion was isolated against the its northern part, of almost the weakest oceanic water northern slope of the Faroe Bank Channel, an oceanic of scarcely more than 35-00 °/00 salinity. The westward water surge behind it having separated it from its and southward boundary of the northern water, as parent mass in the Faroe-Shetland Channel. indicated by the 34-95 °/00 isohaline, like the 2°C In view of the prime objective of the expedition, it isotherm, lay for the most part far across the top of is instructive to consider, irrespective of depth, the the Ridge. Perhaps less saline water than is depicted temperature and salinity conditions on the bottom on Figure 3 :7 on the southern slope of the Ridge might of the region surveyed. For the greater clarity in have been expected, but on the other hand there is delineating these conditions the bottom temperature an evident correspondence in the material parts and salinity distributions for each of the three surveys between the 2°C isotherm of Figure 3:6 and the are illustrated on separate charts, (Figures 3:6 and 35-00°/00 isohaline of Figure 3:7 which points the 3:7 for the first survey, Figures 3:13 and 3:14 for the reality of cold northern water overflow in these parts. (Continued on p. 63) 47
. ° ° 16 15 14° 12° 10 ° 65° 65°
64° 64°
>6
< 3
1500m 63°
>00rn. lOOOm
500m
62° ''<2 62° FAROE Is.
>8 500m 60° 14° 13° 12° 11° 10° 60° Figure 3:6. First Survey: temperature on the bottom. 48 1000m ,1500 m 35-00 3505 1500m 3500 1000m FAROE Is.. 1000m 500 m Figure 3:7. First Survey: salinity on the bottom. 49 500m- OOOrc/ 1500m 500m FAROE Is.. lOCOm 1000m Figure 3:8. Second Survey: surface temperature and salinity. 4 50 as-oo^'v34-95*. \ 1500m 1500m \ FAROE Is., 1000m 500 m Figure 3:9. Second Survey: temperature and salinity at 100 metres. 51 :34-90,' SOOm 35-30> I V •'/• ’ .30Qm-r 1000m 150 Om FAROE Is. 1000m 1000 m 500m 35 ^5 35-40 Figure 3:10. Second Survey: temperature and salinity at 300 metres. 4* 52 •iOÔr-n ’500m •34-90 %. OOm 4 OOr 500m 1000m 1500m «■ 500m 400 m 35-30 1500m FAROE Is. 1000m 5oôm 1000m 400m- 50 Om ^ Figure 3:11. Second Survey: temperature and salinity at 400 metres. 53 15° 14° 12° 11° 65° 65° 34-90 35-25 - 500 m •35-15 ■35-30- . 34-95 35-10 35-00 500m —- 1000 m 35-30 35-30' 63° -163° 35-05 ■34-95 . ' . 500m 35-10. S-35-00 ”35-10 1500m ;35-20 62° 35-25- 62° FAROE Is. 1000m 35-30 ■35-20. - i 35-20 : 500m 35-30 61° 35-30 500m' 500 m 14° 13° 12° 11° 10 ° Figure 3:12. Second Survey: temperature and salinity at 500 metres. 54 1500 m 1500m 1000m' FAROE is. 1000m 500 m" Figure'3:13. Second Survey: temperature on the bottom. 500m 1500m FAROE Is. 3500 34-95-3500 1000m' Figure 3:14. Second Survey: salinity on the bottom. 56 500m. 1500m •35-35 FAROE Is. (35-30 35-35 iooom Figure 3:15. Third Survey: surface/temperature and salinity. 57 34-85-'' / <î'-'3 4 -9 0 34-90 500m 35 25 35-30 S FAROE Is. Figure 3:16. Third Survey: temperature and salinity at 100 metres. 58 34-90 34-90 500m 1000m 1500m 1000m. 1500m FAROE Is. 1000m / 1000m 500 m' 500 nv 500m Figure 3:17. Third Survey: temperature and salinity at 300 metres. 59 34-90 ;o ; o o n '- ' o 34-90 / -— -Jt-oc 34-95 400 35*00 500m-" lOOOrr .. 3f m 1500m . 500m 400m 35-20 1500m /•00m 35-30 FAROE I s ' 400m 35-35 100')rr> >35-30 lOOOm 500 m 500m Ä , 3 i4 û J6o ° 14° 13° 12° 11° 10° 9° Figure 3:18. Third Survey: temperature and salinity at 400 metres. 60 34-90 500 m 1000 m 34-90 1500m 35-00 1500m FAROE Is. 1000 m 500m 1000m 35-25^ -~rr500m Figure 3:19. Third Survey: temperature and salinity at 500 metres. 61 FAROE Is. Figure 3:20. Third Survey: temperature on the bottom. 62 34-90' 500m ,1500m 1500 m 1000m FAROE Is. 34-95-35-00 500m Figure 3:21. Third Survey: salinity on the bottom. 63 Similarly, in the Faroe Bank Channel region the appeared in the third week on the southwestmost 35-00 °/oo isohaline and, within it, that of 34-95 °/00, projection of the Ridge where waters of 2° to 4°C correspond remarkably closely to the 2°G and 1°C occurred before. Taking as a rough guide what may bottom isotherms, thus signifying the more undiluted be looked upon as the “Polar Front” isotherm of 2°C, bottom water cold effluent from this deep Channel. the general effect on the third survey as compared There is on the whole remarkably little difference with the previous two weeks is of a further retraction between the main features of the bottom thermal north to northeastward of the cold bottom water distribution of the second survey (Figure 3:13) and overspill of the Ridge. Practically no water of under those of the first. Deep cold water of less than 2°C 2 G was found on the south or southwest slope of the still completely overtopped the Ridge along a sub Ridge during the third survey which distinguishes it stantial part of its southern boundary during the second more or less markedly from those of the previous two week of the exercise. The warm oceanic vortex at the weeks. northern end of the Ridge persisted as well as two The Faroe Bank Channel cold water effluent of the more southwestward of it, one of them on the Ridge third survey shows a further recession southward along proper and the other in deep water of from 600 to the Channel of the limit of the 0°C isotherm and a 1,000 metres. A cold water complex on a narrower small recession of the 2°C isotherm, although the part of the Ridge southward would appear to have separated body of cold water from this effluent which intensified, while the warm water circulation on the was noted on the second survey as occupying the same part of the Ridge during the first survey, besides adjacent slopes in from 900 to 1,200 metres’ depth being displaced eastward on the second exercise, was approximately, registered on the third survey two almost subdivided into two parts. cores of under 1°C temperature. In the region of the Faroe Bank Channel the While bottom salinity on the third survey (Figure bottom thermal situation was changed on the second 3:21), depicts a southwards advance of the 34-95 °/00 survey only to the extent of a small withdrawal into isohaline on the southern part of the Ridge to the the Channel of the zero isotherm and, probably arising limit of its southern shoulder at 500-metres depth, from a similar tendency, the separation from the main this same isohaline on the northern broader part of effluent of a part of the bottom water mass registering the Ridge was obviously pushed back as it were less than 2°C, the main effluent receding somewhat during the third week of the survey by the advancing into the narrow Channel. oceanic water-mass which achieved a closed circulation Except that there does not appear on Figure 3:14a of greater than 35-20 °/oo central salinity within the separation of correspondingly low saline water from western 500-metres bathymetric. Except for the above- the Faroe Bank Channel effluent, this, on the second mentioned southwards urge of the colder less saline survey is considerably less extensive than it was one northern water on the southern part of the Ridge the week previously. On the Ridge itself there is an 35-00 °/00 isohaline had moved substantially farther appreciable north to northeastward recession of the northeastward across the Ridge summit by the time 34-95 °/00 isohaline between the first and second of the third survey. Likewise, although the relative surveys, with the remaining saline features of Figure 3:7 position of the 34-95 °/00 and 35-00 °/00 isohalines as more or less repeated, with due regard for change of po between the second and third surveys would appear sition, on Figure 3:14, these changes suggesting a small from Figures 3:14 and 3:21 to have been very similar, recession of the cold northern influence before the ad the surrounding conditions, northward and southward vance of oceanic waters over the summit of the Ridge. of the Channel, suggest intensification of the oceanic On the whole, the zero isotherm would appear in influence in the last part of the exercise. the third week of the expedition to have made some On the whole, therefore, these considerations of advance over the northern shoulder of the Ridge horizontal temperature and salinity distributions at (Figure 3:20), particularly in the north where the the various levels from surface to bottom during the oceanic circulation of the first two weeks is practically three weeks from the end of May until 18. June, I960, erased. South of the Rose Garden area, however, the bear the interpretation, despite obviously intensive cold water bottom of the two previous weeks was mixing of the opposing water-masses in the levels replaced by a distinctly warm water circulation, and immediately above the broad Ridge summit, of a another such circulation, even more distinctively receding cold deep-water overspill of the Iceland- oceanic, with a central temperature of over 7°C Faroe Ridge during this period.