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ICES 1990 C.M. 1990/C:34Hydrogr.Committee

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OBSERVATION OF THE AZORES FRONT IN JULY 1987 AND JUNE 1989

byC.M~Afonso Dias, Maria Helena Cavaco and Joaquim L.Pissarra

Instituto Nacional de lnvestigayao das PescasAv. Brasilia, 1400 Lisboa, Portugal

Abstract I - Oceanographic observat iens carried out duri ns exp1oratory fishing surveys of R. V. Noruegain July 1987 and June 1989 between the portuguese continental coast and.the Irving and Atlantis Sear.ounts,are described. The Azores Front, whieh was traversed several times, was identified by the analysis cf theter.perature structures (close sP3ced M3Ts) and the properties of the water masses o~served in 18 hydrographiestations. An attell'lpt is Illade to describe the Front path. It is suggested that the Front, passing on the nQrthof Madeira IsJands, extended eastward to the entrance of the Gulf of Cadiz.

INTRODUCTION

In some early studies on the North Atlantic Ocean circulation (e.g., Jacobsen,1929; Wust, 1935; Stommel et al., '1978) there are indications of a strongeastward current flowing south of the Azores Islands. At present time, theexistence of such a current - the Azores Current - as a permanent feature ofthe general circulation of the North Atlantic Ocean it is well established(Olbers etaI., 1985; Sy, 1988).

Originated in the transition region between the Gulf Stream and the NorthAtlantic Current, near the southeastern Newfoundland Rise (Krauss and Meincke,1982; Gould, 1985; Klein and Seidler, 1989), the Azores Current crosses theMid-Atlantic Ridge near 330N (Sy, 1988) and flows through the Canary Basin asa jetlike, meandering zonal current, being the northern boundary of the NorthAtlantic subtropical gyre (Kase and Siedler, 1982; Gould, 1985; Kase et al.,1985; Siedler etai., 1985; Sy, 1988). Associated with the Azores Current thereis a thermohaline front, the Azores Front, with strong horizontal temperatureand salinity gradients that are not density compensating, resulting in strong. '

geostrophic shears (Gould, 1985; Siedler et al., 1985).

Two distinct bodies of water converge in the Azores Front: water advectedfrom the southern flank of the North Atlantic Current in the northern side,and water fram the inner region of the subtropical gyre with higher salinityand temperature values and less oxygenated than the fonmer in the southern

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side (Gould, 1985; Pollard and Pu, 1985). In this narrow (20 to·50 km wide)frontal zone, temperature and salinity steps of order 2°C and 0.3 p.s.u. canbe observed between 100 and 400 meters depth, a llowing the use of simpleoCE7anographic means (expendable or mechanical bathythermographs) in the searchand observation of the Azores Front. A characteristicfeature often foundabove 200 meters depth in the southern side of the front is athermostad anda correspondent halostad in the 16°-19°C and 36.3-36.7 p.s.U rangesrespectively (Kase et al., 1985,1986). This is believed to be the remainder ofl~cal wintertime convection in the northern Canary Sasin similar to the 18°Water of the Sargasso Sea (Gould, 1985; Kase et al., 1985; Siedler et al.,1987) •

According to Stramma (1984) and to Klein and Siedler (1989) the subtropicalgyre recirculation in the Canary Basin has three major southward bands: justeast of the Mid-Atlantic Ridge, in the central basin, and naar the coast ofwestern Africa. The bifurcation of the Azores Current into the two easternmostbands, separated by Madeira Islands, was previously noted by Siedler et al. ~

(1985). In this region, the flow field is weak below 800-m depth (Stranvna,1984). According to Stramma (1984) and to Stramma and Muller (1989) the AzoresCurrent has a transport of about 106m3s- t to the east between the surface and800-m·. depth (upper main thermocline) with velocities exceeding 10 cm s-1.Nearly half of the transport of the 0-800 m layer is carried in the upper 200m (Stranvna, 1984).

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Independent evidences of .seasonal variations in the northern part of the gyre,namely the southward shift of the Azores Current and the related subtropicalfront (Azores Front) in summer, were found by some authors (Siedler et al.,1985; Stramma and Isemer, 1988; Stramma and Siedler, 1988). Investigating themeridional temperature fluxes in the eastern North Atlantic Stranvna and Isemer(1988) noticed a southwarddisplacement of the Azores Current in summer withthe entire Azores Current located south of 350N. They also found that, framApril to September, thesouthward transport near the African coast is largerthan that fram October to March, when the subtropical gyre is stronger westofthe Canary Islands~ Stramma and Siedler (1988), in their investigation ofthe seasonal changes in the North Atlantic subtropical gyre west of 35~,

found.the same southward shift of the Azores Current in summer and a largerwest-east and.smaller north-south extension of the gyre in su~mer comparedwith winter season. In their study of the seasonal changes in the AzoresCurrent geostrophic flow, Klein and Siedler (1989) found that the currentnarrowsin summer'and moves further south with a strengthening of lateraltemperature and sal~nity gradients .in. the 'associated frontal zone.

In July 1987 and Juno 1989 R.V.Noruega from the portuguese Instituto Nacionalda Investigayao d~s· Pcscas (I.N •.l.P.), undertook two 'expl~ratory fishing

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surveys in the oceanic area fram the portuguese cont inenta1 eoast to theAzores Islands, between 320N and 37~ (F1g. 1). For fishing operationsguidanee, elose spaeed mechanie bathythenmographie (MBT) stations were madealong the main sai led transects in both surveys.' The observed temperaturestructures revealed that the Azores Front was erossed several times. Theresults of the HBT transeets complemented with those obtained with oeeas10nalNansen casts are reported and discussed in this paper. Our purpose is toeontribute to the description of the Front path in the surveyed area inpartieular in the region east of Madeira (17oW).

Fig. t. Kap of the study area. The loeation of main seamounts is shovn. Tha 2000r.eter isobath is represented.

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• OBSERVATIONS ANO OATA

Our data were taken in the periods 2-24 July 1987 (early summer) and 4-11June 1989 (late spring) during two cruises onboard R/V Noruega. :n this paperthe 1987 and 1989 eruises will be identified as AZOR-87 and AZOR-89,respectively. Ouring AZOR-87 106 MBT lowerings (0-275 m) and 6 hydrographiestations (12 Nansen bottles fram the surface·to 300 mdepth) ware made; during

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AZOR-89 46 MBT 10werings and 12 hydrographie stations (14 Nansen bott1es framthe surfaee to 600 m depth) were earried out. In both eruises the spaeing ofthe MBT stations was from 20 to 30 nautiea1 mi1es. The 10eations of the MBTand hydrographie stations occupied during both cruises are shown in Fig. 2aand 2b.

During AZOR-87 the MBT 10werings were d1stributed a10ng five transeets (seeFig. 2a). The first transeet (4-10 Ju1y) followed southwestwards fram Lisbon(38.SoN and 9.51\0 till 32'N and 18tW (BT 1 to BT 26) passing very near theGorringe, Ampere and Seine Seamounts and the Madei ra Is1and. The seeondtranseet (10-13 July) proeeeded northwestwards up to 370Nand 25.3Ow nearby theSanta Maria Island, Azores (BT 26 to BT 44). From a position 24 miles west ofthe last one, the third transeet (16-18 July) proeeeded up to the Irving(Cruiser) Seamount at 320N and 280w (BT 45 to BT 58). The fourth transect (18­20 July) joined the Irving to the Atlantis Seamount (34.1oNand 30.2Ow) passingthrough the Plato Seamount (BT 59 to BT 68). The fifth and last transeet (20-24 Ju1y), about 965 mi1es 10ng, headed to Lisbon from the Atlantis Seamount ~

till 380N and 10.9Ow passing over the Josephine Seamount at 36.7'N and 14.2!W(BT 69 to BT 106).

The MBT 10werings during AZOR-89 were distributed a10ng four transects (seeFig. 2b). The first one (4-6 June) started at 370N and 24.5Ow, about 40"mileseast of Santa Maria Island, and proceeded southeastwards up to 320N and 180w(BT ,1 to BT 18). From this last position the seeond transeet (6-7 June) •fo11owed up to 37cN and 160w passing nearby the Dragon Seamount at 3S'N (BT 18to BT 29). The third transeet went southeastwards from the last position till34.4oNand 12.6Ow passing 15 miles west the Ampere Seamount at 3S!N. Proeeedingalmost eastwards the fourth and last transect reached the entranee of Golf ofCadiz at 3S.30N and 9.7Ow passing S mi1es south of Cora1 Pateh Seamount near35cN.

The loeation of the hydrographie stations oecup1ed during AZOR-87 (H1 to H6)and AZOR-89 (H1 ta H12) are indicated in Figs. 2a and 2b, respective1y.

Sea surfaee temperature (SST) information relative ta the surveyed area wereregularly reeeived (radio-fax) onboard during both eruises. During AZOR-87daily SST isotherm charts were received fram the Spanish Meteoro10gica1Service (Madrid) and during AZOR-89 10-day mean SST reports fram the WestGermany Heteoro1agica1 Office (Hamburg).

Tho basic hydrographie data uti1ized in this report are on file at theI.N.I.P. Department af Oceanagraphy and ean be obtained on request.

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HETHOOS

Temperature at the hydrographie stations was obtained using a pair of,proteeted deep-sea reversing thermometers and the sampling depths wereeontrolled with unproteeted thermometers. 5amples were drawn to determineonbosrd the ~alinitY and the dissolved oxygen at the sampled depths. Aninductivity eoupled salinometer was used for the determination of tho seawatar eonduetivity. Formula~ by Fofonoff and Millard (1984) were used for thesallnity e~leulation. Oissolved oxygen was determined by Winkler titration.During the MBT stations a Nansen bottle was used to determine the temperatureand salinity at the sea surfaee andto calibrate the MBT traees. The seasurfaee temperature measured at engine room intake (3 meters depth) was

. . .eontjnuously recorded utilizing an electrical mereury-ln-steel thermograph•

. Hydrographie station data proeessing, ineluding the dynamie caleulations, was. .

performed using a computer program that follows the standard procedures and~ formulas adopted by the U.5. National Oceanographic Oata Center.

RE5ULT5 AND DI5CU55ION

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General hydrocljmatic condjtions during the surveys

Charts representing average sea surface temperature (55T) distributions duringAZOR-87 and AZOR-89 cruises are shown, respectively, in Figs. 3a and 3b •5hipboard wind velocity and direction observations from both cruises aresummarized in Table 1.

The 55T and wind conditions prevailing during both cruises were in generalagreement with the expected ones (means and extremes) for the respectiveobservation periods (U.5. Naval Oceanographic Office, 1967; Gorshkov, 1978;Isemer and Hasse, 1987).

The AZOR~87 survey was carried out from 4 to 24 July (early summer). In thefirst part of AZOR-87, from 4 to 14 July (1st and 2nd transects), the windswere prodominantly from the north and northwest, whereas in the second part,from 15 to 24 July (last three transects), they were fram the northeast andnorth with large periods of calm. In the whole surveyed area the 55T was 1°to 2°C higher than normal, particularly in the Azores region where 55T valuessurpassod 25°C (see Fig.4). Prevailing weak winds and the oceurrence ofrelatively long periods of calm and cloudless sky were certalnly favorableeonditions for a local warming of the sea surface. Otherwis~, the higher thannormal 55T values observed during July 1987 in the whole studied area southof 400N could be related 'with the 'wa'rm trend of 55T in tho region between

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Lisbon and Madeira during the period 1981-1985 described by Dias eta~ (1989).The SST and wind conditions observed during AZOR-89, from 04 to 14 June, werein agreement with the normal ones for that period (late spring). In thecovered area the SST varied between 19° and 21°C (see Fig.5) and the winds were'blo~ing from the northeast and east with a mean velocity of 14.5 knots.

Temperature structures

The main features of the temperature structure in the upper layers of thesurveyed area during both cruises are revealed by the observed MBT transects.Sea-surface temperature and salinity measured at MBT stations during AZOR-87and AZOR-89 are shoWD in Figs. 4 and 5, respectively. The temperature (MBT)vertical distribution along the transects occupied during AZOR-87 and AZOR­89 are depicted in Figs. 6 and 7, respectively.

July 1987 (AZOR-87)

During AZOR-87 the mlxed surface depth (MLD) ranged from 50 to 15 mwhile thetemperat'ure varied from 19° to 25cC (see Fig. 4). In accordance to thepreviously suggested 10cal warming during the second part of the cruise thelowest MLD (less than 25 m) were coincident with the highest SST values (morethan 22cC) as well as with a strengthening of the seasonal thermocline.

Along the whole transects the course of the isotherms depicted in the verticalsections (Fig. 6) show some important depth variations superposed to a generalshort amplitude (around 20 m) modulation that can be ascribed to internalwaves. Those depth variations are generally related to significant sub-surfacetemperature .structure. changes. In. fact, two distinct type of temperaturestructure can be recognized in the covered area, very si mi lar to thosedescribed byGould et al. (1985) and by Käse et a/. (1985,1986) for the samearea.

The first temperature structure, found south of 340-33~ (from MBT stations16 to 39 andfrom MBT stations 52 to 68), was characterized by a well markedthermostad below the seasonal thermocline. The 16°C isotherm, at nearly thebase of the.thermostad, was 200-250 m deep, whereas the 19°C isotherm, at thetop· of the thermostad, . was at a depth of 50 m. The highest sea surfacesalinity values (36.5 to 36.8 psu) were observed in the region where thisstructure was recognized. However, a strong salinity negativeanomaly (of theorder of 0.5 psu) was observed around the Madeira island (MBT stations 22,23and 24; see ~ig~ 4).'An expran~tion for this feature could no~ be found withthe ava; lable data .. The second t~~perature·:.structure was. found north of 35°­360NJfr~m MBT 'stations: 2 tO\:7 ,..39to 49',. 38to '86 ·and. 93to 106). In this

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structure, characterized by a regular temperature gradient from the base ofthe seasonal thermocline to more than 300 mdepth, the 16°C isotherm was foundat a depth of around 100 m.

The transition between those distinct "southern" and "northern",temperaturestructures occurred across a relatively narrow zone. The frontal character

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of this transition zone was particu1ar1y evident between MBT stations 37 and3~ and also between MBT stations 49 and 51. Definite signals of the frontalzone crossings were not found in the SST continuous records. Otherwise, thesea-surface sa1inity measurements at MBT stations revealed strong surfacesa1inity gradients associated with the sub-surface temperature front.'

Along the' last transect, between the Atlantis seamount (MBTstation 69) andthe portuguese coasta1 waters (MBT station 106), two striking "northern"structure disturbances were observed. Around MBT stations 80 and 89 the sub-

'thermoc1ine isotherms (13°-19°C) formed de'ep inverted domes with maximumvertical displacement of the order of 100 m. Rejecting the hypothesis ofanticyc10nic eddy formation on the poleward flank of the front (Kiel~ann andKäse, 1987) the described features must be interpreted as intersections offront meanders.

Other significant features revea1ed by the MBT sections deserve to be noted.At the beginning of the survey, between MBT stations 1 and 3, the signal ofactive' coastal upwel1ing off Portugal is well-marked by the steep isothermssloping upwards towards the ~oast. The 14°C isotherm, near the surface atstat ion 1 (100 m bottom depth), upwelled from a depth of about 200 m atstation, 3.' The thermoc1 ine degradation that can be seen at station 1 isanother evidence of active coastal upwe1ling. Next to the upwelling zone thesub-surface isotherms disposition" sloping downwards towards the, coast,suggest a sha1low current flowing po1eward~ between the Gorringe seamount andthe portuguese coast. On the other side, the sea-surface temperature andsalinity va1ues registered at MBT station 5 (see Fig. 4), 1.50C and 0.4 psuhigher than those observed at adjacent stations, suggest a northward intrusionof southern surface waters. Finally, over the Josepnhine seamount (MBT station

, 100) a doming of the sub-thermocl ine isotherms was observed. ,This feature,that seems topographica11y induced, was a1ready noted by Käse eta~ (1985).

June 1989 (AZOR-89)

During, AZOR-89 the SST ranged from 19° to 21°C and the MLD varied between a, ' .

minimum of 10. m at ,the Madeira is1and region and a maximum of 40 m front.ofthe Cadiz Gu1f (see Figs. 5'and 7).The temperature structures revea1ed by the 'MBT sections (Fig. 7) were very

'sirrii.lar:to those found dur.in'g the July 1987 survey. The characterist1c'

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"southern" strueture thermostad was we11 defined between MBT stations 12 and22 (17° and 19°C isotherms) and bet\.een MBT stations 36 and 38 (16° and 181bisotherms). The sub-surfaee isotherrns disposition a10ng the vertieal seetionsshows,that the transition frontal zone between the "southern" and "northern"structure areas was interseeted severa1 times. In' partieular, the strenginelination of the isotherrns between MBT stations 8 and 10 and also betweenstat'ions,27 and 29 shows that there the front was erossed by the transeets atnearly right ang1es. In the thermostad near the frontal zone severa1temperature inversions were observed (see' 17° and 17. SOC isotherrns in Fig. 7) ~

As in tli~ July 1.987 survey, sea-surface ther:-mographie 'reeords did not showany signifieant signal of the front erossing. On the other hand, re1ative1ystrong sea-surfa~e salinity gradi~nts assotiated 'with the sub-surfaeetemperature front were onee niore observed.,'·

Water masses ..

In order to investigate· the eharacteristies of the water masses present inthe upper 1ayers of the.survey area, partieularly at the frontal zone, severalhydrographie stations (for temperature, salinity and oxygen) were earried outduring AZOR-87 and AZOR-89. Due to the short time available in both eruisesfor 'hydrographie work, the ~umber of oeeu~ied stations was seriouslyrestrieted, prineipally during the July 1987 survey.' Nevertheless, some ..preliminary results, based espeeially on the AZOR-89 data, are present~d here.

In Jtily 1987 (AZOR-87) the first four hydrographie stations, H1 to H4 (seeFig. 2a), were oeeupied along the transeet between the southwest of theMadeira island to nearby the Porto Santo island (Azores). The eorrespondingvertieal distributionsof temperature,salinity, oxygen '~nd density (at) arerepresented in Fig. 8. In spite of the 1arge station spaeing the main featuresrevealed in.thesame transeet by the MBT seetion are gene~ally well reprodueed ~in the temperature distribution (Fig. 8a). The salinity seetion (Fig. 8b)shows an halostad that eorresponds, in depth and position, to the thermostad.The thernioha1ine eharaeter of the frontal zone ean be verified eomparing thedistributions'of temperature and salinity. The density seetion (Fig. Be) shows'that the strong horizontal thermohaline gradients are not densityeompensating. Therefore, the front is also a density front with eorrespondingbaroelinie eurren~s (Siedler eta~, 19~5). Theoxygen seetion (Fig. 8d) showsa maximum 'at ,approximately' the bottom of the thermoeline and an apparenthigher level of oxygenation of the water north of the front.T~e d'istributions of 'temp~rature, s~linity, oxygen and density (at) from thehydrographie seeticin defined by AZOR-89 stations' H4 to H7 (June 1989)' are

,shown in Fig. 9~ ,nie' exami nat ion of those distr.i but ions confi rms the results

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described behind. The thermostad and the corresponding halostad are clearlydepicted between stations H4 and H5. The temperature inversions revealed bythe MBT sections (Fig. 7) are also well reproduced in the temperature section(F.ig. 9a). 1he salinity section, represented in. Fig. 9b, shows salinityinversions very well correlated with the temperature inversions (see 17° and17.50C isotherms and 36.4 and 36.5 psu isohalines). The density distribution

.; . .(Fig. 9c)· shows that the thermohaline gradients caused by the inversions are~ehsity compensating. The characteristics of the oxygen distributionrepresented in Fig. 9d are quite similar to those of the July 1987 (AZOR-S7). .oxygen section.

Tempe'rature-sal inity (T-5) and temperature-dissolved oxygen (T-02)

'relationships were analyzed for each one of the surveys. The T-5 scatter plotsrelative to AZOR-87 and AZOR-89 cruises (not shown) revealed that most of thethermohaline variabl1ity corresponded, in both cases, to density (at) valueslower .than26.8 kg m-3 whereas, for larger density values, a T-5 almost linearc~rrel~tion was noted. However, a close inspection of the individual T-5 plotsrevealed that··this correlation could pr06eed along two distinct lines up to

.Ot "alues less than 26.8 kg m-3• It was moreover found that these 'two linescould represent the Western North At1antic Central Water (WNACW) as definedby Emery and Meincke (1986) and the Eastern North Atlantic (Central) Water(ENAW) described by Fiuza and Halpern (1982). The WNACW, with a temperaturerange fram 7.0-20.00C and·salinities from 35.0-36.7 psu, corresponds to theNorth Atlantic Central Water identified by 5verdrup et aJ. (1942) and is formed

. by winter.convection in the western North Atlantic. According to Fiuza (1982)the ENAW is apparently formed by mixing of 5ubtropical Water (21.50C;37.3

,psu) " formed near the surface in the southern part of central North Atlantic,and remnants of Antartic Intermediate Water (2.20C;33.8 psu). It was also.found that the stations situated southward of the frontal zone have T-5 plotsthat followed the ENAW definition line while the stations situated northwardhave T-5 plots following the WNACW line •

In order to illustrate·these results Figs. 10a to 10d show the T-5 curvesfram the.hydrographic stations occupied in June 1989 (AZOR-89) cruise, groupedin sets corresponding to aach one of the four main transects. In the sameFigures the WNACW and ENAW definition lines are also shown. In the transectswhere thefrontal zone was more sharply crossed (Figs.' 10a, lOb and 10c) itcanbeseen that at the southernmost stations - H4 and H9 - the upper centralwater (18°-13°C) was clearly cf the ENAW class. On the contrary, the curvescorrespondlng to stations Hl, H2.and H7 show that northwards of the frontalzone the upper central water have WNACW characteristics~ The transitionbetween ·those distinct .central .waters is well documented by the T-5 'curvescor~esponding to stations H3,. H5.and H8~ 'especially in the firsttwo where thethermohal ine inversions were· observed.Reexamining the vertical sections

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represented in Figs. 7 and 9, it ean be seen that those inversions are asignal of ENAW intrusions a10ng isopyena1s aeross the frontal zone into WNACW.Fasham et alo (1985) have deseribed quite similar intrusions revea1ed by"Seasor" sections aeross the front southwest of the Azores.

T-S.plots for the,hydrographic stations occupied during the Ju1y 1987 (AZOR­87) eruise are also shown in Figs. 12a and,12b. Stations H1 to H4 (Fig. 12a)correspond to the Madeira-Azores transect wnere the front was sharply erossed(see Figs. 5 and 8). 'Though not so c1e~rly as in the 1989 observations, thereare someevidence of ENAW at station H1, situated in the southern side of thefront. However, at station H5 and HG, also in the southern side of the front,the upper eentral'water showed WNACW characteristics. These two stations wereoceupied in·the western limit of the surveyed area(between 27° and 30OW) nearthe eastern slope of the Mid At1antic Ridge. So, it is suggested that thepresence of ENAW in the southern side of the frontal zone is a feature limitedto the eastern part of the area under consideration.

Seme additional insight about the water masses concurring into the frontalzone ean be aequired through the analysis of the oxygen data. Temperature­disso1ved oxygen (T-02) re1ationships from the AZOR-89 and AZOR-87hydrographie stations are shown in Figs. 11 and 13, respeetively. In orderto allow a better eomparison, the T-02 diagrams was grouped in the samestation sets as for the T-S plots previous1y discussed. The examination ofFigs. 11 and 13 revea1s three suecessive 1ayers, from the surface to themaximum samp1ing depth, withdifferent T-02 variabi1ity. The first 1ayer, fromthe surfaee to the 02 near-surface maximum, has a 10w variability around a T­02 1ine that corresponds to the 02 saturation values. It is noted that the1arger T-5 vari abil i ty eaused by the seasona1 thermoc1i ne and the strongsurface sa1inity gradients occurred in this same 1ayer. Beneath this first1ayer we can identify a second one where most of the T-02 variability isconeentrated .. The lower limit of th1s layer 1s almost coincident with theintersection point of the WNACW and ENAW lines (~ 130C;35.8 psu). In the thirdlayer, that was reaehed on1y in the 1989 observations (maximum samp1ing depthof 600 m against 300 m in 1987 observations), the T-02 curves showed anapparent tendeney to eonverge in the direction.of the deep 02 minimum. Thedifferent oxygenation 1eve10f the upper central waters - WNACW and ENAW - inthe intermediate layer .is elearly shown in Figs. 11 and 13. The tcmperatureof the near-surface 02 maxima observed at the stations where the ENAW waspresen~ were 1~to 2°C warmer that at the stations where WNACW was insteadpresent •. Noting that the near-:surface 02 maxima are caused by the seasona1heating through the surfaee, we ean assume that the observed'02 maxima areremnants of the, renewed water. from .the previous winter. Therefore, theobserved O,maxima temp'3rat~re. would be ~pproximatel'y the wintertime sea-

.surfaee temperature .in tne respective souree region. Aceording to winte'rtime

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55T maps (e.g. Gorshkov, 1978) it is suggested that the ENAW present in thefrontal zone must be advected northwards from a source region south of 320N.

The Front path in July 1987 and June 1989

As previously referred, the spatial continuity of the Azores Current as ameandering, jet-like current, assoeiated to astrang sub-surfaee thermohalinefront, is now well doeumented. In this eontext, infrared satellite imagery hasbeen successfully used. A partieularly interesting example can be seen inKielman and Käse (1987;Fig. 1a). In fact, the strang meandering of the frontalzone extending in a zonal strip (330-37~) from 2So to 8.SOw in the Gulf ofCadiz is clearly shown in an infrared picture of the ocean 5ST fromapproximately 31° to 39~,6° to 26!W taken from NOAA-7 satel1ite on Mareh 1984.

Assuming the permanent spatial eontinuity of the Azores Current and thereforeof the Azores Front, a description of the Front path during the periods of ourobservations will be derived from the results we have previously presented.Following Gould (1981) we ehoose the depth of the 16°C isotherm (given by theMBT lowerings) as an indieator of the position of the frontal zone. Theresultant maps of the 16°C isotherm topography for July 1987 CAlOR-87) andJune 1989 (AZOR-89) are reproduced in Figs. 14a and 14b, respectively. Inorder to minimize the variability indueed by the internal waves the data(digitized MBT readings) was previously filtered (moving average of 3).Aceording to the adopted eriterion the 150 m contour can represent the Frontaxis path. This interpretation is supported by the results of the analysis ofthe AlOR-87 and AZOR-89 hydrographie data. In particular, it is noted that theFront, passing on the north of the Madeira Islands extends eastwards to theentrance of the Gulf of Cadiz.

In order to verify the baroclinie character of the Front we calculated thesurface dynamie topography relative to 600 dbar from the June 1989observations. The result, shown in Fig. 15, reveals a relatively strangeastward current following a path that is in general agreement with theprevious results. The ealeulated geostrophic veloeity between the stationsH6 and H7 was 6.7 cm s-1 to the east.

5ynthesizing all the results the suggested path of the Front in July 1987(AlOR-87) and June 1989 (AlOR-89) are represented in Fig. 18.

The lang-term persistenee of the Front was demonstrated by Käse and Siedler(1982) eomparing the density (at) at 250 m a10n9 almost eoineident transeetsfrom three different cruises, carried out in January 1981, April 1981 'andApril 1982, in an area southeast of the Azores (260-38~;170-26!W). In order

12 .

to verify the same long-term persistenee of the loealization and thermohalinestrueture of the Front we ehoose sev'eral hydrographie seetions that havecrossed the frontal zone in different epoehs and plaees in the area eoveredby our observations. Hydrographie seetions from four different eruises:Crawford, Oetober 1957, Calypso, August 1958, Origny, Oetober 1967 and LeSuroit, August 1983, are shown in Figs. 16 and 17. The souree of data is givenin Table 2 and the position os the respeetive stations are indieated in Fig.18. The struetures revealed by the Crawford hydrographie seetion (Fig. 16a)eompares fairly well with our AZOR-89 seetion represented in Fig. 9. From theT-S plots (not shown) it verified that upper eentral water (140 to 17~) withENAW eharaeteristies was present at stations 267 to 269 in the southern sideof the Front. The Crawford MBT seetion (Fig. 16b) is partieularlyillustrative of the steepness the Front and demonstrates the importanee of ashort station spaeing to deseribe adequately the frontal zone. In the Calypsoseetion (Fig. 17a)·the ENAW was also identified at stations 288 and 289 andthere are evidenee of an intrusion of ENAW aeross the front at the station 290(see inversion of the 36.4 psu isohaline). A similar intruSl~i1 is' also •depieted in the Origny seetion (Fig. 17b). At last, the temperaturedistribution in the Le Suroit seetion (Fig. He) displays a remarkablesimilarity with the AZOR-87 MBT seetion between stations 45 and 58 (Fig. Sb).

In Fig. 18 we also represent the loealization of two XBT transeets, Meteor,July 1981 (Käse et al., 1985; Fig. 3b) and Poseidon, Oetober 1983 (Breitenbachet al., 1985;Fig. 4.1), are also indicated in Fig. 16. In these XBT seetions •(not shown) the eharaeteristie thermostad as well as the temperature struetureof the frontal zone are elearly documented.

CONCLUSIONS

The results we present in this note are in general agreement with the actualknowledge about the Azores Front in the area covered by our observations. They ~also eonfirm the adequaey of the uti1ization of simple oceanographie means tofind and observe the Front. The extension of the Front into the entrance ofthe Gulf of Cadiz, already suggested by infrared satellite imagery, gains somemore evidence from our results, and reinforces the hypothesis that arelationship ean exists between the Azores Current east of Madeira and thecirculation off the portuguese central and southern coasts. In fact, evidencefor a northeastward infleetion of water flowing east past the Azores has beenprovided by several Authors (e.g. Helland-Hansen and Hansen, 1926; Wust, 1935;Dietrich, 1969; Stommel et al., 1978; Pollard and Pu, 1985), and the presenceof ENAW along the portuguese eontinenta1 ma~gin as far north as 400N wasreported by Fiuza (1982).

.... 13

The Azores Current, as a dominant feature of the North At1antie subtropiea19yre eircu1ation in the Canary Basin, as well as the charaeteristies of theassoeiated frontal zone, are undoubted1y decisive eeo10giea1 factors for someoeeanie fishery resources. In the eastern North Paeifie the assoeiationbetween the a1baeore (Thunnus alalunga) and the frontal struetures of theTransition Zone (Roden, 1971, 1972; Laurs and ,Lynn, 1977) whoseeharaeteristies are rather simi1ar to those of the Azores Front.

The importance of the surface and sub-surface fisheries for tuna and tuna­1ike fishes around the At1antie Is1andscof Canary, Madeira and Azores arewe11 known. However, the relationship between the distribution and migratoria1behavior of the referred resourees and the Azores Current and the assoeiatedfrontal structures remains unknown.

•Acknowledgments. We are gratefu1 to the 'master and erew of the R. V. Noruegafor their' assistance during,the hydrographie surveys, as we11 as to varioushelpers during the station work.

REFERENCES

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November 1983. Ber. lnst. f. Meereskunde, 139, 161 pp.Dias, C.M.A., M.D. Vaeas and, A. Amorim, 1989:' Sea surfaee temperature

variation between the Iber.ian ,coast (Lisbon) and the Madei ra, Islands(Funehal) in the period 1981-1986. lCES C.M. 1989/C:33, 8 pp.

Dietrich, G., 1969: Atlas of the Hydrography of the Northern AtlBntic OCean,Conseil International pour l'Exploration de 1a Her. Charlottenlund Slot,Denmark, 140 pp.

,Emery, W.J. and J. Meineke, '1986: Global water masses: summary and review., ,

Oceanologica Acta, 9(4), 383-391.

Fasham~ M.J.R., 1. Platt, B. Irwin and K. Jones, 1985: Faetors affecting thespatial pattern'ofthe deep chlorophyll maximum in the region of theAzores Front. Progress in Oceanography, ,14, 129~155.

,Fiuza, A.F.G., 1982: The Portuguese Coastal Upwelling, System. in ActualProblems of OceanogrBphy in Portugal (proceedings of a seminar held inLisbon on 20-21 November 1980 under the sponsorship of the NATO MarineSciences Panel), Junta Naeional da Investiga~ao Cientifica e Tecnol6­giea, Lisbon, 45-71.

Fiuza, A.F.G. and'O. Halpern, 1982: Hydrographie observations of the CanaryCu'rr~nt between 21 0N and 25. 5~ in Mareh/Apr; 11974. Rapp.P.-v.Reun.

, .'

Cons.int.Explor.Mer, 180, ',58-54.

14

Fofonoff, H.P. and R.C. Millard Jr., 1984: Algorithms for Camputation offundamental properties of seawater. UNESCO Techn. Pap. in MarineScience, 44, 53 pp.

Fuglister, F.C., 1960: Atlantic Ocean Atlas of temperature and salinity pro­files and data fram the International Geophysical Year of 1957-1958.Woods Hole OCeanographic Institution Atlas Series, 1, 209 pp.

Gorshkov, S',G. (Ed.), 1978. World Ocean Atlas. Vol.2: Atlantic & Indian OCean.Pergamon Press, Oxford, 141 plates.

Gould, W.J., 1981. A front southwest of the Azores. ICES, C.M.1981/C:16,6 pp.Gould, W.J., 1985: Physical oceanography of the Azores front. Progress in

Oceanography, Val. 14, Pergamon, 167-190.·Helland-Hansen, B. and F. Hansen, 1926: The Eastern North Atlantic. Geophys.

Norw., 4, 1-74.Instituto Hidrografico, 1974: MILOC -Outubro de 1967 - n° 2. Minist~rio da

Marinha, Lisboa, Portugal.Isemer, H.-J. and L. Hasse, 1987: The Bunker Climate Atlas of the North

Atlantic Ocean. Vo1.2: Air-Sea Interactions. Springer-Verlag, Berlin, •252 pp.

Jacobsen, J.P., 1929: Contribution to the hydrography of the North Atlantic:the "Dana" Expedition 1920-22. Oceanographical Report edited by, theDana-Committee, 1, 3, 98 pp. .

Käse, R.H., J.F. Price, P.L. Richardson and W. Zenk, 1986: A quasi-synopticsurvey of the thermocline circulation and water mass distribution withinthe Canary Basin. Journal of Geophysical Research, 91 (C8), 9739-9748. •

Käse, R.H. and Siedler, 1982: Meandering of the subtropical front south-eastof the Azores. Nature, 300, 245-246.

Käse, R.H., W. Zenk, T.B. Sanford and W. Hiller, 1985: Currents, fronts andeddy fluxes in _the Canary Basin. Progress in Oceanography, Vol. 14,231- 257.

Kielmann, J. and R.H. Käse, 1987: Numerical modeling of meander and eddy, formation in the Azores Current Frontal Zone. Journal of Physical

, . OCeanography,' 17, 529-541.Klein, B. and G. Siedler, 1989: On the origin of the Azores Current. Journal

of Geophysical Research, 94(C5), '6159-6168.,Krauss, W. and J. Meincke, 1982: Drifting buoy trajectories in the North

Atlantic Current. Nature, '296, 737-740.,Lac6mbe, H. et P. Tcherriia, 1960: Resultats d'observations. Ann~e G~ophysique

International 1957-1958. Participation Franya1se: 11 - Liste des •, Stations M.O.P. 'CALYPSO 241 a 297 (Campagne 1958). Cahiers Oceanographiques,

:" 1~(6), 417-439.'Laurs, R.M. and R.J. Lynn, 1977: Seasonal migration of North Pacific Albacore,

Thunnus alalunga, into North American coastal waters: distribution,'relative abundance, and,association with Transition Zone waters. Fishery

Bulletin, 75(4),795-822.

•

15

Olbers, D.J., H. Wenzel and J. Wlllebrand, 1985: The inference of NorthAtlantic circulation patterns from climatological hydrographie data.Reviews of Geophysics, 23, 313-356.

Pollard, R.T. and S. Pu, 1985: Structure and circulation of the upper AtlanticOcean northeast of the Azores. Progress in OCeanography, 14, 443-462.

Roden, G.I., 1971: Aspects of the Transition Zone in the Northeastern Pacif1c.Journal of Geophysical Research, 76( 15), 3462-3475.

Roden, G.I., 1972: Temperature and Salinity Fronts at the Boundaries of theSubarctic-Subtropical Transition Zone in the Western Pacific. Journalof Geophysical Research, 77(36), 7175-7187.

Siedler, G, A. Kuhl and W. Zenk, 1987: The Madeira Mode Water. JournalofPhysical OCeanography, 17, 1561-1570.

Siedler, G., W. Zenk and W.J. Emery, 1985: Strong currents events related toa subtropical front in the Northeast Atlantic. Journal of PhyslcalOCeanography, 15, 885-897.

Stommel, H., P.P. Niiler and D. Anati, 1978: Dynamic topography andrecirculation of the North Atlantic. Journal of Marine Research, 36,449-468.

Stramma, L., 1984. Geostrophic transport in the Warm Water Sphere of theeastern subtropical North Atlant ic. Journal of Marine Research, 42,537-558.

Stramma, L. and H.-J. Isemer, 1988:. Seasonal variability of meridionaltemperature fluxes in the eastern North Atlantic Ocean. Journal of

Marine Research, 46, 281-299.Stramma, L. and T.J. Muller, 1989: Same observations of the Azores Current

and the North Equatorial Current. Journal of Geophysical Research,94(C3), 3181-3186.

Stramma, L. and G. Siedler, 1988: Seasonal Changes in the North Atlantic Sub­tropical Gyre. Journal of Geophysical Research, 93(C7) , 8111-8118.

Sverdrup, H.U., M.W. Johnson and R.H. Fleming, 1942: The OCeans. TheirPhysics, Chemistry, and General Biology. Prentice-Hall, Inc., New York,1060 pp.

Sy, A., 1988: Investigation of large-scale circulation patterns in the centralNorth Atlantic: The North Atlantic Current, the Azores Current, and theMediterranean Water plume in the area of the Mid-Atlantic Ridge.Deep-Sea Research, 35(3), 383-413.

Topogulf Group, 1986: TOPOGULF - A joint programme initiated by IFREHER, Brestand IfM, Kiel - Data Report, Val. 1. Berichte Inst. Meesreskunde, Kiel.

U.S. Naval Oceanographic Office, 1967: OCeanographlc Atlas ofthe North AtlanticOCean. Section 11, Physical Properties. Washington D.C, Publ. No. 700, 308

I

pp.Wust, G., 1935: Schichtung und Zirkulation des Atlantischen Ozeans: Das Boden­

Wasser und die Stratosphäre. WiSSe Ergeb. Dtsch. Atl. Exped. Meteor,

1925-1927, 6, 1-288.

Table 1. Wind observations summary: frequeney (%) by direetionsand mean velocity l knots).

Cruise Period Freguency (%) Mün~ NW !i NE f ~ Calm (N) Yli...

AZOR-87 04-14 July 5 26 52 8 9 (192) 12.9,15-24 July 6 25 36 5 28 (229) 8.1

AZOR-89 04-14 June 7 49 33 9 2 (108) 14.5

~ Table 2. Source of data for the hydrographie sections represented in Figs.16. 17 and 18. (Hydro= Nansen casts; BT= mechanical bathythermograph; CTO=

conductlvity-temperature-pressure multisonde).

Vessel Cruise Date Station Nos. Reference

• Crawford Cruise 16 Oct . 1957 Hydro 264-269 Flugister, 1960BT 313-327

Calypso I.G. Y. 58 Aug. 1958 Hydro 288-293 Lacombe et al. , 1960Origny MILOC Oct. 1967 Hydro 6-10 Inst.Hidrog., 1974Le Suroit TOPOGULF Aug . 1983 CrD 40-50 Topogulf Group, 1986

•

•

•20'25'30'

"

?J eHnc::v 35'

~ Q

~c?

.~ e30'

Hg. 2. ?~sition of tath1ther:nographic and hydrographie stations froll the R. V. Noruegacruises \al AZOa-37 (04-24 July 19871. and (bI AZOR-69 (04-11 June 1989/.

12"16"20"

.." ,

25~

44"1---~-~~=t----::;;oaol---o;;;;::--J---~N 1----

40r----t--:----+---::~--t--~_j~-.....::..:.....I_~r_-f__1~-_I

32'~---+---- t----·~r_---t

•

17

16"

21

16

20"

36~--+---=:::::::::-_==!:::----_+-'-',~'''':_-_t_--_1,''_l' r-,_••~'9--t-~,-jt_-~,,,,,,'. 20 :" r-......., ,.".

- " ,3t===::t----r~::::__r--I-->L.~I~~i/

Fig.3. Average sea surfaee tellperature loCI distribution du ring the periods (al: 08-23 July1987 Ifrol Spanish Meteorologieal Service, Madrid), and (bI: 30 N&y-09 June (frol West

GermanyKeteorologieal Office, Hamburgl.

Fig. 4. AZOR-8? Sea surface telperature (oC) and salinity (psul at HBT stations. (Nu.ber is at top)

i i i i i i i i i i i i i i i i i i I I i i i i , i i i i i i i i i i.llt1AOEIRAI B,stlHE lUMPEREI IB.GORRINGEI

100

m

68 65.. 60 . 55 . . 50 45

100 I /

rl 11 " /

. 'l/IS 17 I~

I X ~ /200 \: 11 \ u 100

.~~r--: ,t< ~/

•

I B.ATLAHTlS I BIRVINGi i

•

m

• i i I. i i i i i i i i 1,1. i I , I i i

IX) 116

i J i i',JOSl PHII«

Ftg. 5. AZOR~87. Temper&ture (oCI section frei HBT st&tions (Nu.her is &t top).

(-CI

5I

11I I I I

15I

18I

22I

29I I

IPSUI

22

20

18

i i

36.6

36.2

20

18

29I

o

33I

I I ,

200

40I ! I

46I I

36.6

IPSUI

36,4

36.2

•Fig. 6. AZOR-89. Sea surface telperature (oC, and salinity lpsu) at MBT stations. (Nu.ber is at topl

•

1 5 11 18 ZZ 27. Z9o ,!" I '~' " " '~2~' '0

.-.~~~~~-_.~~~:/~"'---:::.-..ly\\~ ~/\.- f\ I ~'~~';"/'-"\\..//,!~.~_\. ~ VA~/(-~'-r .

100 17. ", 'I .' . "" 100I • • '. l'5 • I , •••••

~" I " I. 'I "./A ~....: \ \. j \ . ••••..:'i _~., : '..' ~ ...-

'-...1~·15 --\/ ,~\j" 15

~ ~ ~ m.... ,', i

/ r13,:\ 1\ J: \ ,. /'3(, I r,.. ,i I i i i

200

100

200

Z9 33 ~6o ..L'---I_l.-'--1...'-"I.-.L-...I-,rL--±::-L-:7-''--t--l...-'-r.L-..JL....I.I 0m

• Fig, 1. AZOR·89. Temperature (aC) section frol KBT stations INulber is at top).

·--15--:

-16

Hl HZ H3 H4o -: I:--C::;;; 13...... :-

• 22~2!20'~18'-21:-20_. 11_.

-19 16_. .

300

100

200

32° 34° 35° 36"

(a) TEMPERATURE (OCI (bI SAllNl1Y (PSUI

100

200

300

-5.5.

",4>',

/, <,I\ ...... _-~,.

32° 33° 34° 35° 36°

J J I

36° 37°N

(cl OENSITY (O'"t) (d) OXYGEN (mi/I)

Fig. 8. AZOR·87. Vertical seetions of laI tellperature (oC), (bI salinitYlpsu), lei density la j, and (d) oIygen(lI/lI between hydrographie stations Hl to H4 (10-13 July 1987). Bottle depth are seen as dots.

300

100

300~14

/13

/

H4 HS H6 H7

.-\\ : l,: ,.:\ (:~

100 )~: . '"

. ~ "___

3&S 364

~3&3

20' ~:~. ---,.1;:.-------/'5.9 '/

35.8

. /, I I I I I

32' ))' 34' 35' 36' 37'HI I I I I I

32' B' 34' 3S' 36' 37'N

(al TEMPERATURE ('C) (bI SAllNlTY (PSUI

H4 HS H6 H7o -'.-_.-:---5.5 < , )----_:----- --.:) ,/ .--;..------ . --- ... -.._-:.__....'.

200

100

5.0

"

1,-.

"300 \

I I I I I I

32' 33' 34' 35' 36' 37'H

, .I I I r I J

32' 33' 34' ' 35' 36' 37'N

H4 HS H6 H7o-·~ .~-

~~o-.~-- -- ~~

'----""-26.S__·~~

-_---:.--./;100

200

300

(cIOENSITY (ITl) (d) OXYGEN (millI

Fig. 9. AZOR-89. Vertieal seetions of (al tellperature(oCI, (bI salinity (psul, (cl density (atl, and ld) oxygen(11/11 between hydrographie stations Hl,to H4 (04-06 June 19891',Only the upper 300. is shown. Bottle depth are

seen as dots.

-----------------------

PSU 35,S 36,0 36,S 31,0 PSU 35,5 36,0 36,5 31,0PC pe22 22

20 20

18 18

16 16

IY IY

12 12

10 - AZOR-99 - 10 - AZOR-89 -

e

PSU 35,5 36,0 36,5 31,0 PSU 35,5 36,0 36,5 3',0pe PC

22 •20

18 18

16 16

IY IY

12 12

ID .. AZOR-99 .. ID .. AZOR-89 ..

Fig. 10. AZOR-89. T-S diagrau frol hydrographie stations BI to HI2. Definition lines lsee text) of Western NorthAtlantic Central Vater (WNACWI and Eastern North Atlantic (Central) Water (ENAVI are represented.

t~

18

16

18

12

Dl mi/I

Dl mi/I

--------1

5

· . .· . . .. .· .. .

...........................................· . .· .

· .... .. : : : ;.. 16.. ..

....... : : : :.... 22

· .· .. .. : : ; : :............ 2[]· .

· ..... : : : : :.. T'C

..................................................................... T8f:

.. .. .

· .· .. .......... : :................. .. : ;.......... 20

.. .· . . .. .. .. : : ; :.... .. :..... .. :.. 22· . .. .

................· .· .

.... : : : ... : :.............. Ilf

.....

. : : : : : :.. 10· : . : ** AZOR-uc) ** :

., ... .................................................................................. .. .

· .· .... .................................................................... 12

.. ........................................................................ 10; . : ** AZOR-B9 ** .

. .· . . . . . .· .

16

18

I~

18

16

I~

T'C

Dl mi/I

Ol mi/I

. ......... :. ...... 22. .

6

6

5

5

, •• : •••••••• : ••••••••••••••••••• :. 0" , •• :.. TeC

......... ,.. ....· .· ...... .

· . . . . .......................................................... 10· . . ** AZOR-B9 ** :

4

· ..... .... . ; : ; ; :.. 22

· .,.

· . . ...........................................................· .

· ... : : : : : :.. 20

· .

· .· .. ...........................................................· . . . . .

- -- -------------------',

.. .... . .· . . . . .· .· .................................... ...... Ii?

Fig. 11. AZOR·89. f·02 diagrals frol hydrographie stations Hl to H12.

· ... . ; : : :... 2(]· .

. ...

................. : : : 10: : : ** AZOR-B9 ** .

.. ......... : : ' : :.. ' 12

. . .............. .. . ' ' ..· .

., ... . .................... .. - .. . . . .

........ .· . . . . .· . .

PSU 3S S 36,0 365 31,0 PSU 35,5 36,0 36,5 31,0pe pe

2Lf 2Lf

22 22

20 20

18 18

16

14

12 - AZOR-87 - - AZOR-87 -

Fig. 12. Azoa-81. T-S diagrams from hydrographie stations BI to B6. Definition lines (see textl of Western NorthAtlantic Central Water (WNACWI and Eastern North Atlantic (Centrall Vater (ENAV) are represented.

12

5 Ol mI/I eTO[

24

22

20

18 eH4

..................!Hf AZOR-87 -

20

2Y

22

IY

15

. ... 18

D! mi/I5

.. 12!Hf AZOR-87 - .

5

Fig. 13. AZOR-81. T-02 diagrams from hydrographie stations BI to H6.

".~o••

H

,.~­. \\..:...-.. ~... . '. . ,',, • 1&0

1~'\ß:,., '0--',' \

,

. ':j"L,oo

Fig. 14. Depth of the 16 oe isotherl frol laI AZOR-87, and (bI AZOR-89.Contour interval 50 I. HBT stations are shovn aB dots.

•

r-~.,.-...:;2r-4·-r..,.-r-r-.,..--r--r-T16_·.,.-.,--r-,---,-r--r-,8_·...;.Wr--T"140·H

•

Pig. 15. AZOR-89. Geopotential anolalJ at the sea surfaee relative to 600 db(d,nalic centileters). Dots represent h1drographic station positions. Arrovs

denote geostrophic current.direction.

rII

I

36D-

100

)0. ll" l~· JI. lot.N M· ZZ< z~· »- let. M, . , , , , , , ,! ,

268 lI7 Z!" 265 26~ Z69 211 M' Z" Z6S Z&ls, , J I

••

zoo"""--'--~--r--,---r-

100

zoo

Fig. Ih. CrawfordCruise 16 (LG.Y.I, Oetober 1961. Vertieal seetions of telperatureloe) and salinity (psu) frol stations 264 to 269. Only the upper 300 I is shown. Station

positions are indieated in Fig. 18, Souree of data is given in Table 2.

".------'5

• i i , I i267

~16

,.., I

4iMS

)IZ

, ". , , zr, ' I ,

&J i i iIM

H',m

! !

> Z)" l.t.N, ,)TI Z15

• I ,

•

100

Fig.16b. CrawfordCruise 16 (LG.Y.), Oetober 1961. Bathytheraographie seetion betveenhydrographie stations 265 and 261. (See Fig. 16a). Br station nUlber is at the top. Source

of data is given in Table 2.

..

•

•

100

100

),2- Ir J.... l~· ),'- Lal N

, • • 10

•

100

zoo

100

•Vig. 17. Vertic&1 !ections of tempera.ture (aCI'ud salinity (psul froll: (al Calypso (LG.Y.I, AugUBt 1958j(bI Orign.v(Hilocl. October 1961; (cl Le Suroit(TOPOGULFI. August 1983. OIl!J the upper 300. is .hoVll.

. .Source.of data are given in fable 2.

•

N...,..

:,..METEOR .-­ I.......,

I/~ .../?,'~.e) V-

I

..

Fig, 18, Approximlte plth cf the Azores Front in JU17 1987 (AZOR-811 and in June 1989 (AZOR-891. The positionof h1d~ographie seetions from Crawford!l9571, Calypso!l9581, Origny!l96'7land Le Suroit(19831 eruises are indieated (see Table 21~ Tbe interrupted lines indielte IßT seetions from ~fet~l"cruise51 (1981) ud Poseidon cruise 104 (19831 referred in the telt, The 2000 • depth eontour is represellted.

•