International Couricil forihe Explo~atioii of the Sea

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ICES CM 1997/R:05 'Theme Session R:

ArcHe Oceanographic Piocesses

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,,On tlie Norlh Atlaiidc ,11 Great S3Iinity ADomäiies';• . ' - !: .

IOcean CÜmate' LaboratoTy" National oceanographic, Datci Center, National: Oce~ni~ andAtmospheric Administration, EIOC5, 1315 Easi-West Highway, Si/ver Spn'ng, MD 20910, USA2Shirshov 1nsiiillte o/Oceanology, Rilssian Academy 0/ Sciences, 23 Krasikova Street, Moscowj 17218, Russia '3State Hydrological Institute, St,Petersburg 199053,'Russia ,4Marille Research Institute, SkzUC!gata 4, P,O, Box'I390, 121 Reykjavik, Iceland

. Abstra~t - We revisited the "Great Salinity Anomaly" of tbe 1970s (GSA'70s;, Dickson etal."1988) and documented the newly identified "Great Salinity Anomaly" of the 1980s, termed

, GSA'80s; both propagated around the. Ncirth Atlaritic in a. similar fashion, The, advective'mechanism, initially proposed to explairi the observed sequence oflow-S/Iqw-T events duiing theGSA'70s, apparently holds also for the GSA'80s, The latter was sriccessively ()bserved in theWest Greenland Current (1982), the Labrador Curient (1983), the Fleinish Pass (1984), near theCharlie-Gibhs Fracture'Zone (1984-85); in the Rockall Charmel (1985), south of Iceland(1985~88), iri tho' North Sea (1986-87); Norwegian Sea (1987-88), Barents Sea (1988-89), and Ieeland ,Sea (1989-90). The GSA'80s advection speed exceects the one of the GSA'70s: The GSA'80sreached the Barents ,Sea 6· to 7 years after peakirig in the West Greeriland Current, while theGSA~70s traveled. the same foute in 8 to 10 years. '" ,

These ariomalies, however, seem to be of different origin. The GSA'70s was' apparentlyboosiect remciiely, by a freshwateilsea ice pulse from the Arctic via Fram Strait. Consequently,the GSA'70s was accompaniect by a large sea iceextent anomaly in the Greeruand arid IeelandSeas; propagated into. the Labrador Sea., .' .'. .. . " .' " \ " ,,' ,

On the conti"ary,'the GSA'80s was likely foriTIed locally,in the Labrädor Seä!Baffin Bay ,largely because of the extremely severe winters of the early 1980s, with a possible coritrlbutioriof the Arciic freshwater outflow via the Canadian Archipelligo (facilitated by strong northerlywinds) ,which wciuld enhance stabilityand ice formation. This anomaly was also assoCiatedwith 'a positive sea ice extent äriomaly in the Labrador SeiiIBaffiri Bay which, however, had noupstreäm precursor in the Greenland Sea, Thus th6 GSAs are not necessarily caused solely, byan increased export of freshwater and sea ice from tlle Are:tic via Frain Strait:' .

. These results are corroborated by the early 1990s data when a new fresh, coid anomaly wasformed in the Labrador Sea accompanied by a large positive sea ice exient arlOrriil1y, The harshwinters of the early 1990s were, however, confiried to the Labrador,·Sea!Baffiri Bay area whilethe atmospheric and oceanic coriditions in thc Greenland, Iceland, and Irmiriger Seas were

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normal. The Labrador SeatBaffin Bay area therefore appears to plliy a key foie in formation ofGSAs as weIl as iri propagation of. theGSAs formed upstream. A likely contribution cf the 'enhanced Canadian Archipelago freshwater outflow to the GSA formation also seems to' besignificant. '

Two major modes of.the GSA origin are thus identified,remote (du'e to an enhanced ~rcticOcean freshwater export' via either Fram Strait or the Canadian Archipelago) arid loeal (due tosevere winters in the Labrador SeatBaffin :Say). :Soth modes should be taken into accoimt, tomodel decadal" variabÜity of the coupled oce'im-ice-atrnosphere system in the NOrthAtlantic/Arctic Basin.

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1. IntroductioriTbe "Great SaIinity'Anomali .of,1968-1982 (GSA'70s hereäfter), a pattern of ininirmi in

saIinity (and temperature) time senes observed successively around the northem North AtIariti6could be accounted for by advection of ä fresh (and cold) anomaly aIorig mairi' oceari currerits(Dickson el al., 1988) (Fig.l; after Ellett and Blindheim (1992, Fig.6». The ariomaly was fIrstobserVed in 1965-1971 northeas~ oflcelancl (Malmberg, 1969, 1973), then in 1969-70 in the.:WestGreenland Current (Buch, 1985; Buch arid Stein, 1987), in 1971-72 necir Labrador (Trites, 1982)and Newfoundland (Keeley, 1982), in1972 atOeean Weather Statiori(OWS) ~_'Bravo" in theLabrador Sea (Lazier, 1980), in 1974-75 at OWS "C" ("Charlie") near the ,Charlie-Gibbs FractureZone (Dickson et aL, 1988), in 1975 in the Rockall ChanneI (EIlet!, i979; Ellettand MacDougall,1983), in 1976 in ihe Faroe-Shetland Channel(Dooley et al., 1984; Martin et al.; 1984) and south 'of Iceland (Malmberg, 1984, 1985), in 1977-78 in the Norwegian Sea (Gamnielsr~d arid Holm,1984), in 1978-79 south of Spitsbergen (Dickson arid Blindheim, 1984), arid eventually back tothe Greenland and Icelancl Seas in 1981-83 (Farrelly et ai.~ 1985; Malmberg, i986). : ': . "

Ellett (1980, 1982), Lazier (1980), änd Taylor and Stephens (1980, 1983) have pioneeroo theadveetive explanation of salinity changes recorded in various basins of the North Atlantic.Gariurielsrpd and Holm (1984) implied the northward propagation of TS~rnmimä irithe "Norwegian Current, traced by Dickson and Blindheim (1984) northward up to the BarentS Seaand Spitsbergen. Dicksori et al. (1988) have elaborated a consistent pattern of the GSA'70s 'advection around the noithern North Atlantic, wide1y accepted by the oceanographic communiiy. '

Alternative mechanisms might explain some of these phenomena. For example, Ellett andMacDougall(1983), riooley el al. (1984), and Martin et aL (1984) proposed a 300-km eastwlirdshift of the Polar Front as a cause of temporal TS-variability west of Bntain. Pollard arid Pu(1985) assumed increased in sitzt excess of precipitation over evaporation as tbe primary,causeof loeal freshening. Hansen and Kristiansen (1994) suggested that the simultlineous salinityvariations in different water masses around the Faroes could be only explained by the changing ­dynamical balance of the currerits transporting these water masses. '

Observations and models have shown that the GSA;70s is not likely to be unique"and c~m beregarded rather as manifestation of intrinsic decadal-scale variability of the ocean (Mysak et al.,1990; Mysak arid Power, 1992; Mysak, 1995; Serreze et al., 1992; Delworth ei al.; 1993, i997;Häkkinen, 1993, 1995; Mysak, 1995; Weaver and Hughes;1992; Weaver, 1995; Wohlleben andW.eaver, 1995; Holiand et al., 1995; rieser and Blaekmon, 1993; Kushnir, 1994; Revei"din et al.,1997).

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Ti~e series extended into the 1990s revealed another large TS-a~omaly, ofthe 1980s, termed"GSA'80s" by Belkin et aI. (1997) (Fig.2). Retrospective analyses, have shown that sirriilarariomalies oeeurred in the past, so that large salinity anomalies (usually assoehited withteinperaiure ariomalies) appear to be quasi-regular~ Distiriet TS-ri1inima in time series aeross theNoi-th Atläritie,~bserved.aböut adeeade before and after ~e GSA'70s were noted byM~ers etal. (1989), Ellett, and Blindheirri (1992), and Dnnkwater (1994); quasi-deeadal temperatureoseillations were identified at OWS "C" (Leviius et aI., 1994, 1995).

In this paperwe describe the GSA'80s andcompare ii with the GSA'70s. Thc paper's''stiucture is as folIows. Daia sOUrCes are characterized in Seetion 2. Tbe GSA'80s adveetionMound the northern North Aihintic is descIibed in Sectien 3. Most. imponant problems relatedto GSAs are discussed in Seetion 4. Main tesults are suinrriaiizcd iri Seetion 5. All the tirrie senesused in the anlllysis are referenced in the text and can be fourid in the original werkS arid iri thereview paper by Belkin et al. (1997).

2.'Data. Ai! avaiiable pubÜshoo time senes of T arid S. extended up to 1995, were used to descrlbe

the, GSA'80s. To illustrate iis pröpagation (Fig.2), we used the same eurreni pattern scheineutilized to show advection of the GSA'70s (Fig.l) sinee this sehematic was found to be

consist~rit with the new' da~.: ",." ..,.'. ';, ,'." ,.... . . .' '. Locations of sections and stations used In thlS. work are shown In Flg.3 accompanled by

. Table 1 which provides coordinates arid referenees to sources of the 10eation data. All thepertinent refei"ences to, the iirI'le series daia presented arid analyzed in this work are given in theappropriate places in the text. . .

3. ,r Greät Säliriity Anomaiy" of tlie 1980s

3.1. North Icelaridic 'Vaters (1) . ,S.-A. Malmberg advanced an idea that the very first signatures of the GSA'80s mighi have

actually appeared in the late 1970s in North Icelandic waters (Malmberg ,arid Kristrnanssonn~

1992, Fig.4; Malmberg arid Blrndhdm, 1993; 1994; Malrriberg et al., 1994, Fig.5; Malmberg ctal. , 1996, Fig.5). Indeed, the. years of 1976-79 featiJred very 10w saIinities in the East IcelandicCurrent. apparently defived from the Elist Greeriland Current. Tbc TS-charactedstics of the Easticetandic Curreni iri 1976~79 were of apolar cmerit rather an Arctiecurrent as usuaI (Malmbergand Svansson~ 1982; Malmberg, 1984a,b; fOf water inass defmitions see Hopkins (1991». Theseconditions eould be responsible, in partieular, for the "small salinity anomaly" cf the hi.te 1980sin the Arctic lriterrriediate Water south· of Iceland and in the Greenland-Iceland Seas (Malmberget al., 1990; Bjarni Saemundsson GSP Group, 1991; Malmberg and Kristrnanssonri, 1992)..TbeArctie eonditions (T=I°-3°C, S=34.5-34.8) north of Iceland in 1981-83 are considered to be asignature of the return of the .. GSA'70s (Malinberg, 1986; Malmb~rg and Kristrnanssonn, 1992;Malmbergand Blindheim~ 1994). . .,

The GSA'80s formation north of Iceland in the laie 1970s, however, is disputable. First, alarge negative S-anomaly is expected to be accompanied by a large positive sea iCe anomaly

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(e.g., GSA'70s) because surface freshening enhances 'stability and ice forrri~tion (Maimberg,1969; Marsden et a1., 1991; Section 4.2). However the late 19705 only featured a moderate seaice extent in the Greenland and Iceland Seas (~hapman and \Valsh, 199~, Fig.7; ,Agnew,'1993,Table 1; Section 4.2). Second, the tirrie interval between the suggested, appearance of. theGSA'80s north of Iceland (1976-79)and its passage off West Greenland (1982, Section 3.2) is .too large: To arrive in North Icelaridic waters in 1976-79, the anomaly should have appeared inthe East Greenland Current in 1975-78,4-7 years tiefore 1982 when the GSA'80speakoo iri theWest Greenland Current off the Fylla Bank (Section 3.2). Given the speed of the Eust andWestGreenland Currenis, upto 70 cm/s (Krauss, 1?95), such slow movement of the GSA'80s isunlikelY. Indeed, the GSA'70s covered this distance in just 1-2 years (Dicksori ei aL, 1988).

3.2. West Greenland Current: Fylhi Bank. ," .. ."The exact dllting of the GSA'80s arnvaVforrnation to/off the Fylla Bank is problematic

becausedifferent time series yield different years, 1982 or 1983 (Stehl, 1988; Buch aiid Stein,1987, Figs.2-7; Myers et aL, 1989, Fig.2a; Myerset aL, 1990, Fig.4; Hovgärd and Buch; 1990,Fig.3.2; Drinkwater, 1994, Figs.20-21; Stein, 1995b, Figs.11-13; Stein, 1996a, Figs.9~1O). Some"time- series (e.g. obtained in October-November) deerri urireliable because of the fresh wateroutflow from Godthäb Fjord (Buch, 1982). According to Bucharid Stein' (1987, Figs.2-4, Julytime senes), the GSA'80s peaked over Fylla Bailk in 1982, consistent with annual summaries byDrinkwater (l994~ Figs.20-21), while mid-June T-series by Hovgärd and Buch (199.0, Fig.3.2),autumri TS-time series by Stein (1995b, Figs.1l-12) arid June T-series by Stein (l996a, Fig.9)show the GSA'80s peaked in 1983. '

3.3.0ffshore Labrador Current and ceritral Labrador SeaThe Labrador Current consists of inshore and offshore branches with high mean curreritS arid

relatively low variability (Narayanan et a1., 1996), consideroo separately, in this sectlcin (offshorebranch) and in the next sectlon (inshore branch). The longest time series are available along theSeal Island line off Labrador and Bonavista line off Newfouridland (Stein, 1988; ICES, 1997).

Seal Island.HamiUon Bank (Myers et aLt 1989, ~ig.2b; Stein, 1988). At 50 m, the minimumof 1972 is well-defined, while the minimum of i984 is less pronouncoo though distinct (as weIlas the minimum of 1959-61)., O\VS ~'ßravo". The OWS "Bravo" was withdrawn in 1974. Lazier (i980) arialyzed the 1964­

74 data. Myers et aL (1990) added the data from the Seal Island line Stations 1O-i2, which areelose. to "Bravo'i, ihus substaritially improvirig temporal resolution prior to 1964 arid extendingthe "Bravo" time series up to 1987. Myers et a1. (1990)have shown S-series for the 500-2000m hiyer (their Fig.3a) in which' the ariomalies of the '70s arid '80s are ill-defined; excepi for asharp drop cf S500 in 1972; only the minimum of 1958-59 is elearly seen., .",,:. "

The OWS "Bravo" is not isolated from the Labrador Current because of the lateraloffshoreadvection from the current into the sea's interior (Reyriaud et af, 1995; Lader et al., 1996);therefore the OWS "Bravo" could be considerect representaÜve of the entire sea. "' . .

Central Labrador Sea (Lazier, 1995, Fig.7). The salinity of the Labrador Sen in the 0-250m layer decreased from 1976 to 1984 when it reached its absolute minimum",34.35 (Lazier,1995). The minimum might have occurred before 1984 and might have beeil even morepronounced since the Lazier (1995) time series has a gap in 1981-84 (see also Lazier (1988,

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Fig.2». Th6 previous low-S anomaiy in the Labrador Sea detected in the OWS "Bravo" rlata(Ltiiier, 1980) peaked in 1970-71.

3.4. Irishore Labrador Currerit: Station 27 'station 27 has the langest and mostcompleie TS-time series on the NW Atlantic shelf <urnon

et al., 1995; Myers et al., 1990, Fig.3; Petrie et al., 1992; Figs.3-4; DrihkWater, 1994, Figs.22-23;Drinkwater et aL, 1995, Figs.18-19; Mertz and Myers, 1994, Figs.2 and 4; Hutehings and Myers,1~94~ FigA). The stauon is located just 5 lari from the coast, therefore the advective long-termsignal ~ght be thought to be contamimited bY. local iJrocesses. However, interannüä1 salinityvarhlbility at Sta; 27 isnot correlated with'interannüal variabilitY in runoff into Urigava Bay, orWith ice-melt in Hudsori Bay (Myers et al.. 1990). Apparently, the lang-tenn signäl at Sta; 27 isnot significaritly contiuniriated by processes related to mhind waters. Advectiori by the LabradorCurrent seems to ,be critically important on the langer time scales, from interannual to decada1(Urnoh ei al., ,1995). The lang-term variability at Sta. 27 is thus determiried 1arge1y by' remote .10nlHermvariatlons in the Labrador Current andin the,West Greenland Current..· ," .

The GSA'80s arrived io Sta.27 iri 1983 'arid persisted for tWo years according tO non- 'smoothed monthly data oy Petrie et al. (1992, Fig.3), while smootheddata are biasect to 1984-85as the GSA;80s time period (Petrie et al.;1992, FigA; Drinkwater, 1994, Figs.22-23; Drinkwateret al.; 1995, Figs.18-19;,Mertz and Myers, i994, Figs.2,4).· " , ., The GSA'70s timing is also different according to the non-smootb6d data series versus thesmoothed series: ·1970 versus 197i, respectively (except annua1 tipper 1ayer, SalinitY data. byDrinkwater (i994, Fig.23), showing the GSA'70s in 1970). As noted abave, we always prererdating based ,on original, data, which hai; nöt been ~öw-pass filtered. . ., .. '

. The DnrikWater (1994) data also show ä'pronouriced ininimum in 1991, which might signalthe arrival of anather "great salinity anomaly", of the 1990s. '

, .3.5. Grand Baoks of Newfouridland: Flemish Cap secÜon . ..

, The 1984 S-miri at SO ni is pronounced,as well'as the earHer S-min of 1971 a~1yers et äl.,. 1989, Fig.2b; Stein, 1988). Driring the GSA'80s passage, the temperature at Fleritish cap (Elleti

•" andBliridheirri, 1992; Fig.l3, from data ofTrites and Drinkwater, 1990) decreasect to the absolute

miriimum in 1985 (for the'1972-89 series), aimost coinciding in time (and seeiningly associateet)with the S-min öf 1984 aiong the Flemish.Cap Hne. The thermal manifestatiori (negative T-anoma1y) of the previotis S-anoma1y (GSA'70s) at Flemish Cap was not distinct. '

,3.6. Nortil AtIaritic Currerit Near the CharIfe-Gibbs Fracture ZoneA Russian data seiof repeat transects occupied in the 1970s-80s 'represents the miliri souice

of regular daÜl in 'the Centfal North Atlaritic (Barariov, 1991; Baryshevskaya, 1990; Lappo et al.;1995). To study'long-term variability of the North Si.tbarctic Front (NSAF), associated with the .northernmost branch of the North Atlantic CuiTent (NAC), Belkin arid Levitus (1996) analyzed213 transects· along 7 Bries, iriclridirig seetions S9 SE of ows :~C'\ S10 ac;ross the NAC's"No~hwestCarrier" (Worthingto1?, 1976, p.27; Laiie~, 1994), and S15 along 35~V (Fig.3)..

Seetions S9, SIO, und SI5 (Belkin and Levitüs, 1996; Belkin et aL, 1997). nie S-series far .the NSAF's coldside along seetion S9 reveai6d a sharp drop in early 1984, allowing Belldn and

, Levitus (1996, Fig.6c) to date precisely the GSA'80s arrival to Sec:tiori S9. The low-S äriomaly

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3.8. Rockall Chanriel , ,The data are preserited by Ellett and Biiriclheim (1992, Fig.16),Ellett (1994, Figs.3~5), arid

Ellett (1995, Fig.4); the surface TS-data havebeen published by Ellett and Jones (1994).'Thc GSA'80s reached the Rockatl Channel in early 1985 arid pe~sisted at least4years, up:

to mid-1989. Having the arrival time to seetion S9 detennined reliably as early'1984, OIiecari 'conclude. thai the time lag between the S9 and Rockall Channel events is about 1 Year. ,This ;esiimate is elose to thc time hig of 9 months betWeenthe passage of GSA'70s ~oughOWS"C': '(still uncertain due' to the 18-month data gap in 1974-75) and its arrival at the Rockall Chai1nelin the fall of i975, as determined by: Dickson et al. (1988). . " .• .,

Winter ariomalies of surface salinitles also show aconspicuous minimumin 1976 (GSA~70s)and a less pronounced minimum in 1986-87 (GSA'80s). The T-ininirriil of 1974-75 and 1987 canbe attributed to GSA'70s ~md GSA'80s, respeetivdy; they arc more conspicuous in mean winter(January-March) anomalies. ..... '; ,

In the deep salinity data, the GSA'70s is discemable do~ .10 at least lOOÖ m (with aminimum in 1977-78), while the GSA'80s is barely rioticeable at 500 m as a slight decrease in1987. It should be rioted, however, that these data are the änomlilies from the means for 1975-78(Ellett, 1994), the period of the GSA'70s passage through thc Rockall Channel, hence an anomalyper se. It is unclear also if the S500 decrease in' i989 could be accounted for by, the GSA'80s.According to Ellett (1994), the general trends at this clepth (occupied by Easterri NoIth AtläritlcWater, ENAW) are largely similar' to the winter surface time series. The latterseries, however,does not reveal a sharp SO drop in late 1980s (analogous to the observCd S500 drop in 1989) as .might be, expected based on the above-mentioned similarity between time serie~ at 0 m and 500m, the ENAW depth; instead, the winter surface time senes features the steep increase in 1990noted by Ellett (1994). We thus conclude that the S500 drop of 1989 is rather a forerunner ofthe

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abrupt fresheriirig of deeper layers in 1990.

3.9. Faroe~Siietiarid ellariDe) .Reguiar observations in the Faroe-ShetIä'nd Channel (FSC) wen~ began in 1893 along Noh;o­

FIugga and Fair Isle-Munken sections (TurrelI, 1995, 1997). Several water masses meet in theFSC such äs 'North 'Athintic Water (NA), Modified NA, Arctic Inteimediate Water, andNorwegilin SeäDeep Water (for water mass definitions see Hopkins (1991». Tbe S-series for NA(Turiell, 1995. Fig.3) reveals two conspicucius minima, in 1908, and in 1975-78 (GSA'70s). TIieminimum which might corresporid to the GSA'80s is distinct although less pronounccil tban tbeGSA'70s. Tbc 'timeseries for different water inasses in FSC allowed an alternative explanationof the GSA'70s to be put forWard (Hansen 'and Kristlansen, 1994), which may be correci at least10cally arid which may.aIso.be coriect in the case of the GSA'80s (Seetion :4.13): Tbe sulface­stilbiitY tinie series for the Faroe-Shetland Chänrid (Reverdin et al., 1994; Seetion 8.1) 'also reveal .two conspicuous miriima, arourid 1910 and in the hite 1970s (GSA'70s), arid afew Iess distinctminima, iricluding the one in the Iate 1980s, pre~uiriably associated With th6 GSA-'80s..

iio; ErigÜsh eilannei .The. GSA'70s peaked in the English Channel in 1977, based on the S-series.for the Seven

Stones Lightvessel (Western Approaches to the Channel) (Dickson et al., 1988, p.121 and Fig.15).The signal is strorig enough, and the timing is consistent with the GSA'70spropagationhypothesis; however, the question remains as to the advectlon pllth of.any NAC anorrialy

. supposedly eniering the Cha~riel. The problems is, there is no current branch of the NAC whichcould trarisport the NAC anOlnalies drrectIyto the Engli~h Channel (Krauss, 1986, Fig~19; l'urrelland Shelton, 1993; Fig.3.4; Oito and Van Aken, 1996, Fig.l; Arhan etal.; 1994, p.131l; Belkin

. et aI., 1997). Dickson et al. (1988) did not find any sign of, the GSA'70s in S-series in theEasiem Channel, and irithe southern North Sea (SoUthern Bight and Gennari. Bight); ,theyconClüded that .iin 'these inner pliits of the shelf, the signal has been overwhetmed by the Iocalinputs" (ibid., p.l21). The GSi\s, however, still could reach the southern North Sea from the

. north, if facilitaied by the northerly winds, as can be iriferred from recerit results of Corten and .Van de Kamp (1996) discussed in the next seetion.

3.11. North SeaOceanic anomalies 'cari enter the North Sea from the north and south. In the north, oceanic

anomalies perietraie the North Sea directIy with the NOrWegian Trench Atiantic Inflow, the HastSh6tIand Atlantic Inflow, the Fair Isle CUrrentand its extension~ the Dooley Currerit,(Turrell, .

. 1992a,b; Turrell et al:, 1996), whereas the southem path, through the English Charinel and thestraii of Dover, is an iridirectone (see the previous sectiori) arid is, perhaps,less impoitarit. .

Oceanic ariömalies could ultiinately reach (and circulate through) the Skageriak before leavingthe North Sea with the Norwegian Coastal CUrrent; the GSA'70s ,vas actually observed in theSkager:rak in the hite 1970s (Sveridsen.and Danielssen, 1995; Danielssen et al., 1996).

. The southern North Sea is sporadically inundated by warm, salty' Atlantic' Water inflowsthrough the Strait of Dover caused by persistent southerJy winds. Such inflows could dramaticallyalter TS- arid ecological charactei-istics of the southem North Sea (e.g., Coiten arid Van de Kamp,1996). In the southerri Ncirth Sea such high-S inflows from the south could compleiely obliterate

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any low-S advective signals arriving from the north. The latest high-S inflow occurrecl in 1989­91, apparently penetrating the North Sea from the south (Becker and Dooley, 1995) and the north(Heath et a1., 1991; Ellett and TurreIl, 1992). . . ., . ' '." "

When, however, the southerlies slacken, ,the GSAs signals from the north could reach theSouthern Bight, as infeiTed from Corten and Van de Kamp (1996), who have shown thät TS':'variability and abundance of southern species in the southern North Sea are corr6lated with thesouthefly winds over The Netherlands. Therefore we suggest that 'the low-S anomaly of 1987 inthe southern North Sea (Corten and Van de Kamp, 1996, FigsA,5,7)mighthave been,causedbythe then-prevailing rlOrtherlies which helped the GSA'80s reach the Seuthem Bight froin thenorth, rather than via ihe English Channe1.' ' . ..,' " " , ~

Svendsen and Magmisson (1992, FigA) have demoristratoo,significant iorig-terin variabllityof different TS-indexes of the Atlantic Water(AW) areal spread in the North Sea arid fOllnd thatthe main' subsurface inflow of the AW to the North Sea is best represented by areal spread of themean (50-200 m) salinity greater than 35.1. Both GSA'70s and GSA'80s eire evident iri tinie 'series of a11 these indexes.

Utsira (Norwegian Coastal Current) (Ellett and Blindheim, 1992, Fig.19). ,While oceanlcwaters ean penetnite the North Sea via several entrances diseussed above; they ean leäve the seaonly with the Norwegian Coastal Current, passing by Utsira. Advection of the GSA'80s tbfough'Utsira ean be identified with the 1988-89 minimum in' sUrface TS-series. Commenting', on theseries, Ellett and Blindheim (i992, pp.27-28) notoo that "no signal of the "Great SalmityAnomil1y" (of the 1970s) was seen and ä longer low temperature and salinity period occurrrobetween 1977 ~md 1982." This implies that this reIatively cold and fresh 5-year period is'toolong ,to be eonsidered as a manifestation of the GSA'70s. However, even bnef inspection of lew­S/low-T events associated with the GSA'70s (as weIl as GSA'80s) shows that in 'any palticularplace the anomalies persisted tyPicälly for abollt 2 to 4 years, so that the 5-year time span is not,prohibitively long for such anomalies; In fact, it is the l-year time span of GSA'70s iii the'Rockall Channel that should be.eonsidererl exceptiori~l1Iy short. Therefore we bdieve that the 5­year low-S/low-T period at Utsira was eaused by the propagation'of GSA'70s ,that arrived herein 1977 (about a year after passing through the Rockall Channel) arid peakect in 1980. .

, .3.12. Norwegian Sea '

OWS "Mit (ltMikelt ), southerri Nor,vegian Sea (Gamn1elsr~d et a1., 1992, Figs.3-4». At50 m, the GSA'80s ean be reliably distinguished only. in the S-senes as a sharp,decline in 1986-:­87 persisting through 1990. This anomaly is ri6ticeable also in the density series as agradualdecrease in late 1980s. The GSA'70s, however, is distinct in T also 'which peaked in 1979-80.This anomaly was especially strong in S, with a pronounced,minimum in. 1977-1978.

Isopleth diagrams for the upper 1000 m(Ganimelsr~d ci aL, 1992, FigA) reveal the thickness(vertical exterit) of GSA'70s (and, likely, of GSA'80s as weIl) to be about 500 in, änd show thaithe anomalies first appeared in the sunace layers, so the time lag increased wlthdepth. '

The GSA'70s at OWS "M" was unusual in that S was clearly leading, not T,' as corrirrionlyfourid elsewhere. The eause of this peculiarity is unknown., . ":, "

Sviri~y-N'V, Norwegian Atlantic Current, southern Norwegian Sea (Loenget a1., 1992;FigAa). The stimmer S of the 50-200 m layer reached a minimum iri 1988 (GSA'80s). Th6 T­series is ambiguous: it has two minima, in 1985 and 1988. The GSA'70s eari be seen as 30 S-inin

8

, "

•

•

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

in 1978 (orearlier) and a T-min in 1979.Gims~y-NW, ~orwegiari Atlanti~ Current, northern NorwegianSeä (Loeng ei ai.;·1992;'

FigAb». The S-min associated with GSA'80s öccurred iri 1987-89, while the T-miri occirrrerl in .1985-87. Once again, as itwas ciften.obseiVed elsewhere, T is 'leading, while S is tiillÜrig. TbeGSA'70s cari be seen as a ~-miri in 1978(1) and the S-ittin in 1979.. .

. . ..iii Barents Sea

Fugl~ya~Bjfjrri~ya (Bear Islarad), weStern Barerats Sea (Loeng' et al.~ 1992; Fig.3a). Bothanomalies,of '70sand '80s, are cIear1y seen in TS-ano!Jlaly time series forthe subsurface layer .(50-200 in). Tbe GSA'70s reached its extremum in 1978: the S-miri was observed in late 1978 '(Loi:mg et al., 1992). The GSA'80s peaked in S in 1988; the T-seiies is ambiguous, atthough bothT ärid S rose sharplyin 1989~ " ' • ' ,., ",'. _ . , ,'.. . '

Vard~-N, central ßarents Sea (Loeng,et al., 1992, Fig.3b). Ori this seetion, the pattern issimilar to th.e previcius section: The GSA'70s and GSA'80s are prcinounced hi b0th T.änd S,altheügh in the S-series the dedldal-scale ancimalies are defined beiter th~m in T. The.GSA'70speaked in 1979; the S-miri was observed here about six months 1ater than 011 the jirevious'section(Loeng et al., 1992). The GSA'80s peaked in the winter of 1988-89.:Agam, the S-series allows'a reliable dating~ .while the' T:-series is more complicated. , ,, , Kola-N; southern ßarentS Sen (Loeng ct al., 1992, Fig.7b). For this secticiri we have on1ythe T-sefies fOf the 0-200 ni hiyer thät shows a pronciimced Ininimum in 1979 (GSA'70s) and'an extended perlod cf the decreasing T, with a mininmm in 1988-89 (GSA'80s). ' "

The three Barents'Sea tinie series, discussed above, have mcommon one peculiar featiiie: äri ' "extremely sharp, almost step-1ike retUrn tethe warnier (arid saltler) ~onditions that occurred in1989-90, afterthe GSA'80s. During this dramatic recovery, T arid S cf the Barents Sea sufface .waters reached their maximal values obserVed since 1977. . . . .

Korsbrekke et ai. (1995, FigA.2) presented tbfee time series basecI on, tbe rlata of ,wintersiuveys in the western, ceritral; and eastein Bacents Sea. Once again, th6 GSA'70s and GSA'80sare evident iri th6 data; especially in S.

.i14..' West Spitsbergcn turrent: S0rkal)p~W, , . . ' . ', TheGSA'80s peaked fIrst in T (.1986-88), theri in S (1988) (Löeng et aI.; 1992, Fig.4c). The

GSA,?Os had a siniihir T-S time hig: T reached a'minimum in or before 1978, ~hiIe S peaked'in 1979.

3.15~ Return to the Icehmd Sea "" The dätil are presented by Malmberg arid Blindheim (1994, Figs.5a,b)and Maiml>erget a1.

, (1996, Figs.5,7). MaIriloerg et aI. (1990), have distinguished a "smat1 äriomaly", in the 'ArcticIntermediäte Water north of Iceland in 1989-90, when itS core salinity was 34.92, significantly ,lower thari 34.95 ooserved iri 1987-88. MalInberg et aI. (1990) also rehited this anoma1y to thelow-S anomaly south of Iceland in i985-88 and (hypothetiCaIly) tra~ed the latter back t6 the low-'S anomaiy'of 1975-79 ilOrth of Iceland. His urne ,seriesfrom north arid riortheast of Icelandreveal several low-S events (associated with invasions of Polar Water). The laie 1960s event

'corresponds to iiie oeginning cf the GSA'70s; the late 1970s event(s) might signaltbe GSÄ'70sreturn from the south via the Irrruriger Current, then via the antic-yclonic circulation around .

. . ~ . " . -,' .

, 9

--- ._- -- --------

. ~ , " , ,.' '.' . ,

Iceland; the 1982 event rriight manifest the GSA'70s return, from the north (from the, EastGreenland Current) with the Bast Icelandie Currerit; finally, the, 1988-90 everit is apparentlyassociatedwith the return of the next anomaly, the GSA'80s, either from the:south (with theIrmiriger Current) or from the north (with the East Icelandic Current). .

4. Discussion

4.1; GSA Source: '.'Lo'calversiis Remote" Dilemma' "Accordingtc) Diekson et al. (1988), the GSA'70s was indii~~tly ~'a~soo by.'li high pres'sUre

anomaly cell over Greeriland in the 1~60s (Dicksohet al., 1975), resulting in abncirmallY strcingnortherly winds over tbe Greenland Sea that biought an inereased amoimt of cold, fresh Polarwater to' Ieelarid. When sUrface salinities here decreased below the critical ,value cf 34.7(Malmberg, 1969), convective overturn ceased and ice siarted to fonn. The cold, fresh anomalythus developed subsequently advected Mourid the northern North Atlantic. Althc)tigh DickSonet'al. (1988) consider the keland Sea processes to be' importani for the GSA'70s formation, iheyunequivocally point to the Arctic Ocean as the main source of the anorrialy. , .: ~,' ,,'

Aagaarcl and Carmack (1989) also view, the Arctic Ocean as the feasible source of theGSA'70s and even state that the anomaly Inllst have had originat6d due to an' increasecl fresh 'water discharge via Fram Strait (p.14,485). They claim also that the suggested origi!i in the AfcticOcean "ean be. coritrasted with ari ongin north of ICeIand, as, hyPothesized by, DickSon'et' fit.(1988)" (p.14,495), aithough both works are irideect fairly consonant in regard to the main source

, of the GSA'70s. , """.,:, ,-., The apparent "local versus remote':, dilemma isresolvedby Dieksori (1995, p.312): The sea ,

• ice anorrialy iri the Greenlarid and Iceland Seas in the late 19608 'was c~lUsed partly by remöte 'forcing from the Arctic .Ocean and partly by local preservatiori of the freshwater layer in theIceland Sea, the latter beirig fundamental for the accumulation of the GSA'70s. ; ,

..., .4.2. Sea ~ce·Salinity. Li~k ; "

. Mysak and Manak (1989) have noted that the GSA '70s was acc6mpa.nied by a large sea-iceextent anomaly, arid proposed (ibid., pAOO) that advection of riegative S-anomalies around the "subpolar gyre could accourit for the apparent moverrient cf positive ice anomalies. Exploring theMalmberg (1969) idea of surface freshwater enhancement of sea ice groWth~ Marsden et al.

,(1991) have shown that saIinity anomalies actually lead sea ice anomalies (see also a discussioriiri Houghicin (1996) who concurred with the above coriclusion). The sea-ice propagatiori from the '

, Greenland Sea into the Labrador Sea has been confmned by Mysak et al. (1990) except for thelarge positive 1983 icci ariomaly in the Labrador Sea, whieh hild rio counterpait in the GreeniandSea a few years earlier (Mysak et al., 1990, Fig.3 and p.114).Mysak and"Manak (1989, p,398)considered a hypothesis that the large positive 1972 ice anomaly in the Labrador"Sea was "simplydue to ariomalous Ioeal atmospheric arid oceanic conditlons" and suggesterl that severe', icecondiiions.during 'winters 1983 and 1984 were due to anomalously strang riortherly winds over 'the Labrad~r Se!!, driven by "a' persistent high south of Hudso~ Bay. Their Figs.J8-19 ~learly

show that the 1983:.84 ice al1orrialy. il1 the ß:iffiri ßaylLabrador Sea was not preceded by asimilar upstr~amanomaly in the Greenlari~Sea aCe,,, years earlier (see also Ägriew (1993,

10

, • I

•

•

•

.'

Table 1». This ~onclusion is corroborated by the data of Chapman and Walsh (1993, Fig.7) andParkinson and Cavalieri (1989, Figs.9,li). The GSA'SOs sea ice anomaly of 1984 in DavisStrait/Labrador Sea (407,000 Jcin2) was even larger thanthe GSA'70s 'sea ice anomaly ofi969in the Greenland Sea' (334,000 kin2

) (Agnew, 1993, Table 1). ..... '. ', . Thus the GSA'80s was apparently formed in the Baffin Bay!Labrador Sea region due to the

extreme local. atffiospheric forcing of the early 1980s. The magriiiu4e of this climatle anomalywas exceptiorial: Ai both Egedesminde and Godthäb, 1983 and 1984 were the coldest years onrecord since 1866, with annual air temperaitire anomaIles, respeetively, of -4.3°C and -3Aoe in1983, arid. -4.3°e ~nd -3.7°C in 1984, betow, th~ 1946-60 reference period meari (ClimatlcResearch Unit, 1985) (see the Godthäb record in DrinkWater (1994, Fig.5». ' .. 'Seventy of the 1982-84 arid 1972-74 iee coizditions in ibis region is ccirroboraied by iceberg

dtitil on the arinual number of icebergs pässing by the Grand Ballks arid crossing 48°N (Trivers;1994, Fig.l).This riumber is agciod index of general sea-ice seventy because it correlates wiibsea-ice ,exterit aiid is "relatively irisensitive to iceberg productioii rates arid to flüctUations insoüthedy iceberg fluxes in areas north of Baffm Islarid" (Marko et al. 1994, p.1335)., ,

Mysak et al; (1990) proposed anegative !eedback·/oop, simplified by Mysak arid Power(1992), which explairis' the GSA'70s origin by' teleconnections ,with the. western Arctic, .

. particularly by large runoffs into the western Arctic durmg the mid~1960s. According to ihisscheme, increasect precipitation in nofthern Canada, through the Mackenzie River rerioff into theBeaufort Sea; leads to increased production of sea ice in the western Arctie Ocean, expoI1erl viaFram .Strait into the: Greenlarid arid IceIand S,eas, where it melts, resulting in upper-layerfreshening, .stability .enhancerrient, arid suppression ofconveetive overtürri and of deep water

. formation; a new GsA is thus 'formed. A reduced heat exchange of the. tipper layer withundertying warm Atlantie wäters results in deereased ocean-to-atmosphere heat flux, redueed 'cyclogenesis, alld decreased precipitation over nolthern North Amenea, closirigthe loop. .'

The weakest links of the feedback loop are those relatoo to the'atmospherie hydrologicaleycle, Le. eyclogeriesis arid precipitation, not to mention the relaticinship hetween preeipititionand runoff. As shown by Bjomsson et" a1. (1995); the main source fOf the Mackenzie basinprecipitiltion fluctuaiions is the North' Paeifie, not Atlantic, as implied by the feedback loop.Mysak (1995) argues that the atmospherie link stilleari be rendered operatlonal thanks to resultsbyWalsh et a1. (1994), who studied water vapor fluxes across 700N in 1973-90 andfound themaximum northward flux arourid lOoE (NorWegian Sea) and the maximum southward flux around2600 E (Maekenzie Basin). However, to assert the validity of the suggested link in the case of theGSA'70s, "an iriterarinual variability sttidy of the water vapor fluxes from the NOrWegilin Sea tothe Maekenzie basin, thdr convergence aver the läHer region arid the observect preeipitation iherewould have been carried out for those years just berore, duririg, and just after the GSA" (Mysak,1995, pp.12-13); . ." .',

. The negative feedback loop discussed above was used by Mysak et al. (1990) t6 predietanother' large posiiiye sea iee, extent anömaly in the Greenland sea inthe laie 1980s..Based onthe winter data of 1987 arid 1988, Mysak and Power (1991, pp.88-89) claim the detection of such'an ariomaly. This; however, 'contradicts to the' Agriew (1993, Table 1) dlitil which actuallyrevealsa negative anomaly of -44,000 km2 in 1987 and amoderate positive anomaly of 84,000 km2 in1988 dwarfed by the giani GSA'70s anomaly of 334,000 km2 in 1969. ..

11

·4.3. Remote Forcin!fof GSAs arid tJic ArcHe Ocean Fresli' Water.Budget

Passing the Labrador Coast, the GSA'70s had a sah deficit of 72 x109 'tons (Dickson et al.,1988), Le. the fresh water exeess of 2000 km3

, which equals -50% of the annual fresh water flux,of the East Greenland Current through Fram Strait; the GSA'70s "ean therefore be' aecounted forby a moderate perturbation of the outflow from the Aretic Oeean, for irisüinee, a2-year period

, of fresh water flux 25% above normal" (Aagaard and Carrriaek, 1989, p. 14495; see aiso a 'summary of the Fram Strait flux estirriates iri Simonseri arid Haugan (1996».' How likely is' aperturbation of this magnitude and what rriechanisrri(s) could be aeeolmtlible for it? To ariswer 'these, questions, we should consider the freshwater budget cif the Aretic Oeean. " ' . '

,The main positive eomponents of the Areiic Oeean freshwater budget, are rhrcr ruriofe, theBe'ring Strait inflow, and precipitatiori minus evaporation~ P-E~ aeeording to; Aagaard andCannaek '(1989), the primary referenee on thissubject imtil arecent work by P.Becker (1995) •who analyzed interannual and long-term variabilitj' of river discharge and the~Bering Strait,inflow ignored by Aagaard and Carmaek (1989). Using newly aequired ,Russian data to qmintifythe annual runoff discharge for the Arctic rivers for 1937-86 and the Bering Stniit freshwater flux 'for 1941-87, Becker (1995) amved at arriean annual rive~ discharge cf 2646 km3/year (forthe ,1973-87 period, when the Russian data overlap with the North American datli); and the meanannual fresh water flux through the Bering Strait of 1829 km3/year for the 1941-1987 penod.The least known component of the Arctic Ocean, fresh water budget is, P-E; estimates,.vary .between 400 km3/year and 1400 kffi3/year (Aagaard and Carinack" 1989). Variabiliiy of P,:,E is

" '" , . -, ' ,-'. ,- , " ,still unknown, although it could be estimated through water vapor flux convergence calculated :by niwinsonde daia; using high-Iatitude rawinsonde data for 1973-1990, Walsh et al. (1994) haveshown that the annual totals of the flux convergence are correlaterl with' statiori-denvedprecipitation over the Mackenzie domain and with yeady variations of the Mackerizie dischärge.

Table 2 summarizes estimates of main soUrces of fresh water input into the Aretic.Oceiül andshows that variatioris of positive components of the, Aretic Ocean fresh 'Water ouclgei per se aretoo small to explain a large low-salinityanomaly of the GSA'70s' scale. Moreover; the residencetimes of fresh water inputs in the Arctic Ocean are several decades (Becker and' Björk, 1996),therefore the Arctic Ocean acts to smoqth ~my interannuaf arid niulti-year (multi-ariIuiil) •anomalies offresh water input (Hecker, 1995, Fig.36;'Hecker and Björk, 1996, Fig.15): ThereforeBecker (1995),concl~dedthat the only plausible cause of GSAs could oe wind.. :

4.4. Arctic Contribution I: Northerly Winds and Eiresmere Pack I ;'

The domiriant role of persisterit wind anomalies in generating the GSA'70s has beenpostulated by Dickson et al. (1988), whe einphasized importance of sea level pressure (SLP)anomalies over the Greenland Sea. The wind forcing coricept has heeri supported,arid expandedby Walsh and Chapman (1990), who have showri that "the roots cf the Great Salinity AnomatY·can be traced to the atmospheric circulation not only locally (east of Greenland) but also :overthe Arctic Ocean (ibid., p.1470). In particular. the SLP difference between soiithem Greenland(65°N, 400 W) and the Sibei-ian coast (700 Nj 1500 E) reached its peak value of the 20th centuiy in1969 (Walsh and Chapman, 1990, Fig.lO), coinciding with the commencerrient of the GSA'70s:Moreover, Walsh and Chapman (1990) have shown that the SLP anomaly patterri of 1967-68(their FigA) should have contributed to an enhanced export from the Arctic Ocean of the thickest,oldest (hence less saline) sea ice from offshore of northem Canada and Greenland. Indeecl, the

,12

thick.ness of multi-year pack ice north of Ellesmere Island exceeds7 rri (Bourke arid Gariett,1987. Fig.5)" while its average salinity' could be as low as 2 (e.g., Thorria~ et al., 1996).Therefore an impact on the nortlierri North Atlantic of an enhanced wind-fofeed export oe" theextremely thick, relatively fresh sea ice in late 1960s shoi.tld be especially signifieant.

The likelihood of a' substiultial iee export enhaneement appears to be high: Thomas et al.(1996) hav~ estimatoo that the Fram Strait iCe. export vanes widely, frOm 1100 to 3000 kffi3/year.Using a balance model, Steele ei aI. (1996, Fig.l0a) found that year-to-year chariges in the FramStrait ice export in theearly 19805 reached riearly 0.04 Sv or 1261 km3/yr. Such an anomaly, Ifsustained for two years, inight eause a GSA comparable with the GSA'70s whose fresh waterexeess was -:-2000 km3 (Seetion 4.2). Reeerit obserVations show that the iriteraimiIa1v8.riability ,of the Fram sirait iee export is 1arge enough to aeeount for the GSA'70s (Aagaard et aI., 1996).

· .' The coneepts of 10eal versus remote forcing.of the,GSA'70s are complementafy father than .mutmilly exdusive beeause "it appears that the Aretic eomponent of the foidng provides. a"remote boost" to the local forcing in the sense that the strongest oeeanic impacts (e.g., a "Great

· Salinity Anomaly") will result when the phasing of hotlz the leieal ~ arid the remote fordng isfavorable. An 'enhaneoo outflow of Arcuc ice witlzout favorable local forcing east ofGreenlaridwill evidently not result in noieworthy anomalies of oeeari temperature and saÜnity" (Walsh aridChapman, 1990, p.1471). . ,

. These results have been eorroboratoo by Serreze et al. (1992), who have shown that the meanwinter SLP gradient between ElIes~ere Island and theNorth Pole during 19~6/67-1970nlwas

positive. The corresp0!1dirig southward shift of anticyclonic activity, though nlodest, "may have.contributed to' an anomalous pressure gradient north of Ellesrriere Islarid imd Greenland,.increasirig the eontribution of multiyear iee to the Fram Strait ice outflow" (ibid., p.296). "

The suggested scenario of wind forcing of, the GSA'70s has beeri modeled by, Häkkineri(1993). The model has reprodueed 1arge pulses of Frain Strait sea ice export, followed ey 1arge,persistent positive sea iee anomalies irithe' Greenland Sea. The. model has produced two 1argefresh anomalies in the Areiic Oeeari, whieh entered the Greenlanct Sea in 1963-65 and in 1967- .69. If these low-S anomalies are associatoo with the large ice pulses from Fram' Strriit, assuggesied by the model,. thisoeeurrenee could trigger the GSA'70s... :'.. "

The crucial role of the Arctlc Ocean freshwater outflow in generaung ädvective anomaliesin ihe North Atlantic was demonstrated also by Delworth et aI. (1997) using a coupledocean­

. atmosphere mödel. Iri a 2000-year integration, pronounced 40-80-year oscillations of T ~lßd' S· occur in, the Greeriland Sea, precooed by 1arge-seale riear-surfaee S-anomalies in the Metie, .prop~gatirig via the East Greenland current irito the Labrador Sea arid.the ceriiral Nolth ~tlantic.

~.' t

4.5~. ,Local Origin: Labrador ~ea . , '" ,. The wörks, reviewoo above, emphasized the leading role of remote (read: the Arctie Ocean) .

forcing of GSAs in the North Atlantie, while largely ignoring processes in marginal seas. Suchprocesses, however, could be erucial for development of large-scale TS-anomalies in the NorthAtlantie. The Ulbrador Sea, seems .to be of particular importanee eecause, aso pointed.out by .'

. Wohlleben and Weaver (1995, pA60a): "Reeent mödelling studies (Delworth et al., 1993. Weaveret al., 1994,. Weisse et aL, 1994) ~uggestihai the source cf interdecadal cÜmate variabiiity' forthe Noith AtJantic may welllie in the Labrador Sea."

For exainple, salinity-iriduced density perturbations (henee dynamic topography variations)

13

----_.._------

observed in a fuIly eoupled oeean-atmosphere model by' Deiworth ei al. (1993) ~e largelyconfined to the N\VAtIantie, particularly to the Labrador Sea. As shownby Deser and Blaekrrion(1993), thedecadal variability in the' sea ice extent inthe Labrador Sea is closely link~d todeeadal variations in SST east of Newfoundlarid, with periods ofpositive sea ice extent anomalh~sin the Labrador 'Sea preeeding by ....1-2 years pei-iods of negativeSST ~moirialies east ofNewfoundland (Deser and Timlin, 1996, Fig.3). The Labrador Sea might also play a major rolein development of decadal-scale S-anomalies iri the Nortb Atlwitic, as shown,hy Weisse et al.(1994), who have modeled generalion and propagation' of such ariomalies with tiineseales of 10­40 years, äpplying the white noise freshwater flux fordng to the Labrador Sea alone. whUe the,same forcing applierl everywhen~ exeept the Labrador Sea did not excite. any. sigriificant decadal ,variability' in the North Atlaritic. These results imply that the Labrador Sea is the souree.of th6 .deeadal-seale vanability observed over, the eniire North Atlai1tic: whieh' is causect~y, vanations ..in the loeal freshwater flux and "erucially depends on the relative isolation of the LabradorSea.in order for that basin to act as in integrator of the white rioise time senes of the freshwater flux'"(Weisse et al.. 1994. p.12420b).,,' , . " , : .

Using an ideaÜzed model of the North Atlantie~ Weaver ei al'-(1994) have foinid the LabradorSea to be the souree of a 22-year TS-variability. whieh is however tlzermally driven andinsensitive to th6 freshwaterflux (arid wind forcing) used, contrary to Weisse et al. (i994).

Neither model. however, eontairis an ice eomponent although iee-oeean interactions alone canexcite TS-vanability (Yang and Neelin. i993; Zhang et al.. 1995). " . ~ ,

Labnidor Sea processes also play th6 main roh~ in the interdecadal feedback loop withtimescale of 21 year (Wohlleben and Weaver. 1995. Fig.4). siriülar to the one by Mysak et at(1990) exeept that the riew loop does not iriclude intensified GIN Sea cyclogenesls ärid iricreasedMackenzie Riverofunoff to explain enhanced ice export via Fraffi Strait. Instead. Wohlleben andWeaver(1995) use the idea- (suggestect independently', by, Dicksön (199.5) arid supportedstatistically) that subpolar SST ariömalies over the North Atlantic (niainly, over the Labrador Sea)affect atmospheric sea levelpressure anomalies ' over Greenlarid, resulting in theaoomalousfreshwater/sea ice transport from'the Arctic Ocean via Främ Stciit. Advected into the LabradorSea. these anomalies suppress convection and inerease meridional gradients across the, North e 'Atlaritic eurrent; the intensified eurrent transports increased ainount ()f warm imd sclIty water vhithe Irminger Current into the Labrador Sea. thiJs suirting the second (reverse) päfi of the loop.

The three major eorisecutive sea-ice anoinalies. of the early 1970s, 19808 and i990s. inHudson Bay. Baffin Bay and the Labrador Sea~ are found to befelated 10 the:three strongepisodes of the North Atlantic Oscillation (NAO) anrl the EI.Nifio;'Soiithern Oscillation(ENSO). hased on cross-correlations between sea-ice'exient, air temperatiJre, the NAO index, aridthe Southern Oscillation index (Warig cl al., 1994; Mysak et al., 1996). Üsing similar approäehes;Drinkwater (1994) has found the NW Atlantic air temperatures (henee sea ice conditions) to belinked to the large-scale atmospheric circulation pattern (characterized by the NAO index), whUePrinsenberg et al. (1997) have shown the interanllUal vanability of the sea iee extent along theLabrador ~nd Newfouridland eoasts to be strongiy correlated with large-scale North Athinticatmospheric Cireulation anomalies described by the NAO index. °

14 '

;-

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

4.6~ Arctie Contribution Ii: Canadiaii Archipelago Outriow . ,In Seetions 4.3-4.5 two different modes of the GSA formation are eontrasted. remöteand

loeal; considered ihüs far as ifmutually exclusive. 111 reality they eari be eombiried: The'Ioealformation in the Labrador Sea might be greatly faeilitated by an enhaneed freshwater outflow,throughthe Canadiari Arehipelago (CA). The irriporianee of the Arerlc Oeean remotely boostingthe GSA formation via the CA has been overlooked iri the past. beirig övershadowed by theperceived erucial roie of the Frlmisirait outflow (Seetiori 4.3). therefore "most models negleetthe flow through the, Canadian Arepipelago. or assurne it is small". (Steele et al.~ 1996. p.20847).,. 'The freshwater flow from the Aretie Oeeari threugh the CA irito the Baffin Bay and HudsonStrait. and i-iver discharge into Hudson Bay. are eventually integniied into the Labra.dor Current.'Rudels (1986, p.174) has estimated the total Afetie surface water transport thfough the CA to be0.7Sv given S=32.9 (theCA outflow is thus rriuch fresher tl1an the West Greenland Clirrent, withS:=33.2), while ether, available estimates varied between 1.1 aiid 2.1 Sv.(see his Table 5). Rudels

, (1986, pp.171-174) has also estimaü~d the net ice, export out of Baffin Bay to'be 970 krn?iyr(with its salinity a.ssumed to be 5). Aagaard and Carmack (1989) estiniatecI the CA fres!zwater 'tl1roughflow to be 920 km3/yr on the' average (assuriUrig. however, Üs saliniiy io be 34.2 or 1.3higher, than suggested by Rudels (1986». These estimates seem rather, coriservative compäred'with the latest studies. Using a balance model. Steele et aI. (1996) have estimated the CAfres!zwater flux io be 0.039 Sv or 1230 kIn3/yr er 34% of the total Arcrle Ocean freshwateroutflow. Röss (1992) has measured the Baffin Island CUrrerit total transport in Davls Strait to be3.3 Sv, much iärger than irnplied by the resuIts of Rudels (1986) cited above. Mertz et al.(1993, 'Table 1) found that Baffin Ba.y and Hudson Strmt are the largest contributors of the fres!zwater .flux of tl16 Labrador Current (3-6x104m3s·1 and 3-lOx104m3s'\ respeetively, while the East "GreenlandCUrrerit conti-ibutes only 2.1x104rii3s·1 and iC6 transport adds 1.9x104m3s·I

). Loder etal. ,(1996. Table 11) estimated the fres!zwater transpo~ ef the Baffin Isla~d Current to be 120, 'milli-Sv, Le. 3784 krn?/yr (based on the above results of Ross (1992) arid Mertz (1993», whereasthe East Greenland Ctirrent brlngs intothe Labrador Sea only 29 milli-Sv (915 kin3/yi-) offreshweiter (based on darke (1984b». Mertz et al. (1993) have estimated the Labrador Current!res!zwater transport through the Fleluish Cap section to be 1.7xlOsm3s·1 or 0.17 Sv, comparedfavorably with the mean fres!zwater transport of 0.13±O.03 Sv by Petrie and Buckley (1996).

The above estimaies show that: '. '(1) The Labra.dor eurrent döminates in the total southwardfresllwater transport in the northemNorth Atlantie Oceari (Mertz et al., 1993. pp.293-294). so that significarit long-term variationsof the freshwater eomponent of the Labrador Currerii are of great importance fOf the entire ocean;(2) Th6 CA outflow appears to be a major contdbutof of the freshwater flux of the LabradorCurrent. so that substantiallong-ienn fluciuätions of tl16 CA otitflow might trigger (or, at least,facilitate) formation of GSA in the Labrador Sea. ' '., The possibilÜy of the CA freshwater flux variability being related to internal variability in ,

the Noith Atlantic has been demonstrated by \Veaver (1995) whö used a coarse ocean general­cireulation model to find out that if 1he CA freshwllter flux from the Afctic Ocean into theLabrador Sea is sUfflciently wea~; a 20-year iriü~rnal oscillarlons develop under steädy forcing.

15

4.7. Pröpagation of GSAs in theNorth Atlantic, :"The sequence of analogous events, the minima in S- and T-series, observed all around the

subarctie, gyre and into the Nordie Seas. clearly 'shows the GSA'80s propagation to be 'qualitritively similar to the GSA'70s aclveetion: The GSA'80s adveetion speed, however, washigher: it took just 6 to 7 years for this anomaly to cover the distance between tl1e Fylla Bankand the Barents Sea (Fig. 2), while the GSA'70s imived in the Barents Sea about 8 to 10 yearsafter passing overthe Fylla Bank (Fig.l). Comparisori of both patterns shows that this differeneeeould be aecounted for by an appärentlymore sluggish cireulation of the Subarctic Gyre iri the1970s eompared with the 1980s: The GSA'70s reaehed OWS "C",about 4 to 6 years after passingby the Fylla Bank, while tlle GSA;80s has amved in the vicinity of OWS "C" in eärIy 1984(Belkin and Leviius; 1996, Fig.6), just 2 years,after it was observed at the FylIa Bank.

The iritensity of the Subarctic gyre circulaiiofl ean be evaluated usiiig the Labrador g)rre;its main part, as a proxy, whosemajor limbs are the West Greenland Currentatidthe LabradorCun-ent. Beeause systematie eurrerit measüremerits west of Greenland are absent, ~e Labra,dorCurrent data should be used to estinuite the lorig-term variability of the Labrador (arid Subarctie)gyre. The Labrador Current trimspoit is largely, deteriniried oy thedensity stiUciure, of theLabrador gyre, topography, and boundarY,fIows (Tang et al., 1996). The gyre's d~nsity sinietureappears to be rdated to [arge-seale wind foreiJlg, while the Ioeal wind, stress forCing plays aminor role (Myers et al.; 1988; Myers et al.; i989; Reynaud et al., 1995; Tang ct eil., 1996). Inpartieulär. Myers et aL (1989) have foimd a sh:ong negative correlatlonbetWeenthe summer ~baroelinie transport in the West Greenland and Labrador Currerits and the strength of the mid­latitüde North Atlantie westerlies in the previous summer. The westerlies' interaimual vanabilityis governed mainly by the NoTtIz Atlantic Osei~lation (NAO), so that the low NAO winters are 'associated with enhimced northedy. fIow aeross West Greenland and the Cariadian Arctlc (HurrelI;1995). The winter NAO index exhibits pronouneed deeadal variability (HurrelI, 1995, Fig.la)related to the n'ear-surface (0-400m) T-anomalies in the mid-Iatitude western North Atlantie(Molinari 'et al., 1997) arid also probably associated with the GSA'70s, GSA'80s, and possiblyGSA'90s (Mysak ei al.~ 1996). The winter NAO index reveals also a very distinci multideciidal .'aseellding trend (Hurrell, 1995, Fig.la), which might help explain the apparerit ongoingintensification of the Suoarctie gyre circulaiion and the faster advectiori of the, GSA'80seompared with the' GSA'70s noted above. If this explanation holds also for the GSA'90s, the

, lutter should be transported even faster ihan the, GSA'80s. ., ,.The GSAs propagate llirgely along the shelf-slope areas. The importance of these areas as

conduits for ädvective anornalies has oeen stressed by Greatbatch arid Peterson (1996). Theadveetive faetor (Le. the impact of the TS-anomalies like GSA'70s arid GSA'80s) is criticallyimportant (especially on the longer time scales, from interannual to decadal)'evfm whereother(Ioeal) factors areexpected to be dominant, e.g. at Sta. 27 (see Section 3.4) (Umoh ct al., 1995).

Everi ihOligh the deep water circulation is generally more sluggish comparerl with the suifacecireulation, the GSA signal mighi aetüally propagate mueh faster in the deep water layers of theNW Atlantie with interise western deep bouridary currents once it passed through the DenmarkStrait with the Overflow Water (Lazier, 1988, p.l251; see also Section 4,i 1). ' ,

16

•

4.8. Sült Budget oe GSAsDieksori et aL(1988, pp.138-143) were the first who tried to answer ihe basic question: Is

the GSA'70s, salt deficit observed in the NW Atlantic sufficient to, explain the subsequenifreshening of the NE Atlantic? They estimated thesalt deficit of the GSA'70s io be 72 gigatons(Gt) in the Labrador Current, decreasing to 47 Gt in the Faroe-Shetland Channellargely due tothe North Atlantic Current branching to the north (Irminger Current) and to the southeast.Farther downstream, the Barents Sea branch carries away 16 Gt, ieaving 24 Gt moving northwardin the West Spitsbergen. Current, which eventua1ly splits into the lO-Gt Laptev Sea branch andthe 13-Gt Greerilarid Sea branch. ' . ' . ".' .

This diastic downstream rlecrease from 72 Gt to 13 Gt does not riiean, however, that'the GSAwas dilutOO tinderway; it reflects rather a gradual j5amticining' of the Gi.df Stream Extensionsystem into severaI branclies whieh eventuaIly carry, the bulkof the vohirii6 transport away fromthe Guirsiream itseIf. Indeed; DickSöii ei aI. (1988) assumect 'ci constant sliliiüty anomaly vaIu6 'AS=O.l fortheirsali budget calculations thfoughout most o(the GSA'70s journeyaroUJid the

. riorthern Nortb Atlantie save for (1) IlOrth' of Iceland, where AS=O.4, and(2) the LabradorCurrerit, 'where AS could be computed rigororisly because of the availability 'of repeaterl saliriitYsectlcins across the cÜrre~t. . ' ,'. , .' ' " .' , ,

Salt budget histciries of the GSA'70s and GSA'80s ean be compared using the available time'series (Seetion 3). The coinparison, (for .the oceari upper layer), is give~. ifi' Table 3; the ,appr~priaie literatrire referenees are given in Seetiori 3 arid iii Belkiri et al. (1997).',. .'" .

InspectlOIl ofTable 3., aswell as exarruriiltlon OfSectiOIl 3, reveals that the, GSA'80s wascomparable wiili the GSA'70s as to their salt eoritentbecause of simllar magnitude arid dmaticinof the salinity anomalies. In the northwest lind central North Atlantic; the GSA'80s was in somephices even more conspiCuous' than the GSA'70s (e.g. La~rador Sea änd near 0y/S "~"). In thenortheast North Atlantic, however, the GSA'80s was weaker than the GSA'70s. .

, . '

'-:.. . . ,'" ~ ,~. ~, . . ,. " J". "..' , .

4.9. Recurrerice 'öf GSAs and Their Reguhirity; the GSA'90s(?) " " . .Within ihe framework of the adveetive hyPothesis, one ean erivisage the following scerianos:

1. A GSA disappears after propagating aroririd the Ncifth Atlantic.' .2. A GSA returns to' Üs ofigin and re-appears as the next eiSA. . .

Another dileinIna (which might be somehow rdated io the above one) ean b6 stated as theproblem' of uniqueness of the GSA'70s: Are "'we dealing with a unique, occasiönal, cr reguiar(evencyclieal) everit" (Dickson, 1995, p~31O),? " ".. .'. .', "'" .'

Diebon et aI. (1988) argued that the GSAt70s eould be advected repeaiedly äroürid the. subpolar g)rre. The reeurrence of the GSA'70s was suggestoo also by Clarke (1984a) arid Lazier.(1988), ainong others. While repeated oceurrence of the same anomaly is feasible, this seeIninglydid not happen with the GSA'70s, whieh arrived back to the Greenhind Sea in 1981~82 (Dieksonet al.~ 1988) rind in the Iceland Sea in 1981-83. (Maim1Jerg, 1986), Le. too laie to stärt th'eGSA:80s, whieh by that time was observed in the Labrador Sea. ..' . ' .

. Myers .et aL (1989) has noted three distinet decadal-scale fresheriirigs of the Labrador Sea"arOlirid 1959, i97i, arid 1984 assoCiated' with positive sea-ice extent aricimaIies in the LabradorSea (Mysak arid Manak, 1989). However, only one ofthese freshenirigs, GSA'70s, was correhitedwith a negative S-äriomaly north of Icelarid (Dickson ci al., 1988), therefcire Myers ei al. (1989,pA) conchi~ed: "The data ~o not support' Dickso,ri et al.'s hyPothesis of amultiple passage of the

17

fresh water pulse arourid the North Atlantic. They also suggest that the 1970's anoJ!laly differectiri character from the other anomalies." . 1

Turrell and Shelton (1993) also considered a possibility of recurrenceof the GSA'70s. Theypointed to the reduced TS-characteristics of the Irminger Water in theWest Greenhind area in1976, attributed to the GSA'70s (Buch and Stein, 1989). The Inniriger Water, however. is {oundhere at the 400-600-m depth (Buch, 1984). so the Irminger \Vater anomaly camiot accciunt forthe upper layer anomaly off West Greenland. Turrell arid Shelton (1993. p.68) also argued thaithe GSA'70s re-appeared fIrst in North Icehindic waiers. theri west of Greenhind (in 1982-84) a,ndconcurred that the cold conditions west of Greenlarid in the early 1980s rriight b'e paItiallyaünbuted to tl1e increasect iiiriflow of cold Afctic water from the East Greenlarid Currerit" (Buchand Stein. 1989. p.83). Buch arid Stein (1989), 'however. did not provide any dati to supporttheidea of the enhäncoo inflow of East Greenia'rid waters inici'the Labrador Sea iIi tl1e early. 1980s.

The ädvecuve hyPothesis irnplies that' a GSA could. re-appear .after passing around theSubarctic gyre. While the GSA path in the NW Atlaniic seems to be weil deteriiüried. apparentlycontrolloo by contiriental slope topography (East Greenland Current -- West Greeriland CuITerit -- Labrador Current -- North AtIantic CurreIÜ), there are at least two alternatives for. a GSA torecirculate: The anomaly could follow the "great drcle" via the Rockall ,Chanriel arid. the Faroe­Shetland Channd irito 'the Nortl1 Sea and the Norwegian Sea, then inoving rioi"th with the West'Spitsbergeii Current. 'eventuallyyeeririg west to joil1 th~ East Greenhind Currerit in the,westernGreenland Sea (Route 1)•. ort a,ltematively; it could shortcut the "great circle" and follow the"small circ1e" ~iih the Irmiriger Current to the north then west to join the Bast Greenland CUrfent .in the western iriitinger Sea (Route 2)~ . . . .' .' ...,.. . . .;'

These two different c10sures would have different effects on a GSA. Following Route 1. a'GSAwould remain siirface-intensified (e.g. riumercius fIgures in Dickson arid Blindheiin (1984».whereas following Route 2 "(via the Irminger Current). a sllljace-intensiried dsA would becomea subsuiface one by the time it reaches the West Greenland Cu~erit. where the Iriiliriger Currentwater is observed at iritennediate depths (400-600 m; Buch. 1984). ..'.' .' . .

The problem of recurrence of GSA has beeri reyisited recently by Dickson (1995) who notoothat "we have only inconclusive ~mswers to its'likCly periodicitY,i (p.313) and admitted that,theGSA might" be "a more obvious.- high-litriplitude' iteration of ci regular everiti• ' (p.314)..Notwithstanding the above reserVations, Dickson (1995; p.3i6) concluded: "Altboiigh hcontainsperiodic elements. the Great Salinity Ariomaly [of the ,1970s] is neitber' aperiodie nor afrequently recurring phenomenon. One or possibly two' such events are thought to have occurredduring this century. and the eveiit we observoo in 1968-1982 was driven by ä secular change inthe winter pressure fIeld at Greenlarid.". . . :

The recurrence of GSAs has been, however. corroborated recently by tbe results of'climatological analysis of the rriost complete data base for the Labrador Sea and NewfmindlandBasin(Yashayaev. 1995. 1997)~ Threedistinct low-S anomalies have been found. associated withlow-T anomalies. in the early,1970s. 1980s, <ind 1990s. Deser and TimIin (1996, Fig.3) have alsofound three positive sea ice extent anomil1ies' east of Newfoundlarid in the early 1970s, 1980s,arid 1990s follciwed ....1-2 years later bylow-T anorrialies in the suopolarNorth Atlantic. Reverdin'et al., (1997) confirmed tbedecadal periodicity of TS-anoniaIies in the North Atlantlc arid pointedout that the advective explamition appears to be the likeliest one. "

The latest anomaly, GSA'90s. is also evident in the' most recent I data from the inshore

. 18

, ' .•

•

Labrador Curre~t (Drinkwater, '1994, Figs.22-23) arid elsewhere on the Newfouridiänd Shelf(Colbourne'et al., 1997). The GSA'90s origin seems to be related to the severe winters of theeady 1990s in the Baffin BaY/Labrador, Sea ,area, when, the negative air temperature, monthlyarlOmalies over West Greenland exceeded _10°C (Steiri;'1996a, FigsA-6); the winters of 1992 and1993 at Godthäb. were the' coldest on record since ,1866; the anomaly persistoo thfough March1994 (Climaiic Research Unit" 1995a,b, 1996; Drinkwater, 1994; S.tein, 1995a,0, 1996a,b).

4~10. Thermäl Anomaiies and GSAs 'As repeatciÜy notect and illustratecl above, anomalous salinity everitS from time senes recciided '

aroünd the Nofth Athinticare usuaIly associated With teinperatur:eanorrialies. Tbc open ocean .salinit)r ariomalies could eriter marginal seas ~d likeIy influence their thermal regime as shownby Becker äßd Pauly (1996) who found the larger SST, ariomalies in the North Sea to 00 relatedtosalinity ~lIioriuilies in, the NE Atlaniic ,arid iri the :North, Sea itself. It is ,very interesti~g,therefore, ,to examine advection of individual large-scale teinjjeranire anomalies (the suitable,temperature data are farmore abundant than,salinitydata) which ,c,ould. tJeindicative. of the ,propagation of ,the associated salinity anomalies. , Using the COADS SS! data in the North 'Atlantic for 1948-92, Hansen and Bezdek (1996) have ideritifh~d arid tracked five cold anomalyfeatures and nine warm anomaly features, with individual lifetimes of 3-10 Years;. ~'the longtimescale of these extreme everiis arid the continuit)' cif their movementS suggest auseful degree .of prooictability of SST basooon persisierice and propagation of features" (ibid., p.8749). Mostof the anomälies traveIed around the subarctic 01' subtropical gYres, With the speed of 1-3 kriliday,which is sigriificaritly less than the, iypical mean speed af the.near-suiface, ocean circul~tiori.Hansen and BeZdek (1996, Tabte' 1) have assochited the cold SSTanomalY,C70"observed in1970-76, with the GSA'70s. The next cold SSTanomaly, C83, ooserved in 1983-86, could beassociatoo with the next low-S anomaly, the GSA'80s (D.·V. Hansen; personal commünicatiori,1996), notWithstaneÜrig tWo minor inconsistencies noted below. First, our dauic1early show the :GSA'80s propagating around tl1enorthern North Atlantic, while Hansen and Bezdek (1996) havefound the associat6d e83 thermal anomaly to oe stationary (see the "nil" speed in ,therr Table 1).although a careful examination of their Fig.4 reveals a slow movement of C83 around thesubpolar gyre. Second, the GSA'80shas oeen traced through 1989, while C83'has'been tracedoniythrough 1986 oecause oythat time tl1e anomaly, went into the GIN Sea, so that Hansen andBezdek (1996) could not ideritify it there for their "fjeld of view" was limitCd by 65°N.

• f • "

4.11; Deep ,Waters.aiüidsAs., . ,.Lazier (1988, p.1249) pointed out that in the deep arid near-böttom waters of the Labrador

Sea thc ninge of temperature variability,overthe 1962-86 period andthe magnitUde of time senesextrerria increases with increasing derisity; the temperature extrema being evident on all therleepisopycnals. Because these deep waters odginate from the, Denmark ,Strait, Oveiflow Water(DSOW), thedeep water vanabilityin the Labrador Sea shouldbe assochitoo with the tipperwater variability in the Icelarid Sea. Thus the sillface-intensifiect TS-arioniaÜes in tbe Nordic Seascould tnmslate irita the deep-intensifioo TS-anomalies in the Labra.dor Sea and färtherdowristn~ain associated with the DSOW~' ". . " '

Once in the DSOW; the GSA signai in the NW,Atlantic might sometimes propagate!asterthan the corresponding surface signal thankS to the iritense boundary currents which supply the

'. .19

· ..Labrador Sea deep wate~s; these botlndary currents would actually carry ori the' GSA signal faster'than the ocean surface layer transport dominated by eddy diffusivit}' (Lazier, ,1988, p.1251)..

Aagriard arid Carmack (1994, Fig.2) prop~sed a new schematic to describe,a relationship'betweeri freshwaier supply from the Arctic and convective renewal rate in the North Atlantic, andsuggested (ibid., pp.7-8) that the GSA'70s caused the freshening and cooiing of th~ NorthAtlantic deep water, first described by Brewer et aL (1983) (see also Read arid Gould, 1992).

Häkkinen (1995) usoo a fully prognostic ice-ocean model to show that the Greenland Sea .deep convection (hence deep water mass forination) is controlled bythe Fram siraii ice' exportand/or by the local wiiid conditicins iri the Greenlarid Sea; she has shciwn atso that the Greenland .Gyre salt content changes aredetemunoo by the advection 'of frcsh or salt)' anomalies 'causoo .,either byArctic outfIowsor by the PolarFront's shiftS; ... ., " . . ... ':. :

, Rudels (1995, p.297) pointed o'ut, that'the \'GSA'70s inhibited the conveciive äctivitythroiIghout the entlfe riortherri Ncirth··Atlliritic:,"Then riot only the producrlaii' of Arciic .•....Interinediate water in the Greenliirid and Icelandic Seas was shiit off. The low salinity water alsoentered the Labrador Se'a arid closed down'thc' formation of Labrador Sea deep water. Both the .[Denrriark Strait] overflow arid the Labrador Sea coritribution to the North Atlaniic deep waterwere then reciuced. i. , . " :

Curry rind McCartney (1996) have shown that 14e time history. of the convectivc activity irithe Labrador Sea leaves its irriprint on the Labrador Sea Water(LSW) charactenstics. They poirit'out (ibid., pp.27-28): "The convectiveevents of the 19708 arid late 1980s were precected oy a.sufface buildup of an extremdy law saÜnity cap [GSA;70s'imd GSA;80s] ..~'Thc dowrinmdngofthis fresh cap dramatically loweredthe LSW core ·salinit}'.i. The LSW characterlstics, 'espeCially'its thiCkness, are found to be.liclcoo to the subiroplcal mid-depth warmlrig/coolirig pattern; ~ith .the subiropicat" basin-scale response lagging the subpolar signal by 5-7 years. CurrY arid 'Mcairtriey (1996) have' shown', that' the subtropical. temperature response is .dofninatecI. by ',theLSW thickßess (Le. by the volume of LSW available rar miXing) iather thait' by the LSWterriperahire signal. ',. .. , ,

Dickson et al. (1996) have shciwn that' the coiwectiveactivity (hence the entlre process' 6fdeep and intermediate .water formation) in th6 Greenhind, Labnldor arid Northem Sargasso Seäsunderwent caordinated changes over the last several decades, .. same of them. being. relatoo to •variable horizontal exchange with the Arctic Ocean via Fram Strait,' arid propagation 'of GSA~They also argue that these in-phase chlmges (af different sign) have been caused Iargdy by' "adirect impact of the shifting atrriospheric cITciIlation on the ocean" (Dickson et aL; 1996, 1>.241).

4~12~'Long-Term Vafiability arid GSAs, , . " '. 'Lang-term vanability of th6 ocean on varietyof scales (decadal-to-centenriial) might be of

various kinds. Different mechanisms were invoked to explain the observed long-tenn variabiIitYin the North'Atlantic such as: . ' . ,.., i . .

- a slzift in the pcean regime (Malmberg and Blindheini, 1984; Levitus, 1989a,b,c); " ,- decadal arid mulii-decadal osciliations in the ocean-atmosphere system as indicated by statisticaldata analysis (Deser and Blackrilan, 1993; Levitus et al., 1994; Levitüs and Antonov, 1995;Levitus et aL, 1995; rieser and TimIiri, 1996; Reverdiri et aL, 1997) änd modeÜng experimentS(Weaver ririd Sarachik, 1991; DelwortIl et al., 1993, 1997; Holland et al., 1995); ~

- a secuhir (century-scale) monotonous trend(s), e.g.' acooÜng and freshening of tbe subpolar

20

, .

; " l • ~, •

North Atlantic over the past several d~cades (Brewer et al.. 1983; Levitus"1989a,b,c; Read ,andGould, 1992; Levitusand Ailtonov, 1995), which might ~ave been initiated by the, GSA'70s.

All these. mechanisms are not rriiituallyexclusive arid hence all of them could be ät worksimultarieously. Iri other \-vords, the ocean might oscillate between two or more stable regimes;it might undergo agradual, monotonous change (trend); or it might experience abrupt shifts fromone s18.te to another; arid the ocean actually inight simuItarieously exhibit all of the äbove modesof variability.

4.i3~ Ecolögicai consequences of GSAs and their impäct on fisheries ' ,Circulatingaround the North. Atlantic, die GSA'70s, "had direct arid knock~on 'effectS.upon

mailY trophic levels of theecosystem" (TUiTeIi arid Sheltöri; 1993, p.68). For exin{ple, Cushirig'(1988) has shown that the GSA'70s'adversely äffected the spaWning' success of 11 of 15 stockSof fish, whose breooirig grourids were traversed by the arlOmaIy. The advedive TS:anotnalies perse,' however, are not necessarily !he' 'mahi direci caiise of the adverse' etfect as 'shown byHutchingsandMyers (1994)who,did not fmd any erfeet ofTaridS on recruitrnent ofnorth,emeod. Instead, the anomalies rriighi be rather signaiures of profourid changes in the ocean-scale,currerit patterri; it is the,changing current pattern that likely affects,the ecosystem (e.g~"riorth~south shifts of the Gulf Stream (Taylor, 1995) or quasi-'meridional shifts of the North SubarcticFront associatCd With the riorthemmost bnmch of the North Athintic Current (Belldn and Levitus,1996). Influerice of the GSA'70s onrecruitineni arid migration of fish stocks was feIt even in thesemi-enClosed North' Sea (Svendsen et al.; 1995), where in the late 1970sthe eIltire eco'system ' '"changCd overnight, probably caused by the enirance of ocean water with a different chermcalcorriposition" (Lirideboom et a1.; '1995, p.99). ," . ", ,. " ,." .

.The impact 'of GSAs onrecruitment is, however, disputable. Fm,example: MeitZand Myers ', (1994, p.l) claim that "southof Greenlarid waters therewere no sigriificant terriperature anorrialies,correspondirig to the GSA['70s]." This conclusion coriti-adicts to the resuits of other äiithorspresented 'in Sectioris 3.2 thfough 3~5; and,' ä!so to the result8 of Hansen arid BeZdek (1996,p.8753), descnbed in Section4.9, who have tniced a temperatUre anmnaly (C7Ö) associated withthe GSA'70s. Mertz and Myers (i994, p.l) have also fourid that 'ithe food chäin coupiing ofenvironment to recruiunent (climate to phytoplankt~n to zooplanktori to fish) is riot strang iri thestudy region'" [the' northem Northwest Atlantlc, from West Greenland to the Grand B'awl.Further research is clearly wärianted as, to the, ecologicai impact of GSAs, espeCially riöVi thatwehave twOthoroughly documentCd GsAs (of the 1970s andl980s), arid the thlrd GSA (of the1990s) might well be iri progress. . ' , ,

4.14. Alternative Explanations of GsAs " ., Once the advectlve hypoihesis has been advanced to explairi ihe GSA'70s, alternative

hypotheses have been put forward to account for the observed phenomena. For example, Ellettarid MacDougall (1983); Dooiey et ci1. (1984), arid Martin et al. (1984) explained the temporalTS-variability west of Britain by a hypotheticäi large-scaJe eastWard shift of water masseS,thai.mighi be' caused by a 30D-km ,eästWard shirt of the Polar Front. Unfortiiiuiiety, directconfirmations' of s'uch 'a shirt 'are lacking. . . '

Pollardand Pu (1985) suggested increased in situ surface moistun~ flux (i.e. increäsed excessof precipitation over evaporation) as the prirriiuy cause cf locai freshening., FaCing the apparerit

: " ..

'21

problem 'of explaining the' sou~ce of an "extra" 1.4 m~f fresh wate~ presumably ~dded io thesurface,of the Northeast Atlaritic (riecessary to account for the observed freshenirig), Pollard andPu (1985) insist thüt tbe required excessive atmosphere-to-ocean freshwater flllx went unnoticeddue to the sparse observationil1 network. Revisiting the hypothesis, Pollard et aI. (1996, p.189)argue that "...there is no conflict betweeri the various hyPothesis imt forward io explain thesalinity anomalies... All these mechanisms contribtite, with different balances in different yearsand at different places." , ,,' , ' ,

Furnes (1992, p.252) related the proriounced drop in the rnid-1970s in T and S in the NorthSea and Barents Sea (the latter' being' associated also, with iarge seaAce extent), to, u acOllnterclockwis6 shift of the wind directions towards more southerly wind diiections iii the NorihSea and nolth6asterly dii-ections in the BareritS Sen.':, Hansen arid Kristiansen (1994)noticedsimultaneous salinity variations in water masses around Faroe Islands arid conCludoo thatthe only ,mechimism which could explain this simultaiiehy is the changing' dyriarrucal baiance of th6 threecllrrentS iransporiirig these water masses; 'namely, the North Atlantlc Current, the Continental e 'Slope Current, arid the Eas! Iceland Current. The above simtiitarieityhas beenalso noticed bY.Tllrrell (1995) who concurred With the idea of achanging dynamic balance of the area as themain cause of the .saliIlity, chan'ges in the Faroe-Shetland Channel. " .. , ' ,

Hansen and Kiistiansen (1994), however, do not question thevalidity of the advectivehypothesis in the Nofthwest and Northeast Ätlantic, stressing thai their objeetions are of ratherlocal character, namely,theyquestion. the idea that "the saliriity d6ficit in the Faroe-ShetIandregion rriainlyderived from the West ÄiIantic by advection", (ibid., p.12). They also' note that thesuggested dynäriiic change "may' weIl involve ä'shift of the Polar Frönt south of Iceland, assuggested byDooleyetal. (1984), butdoes not necessarilydo so,and must in any case be Iriorewidespread since it must involve also the East Icelandic Current arid probabiy aiso regions in theeasterri Athiiitic :"outh to about 40oN" (ibid., p.15). These ideas änd the Dooley et a1. (1984)frontal shift hyPothesis should oe iakirig iriio account' to reconciIe the large-scale ,advectlveexplanatiori arid 'some seemirigly unexplairiable phencimena in the central'North ÄtIantic. ' ,

Ariother problem is a signifiearit time lag between T clnd S extrenul obsei-ved in time serlesarourid the North AtIantic (see Sectiön 3). what makes the problem even more difficuIt is thatthe Sigll of the tinie lag ean bedifferent in (liffereiii places, for ~e same äriomaly, be it GSÄ'70s •or '80s. It means thai the leäding parameter cari be either T or S; they also can be synchfonous.We have rioticed; however, that in most cases T leads S, which could be'explained as folIows:(1) A negative air temperature anomaly causes,sunace cooling (negative T-anomhly); ,(2) The sun<ice cooling (possibly combined with initial sunace freshening from a remote sourcesuch as Fram Strait or the Cailadian Archipelago) results in enhanced formation of sea ice;(3) The positive sea ice extent anomaly propagates downstrearri where the sea', ice meIt createsanegative salinityariomaly..' . . . .. ' "

Actually, the time lag problem presents ari imsurmountable obstacle not for tlle advectiveexplanation but for the frontal shift hypothesis becaüse 'ariy temporal varlability (m ci ftXcd point)

'induced by frontal movements of a neai-by front should be sYnchronous in T- and S-tinie seriesrecorded at the fixed pciiritsince T and S are strongly corrdated across oceanic' fronts.

The advective hypothesis ,advocated here. is not. the onl, possible explanation. of iliesuccessiciris of similar everits observed repeatedly aroimd thc riorthern North AtIantic but fatherthe siinplest inechariism which renders a coherent ~space-time pattern of large-scale decadal

22

,"•

variabilitylargely corisisterit with the available data. We refer the read~r to 'the recent stätisticalsiudy by Reverdin et al. (1997) wh~eh strongly cOITobonites the adveetive paradigm.

4.15. "'\"0 Scenarios 'In tbe adveetive frarriework, ät leäst h,'o' scenarios are feasible of thc GSA origiD ärid

propagation:,. .. '. .' '. . " ." . (1) The GSA'70s was causoo by enhancoo iee expoit from the Arcrlc Basiri via Frain sträÜ.Thc GSA'70s pröpagatoo äround the North Auanuc, re-:entered the Bast Greenland Current, re­appeared as the GSA'80s and may ,weIl re-appear as the GSA'90sgiven the ioughly 10-yearpropagation time. Mound the Suoarciic gyre. This seenmö irilplies the existence'cf yet uiikrioWnmechäilism whieh reinforces the. an'omaly uriderWay. it alSo faces '3. problem: If there is a self­suppoIting mechanisms ' accouri.:able .foi the GSA mamtenance,' when arid ,whY. does themechäßism break down, allowing the GSA to dissipate as it äppareritly happeneet witli the GSAof 1908-19101 . '. .',.... . . . ." ,.. ' .. . (2) The seeond scenario envisages!Wo '. main areas of, the '. GSA .origin, Fram Strait aridLabrador Sea. As shown above, the .GSA'70S was likely causoo by tne enhariced Arctic'fieshwater export via Fram Strait, with the assochited positive sea-ice extent anoriiaiy, propagatingdownstream from th6 Greenland Sea to the Uibrador Sea. The sitUation in the 1980s; however,waseritirely different, ~ith ,rio ,sea-ic6 excess in the9reeriland sei Ai tlu~ sametime, in theBaffin Bay:-Labrndor Seä ärea die wiriü~rs ofearly 1980s were extremely severe and tbe sea-iceextent reached the aIi-tirite high. It is the regional climatic situation in the Raffin Bay-LabrndorSea area in the wly i980s that is likety accoriritable foi the GSA'80s, origifi~' . " . " ,

. This hYJiothesis seems to b6 strongly COIToborated by the early 19905 däta; when, agairi, thewinter coriditions in the Baffiri Bay/Labrädor,S~a area,were extremely severe~~th negaiive aiftemperatiJre monthly anomalies tip to, _10°C (Steiri; '1996a. Figs.4-6) and lalge positive sea-iceextent anomalies (Stein, '1995a,b, 1996a,b) (see. also iceberg' datä in Trivers (1994, Fig.l»apparently leadirig to afresh, cold anomaty (GSA'90s) in the 'Ye~t Greenland CuITent änd iri the

.Labrador CUrrent (DnnkWater, 1994; DrinkWäter et al., 1995; Colboüme et al~, 1997),while theupstieam aimosphenc imct 'oceanic conditions in the Greenlarid. Ieeland arid Irillingei Seaswerenormal (Climatic Research Unit, 1995a,b, 1996; Climate Analysis Center, 1994;'Steiri,1995a,b,1996a,b; the dij;olar strueture in the air temperature anomaly field, Le. the seesaw betweeri theLabrador Sea and Greenland Sea during the winters of 1973, 1983, and 1992, has been notect also

.byMysak etat (1996».The annual SST anom,l1y for January-Deceinber 1993 inthe Baffin Bay­Labrador Sea area exceected -3°C, beirig 1>y far the worId's largest SST anomaly of tbe year(Climate Ariaiysis Ceriter, 1994). ' , " ". ' ., '. " ,

5. ,~uriiiiiary ~öd Conc.liIsions . . .' .,' ." ..... . ." .', Using all available pub.lished time series ofT arid S.'exü~ridect into the 19905, we revisitedtheGSA'70s and' documerited the riewly ideritified GSA'80s. Both propagated aroimd the NorthAtlantic in asimilar fashion. The advection mechänism, iriitlally proposed to explain the observectsequenee cif everits duririg the GSA'70s, appareritly holds also for the .GSA.'80s.' "

These two arlOmalies, however, seem to have different origins. Thc GSA'70s was likelytrigriered Ternolei" by a freshwaterlsea iee pulse from the A.retic Basin via Fram Stiait, and wasaeeompanied by a large sea ice extent anomaly in the Greenland and Iedand Seas in th'e late

23

1960s, propagated downstream irito the Labrador Sea in the early 1970s. .. 'On the contrary, the GSA'80s was probably formed locally, in the Labrador Sea, largely

because of the extremely severe winters of the early. i980s. The GSA'80s formati~nmight have. been facilitated by a .likelycontributiön of the Arctic freshwater outflow via the CanadianArchipelago, supposedly enh~nced due to interisification of northerlies observed duririg the event..This fresh, coid, anomaly wasaiso, associated with a positive sea ice.extent ariomaty in theLabrador Sea. which, however, bad no upstream precursor in the Greenland Sea, imlike thc seaice anomaly of the 1970s. '. , . ,:.. .',' . . .... .:', :"

Thc early 1990s pattern seems toconform to the earIy 1980s'. A 'new frcsh; cold anornaly'was. forrnecl in the Labrador Sea'diiiing the harsh'wiriters of the early 19905, accompanied by a large .

positive sea ice extenianomaly. Thesesevereconditions were, however, mostly confined to theLabrador Sea and Baffin'Bay, while tb.c äiinospheric and'oceänic' conditions in the Greenland,.Iceland, ~md Irrriinger Seas were normal. .' . . ',' '. .".; ',: ( .

. . ,

We thus.arriveat i~o major corichisions which dir~hY's~em from'the~ coinpar~tive snidy Q'f.theGSA~70s, GSA'80s, and, rudimeritary, GSA'90s: . . ,.~" .. ,1. Tbe GSAs are riot necessarily caused solely by an enhanced export of fresh~aterand sea icefrom the Arctic Basin 'via Fram Strait ,... ' ,2. The Labrador Se3JBaffiri Bay area can piay a key role in the formation of GSAs, as weii asin propagation'of the GSAs formoo ups~eafn.', " . .': . . " , "..... ' '.,: ". .,

There are two modes of the GSA origin in the North Athintic, remote (duc toan enharicedArctic Ocean freshwater export)and local (due io severe winters in the Labrador Seafflaffin Bayarea). Both modes should betaken ioto aecount in'attempt io morlel deeadal vanabiiity of the.coupled ocean-iee-atmosphere system in' the North Atlaritic/Arctic Basin. . ;'.".' '.. . .

Long-tenn, observations, in fixect locations thus provide iridiSpensable information about ,decädal-scale variations' of ihe"circ~laiion. patt~m .and· its intensity. Accumulation of repe,aied 'registrations of such events as fue "Great Satinity Anomalies" of 1970s and 1980s should allowthe multideearlal vanability cf the ocean circulatlon arid climate to be studied, modelerl andeventually understood. .... ~: . .

6. A-cknowiedgnients . . '. .. . .A synthesis of ibis: kind' would be impossible without elose collabonition, witli~ and

contfibutions from~· scores of colleagues who generously and unselfishly shared with us th.eirlatest findings and ideas. We extend Olir most sincere gratitude to Thorkild Aarup~ Gerd Becker,Peter Becker, Marifred Berseh, Johann Blindheim, Erie Buch, Bill Chapman, Ad Corten, RobeltDickson; Harry Dooley, Ken Drinkwater, David Eliett, Tor GarnrTIelsr~d, Bogi Hanseri, DonllIdHansen, James ~elbig, David Holland, Robert Houghton, Jeffrey: Hutchings: Sigbjom Mehl,Gordon Mertz, Ransorri Myers, lohn Lazier, lohn Lader, Hamld Loerig, LaWrence Mysak,Raymond PoIIard, Gilles Reverdin, Tom Ros'sby, Bert Riideis, Michael Steele, Manfroo Stein,'

.Arnold Taylor, Bill Tu.rreIl, JohnWalsh, Andre~Weaver, imd Igor Yashäyaev. T~is study wascompleted while Igor Belkin and lohn Antonov held, respectively, Senior Research Associateshipand Research Assochiteship with Oceari Ciiinate Laboratory of the NODC, NOAA, awarderl bythe National Research Council (NRC). The constant support by the NRC and the NOAA Climateand 'Global Change Program is greatly apprecÜited. . ' . .

24

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. '.,

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e

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35

Propagation of the "Great Salinity Anorrialy" of the 1970s

.-.

40°

1977

•

, .' ..

.+

50° 40° 300 w 20° _ 10°

Figure 1. Transit dates for the minimal salinities of the GSA'70s (Dickson et al.,1988). The circulation scheme by Ellett and Blindheim (1992, Fig.6) is based onKrauss (1986), modified in the NE Atlantic after Meincke (1986) and others.

36

Propagation of the "Great Salinity Anomaly" of the 1980s

•

.-,

50° 40° 300w 20° 10°

Figure 2. Transit dates for the minimal salinities of the GSA '80s overlayed onthe circulation scheme by Ellett and Blindheim (1992, Fig.6).

37

Figure 3. Standard sections and stations used in this work overlayed on thecirculation scheme by Ellett and Blindheim (1992, Fig.6). Coordinates of thesesections and stations are given in Table I.

38

lOW

-.

.......

30W

.+

40W

Standard Sections and Stations

50W

OWS IICII1965 1970 1975 1980 1985 1990

35.0

34.9_:::3cn0--~

.'t:::

34.8 .cctS

CI)

34.7

•

(a)

~ <>GSA'80s

III

o : 0I

9d> 8

8

.9

II

<> I' <>GSA'70s

IIII

o

8 00

T20.0I

o 0 :I

o :o I

IIII

S20:0IIIII <>

o

o @IIIIIII

o II

t~o

IIIII

i~4' !'

--ü

o 6

1965 1970 1975 1980 1985 1990

(b) .

12

.s:::=. 9...-c 6o~ 3

o-t-.,.-,......,......,..--r--r-r-r--r--r-,--.....,.-r--r-r-r--r--r-,.-,......,..-r-..;.-,r--i-............

1965 1970 1975 1980 1985 1990Figure 4. (a) Temperature (circles) and salinity (diainonds) at 200 m at OceanWeather Station "e". Open (solid) symbols show monthly (annual) means. Barsshow standard deviations about annual means. (b) Availability of monthly means.

39

Table 1. Standard Sections and Stations

ICOd9 Section/Station Name ILocation IReference IIcelandic Waters:

Si Siglunes-N 66°16'N, 18°50~W - 68°00'N, 18°50'W ICES (1997)La Langanes-NE 66°37'N, 14°16'W - 68°00'N, 12°4Q'W ICES (1997)Se Selvogsbanki-SW 63°41'N, 20041'W - 63°00'N, 21~8'W ICES (1997)

Labrador Sea and Grand Banks 0/ New/oundland:Fy Fylla Bank 63°57'N, 52°22'W - 63°12'N, 59°1O'W Stein (1988), ICES (1997)SH Seal Island/Hamilton Bank 53°14'N, 55°39'W - 55°04'N, 52°30'W Stein (1988), ICES (1997)Bo Bonavista 48°44'N, 52°58'W - 50000'N, 49°00'W Stein (1988), ICES (1997)FI Flemish Cap 47°00'N, 52°02'W - 47°00'N, 42°00'W Stein (1988), ICES (1997)

27 Station 27 47°33'N, 52°35'W ICES (1997)

B OWS "B" ("Bravo") 55°4TN,51°53'W ICES (1997)Central North Atlantic:

C OWS "C" ("Charlie") 52°45'N, 35°30'W ICES (1997)SlO SlO 49°04'N, 48°0TW - 52°24'N, 36°41'W Belkin and Levitus (1996);

Belkin et al. (1997) )

S15 S15 36°30'N, 35°00'W - 52°00'N, 35°00'W Belkin and Levitus (1996);Belkin et al. (1997)

S9 S9 52°45'N, 35°30'W - 37°11 'N, 09°13'W Belkin and Levitus (1996);Belkin et al. (1997)

Northeast Atlantic:Ro Malin Head-Rockall (MR) 56°40'N, 06°08'W - 57°3~'N, 13°38'W ICES (1997)NP Nolso-Flugga (FS)* 62°00'N, 06°12'W - 60056'N, OloOO'W ICES (1997); *Faroe-ShetlandFM Fair Isle-Munken (FIM)* 600 1O'N, 03°44'W - 61°12'N, 06°22'W ICES (1997); *Shetland-FaroeUt Utsira 59°17'N,05°02'E ICES (1997)

Norwegian, Barents, and Greenland Seas:M OWS "M" ("Mike") 66°00'N, 02°00'E ICES (1997)Sv Svin~y-NW 62°22'N, 05°12'E - 64°40'N, OooOO'E ICES (1997)Gi Gims~y-NW 68°24'N, 14°05'E - 70024'N, 08°12'E ICES (1997)Bj Bj~rn~ya (Bear Island)-S 70030'N, 20000'E - 74°15'N, 19°1O'E ICES (1997)Va Vardf2l-N 700 30'N, 31°13'E - 76°30'N, 31°13'E ICES (1997)Ko Kola-N 69°30'N, 33°30'E - 79°30'N, 33°30'E Loeng et al. (1992)Se Sem~yene (Sem Islands)-N 69°05'N, 37°20'E - 76°30'N, 3r20'E ICES (1997)So S~rkapp-W 76°20'N, 05°00'E - 76°20'N, 25°00'E Dickson and Blindheim (1984)

40

•

..

•

Table 2. Main sources of fresh water input into the Arctic Ocean(Notations: N/A, Not Available; 0', Standard Deviation)

Source Mean Flux, Variability Time Referencekm3/yr Period

River Runoff 3300 N/A N/A Aagaard and Carmack (1989)2646 0'=150 km3/yr 1973-1987 Becker (1995)1104 N/A N/A Steele et al. (1996)

Bering Strait 1670 N/A N/A Aagaard and Carmack (1989)1829 -914 to 3658 krn3/yr 1941-1987 Becker (1995)1987 N/A N/A Steele et al. (1996)

recipitation Less 900 400 to 1400 krn3/yr N/A Aagaard and Carmack (1989)Evaporation, P-E 1652* +/-50% 1973-1990 Walsh et a1. (1994)

631 N/A N/A Steele et a1. (1996)

Norwegian 250 N/A N/A Aagaard and Carmack (1989)Coastal Current

*Calculated from the 18-year annual mean moisture flux convergence of 17.3 crn/yr (Walsh etal. , 1994) and the Arctic Ocean area of 9.55 x 106 km2 (Aagaard and Carmack, 1989).

41

Table 3. Upper Layer Salinity Anomaliesof the 1970s and 1980s

I Location I GSA'70s I GSA'80s IWest Greenland Current: Fylla Bank max l1So=-0.6 max l1So=-O.4

Central Labrador Sea min SO_2So=34.52 min SD-zso=34.33

Inshore Labrador Current: Sta.27 max l1So=-O.4 max l1So=-0.6

North Atlantic Current: S9 Section, rnin Szoo=34.70 rnin Szoo=34.58SE of OWS "C" ("Charlie") (mainly,34.62-34.71)

OWS "C" ("Charlie") min Szoo=34.78 min S200=34.74

Irminger Current South of Iceland: max l1So=-0.045 max l1So=-0.045Selvogsbanki Section

Rockall Channel, Winter max l1So=-0.12 max l1So=-0.05

Faroe-Shetland Channel min So=35.26 rnin So=35.31(North Atlantic Water)

North Sea, Norwegian Coastal Current: min SlOo=34.54 rnin SlOo=34.66Utsira

Southern Norwegian Sea: Svin~y-NW min Sso_zoo=35.10 rnin Sso_zoo=35.18Section, Summer

Northern Norwegian Sea: Gims~y-NW min Sso_2oo=35.07 rnin SSD-200=35.13Section, Summer

Western Barents Sea: Fugl~ya-Bj~m~ya max ~Sso_2oo=-0.14 max ~Sso_200=-0.05

Section

Western Barents Sea: Fugl~ya-Bj~m~ya min Sso_zoo=34.92 min Sso.200=35.00Section, March Surveys

Central Barents Sea: Vard~-N Section max ~Sso_zoo=-O.13 max ~Sso_200=-0.05

Central Barents Sea: Vard~-N Section, min Sso_zoo=34.83 rnin SSD-200=34.93March Surveys

Eastern Barents Sea: Seml1lyene Seetion, rnin Sso_zoo=34.77 rnin Sso_zoo=34.82January-February Surveys

West Spitsbergen Current: S~rkapp-W min Sso_zoo=34.99 rnin Sso_200=35.00Section, Summer

42

..