However，becausethesurfacesouthwardintrusionoftheOyashiowateriscon丘nedtothenorthoftheBoso Peninsula4），thefurthersouthwardintruSionoftheOyashiowateriscarriedoutonlyinanundersurfacelayer． The southwardintrusion ofthe Oyashio waterinanintemediatelayer has bee

Buu，Fac．Bioresources，MieUniv．  

No．6：83−108   March2臥1991  

0bservationoftheSalinityMimimumIJayer   intheShikokuBasinSouthofJapan  

YoshihikoSEK】NE＊，YuichiSATO＊andIchitaroSAKAMOTO＊†  

＊Facu旺yofBioresources，MieUniversity  

†presentaddress：Shin・NipponMeteorologicaland   Oceanograpl血aiConsultantCo．，Ltd．  

Abstract  

SalinityobservationsintheShikokuBasinsouthofJapanhavebeenmadeduringtheperiodof1983−  

1988．Focusis placedonthe sahnityminimum】ayer，Whichexists at depths of400N600m overa   COntinentalsLopeand／orhdgeslopeandatdepthsof7OOqlOOOmoveraHatdeepbasin．Intheprescnt   report，alJthesaLinitydataalongtheobservationallinesarepresented．   

Someinterestingfeaturesofthesa昆nity丘eldsaredetected．Twodominantsalinityminimumareasare   foundhthesalinityminimumlayer．Oneminimumareaexistsoverthecontinentalslopeandtheother   minimumexistsoverthe且atbasinintheShikokuBasin，Whichlocates200−300kmoffihoretothetbrmer   minimum，Itissuggestedthattheformerminimumisor王girntedbytheintermediateOyashiowater，  

WhichtlowssourthwardalongtheBosoPeninsu】a．The払tterminimumoveratlatbasinisinferredtobe   Orl詳natedなomthesecondOyashiointruSion．Onthewhole，thecharacterwithtwominimumsaunity   areasisobservedinful■thersouthintheSl11kokuBasin．＼＼・hich＼VaSWellobservedinthceastcrnregionto   theIzu−OgasawaraRidge．  

Keywords：Saunityminimumlayer，theOyasl五o，intemlediatewater，Ventilaぬn．  

1．Introduction  

IthasbeenobservedthatsomezooplanktonswhichordinaryhvesinthewateroftheOyashiosystem，  

Copepodacalanu＄andSagittaelegans，arefound魚一OmSaunityminimumlayertobottomlayerintheSagami   Bayl）・2）・3）・ThisねctsuggeststhattheOyashiowaterintrudessouthwardtotheSagamiBay・Itisalsoweu   knownthatasurfaceOyashiowatersometin1eSintrudesremarkabuysouthwarduptooffshoreofasouthernarea   ofIbarakiPrefecture4）・5），WhereasthemeansouthwardムmitofthesuぬceOyashiowaterisabout380−390N．  

However，becausethesurfacesouthwardintrusionoftheOyashiowateriscon丘nedtothenorthoftheBoso   Peninsula4），thefurthersouthwardintruSionoftheOyashiowateriscarriedoutonlyinanundersurfacelayer．   

The southwardintrusion ofthe Oyashio waterinanintemediatelayer has been studied by some   authors6），7）・8）．Recently，YANGetal．（1990）9）pointedoutbythehistoricaldataanalysisthattheintemediate   Oyas山owaterintrudesuptotheSagamiBay，butitdoesnotintrudetoawesternsideofthelzuPeninsula．  

Theyalsoresultedthatlowsahitywaterwithrelativelyhighoxygencorltentisobservedatthesoutheastoだof   the Boso Peninsula，Whjchis carried by the anomalous southward OyashiointruSionin the surfacelayer．  

AcceptedNovember27．1990   

YoshiIlikoSEKINLミ．YuichiSATOandIchitaroS＾KAMOTO  

However，becausetheobservationlinesanalyzedbyYANGetal．（1990）9）arecon餌edtoanorthof33．50N，the   intruSionofthe Oyashio waterin south to thislatitude hasbeennot studied．lnorder to seethe salinity  

distributionto餌rthersouthernarea，Wehaveobservedthesalinity鮎1dsbyuseofthetraining＆researchvessel  

Seisui−maruOfMieUniversity，duringtheperiodof1983to1988．hlthepresentreport，allofthesalinitydatais   presented．Someinteresthgfeaturesofthesahnity5eldsaredetected．  

2．Observations  

劫1theobservationshavebeencarriedoutbythetraining＆researchvesselSeisui−maruOfMieUniversity，  

ofwhichdetailsaretabulatedinTablel．Temperatureandsal最tyareobservedbyCTD，Ofwhichmaximum   depthoftheobservationis3200db− Althoughthismaximumdepthisinsu触ientforthestudyofbottomwater，  

itisenoughtoseethesahityminimumlayeralmostabove1200db．  

Tilblt！1．Observationsnladeb〉′theSeisui−maruforthepresentstudy   Cruisenanle   PeriodsofObservation  

8−12May1983   16−19Jul．1983   25−28Jul．1983   300ct．−3Nov．1983   28Jan．−2Feb．1984   16−25Apr．1984   15−18Jul．1984   25−28Jul．1984   1Jl−20Sep．1984   21−30Nov．1984   17−24May1985   14−17Jul．1985   21−25Jul．1985   10−16May1986   14−17Jul．1986   23−26Jul．1986   28Nov．−10Ⅰ）ec．1986   16−18Jul．1987  

24−26Jul．1987   27Nov．−9Dec．1987  

8−16May1988   270ct．−3Nov．1988  

ウ︼ l 1 2 ウ︼ 4 1 2 3 4 3 1 1 3 1 1 3 1 1 2 1 2  

83MAY   83JUし1   83JUL−2   830CT   8弔AN   84APR   8弔Uし1   8刃Uし2   84SEP   84NOV   85MAY   8封Uし1  

86MAY   8尉Uし1  

86NOV   87JUし1  

87NOV   88MAY   880CT  

3．VcrticaldistributionofsalinitysouthofJapan   

Theobservedsa肋ity氏edlsalongautheobservational血esarepresentedinFig・1・Somecornmon   characteristicsaredetected．Thesal混tyminimumlayerexistsatdepthsof400−600moveracontinental   slope．Asitgoeso触horereglOn，depthofthesaぬityminimumlayerincreases・   

Ifweseethespacialsaunityvariationinthesa血ityminimumlayerr twodominantminimumareasare   

SalinityminimunllayerintheSh血）kuBasin  

∇  

330   320N  

O  

n︶  

∩︶  1  ︵qP︶山∝⊃SS山∝L   ∩︶  ︵U  ▲U  2  

1350   1400   1450 E 

Fig・1・VerticalsectioriOfsal最tyaels（in％0）．ContourintervalisO．1％oandre感OnSlessthan34．3％oare   StippledlThelocationofthe、・ertica】sectionisshownbysolid山1einthebottommap，Wherelocation   OfthemainKuroshioaxisandvelocityvectorsbyJapanHydrographicDepartmentarealsoshown．  

Verticallargearro＼VOVerthe＼・erticalsectionsho＼＼・alocationofmainaxisoftheKuroshio．   

YoshihikoSEKtNE，YuichiSATOandIchitaroSAKAMOTO   86  

︵宅︶山∝⊃SS山∝L    0  0  0  ワー  

135巴45盲  

1350  

1458E  

Fig．1continued（1）   

Salinityminin1um）ayerintheShikokuBasin  

▲U  O  

︻U  l  三 ﹂二〃ご二こ   ︵︺  ○  ︹︶  ︻ノー  

1350  

1458E  

Fig．1continued（2）  

88   Yosは揖koSEXIN軌YuichiSATOandIchitaroSAK旭OTO  

∇   ∇  

て35と4gE   1380E  

†300E   1358  

145GE  

Fig．1continued（3）   

Salinityminlmum払yerintheShikokuBasin  

一U  

▲U  

▲U  †l  

︵ぷP︶山∝⊃∽S山∝m   0  0  ︹︶  2  

′ 135と45E  

1388E   1858   1408  

Fig．1continued（4）   

YoshihikoS7iKl鵬，￥uichiSATOandIchitaroSAKAMOTO  

90   

︵︹弓︶山⊂⊃SS山∝L  

135∑45′E   308N  

1300E   13S0   1400   1450E  

Fig．1con血ued（5）   

SaiinityminimumlayerintheShikokuBasin   91  

1360  

▽  

1コ8■E  

340  330  320N  

▼ i ▼  ▼ l ▼  ▼  も  

ヽ 

言P︶山∝⊃SS山∝L  

1300E   1358   1ヰ伊   1450E  

Fig．1continued（6）   

YoshihikoSEl（lNE．YuichlS＾TOandIchitaroS＾KÅNOTO   92   

︵qP︶山こ⊃SS山∝d  

139∑30′E  

1300E   1350   1400   1450E  

Fi払1continued（7）   

Sa血ityminin1umlayer山theShlkokuBasin  

︵qP︶山U⊃SS山Ud  

135已45′E   1380E    13終45′E  

1300E   1350   1408   1450E  

Fig．1continued（8）  

YoshihikoSlミKINE．YuichiS＾TOandlchitaroS＾K品10TO  

94   

︵︻亘山正⊃SS霊芝  

1300E  

1458E  

Fig．1contblued（9）   

Salinitymi】1imum）aycrinthcSllikokuBasin  

︵qP︶山什≡SS﹈J   ∩︶  0  0  2   

135三45〜E   137已30′E  

1く∋08E  

1350   1400   1458E  

Fig．1continued（10）  

＼  

Yosb肋ikoSEKINE，Yuic昆SATOand王chit群OSÅRAMOTO  

▽  

1甲○ 

1甲0。1チ伊  

りつ0  32   31。   3ぴ  

1300E   1350   1400   1450E  

Fig．1continued（11）   

Salinityminimum）ayerinthcSllikokuBasin  

○  

︵U  

0  1  

︵qP︶﹈U﹁一SS﹈⊂L  

13アユ30竃  

1300∈   1350   1400   1450E  

Fig．1continued（12）  

YosllillikoSEKINLミ．YuichiSATOandlchitaroS∧K∧MOTO  

98  

芸P︶山∝⊃SS山∝d   

13辞30−E  

1300E   1350   川OD   l頑58E  

Fig．1con血ued（13）   

Salinit〉PminimumlayerinthcShlkokuBasin  

︵宅︶山∝コSS山∝L  

13（〕O E  

135D   1400   145D E  

Fig．1continued（14）   

YoshihikoSl三KINlミ，YuichiS＾TOandIchitaroS＾．（＾hlOTO  

100   

︹︶  

∩︶  0  

1  ︵qP︶山∝⊃SS山∝m   ○  ︹U  n︶  2   

136望・30′E  

1800E  

1400  

Fig．1conthued（15）   

SaLinit）・mi山mumlayerintheShikokuBasin  

爪U  0  

0  

↓■  

︵︵宅︶﹈U⊃SS﹈UL   0  ∩︶  ︹︶  つl  

136L30′E  

1300E   1350   1400  

Fig．1continued（16）  

YoshihikoSEKINE，YuichiSATOand‡chitaroSAIくÅMOTO   

か  

1戸90 一戸O0 3第一○罠  

︵qヱ山∝⊃SS山∝L   ︹︶  ︹︶  ▲U  2   

1300E   135b   140。   1450E  

Fig．1conぬued（17）   

Sa】init〉・minimunlla〉PerintheSI血okuBasin  

▽   1甲01守901う00E  

1〇60  1370  

87JUL−1   87JUL−2  

130pE  

1408   1450E  

Fig．1continued（18）   

104   Yoshih紋oSEK削EメYuichiSATOandIcはtaroSÅKんMOTO   

ウ  

1〇40  

13150 E 

く○  

03−3三0 310N  

1300E   1350  

145bE  

Fig．1con血ued（19）   

S血tyminimumlayerintheShikokuBasin  

八U  

︹︶  

∩︶  1  ︵qP︶山こ⊃SS山∝d   O  n︶  ▲U  2  

1300E   135Q   1400   145。E  

Fig．1continued（20）   

YoshihikoSEK！NE，YuichiSATOandIchitaroSARAMOTO  

てざ二 

︵≡︶︶﹈こ﹁一SS山正J  

1300E   135d   140d   1450E  

Fig．1continued（21）   

Sa血ityminimumlayerintheShikokuBasin  

COmmOnlydetected．One＄ahnityminimumexistsoverthe continentalslope，Ofwhichdepthisrelatively   Sha封ow，400−600m．Anothersal最tyminimumexistsovera鮎tareaintheShikokuBasin．Thi＄mi涙mum   arealaocatesabout200−300kmoffshoretothefomerminimumoverthecontinentaisIope．Asthelowerlayer   aowshowsfewdensitystrat漬cation，ithasastrongtendencytoaowalongthegeostrophiccontour（f／h，fisthe   COriousparameter，andhisadepthofocean），Whichisweuapproximatedbytheisoplethofdepth．Fromthis，it   issuggestedthatthesahityminimumoverthecontinentalsiopeisori由natedbytheintermediateOyashio   Water，Which且owssouthwardalongtheBosoPenins山a．TheorlglnOfthiswaterisassociatedwiththe鮎st   OyashiointrusionaowingsouthwardalongtheJapanesecoast．Ontheotherhand，打omthegeographical   positions，thesalirdtyninimumovertheaatbasinisinferredtobeori如ated＆omtheOyashiosecondintruSion   locatedo鮎horereg10ntOthe丘rstintrusionand／oroffshoreOyashiowatertothesecondintruSion．Thiswater  

hasapossibihtytointrude払theShikokuBasinaftergolれgSOuthwardciockwiselyaroundtheIzu−Ogasawara   Ridge．  

比isdsoshownthatthischaracter涙thtwosal最仁y血nimumareasisobservedin餌ぬersou仏hthe   S地相ku王主asinincompari＄On融机heobservationdresultssoおproposed8）・9）．As血sねatureiswe払observed  

intheeasternregiontotheIzu−OgasawaraRidge，itshouldbenotedthatthealmostsimilarfeatureofthesa払ity   鮎1dsexistsinthewesternsideoftheIzu−OgasawaraRidge．AlthoughthediscussionbasedonthedissoIved   OXygendistibutionshouldbemade，thereぬbledataofthedissoivedoxygenwerenotobtainedbytheCTD   SyStemduetoitslongerresponsetimethanthoseoftemperatureandsalinity．Moredetailedanalysesonthese   problemswiubereportedinasucceedingpaper．  

AclⅦOWIedgment  

Wewould臆etothankCaptainsT．）王NNOandI．IsHIKURA，a㍊theo抗cersandthecrewoftheSeisui−maruOf   MieUniversityfortheirskiilfuuassistanceduringthecruises．ThanksareextendedtoMessrs．K．KITAMURA，  

lく．NAKANO，N．K＾SUT＾Nl．Y．M＾EI）AandY．ⅠくoIZUトItfortheirhelpinthehydrograpl血observation．Wealso   thankMessrs．T．HAYAS軋S．KAWÅMATAandD．KIYOHARÅfbrtheirassistanceindrawingsome魚gures．  

Re鎚ren（：eS   

l）OMOR】．M．CahnuscristatusandsubmergenceoftheOyashiowater．Deep−SeaRes．，14：525−532（1967）．  

2）OMORl．M．andO．T＾N入ti＾ Distributionofsomecold−Water SpeCiesofcopepodsinthePacihc＼VaterOffeast・Central    Ho王IShu，Japan．J，Oceanogr．Soc．Japan，23：63−73（1967）．  

3）SEK王GUCHIH．Distdbutionalexpansionofthepela由ccopepodinrelationtoitslarge−SCaleontogeneticverticalmigration．   

Buil．Fac．Fisb，MieUnivり2：19−28（1975）、  

4）SEKiNE，Y．AnomaloussouthwardintrusionoftheOyashioeastofJapan．J．Geophys．Res．，93：2247M2255（1988）．  

5）SEXrNE．Y．Anumericaiexperimentontheanomaloussouthwardintru＄ionoftheOyashio．）．Oceanogr．Soc，Japan，LI4：   

60−67（1988）．  

6）HASUNUMA，K．Furmationoftheintem】ediatesal血tym血mum払theirnorthwesternPacihcocean．BuhOceanRes．   

玩st．Univ．Tokyo，9：ト47（1977）．  

7）KAWAl．H．RingssouthofKuroshioandtheirpo＄Siblero王esinmaintenanceoftheintemediatesalinityminumumand    formationoftheski房ackandalbacore鮎hinggrounds．Rep血tsofthefbrthC．S．K．symposium．27q28（1979）．  

8）YANG，S．K．andY，NAGÅTA Thepropertiesoftheintermediatewaterinthead5acentseaofJapan．Umitosora，66：ト   

14（1990）．   

108   YoshihikoSEKtNE，YuichiSA，roandIchitaroSAKAMOTO  

9）YANG，S．KリY．N＾G＾Ir＾．K．T］uR＾andM．K∫川一ABE（1990）TheintermedjateO）・aShjowaterf）owingsouthwardalongthe    easterncoastofBosoPeninsuLa．Marinesciencemonthly，22：221−229（1990）．  

四国海盆内郭の塩分極小層の観測  

関根 幾彦＊・佐藤 裕一＊・坂本市太郎＊1■  

＊三蕊大学生物資源学部  

†現所属：新日本気象海洋㈱  

1983年から1988年の閣に日本南岸の四国梅盆北部の塩分分瑚の観測を特に塩分榛小柳こ注目して行った。塩分魔小  

僧ほ大陸棚斜面上や海嶺の斜面上では400−600m深程度にあり，平地な大洋底上では700−1000ⅠⅥ孫穏皮にある。  

この報告では観測したすべての補㈱線上の塩分分布の遊瑳データを提示する。   

塩分観測データの解析により，幾つかの特徴的な塩分分布があることが確認された。塩分極小層は明確に大陸靡を面  

上にあるものとそれより200−300km程度押倒の平坦な凶観梅盆上にあるものの二つの領域に別れで存在する。前者  

は房総半島沿岸沿いに南下する親潮の中層水に関連し，後者は親潮の解二潜入以凍の霧下に関連することが示唆され  

た。伊豆海嶺以来では常時観測されるこの二つの塩分極小の存在が伊豆海嶺以西の四国施錠でもみられることが示さ  

れた。