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北太平洋西部における中層亜寒帯水の変質過程と北太平洋中層水の形成
https://fra.repo.nii.ac.jp/records/2001662
https://fra.repo.nii.ac.jp/records/2001662dceee74f-a1ea-454b-9f7a-2a4dc95f5d09
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||||||||
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| 公開日 | 2024-04-08 | |||||||||||
| タイトル | ||||||||||||
| タイトル | 北太平洋西部における中層亜寒帯水の変質過程と北太平洋中層水の形成 | |||||||||||
| 言語 | ja | |||||||||||
| タイトル | ||||||||||||
| タイトル | Modification processes of the intermediate subarctic water in the western North Pacific and its relation to formation of the North Pacific Intermediate Water | |||||||||||
| 言語 | en | |||||||||||
| 言語 | ||||||||||||
| 言語 | eng | |||||||||||
| 資源タイプ | ||||||||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_6501 | |||||||||||
| 資源タイプ | departmental bulletin paper | |||||||||||
| アクセス権 | ||||||||||||
| アクセス権 | metadata only access | |||||||||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||||||||
| 著者 |
河野, 時廣
× 河野, 時廣
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| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | The subarctic western boundary current in the North Pacific, the Oyashio, flows southwestward along the Kuril Islands and Hokkaido. Afterward, it turns to east at the coast of Tohoku district in Japan, and flows eastward along the Oyashio Front. In the present thesis, spatial changes in characteristics of water carried by the Oyashio and salinity minimum structure in the Mixed Water Region between the Oyashio and Kuroshio Fronts are studied with CTD data obtained recently in synoptic and repeated observations reaching the coast and deep layer. The spatial change of water property along the Oyashio around the Kuril Islands is examined in Chapter 3 using CTD data from synoptic observations in September 1989, 1990, 1991, and 1992. The water in the Oyashio around Bussol' Strait and north of the strait has properties of the Okhotsk Sea water, the typical western subarctic water and their mixture. The typical western subarctic water is similar to the original western subarctic water near the Kamchatka Peninsula. On the other hand, the waters south of Bussol' Strait show T-S curves which are concentrated within a relatively small range between the Okhotsk Sea water and the typical western subarctic water. This implies that the water exchange with the Okhotsk Sea occurs at Bussol' Strait and north of the strait, but not south of the strait. The outflow from the Okhotsk Sea through Bussol' Strait is negligible or very weak even though it exists, and thus the modification by the Okhotsk Sea water flowing out through Bussol' Strait is not dominant. Therefore, the water exchange of the Oyashio with the Okhotsk Sea and the modification of the western subarctic water carried by the Oyashio occur along the Kuril Islands in wide area around Bussol' Strait and north of it. The Oyashio separates into two flows at a place between Bussol' Strait and Hokkaido. The coastalpart of the Oyashio flows along the southern coast of Hokkaido, while the offshore part turns southeast just after the separation, and returns northeastward along the Oyashio Front. The coastal flow carries the western subarctic water modified by the Okhotsk Sea water, called the Oyashio Water, to the Hokkaido and Tohoku Areas, while the offshore branch flow carries the less modified water which has a similar property to the typical western subarctic water. The modification of the western subarctic water is limited to the coastal side of the Oyashio. The Oyashio flows along the Kuril Islands meandering around the anti-cyclonic eddies. Its path is variable but locations of the eddies are almost confined southeast of Bussol' Strait and southeast of Shikotan Island. Property of the Oyashio Water moreover changes significantly in the Hokkaido and Tohoku Areas. In Chapter 4, the changes of the water property in these areas are examined along the Oyashio using CTD data from the simultaneous observations made by multiple ships in September 1989. The Oyashio Water is largely modified by layering of the warm and saline waters and mixing with them at the densities less dense than 140cl/ton (26.6σθ). They are the modified Soya Warm Current water flowing out from the Okhotsk Sea through the straits between Iturup Island and Hokkaido, and the Tsugaru Warm Current Water from the Japan Sea through Tsugaru Straits. At the densities denser than 130cl/ton (26.7σθ), the property of the Oyashio Water does not change significantly from southeast of Iturup Island to the coast of Tohoku district at 39'20' N. On the other hand, T-S plots in the eastward Oyashio current region along the Oyashio Front just east of Tohoku district are scattered at the densities less dense than 70cl/ton (27.4σθ). The plots are located between the T-S curves of the Oyashio Water near the coast of Tohoku district and the Kuroshio Water south of the Kuroshio Front. It is concluded that large and sharp modification of the Oyashio Water occurs within 400km from the coast of Tohoku district, i.e. at the westernmost part of the Oyashio Front at about 39˚N. The modification is due to the mixing with the Kuroshio Water and the salinity minimum is formed at the densities around 125cl/ton (26.8σθ) by the modification. The modified Oyashio Water flows northeastward along the Oyashio Front and joins the offshore branch flow separated off the southern Kuril Islands, which carries the typical western subarctic water. The salinity minimum in the Mixed Water Region between the Oyashio and Kuroshio Fronts seems to be an origin of the salinity minimum around 125cl/ton in the subtropical region, called the North Pacific Intermediate Water (NPIW). Water exchange of the Mixed Water Region with the Oyashio and the Kuroshio Extension and the formation mechanism of the salinity minimum in this region are examined in Chapter 5. Mixing ratio RK is defined as (θ-θOY)/(θK-θOY) x100, where θOY, θK, and θ are potential temperature of the Oyashio and Kuroshio Waters and their mixture on the isopycnal surfaces, respectively. RK is illustrated using data obtained by the six observations along 144˚E from February 1990 to May 1991. Generally, RK increases southward from the Oyashio Front to the Kuroshio Front with the range of 20-120%. RK tends to increase largely around the Oyashio and Kuroshio Fronts. The gradient of RK on the isopycnal surfaces is large around the Oyashio Front at the densities less dense than 125cl/ton, while it is large around the Kuroshio Front at the denser densities. RK is averaged for each of the densities over the stations in the Mixed Water Region and it is averaged again over all the observations. The average over all the observations decreases largely with the increase of density at the densities less dense than 125cl/ton, although the profiles for all the observations are not similar. This agrees with the existence of the salinity minimum as dense as the NPIW in the Mixed Water Region in the average salinity profile. Thickness and volume transport of the Oyashio between the isopycnal surfaces near the coast of Hokkaido are calculated using CTD data obtained by the repeated observations from January 1990 to May 1991. They increase largely with density at the densities less dense than 125cl/ton. The formation mechanism is suggested as follows. Water exchange of the Oyashio with the Mixed Water Region is larger below the isopycnal surface of 125cl/ton than above it. The influence of the Kuroshio Water to the mixture in the Mixed Water Region is relatively large above the 125cl/ton surface, and thus the salinity minimum is formed below the saline water largely influenced by the Kuroshio Water. The NPIW density could depend only on the density structure of the Oyashio. | |||||||||||
| 言語 | en | |||||||||||
| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | 親潮は北太平洋亜寒帯循環の西岸境界流であり,ベーリング海を起源とし千島列島沿いを南西に流れる.この流れは千島列島沿いでオホーツク海と海水を交換し北海道·東北海域に至り,さらに40˚N前後で東へと向きを変えて親潮フロントに沿って東へと流れる、大気の影響のない中層では,親潮によって運ばれる中層の亜寒帯水の海水特性は,千島列島の中央にあるブッソル海峡を通って流出するオホーツク海水によって低温·低塩分へと変化すると考えられている、このようにオホーツク海水の影響を受けた後,親潮によってし北海道·東北海域に至った海水は親湖水と呼ばれている。北海道·東北海域では親潮フロントの周辺とそれ以南の海域で塩分極小水が広く分布し,これは親潮水の海水特性は親潮が東に転じたときにいずれかの海域で急激に変化することを示唆している、本研究の第一の目的は中層亜寒帯水の変質過程を総観的な観測結果を用いて明らかにすることである。親潮フロントと黒潮フロントの間の混合水域でみられる塩分極小水は亜寒帯域に広く分布する塩分極小水である北太平洋中層水の起源であるとされている、また混合水域での塩分極小水は,親潮水と黒潮水との混合によって形成され,黑潮水の影響を強く受けた海水の底面に相当することが示唆されている。本研究の第二の目的は混合水域での塩分極小の形成について親潮水の変質の観点から考察を行うことである。親潮は岸近くを流れ,順圧的であり,暖水塊の北上のために短期的な変動が大きいことが明らかとなっている.このため本研究では新たに沿岸かつ深層に至るまで短期間に観測した水温·塩分データを用いた.本論文で明らかにされた親潮の分布と水塊の変質過程は以下の様に要約できる。これまでオホーツク海からの流出があるとされてきた北ウルップ海峡では,オホーツク海からの流出流はほとんどないか存在しても非常に弱い。さらに,親潮は二つの流れに分かれることが明らかとなった、すなわち,千島列島の岸近くの主流部は北海道沿岸域に至り東北沿岸域で東に転じて親潮フロントに沿って北束に流れる。一方,沖側の流れは南部千島列島の南東沖で転流して親潮前線に沿った親潮の主流部と合流する。また,北ウルップ海峡の南束域と色丹島の南東域に時計回りの渦が存在し,親潮はそれらを迂回して流れる、渦の数は時によって異なり,二つの時もあればどちらか一方の時,さらには全くない時もあるが,渦の位置はこの二ケ所に限られているようである。親潮の運ぶ西部亜寒帯水は,オホーツク海の低温低塩分水と混合し変質する.その混合は北ウルップ海峡とその北方海域における親潮の千島列島側で顕著に起きている、変質した西部亜寒帯水は親潮水と呼ばれ,親潮の主流によって北海道·東北近海に運ばれる,親潮の沖側分岐流の運ぶ海水特性は変質前の西部亜寒帯水とほとんど変わらない。親潮の運ぶ海水の特性は,津軽暖流水の影響を受けるごく表層を除くと北ウルップ海峡の南から東北地方沿岸の北緯39˚N付近までほとんど変質しない。大きな変質は親潮が東北地方の沿岸から離岸し,親潮フロントに沿って400km程東に流れる間に起きる。この変質は黒潮水との混合によるもので,その結果中層以浅の塩分が増加し,σθ=26.8付近に塩分極小構造が形成される、変質した親潮水は親潮フロントに沿って北東に運ばれる.塩分極小構造は親潮フロントと親潮フロントの間の混合水域で願著にみられ,北太平洋中層水の主な起源と考えられている,黒潮水に対する親潮水の混合比率は概ね北向きに増加し,その増加率はフロント付近で大きい。とりわけ,d,=26.8よりも深い密度面では黒潮フロントで,浅い密度面では親潮フロントでそれぞれ大きい。比率の鉛直変化をみると,塩分の高い黒潮水の比率が塩分極小の存在する。。= 26.8よりも浅い層で急激に大きくなっている,親潮について等密度面に挟まれた層の厚さを6回の観測どついて平均すると,dg=26.8を境にそれより浅い層で急激に薄くなり,流量も減少している、そのため,すー26.8よりも浅い層では混合水域への親潮水の供給が小さく,相対的に黒潮水の影響が強くなって高塩分水となり,dg=26.8付近に塩分極小の形成されることが示唆された. |
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| 言語 | ja | |||||||||||
| 書誌情報 |
ja : 北海道区水産研究所研究報告 en : Bulletin of the Hokkaido National Fisheries Research Institute 巻 60, p. 145-223, ページ数 79, 発行日 1996-03 |
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| 出版者 | 北海道区水産研究所 | |||||||||||
| 言語 | ja | |||||||||||
| 出版者 | ||||||||||||
| 出版者 | Hokkaido National Fisheries Research Institute | |||||||||||
| 言語 | en | |||||||||||
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| 収録物識別子タイプ | PISSN | |||||||||||
| 収録物識別子 | 0513-2541 | |||||||||||
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| 収録物識別子タイプ | NCID | |||||||||||
| 収録物識別子 | AN1015410X | |||||||||||
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| 識別子タイプ | Local | |||||||||||
| 関連識別子 | hnf_k_60_2 | |||||||||||
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| 識別子タイプ | URI | |||||||||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010541842 | |||||||||||
| 言語 | ja | |||||||||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||||||||
