Cold-Core Anticyclonic Eddies South of the Bussol’ Strait in the Northwestern Subarctic Pacific

Yasuda, Ichiro; Ito, Shin; Shimizu, Yoshihisa; Ichikawa, Kaoru; Ueda, Kenichi; Honma, Takayuki; Uchiyama, Masaaki; Watanabe, Kouichi; Sunou, Noriyuki; Tanaka, Koshi; Koizumi, Koji

doi:10.1175/1520-0485(2000)030<1137:ccaeso>2.0.co;2

Cited by 70 publications

(41 citation statements)

References 22 publications

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“…These problems should be further investigated in the future. Nevertheless, good similarities with observations have been found in our modeling results, in particular regarding the presence of mixed water produced by strong tidal currents in the straits and the presence of many eddies [ Talley and Nagata , 1995; Yasuda et al , 2000]. Moreover, long‐term observations by Kono and Kawasaki [1997] pointed to the fact that pure Okhotsk Sea water hardly reaches offshore of Hokkaido (just downstream of the Kuril Island Chain) and that the East Kamchatka Current water has already been modified before the confluence with Okhotsk Sea water from the Bussol' Strait.…”

Section: Water Exchange Between the Okhotsk Sea And The North Pacificsupporting

confidence: 88%

“…First of all, the effects of large‐scale wind‐driven and thermohaline circulations should be considered. In fact, the presence of significant seasonal and/or interannual variation in transport through the straits is reported [ Kawasaki and Kono , 1992; Yasuda et al , 2000]. This issue has not been well described and is currently under investigation by several researchers.…”

Section: Water Exchange Between the Okhotsk Sea And The North Pacificmentioning

confidence: 99%

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Tidally induced diapycnal mixing in the Kuril Straits and its role in water transformation and transport: A three‐dimensional nonhydrostatic model experiment

Nakamura

2004

J. Geophys. Res.

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Baroclinic processes generated by the K1 tidal flow around the Kuril Straits and their role in the linkage between the Okhotsk Sea and the North Pacific are investigated using a three‐dimensional nonhydrostatic model. Large‐amplitude unsteady lee waves are generated around sill tops all along the Kuril Island Chain and induce significant density inversions from the sea surface down to the ∼27.6 σθ density layer. Along with this wave breaking, a large flow of energy takes place from the swift tidal flow regions to greater depths as a result of the clockwise propagation of both the topographically trapped waves around the islands and the remaining unsteady lee waves. Such wave generation and energy exchange eventually cause intense diapycnal mixing over the shallow topographic features and near the bottom, leading to a maximum diapycnal diffusivity of over 103 cm2 s−1. Even in the deep Bussol' Strait, which is thought to be the main exit of the Okhotsk Sea water, considerable mixing (corresponding to diapycnal diffusivity values of between 10 ∼ 50 cm2 s−1) occurs. Vigorous mixing in the shallow regions produces low potential vorticity (PV) water in the upper layer and high PV water below. Accordingly, PV fronts are formed along the island chain and sustain instabilities that in turn release baroclinic eddies with low core PV values. These features are indicated in recent satellite imagery and in situ observations, suggesting that the tide is the controlling factor in the formation of fronts observed in the Kuril Straits. Tidally induced mean transport across the straits is estimated to reach ∼26 Sv (1 Sv = 106 m3 s−1), which is much larger than in the barotropic case. However, most of the exchanged water tends to circulate around the islands due to the effect of bottom topography, whereas eddies pinched off from the tidal fronts carry the exchanged water offshore. The amount of eddy‐driven offshore transport away from the islands reaches 14 Sv, with roughly half being directed to the North Pacific. This significant offshore transport spreads the effect of the diapycnal mixing taking place in the straits over wider areas of the North Pacific and the Okhotsk Sea. For example, the PV values generated in the eddies differ by 30–40% from the ambient water on average, whereas sea surface salinity within the eddies is 0.1 psu higher than the surroundings, corresponding to the density increase of 0.08 σθ. Thus the eddy transport provides significant PV and salinity fluxes to both the North Pacific and the Okhotsk Sea. Hence we infer that a combination of tidally driven processes taking place at the passages leads to the formation of eddies that play a central role in water transport and transformation and are an essential aspect of the physical interplay between the Okhotsk Sea and the North Pacific.

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Section: Water Exchange Between the Okhotsk Sea And The North Pacificsupporting

confidence: 88%

Section: Water Exchange Between the Okhotsk Sea And The North Pacificmentioning

confidence: 99%

Tidally induced diapycnal mixing in the Kuril Straits and its role in water transformation and transport: A three‐dimensional nonhydrostatic model experiment

Nakamura

2004

J. Geophys. Res.

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“…The number of alkenones in particulate material at 50 m approximately corresponded to those at 10 m in the subarctic area; therefore, the positive U k 0 37 anomaly during the period of low alkenone export at stations KNOT and 50N may reflect a relatively large contribution of alkenones in particulate material produced near the bottom of the subsurface layer, close to the limit of light availability, as a result of the deepening of the surface mixed layer. In the subarctic area of the western North Pacific, a warm-core ring, derived from the Kuroshio Extension, often intrudes into the subarctic (Yasuda et al, 1992), and mesoscale cold eddies observed south of Bussol' Strait near station KNOT (Rogachev et al, 1996;Yasuda et al, 2000) transport water with subtropical and polar properties into the subarctic area. It is possible that a mesoscale warm-core ring transported particles produced in subtropical regions into the subarctic area, thus influencing the export fluxes at our sediment-trap sites and resulting in the difference between alkenone-derived and in situ temperatures.…”

Section: Discussionmentioning

confidence: 99%

“…It is possible that a mesoscale warm-core ring also plays a role in transporting alkenones in particulate material produced in the subtropical region into the subarctic and might affect the export fluxes at our sediment-trap sites, especially during periods of low alkenone export. On the other hand, mesoscale eddies observed south of Bussol' Strait near station KNOT are cold and fresh, and the water in these eddies has properties resembling those of the Oyashio current and the Okhotsk Sea (Rogachev et al, 1996;Yasuda et al, 2000). These eddies are characteristically composed of water masses in which resting Hyalochaete spores are the main opal particles present, and they occur from the beginning of summer to midsummer (Onodera et al, 2003).…”

Section: Alkenone Temperaturementioning

confidence: 99%

Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

Harada

Sato

Shiraishi³

et al. 2006

Geochimica et Cosmochimica Acta

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“…The horizontal position of the vertical sections roughly corresponds to that of line M (Fig. 1b) Okhotsk water outflow from the Bussol Strait (e.g., Yasuda et al 2000), because these are characterized by outflows of relatively light, low-potential-vorticity waters.…”

Section: Introductionmentioning

confidence: 74%

Buoyancy shutdown process for the development of the baroclinic jet structure of the Soya Warm Current during summer

2018

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The Soya Warm Current (SWC), which is the coastal current along the northeastern part of Hokkaido, Japan, has a notable baroclinic jet structure during summer. This study addresses the formation mechanism of the baroclinic jet by analyzing a realistic numerical model and conducting its sensitivity experiment. The key process is the interaction between the seasonal thermocline and the bottom Ekman layer on the slope off the northeastern coast of Hokkaido; the bottom Ekman transport causes subduction of the warm seasonal thermocline water below the cold lower-layer water, so the bottom mixed layer develops with a remarkable cross-isobath density gradient. Consequently, the buoyancy transport vanishes as a result of the thermal wind balance in the mixed layer. The SWC area is divided into two regions during summer: upstream, the adjustment toward the buoyancy shutdown is in progress; downstream, the buoyancy shutdown occurs. The buoyancy shutdown theory assesses the bottom-mixed-layer thickness to be 50 m, consistent with observations and our numerical results. The seasonal thermocline from June to September is strong enough to establish the dominance of the buoyancy shutdown process over the frictional spindown.

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Cold-Core Anticyclonic Eddies South of the Bussol’ Strait in the Northwestern Subarctic Pacific

Cited by 70 publications

References 22 publications

Tidally induced diapycnal mixing in the Kuril Straits and its role in water transformation and transport: A three‐dimensional nonhydrostatic model experiment

Tidally induced diapycnal mixing in the Kuril Straits and its role in water transformation and transport: A three‐dimensional nonhydrostatic model experiment

Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

Buoyancy shutdown process for the development of the baroclinic jet structure of the Soya Warm Current during summer

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