Wind and buoyancy driven intermediate-layer overturning in the Sea of Okhotsk

Matsuda, Junji; Mitsudera, Humio; Nakamura, Tomohiro; Uchimoto, Kiyotaka; Nakanowatari, Takuya; Ebuchi, Naoto

doi:10.1016/j.dsr.2009.04.014

Cited by 23 publications

(47 citation statements)

References 45 publications

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“…Because the simulated SSS was restored to the climatological value, the absence of the warming signal in the simulated data may be related to the fact that the effect of interannual variation in thermodynamic processes in the Sea of Okhotsk was not well represented in this model simulation. This result is consistent with earlier studies, in which significant effects of air temperature variability over the Sea of Okhotsk on ocean temperature at intermediate depths have been shown by observed data (Kashiwase et al 2014) and model simulations (Matsuda et al 2009;Fujisaki et al 2011;Nakanowatari et al 2014) through sea ice production. Furthermore, earlier studies have reported a significant freshening signal in the upper intermediate layer of the Sea of Okhotsk (Hill et al 2003;Ohshima et al 2014).…”

Section: Wongsupporting

confidence: 82%

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Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific: Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

Nakanowatari

Mitsudera

Motoi³

et al. 2015

Journal of Physical Oceanography

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Using oceanographic observations and an eddy-resolving ice-ocean coupled model simulation from 1955 to 2004, the effects of the wind-driven ocean circulation change that occurred in the late 1970s during multidecadal-scale freshening of the North Pacific Intermediate Water (NPIW) at salinity minimum density (;26.8 s u ) were investigated. An analysis of the observations revealed that salinity decreased significantly at the density range of 26.6-26.8 s u in the western subtropical gyre, including the mixed water region (MWR). The temporal variability of the salinity is dominated by the marked change in the late 1970s. With results similar to the observations, the model, selectively forced by the interannual variability of the wind-driven ocean circulation, simulated significant freshening of the intermediate layer over the subtropical gyre. The significant freshening is related to the increase in southward transport of the Oyashio associated with the intensification of the Aleutian low. Accompanying these changes, the intrusion of fresh and low potential vorticity water, originating in the Okhotsk Sea, to the MWR increased, and the freshening signal propagated farther southward in the western subtropical gyre during the subsequent 6 yr, crossing the Kuroshio Extension. These results indicate that the multidecadal-scale freshening of the NPIW is partly caused by intensification of the wind-driven cross-gyre transport of the subarctic water to the subtropical gyre.

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Section: Wongsupporting

confidence: 82%

“…The freshening of surface water would tend to shift the core density of DSW (26.8 s u ) to a lighter density. Thus, there is a possibility that the freshening of surface water leads to a reduction in DSW on the salinity minimum density surface of NPIW and results in a warming and salinification of OSIW (Matsuda et al 2009;Nakanowatari et al 2014).…”

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confidence: 99%

Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific: Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

Nakanowatari

Mitsudera

Motoi³

et al. 2015

Journal of Physical Oceanography

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“…Such a freshening has also been observed in the upper layer of the Okhotsk Sea (Hill et al 2003;Ohshima et al 2014). On the other hand, the stronger wind-driven circulation leads to enhancement of DSW transport through both an increase in DSW density (caused by the northward transport of the saline water from the Pacific) and an increase in DSW transport from the shelf to the interior (Matsuda et al 2009;Sasajima et al 2010). …”

Section: Introductionmentioning

confidence: 80%

“…Matsuda et al (2009) showed that a surface air temperature warming of 38C over the Okhotsk Sea leads to a decrease in DSW, which then results in a warming of the OSIW at 26.8s u by 0.68C. In addition, Fujisaki et al (2011) focused on DSW formation processes from 1998 to 2000, and found that the density of DSW is controlled by ice production: the larger ice production leads to the higher DSW density.…”

Section: Introductionmentioning

confidence: 99%

“…A large amount of sea ice within the Okhotsk Sea is produced along the northwestern coastal polynyas by severe wintertime winds blowing from the Eurasian continent (Martin et al 1998;Ohshima et al 2003;Nihashi et al 2009;Kawaguchi et al 2010), and the brine rejection associated with sea ice production leads to vertical convection of up to 27.0s u [s u is defined as potential density 2 1000 (kg m 23 ); thus, the density of seawater 1027.0 kg m 23 means 27.0s u ], resulting in the formation of cold, oxygen-rich, dense shelf water (DSW) (Kitani 1973;Gladyshev et al 2000;Shcherbina et al 2003;Nakamura et al 2006;Matsuda et al 2009). DSW is transported southward by the cyclonic ocean circulation in the Okhotsk Sea Fukamachi et al 2004), and it then mixes with the warm, saline water originating from the North Pacific.…”

Section: Introductionmentioning

confidence: 99%

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Causes of the Multidecadal-Scale Warming of the Intermediate Water in the Okhotsk Sea and Western Subarctic North Pacific

et al. 2015

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Causes of the multidecadal-scale warming of the intermediate water in the Okhotsk Sea and the western subarctic North Pacific during 1980-2008 are investigated using an ice-ocean coupled model with interannually varying atmospheric forcing. A hindcast experiment qualitatively reproduces the warming and decadal fluctuations of the intermediate water that are similar to those of observations: the warming is significant along the western part of the Okhotsk Sea and subarctic frontal region. The effects of the thermohaline-and wind-driven ocean circulation on the warming are evaluated from perturbation experiments on thermohaline (turbulent heat and freshwater fluxes) and wind causes, respectively. The thermohaline causes are shown to contribute positively to warming in the Okhotsk Sea Intermediate Water (OSIW). The heat budget analysis for the OSIW indicates that the warming is related to a decrease in cold and dense shelf water (DSW) flux, which is caused by a decrease in sea ice and surface water freshening. In contrast, the wind cause has a cooling effect in the OSIW through an increase in DSW. In the subarctic frontal region, the warming is mainly caused by the wind stress change. The heat budget analysis indicates that the warming is related to an increase in the northward advection of the subtropical warm water. These results imply that both thermohaline-and winddriven ocean circulation changes are essential components of the warming in the intermediate water. The atmospheric conditions responsible for the warming are related to a weakened Aleutian low and Siberian high in early and late winter.

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Overturning circulation that ventilates the intermediate layer of the Sea of Okhotsk and the North Pacific: The role of salinity advection

et al. 2015

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Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high-resolution North Pacific Ocean model with a curvilinear grid as fine as 3 km 3 3 km in the Sea of Okhotsk, we succeeded in representing the three-dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and time scales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e., density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong.

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Wind and buoyancy driven intermediate-layer overturning in the Sea of Okhotsk

Cited by 23 publications

References 45 publications

Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific: Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific: Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

Causes of the Multidecadal-Scale Warming of the Intermediate Water in the Okhotsk Sea and Western Subarctic North Pacific

Overturning circulation that ventilates the intermediate layer of the Sea of Okhotsk and the North Pacific: The role of salinity advection

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