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Toshio Suga - One of the best experts on this subject based on the ideXlab platform.

  • Enhanced warming of the subtropical Mode Water in the North Pacific and North Atlantic
    Nature Climate Change, 2017
    Co-Authors: Shusaku Sugimoto, Kimio Hanawa, Toshio Suga, Tomowo Watanabe, Shang-ping Xie
    Abstract:

    Warming of surface ocean Waters is well known, but how the subsurface Waters are changing is less clear. This study shows that subtropical Mode Water in the North Atlantic and North Pacific is warming at twice the rate of the surface Waters. Over the past six decades, the subtropical surface ocean has warmed at rates close to those of global mean surface ocean temperature1 except in western boundary current regions where the surface warming is locally enhanced by a factor of two2. Changes in the subsurface ocean, however, remain unclear because of lack of data. Compiling historical temperature measurements—some available for the first time—here we show that the subtropical Mode Water has warmed over the past six decades in both the North Pacific and North Atlantic. The rate of the warming is twice as large in the Mode Waters than at the surface. Subtropical Mode Waters are important Water masses of vertically uniform temperature that are a few hundred metres thick and distributed widely in the main thermocline of the subtropical oceans3. The enhanced warming of subtropical Mode Waters can be traced back to the surface warming in the formation regions along the western boundary current extensions. Furthermore, we detect increased temperature stratification and decreased dissolved oxygen in the subtropical Mode Waters. The latter change has clear implications for predicting biogeochemical responses to climate warming.

  • Synoptic observation of Central Mode Water in its formation region in spring 2003
    Journal of Oceanography, 2014
    Co-Authors: Eitarou Oka, Toshio Suga, Shinya Kouketsu, Kazuyuki Uehara, Daigo Yanagimoto, Toshiya Nakano, Sachihiko Itoh, Shota Katsura, Lynne D. Talley
    Abstract:

    Hydrographic data east of Japan from five research cruises and Argo profiling floats in spring 2003 have been analyzed to examine the relationship of the formation of Central Mode Water (CMW) and Transition Region Mode Water (TRMW) in late winter 2003 to thermohaline fronts and mesoscale eddies. TRMW and the denser variety of CMW (D-CMW) were formed continuously just south of the subarctic frontal zone between 155°E and 165°W with little relation to eddies, suggesting that the absence of the permanent thermocline and halocline in this area is essential for the formation. The lighter variety of CMW (L-CMW) was formed south of the Kuroshio bifurcation front and east of 165°E, partly in an anticyclonic eddy associated with the Kuroshio Extension. Some portion of D-CMW and L-CMW likely had been subducted to the permanent pycnocline by crossing southward the Kuroshio bifurcation front and the Kuroshio Extension front, respectively. In contrast, the formation of these Waters in the western regions was inactive and was significantly different from that described previously using multiyear Argo float data. West of 155°E, TRMW and D-CMW were formed only in two anticyclonic eddies that had been detached from the Kuroshio Extension 1–2 years ago. L-CMW was hardly formed west of 165°E, which might be related to the upstream Kuroshio Extension being in its stable state characterized by low regional eddy activity.

  • Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability
    Journal of Oceanography, 2012
    Co-Authors: Eitarou Oka, Bo Qiu, Shinya Kouketsu, Kazuyuki Uehara, Toshio Suga
    Abstract:

    Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.

  • The Transition Region Mode Water of the North Pacific and Its Rapid Modification
    Journal of Physical Oceanography, 2011
    Co-Authors: Hiroko Saito, Kimio Hanawa, Toshio Suga, Nobuyuki Shikama
    Abstract:

    AbstractUsing Argo float data, this study examined the formation region, spatial distribution, and modification of transition region Mode Water (TRMW), which is a recently identified pycnostad in the subtropical–subarctic transition region of the North Pacific, the basin-scale boundary region between subtropical and subarctic Water masses. Analyses of the formation fields of Water masses within and around the transition region reveal that TRMW forms in a wide area from the western to central transition region and is separated from the denser variety of central Mode Water (D-CMW) to the south by a temperature and salinity front. TRMW has temperatures of 4°–9°C and salinities of 33.3–34.0, making it colder and fresher than D-CMW. TRMW has a density range of 26.3–26.6 σθ, and thick TRMW is widely distributed in the transition region. However, the range of the T–S properties at TRMW cores is substantially reduced downstream within 10°–20° longitude from the formation region by gradually losing its fresh and c...

  • “Eddy Resolving” Observation of the North Pacific Subtropical Mode Water
    Journal of Physical Oceanography, 2011
    Co-Authors: Eitarou Oka, Katsuya Toyama, Toshio Suga, Chiho Sukigara, Keishi Shimada, Jiro Yoshida
    Abstract:

    AbstractHydrographic data obtained by high-resolution shipboard observations and Argo profiling floats have been analyzed to study the mesoscale structure and circulation of the North Pacific Subtropical Mode Water (STMW). The float data show that in the late winter of 2008, STMW having a temperature of approximately 18.8°, 17.7°, and 16.6°C formed west of 140°E, at 140°–150°E, and east of 150°E, respectively, in the recirculation gyre south of the Kuroshio Extension. After spring, the newly formed STMW gradually shift southward, decreasing in thickness. Simultaneously, the STMWs of 16.6° and 17.7°C are gradually stirred and then mixed in terms of properties. In late fall, they seem to be integrated to form a single group of STMWs having a temperature centered at 17.2°C. Such STMW circulation in 2008 is much more turbulent than that in 2006, which was investigated in a previous study. The difference between the two years is attributed to the more variable state of the Kuroshio Extension in 2008, associate...

Kimio Hanawa - One of the best experts on this subject based on the ideXlab platform.

  • Enhanced warming of the subtropical Mode Water in the North Pacific and North Atlantic
    Nature Climate Change, 2017
    Co-Authors: Shusaku Sugimoto, Kimio Hanawa, Toshio Suga, Tomowo Watanabe, Shang-ping Xie
    Abstract:

    Warming of surface ocean Waters is well known, but how the subsurface Waters are changing is less clear. This study shows that subtropical Mode Water in the North Atlantic and North Pacific is warming at twice the rate of the surface Waters. Over the past six decades, the subtropical surface ocean has warmed at rates close to those of global mean surface ocean temperature1 except in western boundary current regions where the surface warming is locally enhanced by a factor of two2. Changes in the subsurface ocean, however, remain unclear because of lack of data. Compiling historical temperature measurements—some available for the first time—here we show that the subtropical Mode Water has warmed over the past six decades in both the North Pacific and North Atlantic. The rate of the warming is twice as large in the Mode Waters than at the surface. Subtropical Mode Waters are important Water masses of vertically uniform temperature that are a few hundred metres thick and distributed widely in the main thermocline of the subtropical oceans3. The enhanced warming of subtropical Mode Waters can be traced back to the surface warming in the formation regions along the western boundary current extensions. Furthermore, we detect increased temperature stratification and decreased dissolved oxygen in the subtropical Mode Waters. The latter change has clear implications for predicting biogeochemical responses to climate warming.

  • Influence of Kuroshio Path Variation South of Japan on Formation of Subtropical Mode Water
    Journal of Physical Oceanography, 2014
    Co-Authors: Shusaku Sugimoto, Kimio Hanawa
    Abstract:

    AbstractDistributions of subtropical Mode Water (STMW) in the northwestern part of the North Pacific Subtropical Gyre were investigated, using temperature–salinity profiles from 2005 to 2011, with particular reference to the Kuroshio meander and non-meander path states, south of Japan. In spring of meander years, warm STMW with a potential temperature of 19°–20°C (potential density anomaly of 24.6–24.9 kg m−3) was found in the Shikoku Basin, whereas cold STMW below 19°C was distributed throughout the southern region of Japan in non-meander years. The warm STMW was formed in a spatially isolated and warm winter mixed layer (ML) in the Shikoku Basin, where a local recirculation developed in association with the Kuroshio meander path; both the absence of horizontal mixing with a cold ML south of the Kuroshio Extension because of the spatially isolated ML and an increase in horizontal heat advection due to the westward flow associated with this local recirculation caused the ML warming in the Shikoku Basin. A...

  • The Transition Region Mode Water of the North Pacific and Its Rapid Modification
    Journal of Physical Oceanography, 2011
    Co-Authors: Hiroko Saito, Kimio Hanawa, Toshio Suga, Nobuyuki Shikama
    Abstract:

    AbstractUsing Argo float data, this study examined the formation region, spatial distribution, and modification of transition region Mode Water (TRMW), which is a recently identified pycnostad in the subtropical–subarctic transition region of the North Pacific, the basin-scale boundary region between subtropical and subarctic Water masses. Analyses of the formation fields of Water masses within and around the transition region reveal that TRMW forms in a wide area from the western to central transition region and is separated from the denser variety of central Mode Water (D-CMW) to the south by a temperature and salinity front. TRMW has temperatures of 4°–9°C and salinities of 33.3–34.0, making it colder and fresher than D-CMW. TRMW has a density range of 26.3–26.6 σθ, and thick TRMW is widely distributed in the transition region. However, the range of the T–S properties at TRMW cores is substantially reduced downstream within 10°–20° longitude from the formation region by gradually losing its fresh and c...

  • Indian Ocean Subtropical Mode Water: its Water characteristics and spatial distribution
    Ocean Science, 2010
    Co-Authors: Takamasa Tsubouchi, Toshio Suga, Kimio Hanawa
    Abstract:

    Abstract. We have improved a basic description (Water characteristics and spatial distribution) of the Indian Ocean Subtropical Mode Water (IOSTMW) using an isopycnally averaged three-dimensional hydrographic dataset. Two Mode Waters and corresponding wintertime mixed layer depth maxima were observed north of the subtropical front (STF) in the South Indian Ocean: IOSTMW (within 25.8–26.2 σθ) in the region of 28–45° E and another subtropical Mode Water in the subtropical gyre (within 26.4–26.7 σθ) in the 60–80° E longitudinal band. Through careful examination of the spatial distribution and Water characteristics of a core in the layer of minimum vertical temperature gradient (LMVTG), we identified that a mass of LMVTG corresponds to IOSTMW. The average Water characteristics of the IOSTMW during approximately 1960–2004 were 16.54 ± 0.49 °C, 35.51 ± 0.04 psu and 26.0 ± 0.1 σθ. The IOSTMW distribution area was estimated to be 25–50° E, 27–38° S. The formation region and approximate Water characteristics of the second subtropical Mode Water were also estimated. Its probable formation region was 37–42° S, 60–80° E and north of the STF, with approximate Water characteristics of 12.84 ± 0.57 °C, 35.17 ± 0.11 psu and 26.57 ± 0.04 σθ.

  • Ventilation of the North Pacific subtropical pycnocline and Mode Water formation
    Progress in Oceanography, 2008
    Co-Authors: Toshio Suga, Yoshikazu Aoki, Hiroko Saito, Kimio Hanawa
    Abstract:

    Abstract The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical Mode Water (STMW), central Mode Water (CMW), and eastern subtropical Mode Water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σθ) range of the lighter STMW (25.0

Shang-ping Xie - One of the best experts on this subject based on the ideXlab platform.

  • Evolution of the North Pacific Subtropical Mode Water in Anticyclonic Eddies
    Journal of Geophysical Research: Oceans, 2017
    Co-Authors: Shang-ping Xie, Qinyu Liu, Cong Liu, Xiaopei Lin
    Abstract:

    Anticyclonic eddies (AEs) trap and transport the North Pacific subtropical Mode Water (STMW), but the evolution of the STMW trapped in AEs has not been fully studied due to the lack of eddy-tracking subsurface observations. Here we analyze profiles from special-designed Argo floats that follow two STMW-trapping AEs for more than a year. The enhanced daily sampling by these Argo floats swirling around the eddies enables an unprecedented investigation into the structure and evolution of the trapped STMW. In the AEs, the upper (lower) thermocline domes up (concaves downward), and this lens-shaped double thermocline encompasses the thick STMW within the eddy core. The lighter STMW (25.0 ∼ 25.2 σθ) trapped in AEs dissipates quickly after the formation in winter because of the deepening seasonal thermocline, but the denser STMW (25.2 ∼ 25.4 σθ) remains largely unchanged except when the AE passes across the Izu Ridge. The enhanced diapycnal mixing over the ridge weakens the denser STMW appreciably. While many AEs decay upon hitting the ridge, some pass through a bathymetric gap between the Hachijojima and Bonin Islands, forming a cross-ridge pathway for STMW transport. By contrast, the North Pacific Intermediate Water (NPIW) underneath is deeper than the eddy trapping depth (600 m), and hence left behind east of the Izu Ridge. In Argo climatology, the shallow STMW (< 400 m) intrudes through the gap westward because of the eddy transport, while the NPIW (800 m) is blocked by the Izu Ridge.

  • Enhanced warming of the subtropical Mode Water in the North Pacific and North Atlantic
    Nature Climate Change, 2017
    Co-Authors: Shusaku Sugimoto, Kimio Hanawa, Toshio Suga, Tomowo Watanabe, Shang-ping Xie
    Abstract:

    Warming of surface ocean Waters is well known, but how the subsurface Waters are changing is less clear. This study shows that subtropical Mode Water in the North Atlantic and North Pacific is warming at twice the rate of the surface Waters. Over the past six decades, the subtropical surface ocean has warmed at rates close to those of global mean surface ocean temperature1 except in western boundary current regions where the surface warming is locally enhanced by a factor of two2. Changes in the subsurface ocean, however, remain unclear because of lack of data. Compiling historical temperature measurements—some available for the first time—here we show that the subtropical Mode Water has warmed over the past six decades in both the North Pacific and North Atlantic. The rate of the warming is twice as large in the Mode Waters than at the surface. Subtropical Mode Waters are important Water masses of vertically uniform temperature that are a few hundred metres thick and distributed widely in the main thermocline of the subtropical oceans3. The enhanced warming of subtropical Mode Waters can be traced back to the surface warming in the formation regions along the western boundary current extensions. Furthermore, we detect increased temperature stratification and decreased dissolved oxygen in the subtropical Mode Waters. The latter change has clear implications for predicting biogeochemical responses to climate warming.

  • Multicore structure of the North Pacific subtropical Mode Water from enhanced Argo observations
    Geophysical Research Letters, 2016
    Co-Authors: Wendian Gao, Shang-ping Xie, Cong Liu
    Abstract:

    Seventeen Argo profiling floats with enhanced vertical and temporal sampling were deployed in the Kuroshio recirculation gyre in the western North Pacific in late March 2014. The Subtropical Mode Water (STMW) observed in many profiles displays a “multicore structure” with more than one minima in potential vorticity (PV), corroborated by vertical covariations in apparent oxygen utilization (AOU). These cores are classified into four subModes according to density and AOU. The subMode Waters are typically 100 m thick, in which PV varies by 1 × 10−10 m−1 s−1 and AOU by 10 µmole/kg. The STMW multicore structure is most frequently observed in spring, gradually taken over by single-core profiles into summer. The seasonal evolution is suggestive of vertical mixing, especially in STMW of lower density.

  • Fast and slow responses of the North Pacific Mode Water and Subtropical Countercurrent to global warming
    Journal of Ocean University of China, 2013
    Co-Authors: Shang-ping Xie, Qinyu Liu
    Abstract:

    Six coupled general circulation Models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed for examining the full evolution of the North Pacific Mode Water and Subtropical Countercurrent (STCC) under global warming over 400 years following the Representative Concentration Pathways (RCP) 4.5. The Mode Water and STCC first show a sharp weakening trend when the radiative forcing increases, but then reverse to a slow strengthening trend of smaller magnitude after the radiative forcing is stablized. As the radiative forcing increases during the 21st century, the ocean warming is surface-intensified and decreases with depth, strengthening the upper ocean’s stratification and becoming unfavorable for the Mode Water formation. Moving southward in the subtropical gyre, the shrinking Mode Water decelerates the STCC to the south. After the radiative forcing is stabilized in the 2070s, the subsequent warming is greater at the subsurface than at the sea surface, destabilizing the upper ocean and becoming favorable for the Mode Water formation. As a result, the Mode Water and STCC recover gradually after the radiative forcing is stabilized.

  • Response of Mode Water and Subtropical Countercurrent to greenhouse gas and aerosol forcing in the North Pacific
    Journal of Ocean University of China, 2013
    Co-Authors: Liyi Wang, Qinyu Liu, Shang-ping Xie
    Abstract:

    The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950–2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) Mode Waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the Mode Water formation region. The aerosol effect on the SST, Mode Waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40°N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.

Eitarou Oka - One of the best experts on this subject based on the ideXlab platform.

  • Synoptic observation of Central Mode Water in its formation region in spring 2003
    Journal of Oceanography, 2014
    Co-Authors: Eitarou Oka, Toshio Suga, Shinya Kouketsu, Kazuyuki Uehara, Daigo Yanagimoto, Toshiya Nakano, Sachihiko Itoh, Shota Katsura, Lynne D. Talley
    Abstract:

    Hydrographic data east of Japan from five research cruises and Argo profiling floats in spring 2003 have been analyzed to examine the relationship of the formation of Central Mode Water (CMW) and Transition Region Mode Water (TRMW) in late winter 2003 to thermohaline fronts and mesoscale eddies. TRMW and the denser variety of CMW (D-CMW) were formed continuously just south of the subarctic frontal zone between 155°E and 165°W with little relation to eddies, suggesting that the absence of the permanent thermocline and halocline in this area is essential for the formation. The lighter variety of CMW (L-CMW) was formed south of the Kuroshio bifurcation front and east of 165°E, partly in an anticyclonic eddy associated with the Kuroshio Extension. Some portion of D-CMW and L-CMW likely had been subducted to the permanent pycnocline by crossing southward the Kuroshio bifurcation front and the Kuroshio Extension front, respectively. In contrast, the formation of these Waters in the western regions was inactive and was significantly different from that described previously using multiyear Argo float data. West of 155°E, TRMW and D-CMW were formed only in two anticyclonic eddies that had been detached from the Kuroshio Extension 1–2 years ago. L-CMW was hardly formed west of 165°E, which might be related to the upstream Kuroshio Extension being in its stable state characterized by low regional eddy activity.

  • Progress of North Pacific Mode Water research in the past decade
    Journal of Oceanography, 2012
    Co-Authors: Eitarou Oka, Bo Qiu
    Abstract:

    This article reviews the progress in research on North Pacific Mode Waters of the past decade from the physical oceanographic perspective. The accumulation of satellite altimeter sea surface height data, the rapid growth of the Argo profiling float array, and the advancement in eddy-resolving ocean general circulation Models have greatly improved the traditional views on the Mode Waters that were formed prior to the 1990s based on the analyses of historical temperature/salinity data. Areas where significant progress was made include: (1) descriptions of the Mode Waters’ distributions and properties with fine spatial scales, particularly in their formation regions in winter where observational data had been insufficient; (2) clarifications of the Mode Waters’ formation and subduction processes relating to the large-scale mean circulation, as well as to the time-varying mesoscale eddy field; (3) impacts of the Mode Waters’ circulation and dissipation processes on the climate and biogeochemical processes; and (4) dynamic versus thermodynamic causes underlying the Mode Waters’ decadal changes. In addition to the review, future directions for Mode Water research are also presented.

  • Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability
    Journal of Oceanography, 2012
    Co-Authors: Eitarou Oka, Bo Qiu, Shinya Kouketsu, Kazuyuki Uehara, Toshio Suga
    Abstract:

    Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.

  • “Eddy Resolving” Observation of the North Pacific Subtropical Mode Water
    Journal of Physical Oceanography, 2011
    Co-Authors: Eitarou Oka, Katsuya Toyama, Toshio Suga, Chiho Sukigara, Keishi Shimada, Jiro Yoshida
    Abstract:

    AbstractHydrographic data obtained by high-resolution shipboard observations and Argo profiling floats have been analyzed to study the mesoscale structure and circulation of the North Pacific Subtropical Mode Water (STMW). The float data show that in the late winter of 2008, STMW having a temperature of approximately 18.8°, 17.7°, and 16.6°C formed west of 140°E, at 140°–150°E, and east of 150°E, respectively, in the recirculation gyre south of the Kuroshio Extension. After spring, the newly formed STMW gradually shift southward, decreasing in thickness. Simultaneously, the STMWs of 16.6° and 17.7°C are gradually stirred and then mixed in terms of properties. In late fall, they seem to be integrated to form a single group of STMWs having a temperature centered at 17.2°C. Such STMW circulation in 2008 is much more turbulent than that in 2006, which was investigated in a previous study. The difference between the two years is attributed to the more variable state of the Kuroshio Extension in 2008, associate...

  • Formation and Subduction of Central Mode Water Based on Profiling Float Data, 2003–08
    Journal of Physical Oceanography, 2011
    Co-Authors: Eitarou Oka, Katsuya Toyama, Shinya Kouketsu, Kazuyuki Uehara, Taiyo Kobayashi, Shigeki Hosoda, Toshio Suga
    Abstract:

    Abstract Temperature and salinity data from Argo profiling floats in the North Pacific during 2003–08 have been analyzed to study the structure of winter mixed layer north of the Kuroshio Extension and the subsurface potential vorticity distribution in the subtropical gyre in relation to the formation and subduction of the central Mode Water (CMW). In late winter, two zonally elongated bands of deep mixed layer extend at 33°–39° and 39°–43°N, from the east coast of Japan to 160°W. These correspond to the formation region of the lighter variety of CMW (L-CMW) and that of the denser variety of CMW (D-CMW) and the recently identified transition region Mode Water (TRMW), respectively. In the western part of the L-CMW and D-CMW–TRMW formation regions west of 170°E, the winter mixed layer becomes deeper and lighter to the east (i.e., to the downstream). As a result, the formed Mode Water is reentrained into the mixed layer in the farther east in the following winter and modified to the lighter Water and is thus...

Nobuyuki Shikama - One of the best experts on this subject based on the ideXlab platform.

  • The Transition Region Mode Water of the North Pacific and Its Rapid Modification
    Journal of Physical Oceanography, 2011
    Co-Authors: Hiroko Saito, Kimio Hanawa, Toshio Suga, Nobuyuki Shikama
    Abstract:

    AbstractUsing Argo float data, this study examined the formation region, spatial distribution, and modification of transition region Mode Water (TRMW), which is a recently identified pycnostad in the subtropical–subarctic transition region of the North Pacific, the basin-scale boundary region between subtropical and subarctic Water masses. Analyses of the formation fields of Water masses within and around the transition region reveal that TRMW forms in a wide area from the western to central transition region and is separated from the denser variety of central Mode Water (D-CMW) to the south by a temperature and salinity front. TRMW has temperatures of 4°–9°C and salinities of 33.3–34.0, making it colder and fresher than D-CMW. TRMW has a density range of 26.3–26.6 σθ, and thick TRMW is widely distributed in the transition region. However, the range of the T–S properties at TRMW cores is substantially reduced downstream within 10°–20° longitude from the formation region by gradually losing its fresh and c...

  • A role of eddies in formation and transport of North Pacific Subtropical Mode Water
    Geophysical Research Letters, 2003
    Co-Authors: Hiroki Uehara, Kimio Hanawa, Toshio Suga, Nobuyuki Shikama
    Abstract:

    [1] Hydrographic data acquired during 2001 by Argo profiling floats deployed in the Kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of North Pacific Subtropical Mode Water (NPSTMW). That is, the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies. In the succeeding seasons, mesoscale eddies retain NPSTMW during their southwestward movement from the NPSTMW formation region, so that anticylonic eddies contribute substantially to the NPSTMW transportation. The spatial distributions of the mixed layer depth in winter and the NPSTMW thickness in the succeeding seasons, based on the float data, suggest that they are affected by mesoscale eddies. The float data also provide the statistical relations of these quantities against the thermocline depth, which are consistent with our inference.