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Sabrina Speich - One of the best experts on this subject based on the ideXlab platform.

  • A hydrographic section from South Africa to the southern limit of the Antarctic Circumpolar Current at the Greenwich meridian .
    Deep Sea Research Part I: Oceanographic Research Papers, 2008
    Co-Authors: Sergey Gladyshev, Michel Arhan, Alexey Sokov, Sabrina Speich
    Abstract:

    The properties and Circulation of water masses leaving and entering the Atlantic Ocean south of Africa are examined using data from a hydrographic and Lowered acoustic Doppler current profiler section from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC). At the upper levels, the ACC fronts are well determined using either classical water mass definitions or gradient-based criteria. While the locations of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF) seem controlled by the neighbouring ridges, that of the Subtropical Front (STF) is much influenced in this region (not, vert, similar10°E) by northwestward propagating Agulhas rings. No large amount of Subantarctic Mode Water (SAMW) is observed, but two varieties of vertically homogeneous water are found in eddies detached from the Agulhas retroflection: one is remotely (Indian Ocean) formed SAMW, and the other a local variety formed through winter convection in some eddies. The deep front imprints allow one to recognize lower circumpolar deep water (LCDW) from the Drake Passage (south of the SACCF), a mix of LCDW and North Atlantic Deep Water (NADW) injected in the ACC in the Argentine Basin (between the PF and STF), and diluted NADW from a southeastward pathway along the African continental slope (north of the STF in these data). The Abyssal Circulation, much controlled by ridges transverse to the ACC, shows a westward entry of diluted WSDW into the Cape Basin below the PF and two cyclonic patterns in the southern and central Cape Basin superimposed on a wider eastward trend. Transport estimates are given for the ACC, its fronts, and the Abyssal Circulation. The baroclinic and total ACC transports are not, vert, similar136 and not, vert, similar153 Sv, respectively. Bottom-intensified westward flows O(20 Sv) have only a limited effect on the ACC net transport, being laterally compensated. They, however, affect the frontal structure: the not, vert, similar15 Sv entry of diluted WSDW seems related to a branching of the PF, and its eastward reCirculation widens the full-depth transport signature of the SAF.

  • A hydrographic section from South Africa to the southern limit of the Antarctic Circumpolar Current at the Greenwich meridian
    Deep Sea Research Part I: Oceanographic Research Papers, 2008
    Co-Authors: Sergey Gladyshev, Michel Arhan, Alexey Sokov, Sabrina Speich
    Abstract:

    Abstract The properties and Circulation of water masses leaving and entering the Atlantic Ocean south of Africa are examined using data from a hydrographic and Lowered acoustic Doppler current profiler section from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC). At the upper levels, the ACC fronts are well determined using either classical water mass definitions or gradient-based criteria. While the locations of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF) seem controlled by the neighbouring ridges, that of the Subtropical Front (STF) is much influenced in this region (∼10°E) by northwestward propagating Agulhas rings. No large amount of Subantarctic Mode Water (SAMW) is observed, but two varieties of vertically homogeneous water are found in eddies detached from the Agulhas retroflection: one is remotely (Indian Ocean) formed SAMW, and the other a local variety formed through winter convection in some eddies. The deep front imprints allow one to recognize lower circumpolar deep water (LCDW) from the Drake Passage (south of the SACCF), a mix of LCDW and North Atlantic Deep Water (NADW) injected in the ACC in the Argentine Basin (between the PF and STF), and diluted NADW from a southeastward pathway along the African continental slope (north of the STF in these data). The Abyssal Circulation, much controlled by ridges transverse to the ACC, shows a westward entry of diluted WSDW into the Cape Basin below the PF and two cyclonic patterns in the southern and central Cape Basin superimposed on a wider eastward trend. Transport estimates are given for the ACC, its fronts, and the Abyssal Circulation. The baroclinic and total ACC transports are ∼136 and ∼153 Sv, respectively. Bottom-intensified westward flows O(20 Sv) have only a limited effect on the ACC net transport, being laterally compensated. They, however, affect the frontal structure: the ∼15 Sv entry of diluted WSDW seems related to a branching of the PF, and its eastward reCirculation widens the full-depth transport signature of the SAF.

Sergey Gladyshev - One of the best experts on this subject based on the ideXlab platform.

  • A hydrographic section from South Africa to the southern limit of the Antarctic Circumpolar Current at the Greenwich meridian .
    Deep Sea Research Part I: Oceanographic Research Papers, 2008
    Co-Authors: Sergey Gladyshev, Michel Arhan, Alexey Sokov, Sabrina Speich
    Abstract:

    The properties and Circulation of water masses leaving and entering the Atlantic Ocean south of Africa are examined using data from a hydrographic and Lowered acoustic Doppler current profiler section from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC). At the upper levels, the ACC fronts are well determined using either classical water mass definitions or gradient-based criteria. While the locations of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF) seem controlled by the neighbouring ridges, that of the Subtropical Front (STF) is much influenced in this region (not, vert, similar10°E) by northwestward propagating Agulhas rings. No large amount of Subantarctic Mode Water (SAMW) is observed, but two varieties of vertically homogeneous water are found in eddies detached from the Agulhas retroflection: one is remotely (Indian Ocean) formed SAMW, and the other a local variety formed through winter convection in some eddies. The deep front imprints allow one to recognize lower circumpolar deep water (LCDW) from the Drake Passage (south of the SACCF), a mix of LCDW and North Atlantic Deep Water (NADW) injected in the ACC in the Argentine Basin (between the PF and STF), and diluted NADW from a southeastward pathway along the African continental slope (north of the STF in these data). The Abyssal Circulation, much controlled by ridges transverse to the ACC, shows a westward entry of diluted WSDW into the Cape Basin below the PF and two cyclonic patterns in the southern and central Cape Basin superimposed on a wider eastward trend. Transport estimates are given for the ACC, its fronts, and the Abyssal Circulation. The baroclinic and total ACC transports are not, vert, similar136 and not, vert, similar153 Sv, respectively. Bottom-intensified westward flows O(20 Sv) have only a limited effect on the ACC net transport, being laterally compensated. They, however, affect the frontal structure: the not, vert, similar15 Sv entry of diluted WSDW seems related to a branching of the PF, and its eastward reCirculation widens the full-depth transport signature of the SAF.

  • A hydrographic section from South Africa to the southern limit of the Antarctic Circumpolar Current at the Greenwich meridian
    Deep Sea Research Part I: Oceanographic Research Papers, 2008
    Co-Authors: Sergey Gladyshev, Michel Arhan, Alexey Sokov, Sabrina Speich
    Abstract:

    Abstract The properties and Circulation of water masses leaving and entering the Atlantic Ocean south of Africa are examined using data from a hydrographic and Lowered acoustic Doppler current profiler section from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC). At the upper levels, the ACC fronts are well determined using either classical water mass definitions or gradient-based criteria. While the locations of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF) seem controlled by the neighbouring ridges, that of the Subtropical Front (STF) is much influenced in this region (∼10°E) by northwestward propagating Agulhas rings. No large amount of Subantarctic Mode Water (SAMW) is observed, but two varieties of vertically homogeneous water are found in eddies detached from the Agulhas retroflection: one is remotely (Indian Ocean) formed SAMW, and the other a local variety formed through winter convection in some eddies. The deep front imprints allow one to recognize lower circumpolar deep water (LCDW) from the Drake Passage (south of the SACCF), a mix of LCDW and North Atlantic Deep Water (NADW) injected in the ACC in the Argentine Basin (between the PF and STF), and diluted NADW from a southeastward pathway along the African continental slope (north of the STF in these data). The Abyssal Circulation, much controlled by ridges transverse to the ACC, shows a westward entry of diluted WSDW into the Cape Basin below the PF and two cyclonic patterns in the southern and central Cape Basin superimposed on a wider eastward trend. Transport estimates are given for the ACC, its fronts, and the Abyssal Circulation. The baroclinic and total ACC transports are ∼136 and ∼153 Sv, respectively. Bottom-intensified westward flows O(20 Sv) have only a limited effect on the ACC net transport, being laterally compensated. They, however, affect the frontal structure: the ∼15 Sv entry of diluted WSDW seems related to a branching of the PF, and its eastward reCirculation widens the full-depth transport signature of the SAF.

Minoru Nakata - One of the best experts on this subject based on the ideXlab platform.

  • Modelling of Western Pacific Abyssal Circulation – Preliminary Experiment
    Deep Ocean Circulation - Physical and Chemical Aspects, 1993
    Co-Authors: Nobuo Suginohara, Shigeaki Aoki, Minoru Nakata
    Abstract:

    Abstract As a first step to model the western Pacific Abyssal Circulation, buoyancydriven Circulation in a basin which has a simple geometry but retains characteristic features of the western Pacific is studied using a multi-level numerical model. The Circulation is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. It is clearly demonstrated that the bottom and deep waters take different paths from the southern ocean to the Philippine Basin. The bottom water flows northward along the western boundary crossing the equator, and at the northern end of the Marshall Islands it turns westward to flow to the opening of the Philippine Basin. On the other hand, the deep water at mid-depths flows directly into the Philippine Basin along the coasts. Numerical modelling studies which the present study is based upon are reviewed.

  • modelling of western pacific Abyssal Circulation preliminary experiment
    Elsevier oceanography series, 1993
    Co-Authors: Nobuo Suginohara, Shigeaki Aoki, Minoru Nakata
    Abstract:

    Abstract As a first step to model the western Pacific Abyssal Circulation, buoyancydriven Circulation in a basin which has a simple geometry but retains characteristic features of the western Pacific is studied using a multi-level numerical model. The Circulation is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. It is clearly demonstrated that the bottom and deep waters take different paths from the southern ocean to the Philippine Basin. The bottom water flows northward along the western boundary crossing the equator, and at the northern end of the Marshall Islands it turns westward to flow to the opening of the Philippine Basin. On the other hand, the deep water at mid-depths flows directly into the Philippine Basin along the coasts. Numerical modelling studies which the present study is based upon are reviewed.

  • Effects of a continental slope along the western boundary on the Abyssal Circulation
    Journal of Oceanography, 1992
    Co-Authors: Minoru Nakata, Shigeaki Aoki, Nobuo Suginohara
    Abstract:

    To investigate effects of a continental slope along the western boundary on the Abyssal Circulation, numerical experiments using multi-level models were carried out. An ocean which extends over the northern and southern hemispheres is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. When the reference density for the cooling is vertically uniform, effects of the slope emerge clearly for the slope with considerably broad width. The deep western boundary current flowing over the slope feeds no bottom flows in the southern hemisphere, and carries the warmed deep water into the northern hemisphere. This leads to the increased meridional density gradient, which results in the modification of deep flow patterns. When the reference density is vertically distributed, the upper and lower northward flowing western boundary currents form in the deep layer. As the density stratification relaxes the topographic control, the westward intensification of the upper boundary current is achieved over the slope. The intensified flow is accompanied by the countercurrent and they form the horizontal reCirculation over the slope. However, the effects are confined around the slope region and the interior flow patterns do not change. The lower boundary current is not significantly affected by the slope and has the large width with no countercurrent. It is found that the actual continental slope does not have significant effects on the gross feature of the thermohaline Circulation.

John Wilkin - One of the best experts on this subject based on the ideXlab platform.

  • Abyssal Circulation around New Zealand—a comparison between observations and a global Circulation model
    Marine Geology, 1999
    Co-Authors: Lionel Carter, John Wilkin
    Abstract:

    Abstract Observations of Abyssal currents off eastern New Zealand are compared to results from the Los Alamos National Laboratory (LANL) global ocean Circulation model. Physical oceanographic measurements are few along the 6000-km long path of the Abyssal flow so they are supplemented by geological data including bottom photographs, nephelometer profiles, sediment analyses, and high resolution seismic profiles. While greatly increasing the spatial coverage of the observations, the geological data have limitations concerning temporal aspects of the Circulation, e.g., the resolution of seismic records restricts identification of bottom current action to periods of ∼12,000 years or more. Despite these limitations, the model compares well with observations for the region south of Chatham Rise (43°S). There, the model shows a highly energetic, topographically steered flow that coincides with zones of seafloor erosion, active bedload transport, and prominent benthic nepheloid layers. In contrast, correlation is less clear to the north of Chatham Rise. Model output and observations agree on flow directions in regions of marked topography, but in areas of subdued relief, model current directions depart from reality. Such departures are because the model bathymetry has (1) a grid too coarse to resolve small but key current pathways, and (2) step-like contours that artificially guide the flow even though in nature the seabed may have low relief. The model also underestimates current intensity as measured by eddy kinetic energy (EKE) and volume transport. However, these deficiencies can be reduced by improving the model bathymetry and better representating the oceanic processes such as the interaction of Rossby waves with the bathymetry.

  • Abyssal Circulation around new zealand a comparison between observations and a global Circulation model
    Marine Geology, 1999
    Co-Authors: Lionel Carter, John Wilkin
    Abstract:

    Abstract Observations of Abyssal currents off eastern New Zealand are compared to results from the Los Alamos National Laboratory (LANL) global ocean Circulation model. Physical oceanographic measurements are few along the 6000-km long path of the Abyssal flow so they are supplemented by geological data including bottom photographs, nephelometer profiles, sediment analyses, and high resolution seismic profiles. While greatly increasing the spatial coverage of the observations, the geological data have limitations concerning temporal aspects of the Circulation, e.g., the resolution of seismic records restricts identification of bottom current action to periods of ∼12,000 years or more. Despite these limitations, the model compares well with observations for the region south of Chatham Rise (43°S). There, the model shows a highly energetic, topographically steered flow that coincides with zones of seafloor erosion, active bedload transport, and prominent benthic nepheloid layers. In contrast, correlation is less clear to the north of Chatham Rise. Model output and observations agree on flow directions in regions of marked topography, but in areas of subdued relief, model current directions depart from reality. Such departures are because the model bathymetry has (1) a grid too coarse to resolve small but key current pathways, and (2) step-like contours that artificially guide the flow even though in nature the seabed may have low relief. The model also underestimates current intensity as measured by eddy kinetic energy (EKE) and volume transport. However, these deficiencies can be reduced by improving the model bathymetry and better representating the oceanic processes such as the interaction of Rossby waves with the bathymetry.

  • Pacific Ocean Heat Transport at 24°N in a High-Resolution Global Model
    Journal of Physical Oceanography, 1995
    Co-Authors: John Wilkin, James V. Mansbridge, J. Stuart Godfrey
    Abstract:

    Abstract Meridional heat transport in the North Pacific Ocean in a seasonally forced high-resolution global ocean general Circulation model is compared to observations. At 24°N, annual mean heat transport in the model of 0.37×1011W is half the most recent direct estimate of 0.76±0.3×1015W from hydrographic data. The model value is low because the model ocean loses too little heat in the region of the Kuroshio Current Extension. The water ventilated in this region returns southward across 24°N at depth between 200 m and 500 m approximately 2°−4°C too warm. If the model surface temperature were relaxed to a temperature adjusted for the influence of persistent atmospheric cooling in this region, rather than relaxed to climatological sea surface temperature, the model heat transport would improve. Assumptions inherent in estimating meridional heat transport from hydrographic sections are tested by examining the model. Rather than the Abyssal Circulation being steady, the model's deep western boundary currents...

Nobuo Suginohara - One of the best experts on this subject based on the ideXlab platform.

  • Modelling of Western Pacific Abyssal Circulation – Preliminary Experiment
    Deep Ocean Circulation - Physical and Chemical Aspects, 1993
    Co-Authors: Nobuo Suginohara, Shigeaki Aoki, Minoru Nakata
    Abstract:

    Abstract As a first step to model the western Pacific Abyssal Circulation, buoyancydriven Circulation in a basin which has a simple geometry but retains characteristic features of the western Pacific is studied using a multi-level numerical model. The Circulation is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. It is clearly demonstrated that the bottom and deep waters take different paths from the southern ocean to the Philippine Basin. The bottom water flows northward along the western boundary crossing the equator, and at the northern end of the Marshall Islands it turns westward to flow to the opening of the Philippine Basin. On the other hand, the deep water at mid-depths flows directly into the Philippine Basin along the coasts. Numerical modelling studies which the present study is based upon are reviewed.

  • modelling of western pacific Abyssal Circulation preliminary experiment
    Elsevier oceanography series, 1993
    Co-Authors: Nobuo Suginohara, Shigeaki Aoki, Minoru Nakata
    Abstract:

    Abstract As a first step to model the western Pacific Abyssal Circulation, buoyancydriven Circulation in a basin which has a simple geometry but retains characteristic features of the western Pacific is studied using a multi-level numerical model. The Circulation is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. It is clearly demonstrated that the bottom and deep waters take different paths from the southern ocean to the Philippine Basin. The bottom water flows northward along the western boundary crossing the equator, and at the northern end of the Marshall Islands it turns westward to flow to the opening of the Philippine Basin. On the other hand, the deep water at mid-depths flows directly into the Philippine Basin along the coasts. Numerical modelling studies which the present study is based upon are reviewed.

  • Effects of a continental slope along the western boundary on the Abyssal Circulation
    Journal of Oceanography, 1992
    Co-Authors: Minoru Nakata, Shigeaki Aoki, Nobuo Suginohara
    Abstract:

    To investigate effects of a continental slope along the western boundary on the Abyssal Circulation, numerical experiments using multi-level models were carried out. An ocean which extends over the northern and southern hemispheres is forced by cooling inside the ocean at the southwest corner of the basin and uniform heating through the sea surface. When the reference density for the cooling is vertically uniform, effects of the slope emerge clearly for the slope with considerably broad width. The deep western boundary current flowing over the slope feeds no bottom flows in the southern hemisphere, and carries the warmed deep water into the northern hemisphere. This leads to the increased meridional density gradient, which results in the modification of deep flow patterns. When the reference density is vertically distributed, the upper and lower northward flowing western boundary currents form in the deep layer. As the density stratification relaxes the topographic control, the westward intensification of the upper boundary current is achieved over the slope. The intensified flow is accompanied by the countercurrent and they form the horizontal reCirculation over the slope. However, the effects are confined around the slope region and the interior flow patterns do not change. The lower boundary current is not significantly affected by the slope and has the large width with no countercurrent. It is found that the actual continental slope does not have significant effects on the gross feature of the thermohaline Circulation.