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Abyssal Circulation

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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.