On the role of mesoscale eddies in the ventilation of Antarctic intermediate water

Zouhair Lachkhar, James C. Orr, Jean Claude Dutay, Pascale Delecluse

    Research output: Contribution to journalArticle

    Abstract

    The spatial distribution of Antarctic intermediate water (AAIW) formation and ventilation remains a matter of debate. Some studies suggest that AAIW forms nearly homogeneously in a circumpolar pattern, whereas others favor more localized formation particularly in the southeast Pacific Ocean. We show here that the patterns and magnitude of AAIW formation and ventilation are substantially affected by mesoscale eddies. To diagnose the role of eddies, we made global CFC-11 simulations in two versions of the ocean general circulation model OPA9, a "non-eddying", coarse-resolution version (2{ring operator} cos φ{symbol} × 2{ring operator}, ORCA2) and an "eddying" or eddy-permitting version (frac(1, 2){ring operator} cos φ{symbol} × frac(1, 2){ring operator}, ORCA05). In the non-eddying simulation, AAIW subducts in a near homogeneous, circumpolar pattern; in the eddying simulation, the distribution of AAIW ventilation is patchier. Increasing resolution causes the AAIW layer to thin by 32% on average in the Indian sector, but only by 11% in the Pacific sector. This patchiness appears due to the zonal wind stress, which is weak over much of the Pacific and southwest Atlantic sectors but is strong over the Indian sector. Consequently, the effect of eddies is largest in the Indian Ocean, moderate in the Atlantic, and smallest in the Pacific basin. Although the Gent and McWilliams (GM) eddy parameterization improves the overall vertical structure of density in the Southern Ocean, applying it in our non-eddying model still results in the nearly uniform circumpolar distribution of AAIW ventilation, in contrast to the observations.

    Original languageEnglish (US)
    Pages (from-to)909-925
    Number of pages17
    JournalDeep-Sea Research Part I: Oceanographic Research Papers
    Volume56
    Issue number6
    DOIs
    StatePublished - Jun 1 2009

    Fingerprint

    Antarctic Intermediate Water
    mesoscale eddy
    ventilation
    eddy
    water
    ocean
    oceans
    simulation
    General Circulation Models
    CFC
    patchiness
    zonal wind
    wind stress
    Indian Ocean
    Pacific Ocean
    general circulation model
    parameterization
    spatial distribution
    basins
    basin

    Keywords

    • AAIW
    • CFC-11
    • Mesoscale eddies
    • Southern Ocean
    • Ventilation

    ASJC Scopus subject areas

    • Oceanography
    • Aquatic Science

    Cite this

    On the role of mesoscale eddies in the ventilation of Antarctic intermediate water. / Lachkhar, Zouhair; Orr, James C.; Dutay, Jean Claude; Delecluse, Pascale.

    In: Deep-Sea Research Part I: Oceanographic Research Papers, Vol. 56, No. 6, 01.06.2009, p. 909-925.

    Research output: Contribution to journalArticle

    Lachkhar, Zouhair ; Orr, James C. ; Dutay, Jean Claude ; Delecluse, Pascale. / On the role of mesoscale eddies in the ventilation of Antarctic intermediate water. In: Deep-Sea Research Part I: Oceanographic Research Papers. 2009 ; Vol. 56, No. 6. pp. 909-925.
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    abstract = "The spatial distribution of Antarctic intermediate water (AAIW) formation and ventilation remains a matter of debate. Some studies suggest that AAIW forms nearly homogeneously in a circumpolar pattern, whereas others favor more localized formation particularly in the southeast Pacific Ocean. We show here that the patterns and magnitude of AAIW formation and ventilation are substantially affected by mesoscale eddies. To diagnose the role of eddies, we made global CFC-11 simulations in two versions of the ocean general circulation model OPA9, a {"}non-eddying{"}, coarse-resolution version (2{ring operator} cos φ{symbol} × 2{ring operator}, ORCA2) and an {"}eddying{"} or eddy-permitting version (frac(1, 2){ring operator} cos φ{symbol} × frac(1, 2){ring operator}, ORCA05). In the non-eddying simulation, AAIW subducts in a near homogeneous, circumpolar pattern; in the eddying simulation, the distribution of AAIW ventilation is patchier. Increasing resolution causes the AAIW layer to thin by 32{\%} on average in the Indian sector, but only by 11{\%} in the Pacific sector. This patchiness appears due to the zonal wind stress, which is weak over much of the Pacific and southwest Atlantic sectors but is strong over the Indian sector. Consequently, the effect of eddies is largest in the Indian Ocean, moderate in the Atlantic, and smallest in the Pacific basin. Although the Gent and McWilliams (GM) eddy parameterization improves the overall vertical structure of density in the Southern Ocean, applying it in our non-eddying model still results in the nearly uniform circumpolar distribution of AAIW ventilation, in contrast to the observations.",
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    AB - The spatial distribution of Antarctic intermediate water (AAIW) formation and ventilation remains a matter of debate. Some studies suggest that AAIW forms nearly homogeneously in a circumpolar pattern, whereas others favor more localized formation particularly in the southeast Pacific Ocean. We show here that the patterns and magnitude of AAIW formation and ventilation are substantially affected by mesoscale eddies. To diagnose the role of eddies, we made global CFC-11 simulations in two versions of the ocean general circulation model OPA9, a "non-eddying", coarse-resolution version (2{ring operator} cos φ{symbol} × 2{ring operator}, ORCA2) and an "eddying" or eddy-permitting version (frac(1, 2){ring operator} cos φ{symbol} × frac(1, 2){ring operator}, ORCA05). In the non-eddying simulation, AAIW subducts in a near homogeneous, circumpolar pattern; in the eddying simulation, the distribution of AAIW ventilation is patchier. Increasing resolution causes the AAIW layer to thin by 32% on average in the Indian sector, but only by 11% in the Pacific sector. This patchiness appears due to the zonal wind stress, which is weak over much of the Pacific and southwest Atlantic sectors but is strong over the Indian sector. Consequently, the effect of eddies is largest in the Indian Ocean, moderate in the Atlantic, and smallest in the Pacific basin. Although the Gent and McWilliams (GM) eddy parameterization improves the overall vertical structure of density in the Southern Ocean, applying it in our non-eddying model still results in the nearly uniform circumpolar distribution of AAIW ventilation, in contrast to the observations.

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