Water Mass Transformation in the Southern Ocean of a Global Isopycnal Coordinate GCM

Marsh, Robert; Nurser, A. J. George; Megann, Alex; New, Adrian L.

doi:10.1175/1520-0485(2000)030<1013:wmtits>2.0.co;2

Cited by 74 publications

(82 citation statements)

References 52 publications

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“…The overturning streamfunction of the Eulerian mass¯ow is by now a standard diagnostic output of numerical ocean models. It became evident by a Lagrangian-oriented analysis (averaging along isopycnals instead of geopotentials) that the prominent Deacon cell in the Southern Ocean overturning does not represent pathways of water-masses (DoÈ oÈ s and Webb 1994; Karoly et al 1997;Marsh et al 2000;Speer et al 2000). Eddy-driven¯ow transports mass and tracers meridionally in cells of narrow vertical extent and compensates in part for the northward Ekman branch and deep geostrophic return¯ow associated with the bottom form stress.…”

Section: Introductionmentioning

confidence: 99%

On the meridional circulation and balance of momentum in the Southern Ocean of POP

Olbers¹,

Ivchenko²

2001

Ocean Dynamics

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The circulation of the Southern Ocean is studied in the eddy-resolving model POP (Parallel Ocean Program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration of the zonal current by density¯uxes in a zonally integrated frame. The latter acceleration term is directly related to the surface¯ux of density and interior¯uxes due to the resolved and unresolved eddies. The eddy-induced circulation is extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid¯uxes which are strong in the upper few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving models; a new aspect is the clear identi®cation of density eects in the zonally integrated balance. We show that the wind stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species result in a braking. Finally, we extend the Johnson±Bryden model of zonal transport to incorporate all relevant terms from the zonal momentum balance. It is shown that wind stress and induction by the residual circulation carry an eastward transport while bottom form stress and the stress induced by standing eddies yield westward components of transport.

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Section: Introductionmentioning

confidence: 99%

On the meridional circulation and balance of momentum in the Southern Ocean of POP

Olbers¹,

Ivchenko²

2001

Ocean Dynamics

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“…The Southern Ocean ventilates large regions of the World Oceans, with its signatures found even in the North Atlantic intermediate waters (Marsh et al;. This role in ventilation stresses the importance of the Southern Ocean to the global climate.…”

Section: Meridional Transportsmentioning

confidence: 88%

“…Analysis of model output, however, shows large discrepancies from the established picture (Marsh et al;. This raises questions as to whether it is even possible to simplify the entire Southern Ocean general circulation into two-dimensional pictures.…”

Section: Introductionmentioning

confidence: 98%

“…They are the world's largest oceanic sink of CO 2 (Patra et al; and wind energy . The signature of water masses formed in this ocean are found throughout the world (Marsh et al;. Despite the Southern Ocean's significance, the circulation and variability of these waters are poorly understood.…”

Section: Introductionmentioning

confidence: 99%

“…Descriptions of the Southern Ocean flow coming from inferences from these in situ (e.g. Marsh et al (2000)) and satellite (e.g. Gille (1995Gille ( , 1997) observations give a basic understanding of the density structure, mass transport, and variability in the Southern Ocean.…”

Section: Introductionmentioning

confidence: 99%

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Production and analysis of a Southern Ocean state estimate

Mazloff¹

2006

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A modern general circulation model of the Southern Ocean with one-sixth of a degree resolution is optimized to the observed ocean in a weighted least squares sense. Convergence toward the state estimate solution is carried out by systematically adjusting the control variables (prescribed atmospheric state, initial conditions, and open northern boundary at 24.7 o S) using the adjoint method. A cost function compares the model state to data from CTD synoptic sections, hydrographic climatology, satellite altimetry, and XBTs. Costs attributed to control variable perturbations ensure a physically realistic solution. An optimized solution is determined by the weights placed on the cost function terms. The state estimation procedure, along with the weights used, is described. A significant result is that the adjoint method is shown to

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Temporal variability of transformation, formation, and subduction rates of upper Southern Ocean waters

Kwon

2013

J. Geophys. Res. Oceans

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[1] Kinematic and thermodynamic approaches are employed to diagnose the timedependent transformation, formation, and subduction rates of upper Southern Ocean waters in a multidecadal simulation within an eddy-permitting coupled climate model. In the Subantarctic Mode Water (SAMW) density class, a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter. A portion of this water is detrained into the pycnocline during early spring, when surface heating restratifies the deep winter mixed layer. The annually averaged subduction rate of SAMW shows pronounced interannual variability, partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next. No significant correlation between the Southern Annular Mode (SAM) and the isopycnally integrated SAMW subduction rate is apparent. However, Ekman downwelling/upwelling intensities modulated by the SAM influence interannual variations in the subduction rates of water masses lighter and heavier than SAMW with an opposing sign: during positive phases of the SAM, more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the Antarctic Intermediate Water density class, whereas more mixed layer waters are subducted into the pycnocline within the Subtropical Mode Water density class. Such distinct responses of upper Southern Ocean water masses to the SAM are qualitatively consistent with observational constraints. Based on a comparison between offline kinematic and thermodynamic diagnostics, we infer that diapycnal mixing within the mixed layer may contribute up to 50% of the formation rate of SAMW on interannual timescales.

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Water Mass Transformation in the Southern Ocean of a Global Isopycnal Coordinate GCM

Cited by 74 publications

References 52 publications

On the meridional circulation and balance of momentum in the Southern Ocean of POP

On the meridional circulation and balance of momentum in the Southern Ocean of POP

Production and analysis of a Southern Ocean state estimate

Temporal variability of transformation, formation, and subduction rates of upper Southern Ocean waters

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