Research ArticleATMOSPHERIC SCIENCE

Opening the window to the Southern Ocean: The role of jet dynamics

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Science Advances  03 Oct 2018:
Vol. 4, no. 10, eaao4719
DOI: 10.1126/sciadv.aao4719

Figures

  • Fig. 1 Numerical simulation of the Southern Ocean ventilation.

    (A) Time- and depth-mean zonal velocities for the modern wind stress (color) and ocean depth (contours). Both the KP and the South East Indian Ridge (SEIR) are marked. Colored lines show locations of vertical transects shown in Figs. 3 and 4. (B) Wind stress (N m−2) of the six perturbation experiments (the red line represents modern conditions). Only the westerly components of the wind stress are changed. (C) Changes in Southern Ocean ventilation as a function of changes in wind stress, where zero marks the annual and zonal average winds of 2005. The blue line shows changes in Southern Ocean overturning, the red line shows changes in tracer uptake integrated between water depths of 500 and 1500 m, and the black line shows the 1:1 line, that is, where wind changes equal ventilation changes. Circular markers show the different perturbation experiments.

  • Fig. 2 Tracer ventilation as a function of jet dynamics.

    Tracer concentration at a depth of 200 m for a wind stress of (A) τ, 8 months after the tracer is first introduced, and a wind stress of (B) 2*τ, 4 months after the tracer is introduced. Black contours show time-mean velocities at 200 m to highlight the position of the Kerguelen jet. Note the different color scales.

  • Fig. 3 Location of tracer ventilation.

    Time-mean tracer forcing at the ocean surface for the perturbation experiment with a wind stress of (A) τ and a wind stress of (B) 2*τ. Time-mean vertical tracer advection at a depth 200 m for the perturbation experiment with a wind stress of (C) τ and a wind stress of (D) 2*τ.

  • Fig. 4 Tracer ventilation as a function of wind forcing.

    Vertical section along a latitude of 43°S (cyan transect in Fig. 1A) showing tracer concentration (color; on a log10 scale) and salinity (psu, practical salinity unit) (contours) for the perturbation experiment with wind stresses of (A) 0.5*τ, (B) τ, and (C) 2*τ. Vertical section along a longitude of 129°E (magenta transect in Fig. 1A) showing tracer concentration (color; on a log10 scale) and salinity (contours) for the perturbation experiment with wind stresses of (D) 0.5*τ, (E) τ, and (F) 2*τ.

  • Fig. 5 Hydrographic sections across the Kerguelen jet.

    Colors show vertical sections along the green transect in Fig. 1A of time-mean (A, D, and G) zonal velocity (meters per second), (B, E, and H) buoyancy frequency (per second), and (C, F, and I) salinity (psu), for the perturbation experiments with wind stresses of (A to C) 0.5*τ, (D to F) τ, and (G to I) 2*τ. White contours are time-mean isopycnals, and the green line is the time-mean mixed layer depth. The black feature is the northern slope of the KP. The red patch in (H) marks a region of time-mean convection. Horizontal sections of time-mean buoyancy frequency (per second) on a log10 scale at a depth of 120 m, chosen to represent the depth of the base of the SML, for the perturbation experiments with wind stresses of (J) 0.5*τ, (K) τ, and (L) 2*τ. Hovmöller diagrams of zonal surface velocities along the green transect in Fig. 1 for (M) 0.5*τ, (N) τ, and (O) 2*τ.

  • Fig. 6 Dynamics of the Kerguelen jet.

    Jet properties are time- and zonal-mean values calculated between 66°E and 70°E. (A) Solid lines represent vertical profiles of zonal velocities in the core [at 45°S; solid gray line in (B) to (D)] of the eastward jet. Dashed lines represent vertical profiles of zonal velocities at the northern flank [at 43°S; dashed gray line in (B) to (D)] of the jet. (B) Depth-mean zonal velocities across the jet. (C) Depth mean EKE across the jet. (D) Smoothed potential vorticity (PV) gradient β* = β − Uyy, where β is the meridional gradient of the Coriolis force and Uyy is the meridional shear of the depth-mean zonal velocity. Colors represent the different wind perturbation experiments shown in Fig. 1B.

  • Fig. 7 The dependence of Rossby numbers on wind stress.

    Rossby numbers Ro = ζ/f, where ζ = vxuy is the relative vorticity and f is the planetary vorticity, at the ocean surface for (A) 0.5*τ, (B) τ, and (C) 2*τ.

  • Fig. 8 Properties of equilibrated perturbation experiments.

    Equilibrated mean EKE (blue line), baroclinic transport (Tbci; green line), barotropic transport (Tbtp; red line), and maximum MOC (Ψ; cyan line) are shown for all the perturbation experiments. Transports are given in units of Sverdrup, where 1 Sverdrup = 106 m3 s−1.

  • Fig. 9 Transients of tracer ventilation.

    Changes of tracer concentration integrated between depths of 500 and 1500 m with time. Colors represent the different wind perturbation experiments shown in Fig. 1B.

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