Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

Hogg, Andrew McC.; Munday, David R.

doi:10.1098/rsta.2013.0050

Cited by 15 publications

(24 citation statements)

References 27 publications

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“…What remains is to adequately quantify the changes in SST due to changes in the subpolar ocean circulation and to disentangle these from SST changes induced by other mechanisms like CO 2 increase or ice growth. The quantification of the ocean gateway mechanism relates to several aspects like (i) the sufficient conditions for the onset of a circumpolar current within the Southern Ocean, (ii) the quantitative partitioning of the resulting subpolar flow field into circumpolar current and subpolar gyre system, and (iii) the corresponding changes in meridional heat transports and SST. These aspects are likely highly sensitive to ocean modeling details.This concerns the dependence on resolution since different representations of both mesoscale eddies and topographic details can lead to significantly different interactions between mean flow, mesoscale eddies, and topography [ Hogg and Munday , ; Abernathey and Cessi , ]. Furthermore, this concerns the bathymetric details on their own since paleogeographic reconstructions face substantial uncertainties due to inaccuracies in proxies or plate tectonic reconstructions [ Baatsen et al , ].…”

Section: Discussionmentioning

confidence: 99%

Effects of Drake Passage on a strongly eddying global ocean

et al. 2016

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The climate impact of ocean gateway openings during the Eocene‐Oligocene transition is still under debate. Previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized. We present results of a state‐of‐the‐art eddy‐resolving global ocean model with a closed Drake Passage and compare with results of the same model at noneddying resolution. An analysis of the pathways of heat by decomposing the meridional heat transport into eddy, horizontal, and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions. Closing Drake Passage induces (i) sea surface warming around Antarctica due to equatorward expansion of the subpolar gyres, (ii) the collapse of the overturning circulation related to North Atlantic Deep Water formation leading to surface cooling in the North Atlantic, and (iii) significant equatorward eddy heat transport near Antarctica. However, quantitative details significantly depend on the chosen resolution. The warming around Antarctica is substantially larger for the noneddying configuration (∼5.5°C) than for the eddying configuration (∼2.5°C). This is a consequence of the subpolar mean flow which partitions differently into gyres and circumpolar current at different resolutions. We conclude that for a deciphering of the different mechanisms active in Eocene‐Oligocene climate change detailed analyses of the pathways of heat in the different climate subsystems are crucial in order to clearly identify the physical processes actually at work.

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Section: Discussionmentioning

confidence: 99%

Effects of Drake Passage on a strongly eddying global ocean

et al. 2016

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“…A sufficiently eddying current can show zero sensitivity of its circumpolar transport to wind stress, due to increased eddy activity, even in the limit of zero wind stress [ Munday et al , ]. However, the details of this sensitivity can depend upon the specific geometry of the chosen model domain [ Hogg and Munday , ]. Furthermore, surface temperature and salinity forcing play a role in setting the transport, and its sensitivity, due to changes in stratification that accompany, e.g., increased heat fluxes [ Hogg , ].…”

Section: Introductionmentioning

confidence: 99%

The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current

2015

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The date of inception of the Antarctic Circumpolar Current is debated due to uncertainty in the relative opening times of Drake Passage and the Tasman Seaway. Using an idealized eddy‐resolving numerical ocean model, we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current. We find that overlapping continental barriers do not impede a circumpolar transport in excess of 50Sv, as long as a circumpolar path can be traced around the barriers. However, the presence of overlapping barriers does lead to an increased sensitivity of the current's volume transport to changes in wind stress. This change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress. Specifically, when the pressure drop across continents is the main balancing sink of momentum, the zonal volume transport is sensitive to changes in wind stress. Changes in zonal volume transport take place via altering the depth‐independent part of the circumpolar transport rather than that arising from thermal wind shear. In such a scenario, isopycnals continue to slope steeply across the model Southern Ocean, implying a strong connection between the deep and surface oceans. This may have consequences for the meridional overturning circulation and its sensitivity to wind stress.

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“…Full details of the configuration are given in Marshall et al (1997a,b), Munday et al (2013), Hogg and Munday (2014), and Munday et al (2014), although a brief exposition follows.…”

Section: B Sector Model Setupmentioning

confidence: 99%

“…The mean slope of interior Southern Ocean isopycnals is thought to be set by a balance between the steepening effect of wind stress and buoyancy fluxes and the flattening effect of energetic, mesoscale eddies (Karsten and Marshall 2002). This balance affects many facets of global ocean circulation across different time scales, including the sensitivity of the overturning circulation to changes in Southern Hemispheric wind stress and the strength of the Southern Ocean carbon sink (Lovenduski and Ito 2009;Abernathey et al 2011;Munday et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Planetary–Geometric Constraints on Isopycnal Slope in the Southern Ocean

Jones

Ito

Birner

et al. 2015

Journal of Physical Oceanography

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On planetary scales, surface wind stress and differential buoyancy forcing act together to produce isopycnal surfaces that are relatively flat in the tropics/subtropics and steep near the poles, where they tend to outcrop. Tilted isopycnals in a rapidly rotating fluid are subject to baroclinic instability. The turbulent, mesoscale eddies generated by this instability have a tendency to homogenize potential vorticity (PV) along density surfaces. In the Southern Ocean (SO), the tilt of isopycnals is largely maintained by competition between the steepening effect of surface forcing and the flattening effect of turbulent, spatially inhomogeneous eddy fluxes of PV. Here quasigeostrophic theory is used to investigate the influence of a planetary-geometric constraint on the equilibrium slope of tilted density/buoyancy surfaces in the SO. If the meridional gradients of relative vorticity and PV are small relative to b, then quasigeostrophic theory predicts ds/dz 5 b/f 0 5 cot(f 0 )/a, or equivalently r [ j› z s/(b/f 0 )j 5 1, where f is the Coriolis parameter, b is the meridional gradient of f, s is the isopycnal slope, f 0 is a reference latitude, a is the planetary radius, and r is the depth-averaged criticality parameter. It is found that the strict r 5 1 condition holds over specific averaging volumes in a large-scale climatology. A weaker r 5 O(1) condition for depth-averaged quantities is generally satisfied away from large bathymetric features. The r 5 O(1) constraint is employed to derive a depth scale to characterize large-scale interior stratification, and an idealized sector model is used to test the sensitivity of this relationship to surface wind forcing. Finally, the possible implications for eddy flux parameterization and for the sensitivity of SO circulation/stratification to changes in forcing are discussed.

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Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

Cited by 15 publications

References 27 publications

Effects of Drake Passage on a strongly eddying global ocean

Effects of Drake Passage on a strongly eddying global ocean

The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current

Planetary–Geometric Constraints on Isopycnal Slope in the Southern Ocean

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