The Relationship of Weddell Polynya and Open-Ocean Deep Convection to the Southern Hemisphere Westerlies

Cheon, Woo Geun; Park, Young-Gyu; Toggweiler, J. R.; Lee, Sang Ki

doi:10.1175/jpo-d-13-0112.1

Cited by 46 publications

(46 citation statements)

References 53 publications

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“…increase in the meridional pressure gradient, as reported in previous modeling studies (Hirabara et al 2012;Shakespeare and Hogg 2012;Cheon et al 2014;Spence et al 2014).…”

supporting

confidence: 76%

Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean

Dufour

Griffies

Souza

et al. 2015

Journal of Physical Oceanography

122

136

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This study examines the role of processes transporting tracers across the Polar Front (PF) in the depth interval between the surface and major topographic sills, which this study refers to as the ''PF core.'' A preindustrial control simulation of an eddying climate model coupled to a biogeochemical model [GFDL Climate Model, version 2.6 (CM2.6)-simplified version of the Biogeochemistry with Light Iron Nutrients and Gas (miniBLING) 0.18 ocean model] is used to investigate the transport of heat, carbon, oxygen, and phosphate across the PF core, with a particular focus on the role of mesoscale eddies. The authors find that the total transport across the PF core results from a ubiquitous Ekman transport that drives the upwelled tracers to the north and a localized opposing eddy transport that induces tracer leakages to the south at major topographic obstacles. In the Ekman layer, the southward eddy transport only partially compensates the northward Ekman transport, while below the Ekman layer, the southward eddy transport dominates the total transport but remains much smaller in magnitude than the near-surface northward transport. Most of the southward branch of the total transport is achieved below the PF core, mainly through geostrophic currents. This study finds that the eddy-diffusive transport reinforces the southward eddy-advective transport for carbon and heat, and opposes it for oxygen and phosphate. Eddy-advective transport is likely to be the leading-order component of eddy-induced transport for all four tracers. However, eddy-diffusive transport may provide a significant contribution to the southward eddy heat transport due to strong along-isopycnal temperature gradients.

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“…increase in the meridional pressure gradient, as reported in previous modeling studies (Hirabara et al 2012;Shakespeare and Hogg 2012;Cheon et al 2014;Spence et al 2014).…”

supporting

confidence: 76%

Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean

Dufour

Griffies

Souza

et al. 2015

Journal of Physical Oceanography

122

136

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“…4b). The lower cell response is largely due to an open-ocean polynya in the Weddell Sea, which is commonly generated by wind stress perturbations in models (Cheon et al 2014). This polynya can be recognized in the model mixed layer depth (shown for years 510-520 in Fig.…”

Section: Resultsmentioning

confidence: 99%

The Energetics of Southern Ocean Upwelling

Hogg

Spence

Saenko

et al. 2017

Journal of Physical Oceanography

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The ocean's meridional overturning circulation is closed by the upwelling of dense, carbon-rich waters to the surface of the Southern Ocean. It has been proposed that upwelling in this region is driven by strong westerly winds, implying that the intensification of Southern Ocean winds in recent decades may have enhanced the rate of upwelling, potentially affecting the global overturning circulation. However, there is no consensus on the sensitivity of upwelling to winds or on the nature of the connection between Southern Ocean processes and the global overturning circulation. In this study, the sensitivity of the overturning circulation to changes in Southern Ocean westerly wind stress is investigated using an eddy-permitting ocean-sea ice model. In addition to a suite of standard circulation metrics, an energy analysis is used to aid dynamical interpretation of the model response. Increased Southern Ocean wind stress enhances the upper cell of the overturning circulation through creation of available potential energy in the Southern Hemisphere, associated with stronger upwelling of deep water. Poleward shifts in the Southern Ocean westerlies lead to a complicated transient response, with the formation of bottom water induced by increased polynya activity in the Weddell Sea and a weakening of the upper overturning cell in the Northern Hemisphere. The energetic consequences of the upper overturning cell response indicate an interhemispheric connection to the input of available potential energy in the Northern Hemisphere.

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“…A complete understanding of the mechanism of deep convection is beyond the scope of this paper. We note that the changes in wind stress and sea ice extent would also contribute to recovery and overshoot of deep convection in the Southern Ocean [ Meissner et al , ; Cheon et al , ].…”

Section: Deep Ocean Convection In the Weddell Seamentioning

confidence: 99%

Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long‐term global warming

Yamamoto

Abe‐Ouchi

Shigemitsu

et al. 2015

Global Biogeochemical Cycles

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Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here we simulate multimillennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere-ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.

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The Relationship of Weddell Polynya and Open-Ocean Deep Convection to the Southern Hemisphere Westerlies

Cited by 46 publications

References 53 publications

Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean

Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean

The Energetics of Southern Ocean Upwelling

Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long‐term global warming

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