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Michael P. Meredith, Alberto C. Naveira Garabato, Arnold L. Gordon, and Gregory C. Johnson

denser outflow through these gaps would act to block the southwestward flow of Lower WSDW through Georgia Passage into the Scotia Sea abyss). Consequently, 1999 was the only year of the three that showed the influence of the more saline type of Lower WSDW, resulting from the reversals in the direction of abyssal flow at the northeastern and eastern edges of the Scotia Sea before and after this date. 6. Conclusions A hydrographic section in the eastern Scotia Sea of the Southern Ocean was occupied

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Hailu Kong and Malte F. Jansen

1. Introduction The Southern Ocean plays a crucial role in Earth’s climate and global ocean dynamics. It connects major ocean basins through its Antarctic Circumpolar Current (ACC) and the associated meridional overturning circulation (MOC). Both of these components are fundamentally driven by surface wind stress, which has been increasing for decades and is projected to further increase in the future (e.g., Swart and Fyfe 2012 ). An important question therefore is how the ACC and MOC respond

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Alexander Sen Gupta, Agus Santoso, Andréa S. Taschetto, Caroline C. Ummenhofer, Jessica Trevena, and Matthew H. England

1. Introduction The Southern Ocean acts as the engine room to the world’s overturning circulation, drawing its energy from the powerful midlatitude westerlies acting over a zonally continuous ocean. A high-latitude wind-driven divergence draws deep waters to the surface. Subsequently, these upwelled waters are driven both north and south via Ekman fluxes and buoyancy-driven sinking around the Antarctic margin. The northward flow subducts to form the basis of the thermocline, mode, and

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Kewei Lyu, Xuebin Zhang, John A. Church, and Quran Wu

1. Introduction More than 90% of the excess heat stored in the climate system from anthropogenic greenhouse gas emissions is stored in the ocean, leading to global ocean thermal expansion and sea level rise ( Church et al. 2011 ; Rhein et al. 2013 ). The Southern Hemisphere (SH) oceans are one of the key regions in absorbing and storing the anthropogenic heat. For example, the oceans south of 30°S, while occupying only 30% of the global ocean surface area, account for 75% of ocean surface heat

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A. M. Treguier, J. Le Sommer, J. M. Molines, and B. de Cuevas

depletion have been shown to contribute to the SAM upward trend, which is expected to continue in the future ( Arblaster and Meehl 2006 ). Ocean biogeochemistry is suspected to respond strongly to this climate signal. The SAM upward trend could have increased the ventilation of carbon rich deep water, possibly controlling the strength of the Southern Ocean carbon dioxide sink ( Lenton and Matear 2007 ; Lovenduski et al. 2008 ; Le Quéré et al. 2007 ) and accelerating ocean acidification ( Lenton et al

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Madeleine K. Youngs, Glenn R. Flierl, and Raffaele Ferrari

1. Introduction The Southern Ocean is a dominant contributor to the global carbon and heat budgets, and thus helps determine global climate. The dynamics of the Southern Ocean are dominated by two counterrotating residual overturning cells of about ~10 Sv (1 Sv ≡ 10 6 m 3 s −1 ) each ( Lumpkin and Speer 2007 ) forced by surface buoyancy fluxes that transfer tracers from the deep to the surface along isopycnals. In particular, the isopycnal slopes, or equivalently the thermal wind transport

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Andrew Mc C. Hogg, Michael P. Meredith, Jeffrey R. Blundell, and Chris Wilson

1. Introduction The Antarctic Circumpolar Current (ACC) is a dynamically unique current encircling the Antarctic continent ( Rintoul et al. 2001 ). The ACC plays a vital role in communicating water masses between the three major ocean basins, as well as controlling the oceanic poleward heat flux in the Southern Hemisphere. The primary mechanisms for heat transport in the surface waters are eddy heat flux and ageostrophic Ekman transport, since there is no mean geostrophic flow across the

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Zachary S. Kaufman, Nicole Feldl, Wilbert Weijer, and Milena Veneziani

high-latitude atmospheric circulation anomalies and strong polar cyclones over the Weddell Sea ( Francis et al. 2018 ; Jena et al. 2019 ; Cheon and Gordon 2019 ; Campbell et al. 2019 ). While both the 1974–76 and 2016–17 events demonstrate connections between deep convection and interannual high-latitude climate variability, observations of open-ocean polynyas in the Southern Hemisphere high latitudes are still sparse. Important questions remain regarding how polynya heat loss may have

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Taka Ito and John Marshall

1. Introduction The abyssal ocean contains by far the largest volume of waters in the global ocean, dominating the oceanic inventory of heat, nutrients, carbon, and other geochemical tracers. The deep meridional overturning circulation ventilates the deep waters from a few selected regions in the northern North Atlantic and the polar Southern Ocean. Our focus in this paper is on the deep overturning circulation of the Southern Ocean. The circulation of the Southern Ocean is dominated by the

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Alice Barthel, Andrew McC. Hogg, Stephanie Waterman, and Shane Keating

1. Introduction Southern Ocean dynamics impact the distribution of heat, salt, and nutrients in the global ocean, thus affecting climate and fisheries worldwide ( Rintoul and Naveira Garabato 2013 ). These dynamics also play an essential role in air–sea fluxes of CO 2 ( Le Quéré et al. 2007 ). The circulation in the Southern Ocean is expected to change in a warming climate through the combined effects of changes in freshwater fluxes ( Downes and Hogg 2013 ) and a projected increase, and

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