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Ryan Abernathey, John Marshall, Matt Mazloff, and Emily Shuckburgh

1. Introduction The Southern Ocean is a place of both strong eddy activity and strong mean flows. One might expect vigorous eddies to be efficient at mixing tracers. However, strong jets can inhibit transport across their axes. In fact, spatially inhomogeneous mixing and the jet-formation mechanism appear to be fundamentally linked through potential vorticity (PV) dynamics ( Haynes et al. 2007 ; Dritschel and McIntyre 2008 ). Furthermore, baroclinic currents can have different transport

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Raffaele Ferrari and Maxim Nikurashin

rms eddy velocity and ℓ is a mixing length. The eddy velocity was estimated from gradients of surface height through the geostrophic relation. The mixing length was set proportional to the observed eddy size. The inferred K peaked in the core of strong currents, such as the western boundary currents and the Antarctic Circumpolar Current (ACC) of the Southern Ocean, where eddy velocities are largest. Marshall et al. (2006) took a different approach to estimating K from altimetric measurements

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Jan D. Zika, Julien Le Sommer, Carolina O. Dufour, Jean-Marc Molines, Bernard Barnier, Pierre Brasseur, Raphaël Dussin, Thierry Penduff, Daniele Iudicone, Andrew Lenton, Gurvan Madec, Pierre Mathiot, James Orr, Emily Shuckburgh, and Frederic Vivier

1. Introduction The Southern Ocean is a critical junction in the global oceanic circulation. The Southern Ocean overturning, in particular, exposes a substantial fraction of the deep ocean’s water masses to the atmosphere and the Southern Ocean has contributed to around 40% of the oceanic uptake of anthropogenic CO 2 ( Sabine et al. 2004 ). The precise dynamics of the Southern Ocean overturning are thus critical to our understanding of the climate system and its sensitivity (see Rintoul et al

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Stephanie M. Downes, Nathaniel L. Bindoff, and Stephen R. Rintoul

1. Introduction The Southern Ocean water masses play an important role in the global climate system by storing heat, freshwater, and dissolved gases and absorbing a large portion of the global anthropogenic CO 2 ( Sarmiento et al. 1998 ; Sabine et al. 1999 ). Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) make up the upper limb of the Southern Ocean’s thermohaline circulation and can extend as far as 30°N ( Drijfhout et al. 2005 ), ventilating the subtropical gyres and

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Daniel C. Jones, Takamitsu Ito, Thomas Birner, Andreas Klocker, and David Munday

1. Introduction The Southern Ocean is a unique and dynamic component of Earth’s climate system. As an important site of mode-water, intermediate-water, and deep-water formation, the Southern Ocean hosts a dominant transport pathway between the atmosphere and the interior ocean ( Russell et al. 2006 ). This pathway is set in part by steeply tilted isopycnal surfaces that outcrop at high southern latitudes. Through this window, atmospheric carbon is exchanged with the interior ocean, potentially

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Xia Lin, Xiaoming Zhai, Zhaomin Wang, and David R. Munday

1. Introduction The Southern Hemisphere (SH) surface westerly wind stress is a major forcing for driving the Antarctic Circumpolar Current (ACC) and upwelling of deep waters in the Southern Ocean (SO). The SH westerly wind stress has strengthened significantly over the last few decades and is projected to continue to do so in the future, which may have important implications for the global climate system via modulating the rate at which the SO uptakes heat and carbon (e.g., Thompson and

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Andrew F. Thompson, Sophia K. Hines, and Jess F. Adkins

SH ( Crowley 1992 ). However, this theory does not account for the upwelling of NADW along density surfaces in the Southern Ocean ( Talley 2013 ; Armour et al. 2016 ), nor does it consider coincident changes in the abyssal stratification and circulation. The differing rates of warming and cooling in each hemisphere during the DO life cycle ( Fig. 1c ) have led to the suggestion that an oceanic “thermal reservoir” could explain smoother transitions in temperature observed in Antarctic ice cores

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Anand Gnanadesikan, Cassidy M. Speller, Grace Ringlein, John San Soucie, Jordan Thomas, and Marie-Aude Pradal

many models that were part of the CMIP5 climate suite open-ocean deep convection within the Weddell Sea determines the temperature, salinity, and density of the Antarctic Bottom Waters ( Heuzé et al. 2013 ). Cessation of such convection in CMIP5 models was found by de Lavergne et al. (2014) to be associated with a more realistic lag in the warming of the Southern Ocean over the past century. A number of current climate models exhibit regular, long-period variability in this convection. Models

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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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