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Paul Spence, John C. Fyfe, Alvaro Montenegro, and Andrew J. Weaver

1. Introduction Observations from the past few decades indicate that a section of the Southern Ocean between 40° and 60°S has been warming at nearly twice the rate of the global ocean ( Gille 2002 ; Aoki et al. 2003 ; Gille 2008 ). Concurrent atmospheric observations reveal a poleward shift and strengthening of Southern Hemisphere westerly winds, identified as a shift in the Southern Annual Mode (SAM) toward a higher index state ( Thompson and Solomon 2002 ). The change in the southern winds

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William G. Large, Edward G. Patton, and Peter P. Sullivan

1. Introduction Ocean general circulation models (OGCMs) have long struggled to represent the Southern Ocean faithfully. Nevertheless, they typically have substantial biases in mixed layer depth (MLD) both when coupled to an atmosphere model ( Sallée et al. 2013 ), or when uncoupled and forced by observation based surface fluxes ( Downes et al. 2014 ). The magnitude of these shallow biases in late winter is truly remarkable, exceeding 400 m in a nearly circumpolar deep mixing band (DMB) between

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Maxim Nikurashin and Raffaele Ferrari

1. Introduction Ocean mixing sets the stratification of much of the global ocean by the upwelling of dense, deep waters formed in polar regions ( Wunsch and Ferrari 2004 ). Mixing is especially important in the Southern Ocean where the meridional overturning circulation (MOC) of the global ocean is largely powered. However, little is known about what dynamics supports that mixing. The Southern Ocean limb of the MOC can be described as being composed of an upper and a lower cell ( Speer et al

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Lukas Papritz, Stephan Pfahl, Irina Rudeva, Ian Simmonds, Harald Sodemann, and Heini Wernli

, which over the Southern Ocean (SO) leads to significant biases in the estimation of the mean fluxes ( Simmonds and Dix 1989 ). Nowadays, satellite observations allow us to monitor the water cycle on synoptic time scales with an almost global coverage. Nevertheless, the quantity E − P remains very difficult to estimate and one of the best ways to do so is by using atmospheric reanalyses. These datasets are based on all available observations, are constrained by the fundamental physical laws, and

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Christopher C. Chapman and Rosemary Morrow

1. Introduction The circulation in the Southern Ocean is dominated by the Antarctic Circumpolar Current (ACC), which is composed of a series of strong, narrow eastward currents known as jets ( Rintoul et al. 2001 ). Jets are a common feature in geophysical fluids having been found in the midlatitude troposphere and stratosphere, in the atmospheres of gas giant planets, and numerous laboratory flows ( Thompson 2008 ). They consist of large-scale, predominantly zonal flow that persists with time

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Ivana Cerovečki, Lynne D. Talley, and Matthew R. Mazloff

1. Introduction and outline The Southern Ocean (SO) plays a fundamental role in setting the global climate, making detailed understanding of air–sea buoyancy fluxes in the region indispensable for climate modeling and prediction. However, the sparseness of both conventional and remotely sensed observations causes the availability and accuracy of air–sea buoyancy flux estimates to be especially poor in this region ( Josey et al. 1999 ; Taylor 2000 ; Kubota et al. 2003 ; Dong et al. 2007

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Shenfu Dong, Sarah T. Gille, and Janet Sprintall

1. Introduction Southern Ocean mixed layer processes are an important component of the global climate system. One conceptual model of global meridional overturning circulation posits that water flows southward at middepth into the Southern Ocean where it is upwelled to the surface and carried northward through Ekman processes (e.g., Speer et al. 2000 ; Karsten and Marshall 2002 ; Marshall and Radko 2003 ). While at the ocean surface, water mass properties are transformed as water in the

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Thomas L. Frölicher, Jorge L. Sarmiento, David J. Paynter, John P. Dunne, John P. Krasting, and Michael Winton

1. Introduction The Southern Ocean is the main source of much of the deep water of the world’s ocean and also provides the primary return pathway for this deep water to the surface ( Toggweiler and Samuels 1995 ; Marshall and Speer 2012 ). Strongly divergent wind-driven flow drives upwelling of large amounts of deep water to the ocean’s surface in the open channel around the Antarctic Continent. Part of this deep water is freshened and warmed at the surface and transported northward, where it

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Andrew L. Stewart and Andrew F. Thompson

1. Introduction The meridional overturning circulation (MOC) describes the global-scale meridional transport of ocean water masses ( Talley et al. 2003 ). It exerts a substantial influence over climate via interhemispheric transport of heat and salt, in addition to biogeochemical tracers such as oxygen and carbon ( Kuhlbrodt et al. 2007 ; Lynch-Stieglitz et al. 2007 ). This article focuses on the Southern Ocean, which has been identified as a region of particular dynamical and climatic

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Emily Shuckburgh, Helen Jones, John Marshall, and Chris Hill

1. Introduction Throughout the ocean, satellite altimetry data reveal a complex regional eddy kinetic energy (EKE) distribution ( Stammer 1997 ; Stammer et al. 2006 ). Significant enhancement in eddy activity is observed in the vicinity of strong currents: the Gulf Stream in the Atlantic, the Kuroshio and its extension in the Pacific, and the Antarctic Circumpolar Current (ACC) in the Southern Ocean. Much of this eddy activity arises through baroclinic instability, although barotropic

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