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Matthew R. Mazloff, Raffaele Ferrari, and Tapio Schneider

1. Introduction The Southern Ocean (SO) plays a crucial role in transforming and transporting ocean water masses. The Atlantic, Pacific, and Indian Oceans are connected through the SO, and no description of the global ocean circulation is complete without a full understanding of this region. One wishes to understand the Antarctic Circumpolar Current (ACC) system, the polar gyres, and the meridional overturning circulation (MOC), which are linked as they represent branches of the three

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F. Sévellec, A. C. Naveira Garabato, J. A. Brearley, and K. L. Sheen

motions; e.g., Polzin et al. 1997 ; D’Asaro et al. 2007 ; Waterman et al. 2013 ; Sheen et al. 2013 ) to near-bottom frictional Ekman currents along sloping topographic boundaries ( Garrett et al. 1993 ), wind-driven Ekman motions, and rectified mesoscale eddy flows along sloping isopycnals ( Marshall and Speer 2012 , and references therein). The latter two mechanisms are believed to extensively underpin vertical flow in the Southern Ocean, a region hosting a prominent large-scale vertical

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Emma J. D. Boland, Emily Shuckburgh, Peter H. Haynes, James R. Ledwell, Marie-José Messias, and Andrew J. Watson

only estimated diapycnal diffusivity but also provoked a lively debate about other mixing processes that lead to horizontal spreading of tracer and, acting in opposition to quasi-horizontal deformation by the mesoscale eddy field, limit the thinning of tracer filaments. In this paper, we examine whether corresponding information on such mixing processes can be obtained from other tracer measurements, such as those made in the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES

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L. St. Laurent, A. C. Naveira Garabato, J. R. Ledwell, A. M. Thurnherr, J. M. Toole, and A. J. Watson

1981 ; Polzin 2004 ; MacKinnon and Winters 2005 ); that energy in turn can support turbulence and mixing of the ocean’s buoyancy field. In contrast to most midocean regions of the subtropical basins, the Southern Ocean is a site of strong, deep-reaching geostrophic flow: the Antarctic Circumpolar Current (ACC). The ACC consists of a series of frontal zones where the flow is most enhanced—the Southern ACC Front (SACCF) to the south, the Polar Front (PF) in the middle, and the Subantarctic Front

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Jesse M. Cusack, Alberto C. Naveira Garabato, David A. Smeed, and James B. Girton

many regions of the ocean where bottom flows are not sufficiently strong and topography is not of the correct scale to excite such a frequency. Global maps of energy input to lee waves from geostrophic flows ( Scott et al. 2011 ; Nikurashin and Ferrari 2011 ) highlight the importance of the Southern Ocean because it contains many regions that meet the dynamical requirements, usually centered on ridges and fracture zones such as Phoenix Ridge and the Shackleton Fracture Zone (SFZ) in Drake Passage

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Ross Tulloch, Raffaele Ferrari, Oliver Jahn, Andreas Klocker, Joseph LaCasce, James R. Ledwell, John Marshall, Marie-Jose Messias, Kevin Speer, and Andrew Watson

1. Introduction At the latitudes of the Antarctic Circumpolar Current (ACC), waters from the Atlantic, Indian, and Pacific Oceans are brought to the surface by the Roaring Forties to be transformed into Subantarctic Mode Waters to the north and Antarctic Bottom Waters to the south ( Marshall and Speer 2012 ). This global transformation of water masses is achieved by intense air–sea exchange of heat, freshwater, carbon, and other chemical tracers in the Southern Ocean and exerts a strong control

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J. H. LaCasce, R. Ferrari, J. Marshall, R. Tulloch, D. Balwada, and K. Speer

1. Introduction The goal of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) was to measure isopycnal and vertical diffusivities in the region west and east of the Drake Passage. The vertical diffusivity results, based on microstructure and tracer measurements, were discussed by Ledwell et al. (2011) and St. Laurent et al. (2012) . The isopycnal dispersion was measured using both the tracer and floats. The present paper concerns the latter. The tracer dispersion is

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Dhruv Balwada, Kevin G. Speer, Joseph H. LaCasce, W. Brechner Owens, John Marshall, and Raffaele Ferrari

and the Kerguelen Plateau. In these layers, simple theory suggests that there is no mean geostrophic flow across the 500-km band of the ACC ( Warren 1990 ). It is often argued that the dynamics in these layers is like that of the atmosphere, where the action of eddies can produce a mean residual flux that on large scales in the Southern Ocean is toward the south ( Thompson 2008 ). To quantify the transport of this residual flux, in the absence of accurate deep velocity measurements, one needs to

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Marina Frants, Gillian M. Damerell, Sarah T. Gille, Karen J. Heywood, Jennifer MacKinnon, and Janet Sprintall

1994 ; Klymak et al. 2008 ; Ferron et al. 1998 ). However, ship motion effects and low-stratification conditions can affect the accuracy of finescale methods in extreme environments such as the Southern Ocean. Because finescale methods offer the promise of inexpensive global maps of vertical diffusivity, there is a strong impetus to apply them to the existing archive of hydrographic data. Density profiles are of particular interest because there is a long historical archive of density data, and

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J. Alexander Brearley, Katy L. Sheen, Alberto C. Naveira Garabato, David A. Smeed, and Stephanie Waterman

downstream of Drake Passage ( Gille 1994 ; Morrow et al. 1994 ). The strength of this Southern Ocean eddy field is believed to be sensitive to climatic changes in forcing on a range of time scales ( Thompson and Solomon 2002 ; Meredith and Hogg 2006 ; Meredith et al. 2012 ). While the upscale transfer of eddy energy from high- to low-baroclinic modes (and ultimately to the barotropic mode) is relatively well quantified ( Scott and Wang 2005 ), the processes by which eddy energy is dissipated are

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