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Dhruv Balwada, Joseph H. LaCasce, Kevin G. Speer, and Raffaele Ferrari

1. Introduction Oceanic flows are turbulent over a large range of length scales and are very efficient at stirring tracers along isopycnals, enhancing the effects of molecular diffusion by many orders of magnitude ( Garrett 2006 ). The parameterization of this lateral stirring is key to the proper representation of the oceanic transport of heat, carbon, nutrients, and other climatically important tracers in climate models (e.g., Gnanadesikan et al. 2015 ; Fox-Kemper et al. 2013 ). The details

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

measurements. More recently, Sheen et al. (2013) found middepth turbulent dissipation rates increasing by an order of magnitude between the southeastern Pacific and the Scotia Sea. While finescale estimates might be predicted to overestimate the magnitude of turbulent diapycnal mixing in the ocean due to the effects of instrument noise on density profiles and spectra, at a minimum we expect that a successful diapycnal diffusivity estimate should be able to capture the differences in the magnitude of the

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Sophia T. Merrifield, Louis St. Laurent, Breck Owens, Andreas M. Thurnherr, and John M. Toole

Subantarctic Front and Polar Front regions, downstream of the Phoenix Ridge and extending over the seafloor topography of the Shackleton Fracture Zone. Each cruise included fine- and microstructure profiling, CTD hydrographic measurements, and ship and lowered acoustic Doppler current profiling (SADCP and LADCP) of the oceanic velocity structure. Velocity measurements from two instruments, a 300-kHz LADCP and a modular acoustic velocity sensor (MAVS), which is part of the High Resolution Profiler 2 (HRP2

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

E 0 = 6.3 × 10 −5 ; b is the stratification e -folding scale taken as 1000 m in the Drake Passage ( Thurnherr et al. 2015 ); is the peak wavenumber, which quantifies the bandwidth of the internal wave field; ; and N 0 = 5.3 × 10 3 rad s −1 . Analysis of vertical velocity from lowered acoustic Doppler current profilers (LADCPs) measurements ( Thurnherr et al. 2015 ) find that such a spectrum holds in many regions of the ocean, spanning a range of latitudes, up to a limiting wavenumber

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Byron F. Kilbourne and James B. Girton

1. Introduction The study of near-inertial oscillations and internal waves began with the advent of moored, self-recording current meter measurements in the 1960s. These instruments revealed considerable variance near the local inertial frequency ( Webster 1968 ) and motivated a series of efforts to better understand near-inertial variability, its predominant generation mechanisms, and its role in other ocean processes such as diapycnal mixing and energy transport: Pollard and Millard (1970

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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

velocity from altimetry and by Marshall et al. (2006) who advected numerical tracers with the altimetric velocity field. Phillips and Rintoul (2000) attempted to estimate the fluxes of heat and momentum from mooring data, but not the rate at which tracers are mixed. Here we present the first direct measurements based on the spreading of a tracer deliberately released as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The mixing is quantified with an eddy

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

-wave theory, several Southern Ocean observational programs have found dissipation to be strongest in regions of rough topography, such as the western Drake Passage ( Naveira Garabato et al. 2004 ) or around the Kerguelen Plateau ( Waterman et al. 2013a ). This signal has been observed by tracer measurements, which yield a time-integrated measure of diffusivity ( Ledwell et al. 2011 ; Watson et al. 2013, manuscript submitted to Nature ) and by spot measurements made using microstructure instruments, which

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