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We examine the vertical structure of the horizontal flow and diagnose vertical velocities in the Antarctic Circumpolar Current (ACC) near the Kerguelen Plateau using EM-APEX profiling floats. Eight floats measured horizontal velocity, temperature and salinity profiles to 1600 dbar, with a vertical spacing of 3-5 dbar four times per day over a period of approximately 3 months. Horizontal velocity profiles show a complex vertical structure with strong rotation of the velocity vector through the water column The distribution of rotation angles from 1247 profiles is approximately Gaussian and rotations of either sign are equally likely. Forty percent of profiles with speed greater than 5 cms^-1 have a depth integrated rotation of less than 15 degrees over 1300 dbar, while the other 60% demonstrate significantly stronger rotation. Consequently, most profiles do not conform to the equivalent barotropic model (deep flow parallel and proportional to the surface flow) used in simplified dynamic models and in Gravest Empirical Mode climatologies of the ACC. Nevertheless, since we find the mean rotation to be zero, an equivalent barotropic assumption is valid to first order. Vertical velocities inferred using conservation of mass and a gradient wind balance in natural coordinates have magnitudes on the order of 100 m/day. We find robust patterns of upwelling and downwelling phase-locked to meanders in the flow, as found in earlier studies. With the advent of high-resolution observations such as those presented here, and high-resolution models, we can advance to a more complete understanding of the rich variability in ACC structure that is neglected in the equivalent barotropic model.

Item Type:	Refereed Article
Keywords:	Antarctic Circumpolar Current, velocity, observations, EM-APEX, equivalent barotropic
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Physical oceanography
Objective Division:	Environmental Policy, Climate Change and Natural Hazards
Objective Group:	Understanding climate change
Objective Field:	Climate variability (excl. social impacts)
UTAS Author:	Phillips, HE (Associate Professor Helen Phillips)
UTAS Author:	Bindoff, NL (Professor Nathan Bindoff)
ID Code:	93312
Year Published:	2014
Funding Support:	Australian Research Council (DP0877098)
Web of Science® Times Cited:	19
Deposited By:	IMAS Research and Education Centre
Deposited On:	2014-07-25
Last Modified:	2017-11-01
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