<div>Kaihe Yamazaki<sup>1,2,3</sup>, Shigeru Aoki<sup>1</sup>,
Kohei Mizobata<sup>4</sup></div><div><sup>1</sup> Institute of Low Temperature Science, Hokkaido
University, Hokkaido, Japan</div><div><sup>2</sup> Graduate School of Environmental Science, Hokkaido
University, Hokkaido, Japan</div><div><sup>3</sup> National Institute of Polar Research, Tokyo, Japan</div><div><sup>4</sup> Tokyo University of Marine Science and Technology,
Tokyo, Japan</div><div>Corresponding author: Kaihe Yamazaki (kaiheyamazaki@gmail.com)</div><div>Key Points</div><ul><li>Eddy diffusivity in the subpolar Southern Ocean is estimated to be
100–500 m<sup>2</sup> s<sup>-1</sup> based on
hydrographic variability and satellite altimetry.</li><li>Eddy heat flux towards the Wilkes Land is ~3.6 TW,
nearly balancing with surface freezing, glacial melt, and solar
heating.</li><li>The thickness gradient controls mixing length and eddy diffusivity in
the subpolar zone.</li></ul><div>Abstract</div><div>Warm, salty Circumpolar Deep Water (CDW) is recognized as the primary
driver for Antarctic glacial melt, but the mechanism by which it reaches
the continental shelves remains highly uncertain from an observational
standpoint. With the scarcity of eddy flux estimation in the Antarctic
margin, we quantify the isopycnal diffusivity of CDW using hydrographic
variability and satellite altimetry under the mixing length framework.
For comparison, the spiciness and thickness are used as isopycnal
tracers, and the two tracers yield qualitatively similar estimates. Over
the Antarctic Circumpolar Current (ACC), spatial variation of mixing
length is generally aligned with the jet-induced mixing suppression
theory, including its exception in the lee of the topography. In
contrast, the mixing length does not depend on the mean flow in the
subpolar zone, likely reflecting the relatively quiescent flow regime.
The estimated isopycnal diffusivity ranges from 100 to 500
m<sup>2</sup> s<sup>-1</sup> south of the ACC. The eddy
diffusivity tends to be enhanced where the gradient of isopycnal
thickness becomes small and CDW intrudes onshore. The cross-slope eddy
CDW flux is estimated, and the associated onshore heat flux across is
calculated as ~3.6 TW in the eastern Indian sector. The
eddy heat flux and coastal solar heating are generally balanced with
cryospheric heat sinks including glacial melting and surface freezing,
suggesting that the eddy advection is substantial for the onshore CDW
flux. The thickness field is essential for determining mixing length and
eddy fluxes in the subpolar zone, whereas the situation does not hold
for the ACC domain.</div>