K. Yamazaki1,2†, S. Aoki1, K.
Mizobata3
1 Institute of Low Temperature Science, Hokkaido
University, Hokkaido, Japan.
2 Graduate School of Environmental Science, Hokkaido
University, Hokkaido, Japan.
3 Tokyo University of Marine Science and Technology,
Tokyo, Japan.
Corresponding author: Kaihe Yamazaki (kaiheyamazaki@gmail.com)
† Address from 2022 Apr: National Institute of Polar Research, Tokyo,
Japan.
Key Points:
- Eddy diffusivity in the Antarctic margin is 100–500
m2 s-1, likely enhanced where the
recirculating gyres localize the onshore CDW flux.
- Onshore CDW flux is ~3.6 TW in the eastern Indian
sector, consistent with coastal heat sinks by surface freezing and
glacial melt.
- Isopycnal thickness gradient is a good predictor of mixing length and
eddy diffusivity.
Abstract
Warm, salty Circumpolar Deep Water (CDW) has long been regarded as the
climatological driver for Antarctica, but the mechanism of how it can
reach the continental shelf remains unsettled. Motivated by the absence
of observational eddy flux estimation in the Antarctic margin, we
quantify isopycnal diffusivity of CDW by hydrographic records and
satellite altimetry under the mixing length framework. For comparison,
spiciness and thickness are used as the isopycnal tracer. Over the
extent of the Antarctic Circumpolar Current (ACC), we find a general
agreement with the mixing suppression theory and its exception in the
lee of the topography as previously reported. In contrast, mixing length
does not depend on mean flow to the pole, reflecting a stagnant flow
regime in the Antarctic margin. Estimated isopycnal diffusivity ranges
100–500 m2 s-1 to the south of the
ACC. Eddy diffusion is likely enhanced where the CDW intrusion is
localized by the recirculating gyres, primarily attributable to the
small gradient of isopycnal thickness. Volume transport is then
estimated by the layer thickness gradient. Associated onshore heat flux
across the continental slope by CDW is calculated as
~3.6 TW and ~1.2 TW in the eastern and
western Indian sectors, respectively. The estimates are quantitatively
consistent with cryospheric heat sinks by sea ice formation and ice
shelf basal melt, suggesting that the isopycnal eddy diffusion is the
leading cause of the onshore CDW intrusion. We emphasize that the
thickness field is essential for determining the eddy fluxes in the
Antarctic margin.