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Topographic enhancement of vertical turbulent mixing in the Southern Ocean

Topographic enhancement of vertical turbulent mixing in the Southern Ocean
Topographic enhancement of vertical turbulent mixing in the Southern Ocean
It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation.
Mashayek, A.
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Ferrari, R.
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Merrifield, S.
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Ledwell, J. R.
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St Laurent, L.
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Garabato, A. Naveira
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Mashayek, A.
9c64bac5-6f26-4086-aaf4-f38dc163c854
Ferrari, R.
d785df74-e6bb-4f6f-bd27-50ca42032e42
Merrifield, S.
6bc77df3-5286-46ca-99c0-8b6c65f44630
Ledwell, J. R.
c369f91d-fa36-42dd-9391-910486f60c2d
St Laurent, L.
745fc400-a419-4bce-859b-89e63b0cd80d
Garabato, A. Naveira
97c0e923-f076-4b38-b89b-938e11cea7a6

Mashayek, A., Ferrari, R., Merrifield, S., Ledwell, J. R., St Laurent, L. and Garabato, A. Naveira (2017) Topographic enhancement of vertical turbulent mixing in the Southern Ocean. Nature Communications, 8, [14197]. (doi:10.1038/ncomms14197).

Record type: Article

Abstract

It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation.

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Accepted/In Press date: 6 December 2016
e-pub ahead of print date: 6 March 2017
Published date: 6 March 2017
Organisations: Ocean and Earth Science, Physical Oceanography

Identifiers

Local EPrints ID: 406964
URI: http://eprints.soton.ac.uk/id/eprint/406964
PURE UUID: 53b3ba17-9618-4d42-a4ec-3c594332e34d

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Date deposited: 29 Mar 2017 01:04
Last modified: 27 Apr 2022 12:18

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Contributors

Author: A. Mashayek
Author: R. Ferrari
Author: S. Merrifield
Author: J. R. Ledwell
Author: L. St Laurent

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