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On the consumption of Antarctic Bottom Water in the abyssal ocean

On the consumption of Antarctic Bottom Water in the abyssal ocean
On the consumption of Antarctic Bottom Water in the abyssal ocean
The abyssal ocean is primarily filled by cold, dense waters formed around Antarctica and collectively referred to as Antarctic Bottom Water (AABW). At steady state, AABW must be consumed in the ocean interior at the same rate it is produced, but how and where this consumption is achieved remains poorly understood. Here, we present estimates of abyssal water mass transformation by geothermal heating and parameterized internal wave-driven mixing. We use maps of the energy input to internal waves by tidal and geostrophic motions interacting with topography combined with assumptions about the distribution of energy dissipation to evaluate dianeutral transports induced by breaking internal tides and lee waves. Geothermal transformation is assessed based on a map of geothermal heat fluxes. Under the hypotheses underlying the constructed climatologies of buoyancy fluxes, we calculate that locally-dissipating internal tides and geothermal heating contribute respectively about 8 and 5 Sv of AABW consumption (upwelling), mostly north of 30°S. In contrast, parameterized lee wave-driven mixing causes significant transformation only in the Southern Ocean, where it forms about 3 Sv of AABW, decreasing the mean density but enhancing the northward flow of abyssal waters. The possible role of remotely-dissipating internal tides in complementing AABW consumption is explored based on idealized distributions of mixing energy. Depending mostly on the chosen vertical structure, such mixing could drive 1 to 28 Sv of additional AABW upwelling, highlighting the need to better constrain the spatial distribution of remote dissipation. Though they carry large uncertainties, these climatological transformation estimates shed light on the qualitative functioning and key unknowns of the diabatic overturning.
0022-3670
635-661
de Lavergne, Casimir
fb15659a-82a1-4bf0-8cda-504f90a2f029
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Le Sommer, Julien
d442f04e-83e5-4818-a148-eeca9cb4e36a
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
de Lavergne, Casimir
fb15659a-82a1-4bf0-8cda-504f90a2f029
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Le Sommer, Julien
d442f04e-83e5-4818-a148-eeca9cb4e36a
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6

de Lavergne, Casimir, Madec, Gurvan, Le Sommer, Julien, Nurser, A.J. George and Naveira Garabato, Alberto C. (2016) On the consumption of Antarctic Bottom Water in the abyssal ocean. Journal of Physical Oceanography, 46 (2), 635-661. (doi:10.1175/JPO-D-14-0201.1).

Record type: Article

Abstract

The abyssal ocean is primarily filled by cold, dense waters formed around Antarctica and collectively referred to as Antarctic Bottom Water (AABW). At steady state, AABW must be consumed in the ocean interior at the same rate it is produced, but how and where this consumption is achieved remains poorly understood. Here, we present estimates of abyssal water mass transformation by geothermal heating and parameterized internal wave-driven mixing. We use maps of the energy input to internal waves by tidal and geostrophic motions interacting with topography combined with assumptions about the distribution of energy dissipation to evaluate dianeutral transports induced by breaking internal tides and lee waves. Geothermal transformation is assessed based on a map of geothermal heat fluxes. Under the hypotheses underlying the constructed climatologies of buoyancy fluxes, we calculate that locally-dissipating internal tides and geothermal heating contribute respectively about 8 and 5 Sv of AABW consumption (upwelling), mostly north of 30°S. In contrast, parameterized lee wave-driven mixing causes significant transformation only in the Southern Ocean, where it forms about 3 Sv of AABW, decreasing the mean density but enhancing the northward flow of abyssal waters. The possible role of remotely-dissipating internal tides in complementing AABW consumption is explored based on idealized distributions of mixing energy. Depending mostly on the chosen vertical structure, such mixing could drive 1 to 28 Sv of additional AABW upwelling, highlighting the need to better constrain the spatial distribution of remote dissipation. Though they carry large uncertainties, these climatological transformation estimates shed light on the qualitative functioning and key unknowns of the diabatic overturning.

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More information

Accepted/In Press date: 24 November 2015
e-pub ahead of print date: 2015
Published date: February 2016
Organisations: Marine Systems Modelling, Physical Oceanography

Identifiers

Local EPrints ID: 386571
URI: http://eprints.soton.ac.uk/id/eprint/386571
ISSN: 0022-3670
PURE UUID: 7f888943-9522-47d8-8f9a-12288c3862e1
ORCID for Alberto C. Naveira Garabato: ORCID iD orcid.org/0000-0001-6071-605X

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Date deposited: 28 Jan 2016 13:17
Last modified: 15 Mar 2024 03:24

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Contributors

Author: Casimir de Lavergne
Author: Gurvan Madec
Author: Julien Le Sommer
Author: A.J. George Nurser

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