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Diagnosing the Southern Ocean Overturning from Tracer Fields

Diagnosing the Southern Ocean Overturning from Tracer Fields
Diagnosing the Southern Ocean Overturning from Tracer Fields
The strength and structure of the Southern Hemisphere meridional overturning circulation (SMOC) is related to the along-isopycnal and vertical mixing coefficients by analyzing tracer and density fields from a hydrographic climatology. The meridional transport of Upper Circumpolar Deep Water (UCDW) across the Antarctic Circumpolar Current (ACC) is expressed in terms of the along-isopycnal (K) and diapycnal (D) tracer diffusivities and in terms of the along-isopycnal potential vorticity mixing coefficient (KPV). Uniform along-isopycnal (<600 m2 s?1) and low vertical mixing (10?5 m2 s?1) can maintain a southward transport of less than 60 Sv (Sv = 106 m2 s?1) of UCDW across the ACC, which is distributed largely across the South Pacific and east Indian Ocean basins. For vertical mixing rates of O(10?4 m2 s?1) or greater, the inferred transport is significantly enhanced. The transports inferred from both tracer and density distributions suggest a ratio K to D of O(2 × 106) particularly on deeper layers of UCDW. Given the range of observed southward transports of UCDW, it is found that K = 300 ± 150 m2 s?1 and D = 10?4 ± 0.5 × 10?4 m2 s?1 in the Southern Ocean interior. A view of the SMOC is revealed where dense waters are converted to lighter waters not only at the ocean surface, but also on depths below that of the mixed layer with vertical mixing playing an important role.
Southern Ocean, Ocean circulation, Meridional Overturning Circulation, Tracers, Southern Hemisphere
0022-3670
2926-2940
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
Sloyan, Bernadette M.
76a5a33f-4e74-4bfa-a330-688351a53717
McDougall, Trevor J.
06a3853b-ba2c-4203-8a7d-34dd0e0a8836
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
Sloyan, Bernadette M.
76a5a33f-4e74-4bfa-a330-688351a53717
McDougall, Trevor J.
06a3853b-ba2c-4203-8a7d-34dd0e0a8836

Zika, Jan D., Sloyan, Bernadette M. and McDougall, Trevor J. (2009) Diagnosing the Southern Ocean Overturning from Tracer Fields. Journal of Physical Oceanography, 39 (11), 2926-2940. (doi:10.1175/2009JPO4052.1).

Record type: Article

Abstract

The strength and structure of the Southern Hemisphere meridional overturning circulation (SMOC) is related to the along-isopycnal and vertical mixing coefficients by analyzing tracer and density fields from a hydrographic climatology. The meridional transport of Upper Circumpolar Deep Water (UCDW) across the Antarctic Circumpolar Current (ACC) is expressed in terms of the along-isopycnal (K) and diapycnal (D) tracer diffusivities and in terms of the along-isopycnal potential vorticity mixing coefficient (KPV). Uniform along-isopycnal (<600 m2 s?1) and low vertical mixing (10?5 m2 s?1) can maintain a southward transport of less than 60 Sv (Sv = 106 m2 s?1) of UCDW across the ACC, which is distributed largely across the South Pacific and east Indian Ocean basins. For vertical mixing rates of O(10?4 m2 s?1) or greater, the inferred transport is significantly enhanced. The transports inferred from both tracer and density distributions suggest a ratio K to D of O(2 × 106) particularly on deeper layers of UCDW. Given the range of observed southward transports of UCDW, it is found that K = 300 ± 150 m2 s?1 and D = 10?4 ± 0.5 × 10?4 m2 s?1 in the Southern Ocean interior. A view of the SMOC is revealed where dense waters are converted to lighter waters not only at the ocean surface, but also on depths below that of the mixed layer with vertical mixing playing an important role.

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More information

Published date: November 2009
Keywords: Southern Ocean, Ocean circulation, Meridional Overturning Circulation, Tracers, Southern Hemisphere
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 337462
URI: https://eprints.soton.ac.uk/id/eprint/337462
ISSN: 0022-3670
PURE UUID: 6ded4e63-312a-4723-bd9a-dafc78bbf407

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Date deposited: 25 Apr 2012 12:54
Last modified: 18 Jul 2017 06:03

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