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Tracking the spread of a passive tracer through Southern Ocean water masses

Tracking the spread of a passive tracer through Southern Ocean water masses
Tracking the spread of a passive tracer through Southern Ocean water masses
A dynamically passive inert tracer was released in the interior South Pacific Ocean at latitudes of the Antarctic Circumpolar Current. Observational cross sections of the tracer were taken over 4 consecutive years as it drifted through Drake Passage and into the Atlantic Ocean. The tracer was released within a region of high salinity relative to surrounding waters at the same density. In the absence of irreversible mixing a tracer remains at constant salinity and temperature on an isopycnal surface. To investigate the process of irreversible mixing we analysed the tracer in potential density-versus-salinity-anomaly coordinates. Observations of high tracer concentration tended to be collocated with isopycnal salinity anomalies. With time, an initially narrow peak in tracer concentration as a function of salinity at constant density broadened with the tracer being found at ever fresher salinities, consistent with diffusion-like behaviour in that coordinate system. The second moment of the tracer as a function of salinity suggested an initial period of slow spreading for approximately 2 years in the Pacific, followed by more rapid spreading as the tracer entered Drake Passage and the Scotia Sea. Analysis of isopycnal salinity gradients based on the Argo programme suggests that part of this apparent change can be explained by changes in background salinity gradients while part may be explained by the evolution of the tracer patch from a slowly growing phase where the tracer forms filaments to a more rapid phase where the tracer mixes at 240–550 m2 s−1.
1812-0792
323-336
Zika, Jan D.
319f1954-ca52-4695-a7cc-cce1009ea620
Sallée, Jean-baptiste
286cb991-56c7-4468-92a7-860a23aeed7a
Meijers, Andrew J. S.
747ecd45-cdbe-47be-b952-4b724096f9d5
Naveira-Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Watson, Andrew J.
55e619df-85a4-4079-922b-8cb1f17290a8
Messias, Marie-jose
c8227a05-a3e2-4146-975d-0906ae5eacb1
King, Brian A.
960f44b4-cc9c-4f77-b3c8-775530ac0061
Zika, Jan D.
319f1954-ca52-4695-a7cc-cce1009ea620
Sallée, Jean-baptiste
286cb991-56c7-4468-92a7-860a23aeed7a
Meijers, Andrew J. S.
747ecd45-cdbe-47be-b952-4b724096f9d5
Naveira-Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Watson, Andrew J.
55e619df-85a4-4079-922b-8cb1f17290a8
Messias, Marie-jose
c8227a05-a3e2-4146-975d-0906ae5eacb1
King, Brian A.
960f44b4-cc9c-4f77-b3c8-775530ac0061

Zika, Jan D., Sallée, Jean-baptiste, Meijers, Andrew J. S., Naveira-Garabato, Alberto C., Watson, Andrew J., Messias, Marie-jose and King, Brian A. (2020) Tracking the spread of a passive tracer through Southern Ocean water masses. Ocean Science, 16 (2), 323-336. (doi:10.5194/os-16-323-2020).

Record type: Article

Abstract

A dynamically passive inert tracer was released in the interior South Pacific Ocean at latitudes of the Antarctic Circumpolar Current. Observational cross sections of the tracer were taken over 4 consecutive years as it drifted through Drake Passage and into the Atlantic Ocean. The tracer was released within a region of high salinity relative to surrounding waters at the same density. In the absence of irreversible mixing a tracer remains at constant salinity and temperature on an isopycnal surface. To investigate the process of irreversible mixing we analysed the tracer in potential density-versus-salinity-anomaly coordinates. Observations of high tracer concentration tended to be collocated with isopycnal salinity anomalies. With time, an initially narrow peak in tracer concentration as a function of salinity at constant density broadened with the tracer being found at ever fresher salinities, consistent with diffusion-like behaviour in that coordinate system. The second moment of the tracer as a function of salinity suggested an initial period of slow spreading for approximately 2 years in the Pacific, followed by more rapid spreading as the tracer entered Drake Passage and the Scotia Sea. Analysis of isopycnal salinity gradients based on the Argo programme suggests that part of this apparent change can be explained by changes in background salinity gradients while part may be explained by the evolution of the tracer patch from a slowly growing phase where the tracer forms filaments to a more rapid phase where the tracer mixes at 240–550 m2 s−1.

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Accepted/In Press date: 16 January 2020
Published date: 12 March 2020

Identifiers

Local EPrints ID: 439111
URI: http://eprints.soton.ac.uk/id/eprint/439111
ISSN: 1812-0792
PURE UUID: ac443d88-a2cf-478e-9db4-7b8016c2be8d

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Date deposited: 03 Apr 2020 16:30
Last modified: 06 Oct 2020 22:50

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