The University of Southampton
University of Southampton Institutional Repository

On the variability of the deep meridional transports in the tropical North Atlantic

On the variability of the deep meridional transports in the tropical North Atlantic
On the variability of the deep meridional transports in the tropical North Atlantic
A 5-year-long time series of meridional transport below 1180 dbar—zonally integrated across a section spanning, the western basin of the tropical North Atlantic—is analyzed. It has been inferred from (i) zonally integrated meridional geostrophic transports derived from density and bottom pressure measurements at the end points of a 1000 km wide section bounded by the base of the western continental rise and the Mid-Atlantic Ridge and (ii) mooring-based direct current meter measurements over the steep Lesser Antilles continental rise. The southward time mean transport of North Atlantic Deep Water (NADW) transport is 15.9 Sv. The vertical shear of the geostrophic transport profiles in the western and eastern part of the section each show two layers of maximum southward transport within the NADW. The transport time series reveals changes of 7.7 Sv rms at periods of 1 month and longer, at times showing changes of up to 40 Sv within a month's time. The baroclinic (internal) contribution of the geostrophic flow (relative to 4950 dbar), yields fluctuations of 6.6 Sv rms. Adding transports over the steep continental rise reduces the overall transport variability to 5.2 Sv rms. As a result of this reduction in shorter-period variability, the lower-frequency variability becomes more pronounced, part of which is expected to be linked to the meridional overturning circulation (MOC). The transport variability is consistent with baroclinic Rossby waves (at periods between 3 and 9 months), dominating in the eastern and central part of the section, and with changes in deep western boundary current (DWBC) strength, DWBC re-circulation patterns and eddies that become important in the western part of the section. The reference-level (external) geostrophic transport variability displays long-wavelength (>2000 km) fluctuations of 7.5 Sv rms on periods less than 2 weeks that are consistent with barotropic Rossby waves.
Numerical model simulations imply that the observed zonally integrated deep transport changes in the western basin have moderate skill in sensing changes in the MOC and in meridional heat transport, and that a now implemented extension of the array's integration scale into the eastern basin of the Atlantic would substantially improve the performance of the array as an MOC observing system.
Ocean transport, North Atlantic Deep Water, Density, Bottom pressure, Time series, Monitoring, Meridional overturning circulation, Geostrophy, Mooring array, Tropical Atlantic, Rossby waves, Deep western boundary current, Re-circulation
0967-0637
1601-1623
Kanzow, T.
ede4d92e-c4b2-48d0-83bf-a03f881aa819
Send, U.
e4f7234f-b5b3-4472-a57e-d15bc1e2c2a2
McCartney, M.
28e2b6ed-9b4a-45a2-ae66-b779797baa3f
Kanzow, T.
ede4d92e-c4b2-48d0-83bf-a03f881aa819
Send, U.
e4f7234f-b5b3-4472-a57e-d15bc1e2c2a2
McCartney, M.
28e2b6ed-9b4a-45a2-ae66-b779797baa3f

Kanzow, T., Send, U. and McCartney, M. (2008) On the variability of the deep meridional transports in the tropical North Atlantic. Deep Sea Research Part I: Oceanographic Research Papers, 55 (12), 1601-1623. (doi:10.1016/j.dsr.2008.07.011).

Record type: Article

Abstract

A 5-year-long time series of meridional transport below 1180 dbar—zonally integrated across a section spanning, the western basin of the tropical North Atlantic—is analyzed. It has been inferred from (i) zonally integrated meridional geostrophic transports derived from density and bottom pressure measurements at the end points of a 1000 km wide section bounded by the base of the western continental rise and the Mid-Atlantic Ridge and (ii) mooring-based direct current meter measurements over the steep Lesser Antilles continental rise. The southward time mean transport of North Atlantic Deep Water (NADW) transport is 15.9 Sv. The vertical shear of the geostrophic transport profiles in the western and eastern part of the section each show two layers of maximum southward transport within the NADW. The transport time series reveals changes of 7.7 Sv rms at periods of 1 month and longer, at times showing changes of up to 40 Sv within a month's time. The baroclinic (internal) contribution of the geostrophic flow (relative to 4950 dbar), yields fluctuations of 6.6 Sv rms. Adding transports over the steep continental rise reduces the overall transport variability to 5.2 Sv rms. As a result of this reduction in shorter-period variability, the lower-frequency variability becomes more pronounced, part of which is expected to be linked to the meridional overturning circulation (MOC). The transport variability is consistent with baroclinic Rossby waves (at periods between 3 and 9 months), dominating in the eastern and central part of the section, and with changes in deep western boundary current (DWBC) strength, DWBC re-circulation patterns and eddies that become important in the western part of the section. The reference-level (external) geostrophic transport variability displays long-wavelength (>2000 km) fluctuations of 7.5 Sv rms on periods less than 2 weeks that are consistent with barotropic Rossby waves.
Numerical model simulations imply that the observed zonally integrated deep transport changes in the western basin have moderate skill in sensing changes in the MOC and in meridional heat transport, and that a now implemented extension of the array's integration scale into the eastern basin of the Atlantic would substantially improve the performance of the array as an MOC observing system.

This record has no associated files available for download.

More information

Published date: December 2008
Keywords: Ocean transport, North Atlantic Deep Water, Density, Bottom pressure, Time series, Monitoring, Meridional overturning circulation, Geostrophy, Mooring array, Tropical Atlantic, Rossby waves, Deep western boundary current, Re-circulation

Identifiers

Local EPrints ID: 63934
URI: http://eprints.soton.ac.uk/id/eprint/63934
ISSN: 0967-0637
PURE UUID: 656b1a1f-26e8-496e-92a6-5fa9c6cc8f5b

Catalogue record

Date deposited: 19 Nov 2008
Last modified: 15 Mar 2024 11:45

Export record

Altmetrics

Contributors

Author: T. Kanzow
Author: U. Send
Author: M. McCartney

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×