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Historical variability in Atlantic meridional baroclinic transport at 26.5°N from boundary dynamic height observations

Historical variability in Atlantic meridional baroclinic transport at 26.5°N from boundary dynamic height observations
Historical variability in Atlantic meridional baroclinic transport at 26.5°N from boundary dynamic height observations
The strength of the Atlantic Meridional Overturning Circulation (MOC) at 26.5°N may be inferred from the combination of Florida Straits transport (derived from cable measurements), Ekman transport estimated from wind stress climatologies and mid-ocean geostrophic shear (traditionally obtained from hydrographic sections) with application of mass balance to the section to yield the mid-ocean barotropic flow. The recent Rapid monitoring project has provided time series information for the mid-ocean geostrophic shear since 2004. This work presents methods to assemble a comparable dataset from CTD end stations and boundary mooring temperature and pressure time series to estimate the past variability from 1980 to 2005. Variability in the end station derived transport anomalies suggests that the MOC has fluctuated by more than 10 Sv, encompassing all MOC estimates reported in the literature. Interannual changes in MOC transport are masked by this variability and calculated trends in layer transports are not statistically significant. More extensive datasets of CTD casts and moored temperature records at the western boundary do show significant changes with warming in the thermocline and long-term freshening of the deep waters between the 1980s and 2005. These changes are associated with stronger southward flow in the upper waters and weaker southward flow in the deep waters, and suggest a decrease in the MOC strength of 2–4 Sv. Any such decrease, however, is masked by the scale of variability in layer transports derived from the historical database of CTD end stations.
Atlantic circulation, Meridional overturning circulation, Climate change, Thermocline recirculation, Deep western boundary current
0967-0645
1754-1767
Longworth, Hannah R.
af733d01-ca58-42b8-9ec7-ee34dac105c3
Bryden, Harry L.
7f823946-34e8-48a3-8bd4-a72d2d749184
Baringer, Molly O.
05e0f722-83ee-4dc2-ac6e-2505c8b29f31
Longworth, Hannah R.
af733d01-ca58-42b8-9ec7-ee34dac105c3
Bryden, Harry L.
7f823946-34e8-48a3-8bd4-a72d2d749184
Baringer, Molly O.
05e0f722-83ee-4dc2-ac6e-2505c8b29f31

Longworth, Hannah R., Bryden, Harry L. and Baringer, Molly O. (2011) Historical variability in Atlantic meridional baroclinic transport at 26.5°N from boundary dynamic height observations. Deep Sea Research Part II: Topical Studies in Oceanography, 58 (17-18), 1754-1767. (doi:10.1016/j.dsr2.2010.10.057).

Record type: Article

Abstract

The strength of the Atlantic Meridional Overturning Circulation (MOC) at 26.5°N may be inferred from the combination of Florida Straits transport (derived from cable measurements), Ekman transport estimated from wind stress climatologies and mid-ocean geostrophic shear (traditionally obtained from hydrographic sections) with application of mass balance to the section to yield the mid-ocean barotropic flow. The recent Rapid monitoring project has provided time series information for the mid-ocean geostrophic shear since 2004. This work presents methods to assemble a comparable dataset from CTD end stations and boundary mooring temperature and pressure time series to estimate the past variability from 1980 to 2005. Variability in the end station derived transport anomalies suggests that the MOC has fluctuated by more than 10 Sv, encompassing all MOC estimates reported in the literature. Interannual changes in MOC transport are masked by this variability and calculated trends in layer transports are not statistically significant. More extensive datasets of CTD casts and moored temperature records at the western boundary do show significant changes with warming in the thermocline and long-term freshening of the deep waters between the 1980s and 2005. These changes are associated with stronger southward flow in the upper waters and weaker southward flow in the deep waters, and suggest a decrease in the MOC strength of 2–4 Sv. Any such decrease, however, is masked by the scale of variability in layer transports derived from the historical database of CTD end stations.

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More information

Published date: September 2011
Keywords: Atlantic circulation, Meridional overturning circulation, Climate change, Thermocline recirculation, Deep western boundary current

Identifiers

Local EPrints ID: 194427
URI: http://eprints.soton.ac.uk/id/eprint/194427
ISSN: 0967-0645
PURE UUID: 310e05ae-ba5a-479c-9e0b-2a105a9b4e5f
ORCID for Harry L. Bryden: ORCID iD orcid.org/0000-0002-8216-6359

Catalogue record

Date deposited: 27 Jul 2011 16:08
Last modified: 26 Nov 2021 02:38

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Contributors

Author: Hannah R. Longworth
Author: Harry L. Bryden ORCID iD
Author: Molly O. Baringer

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