The University of Southampton
University of Southampton Institutional Repository

Upper Ocean Transport Variability in the Subtropical North Atlantic

Upper Ocean Transport Variability in the Subtropical North Atlantic
Upper Ocean Transport Variability in the Subtropical North Atlantic
Many general circulation models predict a reduction in overturning strength in the 21st century as a response to anthropogenic forcing, meaning that novel methods of monitoring individual components of the subtropical North Atlantic circulation are required. This observational study outlines efforts to monitor upper ocean transports near the 36°N latitude line and to identify possible forcing mechanisms. Specifically, an optimal interpolation scheme is employed to synthesise annual and seasonal sections of the Atlantic using T/S data from Argo floats and the Line W array from 2002 to 2007. Combining these data with an estimate of the barotropic velocity yields accurate values of the interior geostrophic transport above 1000 dbar. Close to the western boundary, where errors incurred by the scheme are larger, altimetric SSH differences are used to quantify the Gulf Stream transport above 2000 dbar at 10-day resolution. Finally, a detailed analysis of wind stress and wind stress curl fields of the subtropical North Atlantic is used to estimate both the Ekman and Sverdrup transports and to isolate the dominant time and space scales of variability.

The mean zonally integrated interior transport above 1000 dbar between the eastern boundary and the Gulf Stream was -48.0 ± 3.3 Sv, where the error represents the standard error of the seasonal baroclinic transport estimates. The size of the variability between seasons was similar to the interannual variability (standard deviations of 6.6 Sv and 7.7 Sv). Most variability at interannual timescales arises from changes in the density structure of the main thermocline west of 40°W. Neither interannual nor seasonal variability in the interior transport correlate with changes in the Sverdrup transport, though the Sverdrup relation does account for the mean upper ocean transport in the eastern basin. Gulf Stream transport across Line W in the period 2002 to 2008 was estimated to be 87.6 (± 0.8 Sv standard error) in the upper 1000 dbar, with a peak transport in late summer. In line with earlier studies, the seasonal cycle of the transport appears to be correlated with local wind stress curl forcing but determining the precise mechanism requires further theoretical and modelling work.
Brearley, James Alexander
f33b7738-c740-4494-b900-179cf7f49343
Brearley, James Alexander
f33b7738-c740-4494-b900-179cf7f49343

Brearley, James Alexander (2010) Upper Ocean Transport Variability in the Subtropical North Atlantic. University of Southampton, School of Ocean and Earth Science, Doctoral Thesis, 303pp.

Record type: Thesis (Doctoral)

Abstract

Many general circulation models predict a reduction in overturning strength in the 21st century as a response to anthropogenic forcing, meaning that novel methods of monitoring individual components of the subtropical North Atlantic circulation are required. This observational study outlines efforts to monitor upper ocean transports near the 36°N latitude line and to identify possible forcing mechanisms. Specifically, an optimal interpolation scheme is employed to synthesise annual and seasonal sections of the Atlantic using T/S data from Argo floats and the Line W array from 2002 to 2007. Combining these data with an estimate of the barotropic velocity yields accurate values of the interior geostrophic transport above 1000 dbar. Close to the western boundary, where errors incurred by the scheme are larger, altimetric SSH differences are used to quantify the Gulf Stream transport above 2000 dbar at 10-day resolution. Finally, a detailed analysis of wind stress and wind stress curl fields of the subtropical North Atlantic is used to estimate both the Ekman and Sverdrup transports and to isolate the dominant time and space scales of variability.

The mean zonally integrated interior transport above 1000 dbar between the eastern boundary and the Gulf Stream was -48.0 ± 3.3 Sv, where the error represents the standard error of the seasonal baroclinic transport estimates. The size of the variability between seasons was similar to the interannual variability (standard deviations of 6.6 Sv and 7.7 Sv). Most variability at interannual timescales arises from changes in the density structure of the main thermocline west of 40°W. Neither interannual nor seasonal variability in the interior transport correlate with changes in the Sverdrup transport, though the Sverdrup relation does account for the mean upper ocean transport in the eastern basin. Gulf Stream transport across Line W in the period 2002 to 2008 was estimated to be 87.6 (± 0.8 Sv standard error) in the upper 1000 dbar, with a peak transport in late summer. In line with earlier studies, the seasonal cycle of the transport appears to be correlated with local wind stress curl forcing but determining the precise mechanism requires further theoretical and modelling work.

PDF
Brearley_2010_PhD.pdf - Other
Available under License University of Southampton Thesis Licence.
Download (19MB)
Microsoft Word
Copyright_acknowledgements.doc - Other
Available under License University of Southampton Thesis Licence.
Download (24kB)

More information

Published date: September 2010
Organisations: University of Southampton, Ocean and Earth Science

Identifiers

Local EPrints ID: 191959
URI: https://eprints.soton.ac.uk/id/eprint/191959
PURE UUID: 2d53ce19-83e9-4452-9400-62dbe2f5c1f6

Catalogue record

Date deposited: 28 Jun 2011 13:18
Last modified: 18 Jul 2017 11:34

Export record

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 https://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.

×