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Estimating the deep overturning transport variability at 26°N using bottom pressure recorders

Estimating the deep overturning transport variability at 26°N using bottom pressure recorders
Estimating the deep overturning transport variability at 26°N using bottom pressure recorders
The RAPID mooring array at 26°N in the Atlantic has been observing the Atlantic meridional overturning circulation (AMOC) since 2004, with estimates of AMOC strength suggesting that it has declined over the 2004–2016 period. When AMOC transport is estimated, an external transport is added to the observed Ekman, Florida Straits, and baroclinic geostrophic transports to ensure zero net mass transport across the section. This approach was validated using the first year of RAPID data by estimating the external component directly from in situ bottom pressure data. Since bottom pressure recorders commonly show low‐frequency instrument drift, bottom pressure data had to be dedrifted prior to calculating the external component. Here we calculate the external component from 10 years of in situ bottom pressure data and evaluate two choices for dedrifting the records: traditional and adjusted using a Gravity Recovery and Climate Experiment (GRACE) bottom pressure solution. We show that external transport estimated from GRACE‐adjusted, in situ bottom pressure data correlates better with the RAPID compensation transport (r=0.65,p<0.05) than using individually dedrifted bottom pressure recorders, particularly at low frequencies on timescales shorter than 10 years, demonstrating that the low‐frequency variability added from GRACE is consistent with the transport variability at RAPID. We further use the bottom pressure‐derived external transport to evaluate the zonal distribution of the barotropic transport variability and find that the transport variability is concentrated west of the Mid‐Atlantic Ridge rather than uniformly distributed across the basin, as assumed in the RAPID calculation.
2169-9275
Worthington, E. L.
bfd4e9a7-3080-4bf7-b1dc-b0cc8803e97f
Frajka-williams, E.
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
Mccarthy, G. D.
fd87927d-feb3-447a-9cda-9558916df99f
Worthington, E. L.
bfd4e9a7-3080-4bf7-b1dc-b0cc8803e97f
Frajka-williams, E.
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
Mccarthy, G. D.
fd87927d-feb3-447a-9cda-9558916df99f

Worthington, E. L., Frajka-williams, E. and Mccarthy, G. D. (2018) Estimating the deep overturning transport variability at 26°N using bottom pressure recorders. Journal of Geophysical Research: Oceans. (doi:10.1029/2018JC014221).

Record type: Article

Abstract

The RAPID mooring array at 26°N in the Atlantic has been observing the Atlantic meridional overturning circulation (AMOC) since 2004, with estimates of AMOC strength suggesting that it has declined over the 2004–2016 period. When AMOC transport is estimated, an external transport is added to the observed Ekman, Florida Straits, and baroclinic geostrophic transports to ensure zero net mass transport across the section. This approach was validated using the first year of RAPID data by estimating the external component directly from in situ bottom pressure data. Since bottom pressure recorders commonly show low‐frequency instrument drift, bottom pressure data had to be dedrifted prior to calculating the external component. Here we calculate the external component from 10 years of in situ bottom pressure data and evaluate two choices for dedrifting the records: traditional and adjusted using a Gravity Recovery and Climate Experiment (GRACE) bottom pressure solution. We show that external transport estimated from GRACE‐adjusted, in situ bottom pressure data correlates better with the RAPID compensation transport (r=0.65,p<0.05) than using individually dedrifted bottom pressure recorders, particularly at low frequencies on timescales shorter than 10 years, demonstrating that the low‐frequency variability added from GRACE is consistent with the transport variability at RAPID. We further use the bottom pressure‐derived external transport to evaluate the zonal distribution of the barotropic transport variability and find that the transport variability is concentrated west of the Mid‐Atlantic Ridge rather than uniformly distributed across the basin, as assumed in the RAPID calculation.

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Worthington_et_al-2019-Journal_of_Geophysical_Research__Oceans - Version of Record
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Accepted/In Press date: 19 December 2018
e-pub ahead of print date: 21 December 2018

Identifiers

Local EPrints ID: 427918
URI: http://eprints.soton.ac.uk/id/eprint/427918
ISSN: 2169-9275
PURE UUID: a70ea257-5d43-48d8-9947-a8dd4752dd17
ORCID for E. L. Worthington: ORCID iD orcid.org/0000-0002-6444-6461
ORCID for E. Frajka-williams: ORCID iD orcid.org/0000-0001-8773-7838

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Date deposited: 04 Feb 2019 17:30
Last modified: 30 Jan 2020 01:45

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