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A Multimodel Study of Sea Surface Temperature and Subsurface Density Fingerprints of the Atlantic Meridional Overturning Circulation

A Multimodel Study of Sea Surface Temperature and Subsurface Density Fingerprints of the Atlantic Meridional Overturning Circulation
A Multimodel Study of Sea Surface Temperature and Subsurface Density Fingerprints of the Atlantic Meridional Overturning Circulation
The Atlantic meridional overturning circulation (AMOC) is an important component of the North Atlantic climate system. Here, simulations from 10 coupled climate models are used to calculate patterns of sea surface temperature (SST) and subsurface density change associated with decadal AMOC variability. The models are evaluated using observational constraints and it is shown that all 10 models suffer from North Atlantic Deep Water transports that are too shallow, although the biases are least severe in the Community Climate System Model, version 4 (CCSM4). In the models that best compare with observations, positive AMOC anomalies are associated with reduced Labrador Sea stratification and increased midocean (800–1800 m) densities in the subpolar gyre. Maximum correlations occur when AMOC anomalies lag Labrador Sea stratification and subsurface density anomalies by 2–6 yr and 0–3 yr, respectively. In all 10 models, North Atlantic warming follows positive AMOC anomalies, but the patterns and magnitudes of SST change are variable. A simple detection and attribution analysis is then used to evaluate the utility of Atlantic midocean density and Labrador Sea stratification indices for detecting changes to the AMOC in the presence of increasing CO2 concentrations. It is shown that trends in midocean density are identifiable (although not attributable) significantly earlier than trends in the AMOC. For this reason, subsurface density observations could be a useful complement to transport observations made at specific latitudes and may help with the more rapid diagnosis of basin-scale changes in the AMOC. Using existing observations, it is not yet possible to detect a robust trend in the AMOC using either midocean densities or transport observations from 26.5°N.
North Atlantic Ocean, Thermohaline circulation, Coupled models, Climate variability, Multidecadal variability, Oceanic variability
0894-8755
9155-9174
Roberts, Christopher D.
4f3eb6ea-2941-481b-a3fc-ac5ce444167d
Garry, Freya K.
5810f34e-1069-4efb-ba9e-ec13e1f3441d
Jackson, Laura C.
c610e2ea-b151-4317-b44b-f4ac7a7e2070
Roberts, Christopher D.
4f3eb6ea-2941-481b-a3fc-ac5ce444167d
Garry, Freya K.
5810f34e-1069-4efb-ba9e-ec13e1f3441d
Jackson, Laura C.
c610e2ea-b151-4317-b44b-f4ac7a7e2070

Roberts, Christopher D., Garry, Freya K. and Jackson, Laura C. (2013) A Multimodel Study of Sea Surface Temperature and Subsurface Density Fingerprints of the Atlantic Meridional Overturning Circulation. Journal of Climate, 26 (22), 9155-9174. (doi:10.1175/JCLI-D-12-00762.1).

Record type: Article

Abstract

The Atlantic meridional overturning circulation (AMOC) is an important component of the North Atlantic climate system. Here, simulations from 10 coupled climate models are used to calculate patterns of sea surface temperature (SST) and subsurface density change associated with decadal AMOC variability. The models are evaluated using observational constraints and it is shown that all 10 models suffer from North Atlantic Deep Water transports that are too shallow, although the biases are least severe in the Community Climate System Model, version 4 (CCSM4). In the models that best compare with observations, positive AMOC anomalies are associated with reduced Labrador Sea stratification and increased midocean (800–1800 m) densities in the subpolar gyre. Maximum correlations occur when AMOC anomalies lag Labrador Sea stratification and subsurface density anomalies by 2–6 yr and 0–3 yr, respectively. In all 10 models, North Atlantic warming follows positive AMOC anomalies, but the patterns and magnitudes of SST change are variable. A simple detection and attribution analysis is then used to evaluate the utility of Atlantic midocean density and Labrador Sea stratification indices for detecting changes to the AMOC in the presence of increasing CO2 concentrations. It is shown that trends in midocean density are identifiable (although not attributable) significantly earlier than trends in the AMOC. For this reason, subsurface density observations could be a useful complement to transport observations made at specific latitudes and may help with the more rapid diagnosis of basin-scale changes in the AMOC. Using existing observations, it is not yet possible to detect a robust trend in the AMOC using either midocean densities or transport observations from 26.5°N.

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More information

Published date: 2013
Keywords: North Atlantic Ocean, Thermohaline circulation, Coupled models, Climate variability, Multidecadal variability, Oceanic variability
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 360170
URI: http://eprints.soton.ac.uk/id/eprint/360170
ISSN: 0894-8755
PURE UUID: 18185222-bb74-4b32-bb82-ddb19b115077
ORCID for Freya K. Garry: ORCID iD orcid.org/0000-0002-9640-6675

Catalogue record

Date deposited: 27 Nov 2013 15:06
Last modified: 07 Jan 2022 21:32

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Contributors

Author: Christopher D. Roberts
Author: Freya K. Garry ORCID iD
Author: Laura C. Jackson

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