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Atlantic Meridional Overturning Circulation slowdown cooled the subtropical ocean.

Cunningham SA, Roberts CD, Frajka-Williams E, Johns WE, Hobbs W, Palmer MD, Rayner D, Smeed DA, McCarthy G - Geophys Res Lett (2013)

Bottom Line: [1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011.We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N.This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures.

View Article: PubMed Central - PubMed

Affiliation: Now at Scottish Association for Marine Science, Scottish Marine Institute Oban, UK ; National Oceanography Centre Southampton, UK.

ABSTRACT

[1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011. We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N. This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures. Here we connect, for the first time, variability in the northward heat transport carried by the Atlantic Meridional Overturning Circulation to widespread sustained cooling of the subtropical North Atlantic, challenging the prevailing view that the ocean plays a passive role in the coupled ocean-atmosphere system on monthly-to-seasonal timescales.

No MeSH data available.


Related in: MedlinePlus

(a) Time series of observed relative heat content above the 4°C isotherm determined from the EN3 v2a Argo data set 6 month low-pass filtered. Uncertainties for OHC above the 4°C isotherm are approximated by the uncertainty in OHC above 2000 m. (b) Integrated ocean heat transport divergence between 26.5°N and 41°N. (c) Integrated ocean-atmosphere surface flux from ERA-interim reanalysis. (d) OHC budget residual (Figures 3a − (3b + 3c)). OHC 1022J.
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fig03: (a) Time series of observed relative heat content above the 4°C isotherm determined from the EN3 v2a Argo data set 6 month low-pass filtered. Uncertainties for OHC above the 4°C isotherm are approximated by the uncertainty in OHC above 2000 m. (b) Integrated ocean heat transport divergence between 26.5°N and 41°N. (c) Integrated ocean-atmosphere surface flux from ERA-interim reanalysis. (d) OHC budget residual (Figures 3a − (3b + 3c)). OHC 1022J.

Mentions: [9.] To calculate the OHC change in the subtropical Atlantic due to changes in ocean MHT and atmospheric heat fluxes, we integrate the ocean MHT divergence between 26.5°N and 41°N and ERA-interim air-sea heat fluxes through time (section S7). OHC decreases abruptly in the last months of 2009 and early 2010 (Figures 3b and 3c), due to MHT divergence and reduced surface fluxes into the subtropical North Atlantic. The relatively abrupt increases in heat loss due to air-sea fluxes in DJF 2009/2010 and December 2010 coincide with two exceptionally negative phases of the NAO, such that increased wind speeds over the subtropical gyre result in large anomalies in latent heat loss to the atmosphere (section S8). In contrast, the MHT divergence anomaly, that we have shown to be dominated by the AMOC at 26.5°N, is more sustained and acts to cool the subtropical Atlantic through 2010.


Atlantic Meridional Overturning Circulation slowdown cooled the subtropical ocean.

Cunningham SA, Roberts CD, Frajka-Williams E, Johns WE, Hobbs W, Palmer MD, Rayner D, Smeed DA, McCarthy G - Geophys Res Lett (2013)

(a) Time series of observed relative heat content above the 4°C isotherm determined from the EN3 v2a Argo data set 6 month low-pass filtered. Uncertainties for OHC above the 4°C isotherm are approximated by the uncertainty in OHC above 2000 m. (b) Integrated ocean heat transport divergence between 26.5°N and 41°N. (c) Integrated ocean-atmosphere surface flux from ERA-interim reanalysis. (d) OHC budget residual (Figures 3a − (3b + 3c)). OHC 1022J.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4459181&req=5

fig03: (a) Time series of observed relative heat content above the 4°C isotherm determined from the EN3 v2a Argo data set 6 month low-pass filtered. Uncertainties for OHC above the 4°C isotherm are approximated by the uncertainty in OHC above 2000 m. (b) Integrated ocean heat transport divergence between 26.5°N and 41°N. (c) Integrated ocean-atmosphere surface flux from ERA-interim reanalysis. (d) OHC budget residual (Figures 3a − (3b + 3c)). OHC 1022J.
Mentions: [9.] To calculate the OHC change in the subtropical Atlantic due to changes in ocean MHT and atmospheric heat fluxes, we integrate the ocean MHT divergence between 26.5°N and 41°N and ERA-interim air-sea heat fluxes through time (section S7). OHC decreases abruptly in the last months of 2009 and early 2010 (Figures 3b and 3c), due to MHT divergence and reduced surface fluxes into the subtropical North Atlantic. The relatively abrupt increases in heat loss due to air-sea fluxes in DJF 2009/2010 and December 2010 coincide with two exceptionally negative phases of the NAO, such that increased wind speeds over the subtropical gyre result in large anomalies in latent heat loss to the atmosphere (section S8). In contrast, the MHT divergence anomaly, that we have shown to be dominated by the AMOC at 26.5°N, is more sustained and acts to cool the subtropical Atlantic through 2010.

Bottom Line: [1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011.We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N.This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures.

View Article: PubMed Central - PubMed

Affiliation: Now at Scottish Association for Marine Science, Scottish Marine Institute Oban, UK ; National Oceanography Centre Southampton, UK.

ABSTRACT

[1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011. We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N. This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures. Here we connect, for the first time, variability in the northward heat transport carried by the Atlantic Meridional Overturning Circulation to widespread sustained cooling of the subtropical North Atlantic, challenging the prevailing view that the ocean plays a passive role in the coupled ocean-atmosphere system on monthly-to-seasonal timescales.

No MeSH data available.


Related in: MedlinePlus