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| Titel |
Water mass variability in the Atlantic Subtropical Gyre reveals the mechanisms of recent Meridional Overturning changes |
| VerfasserIn |
Dafydd Gwyn Evans, John Toole, Gael Forget, Jan Zika, A. George Nurser, Alberto Naveira Garabato, Lisan Yu |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112046
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| Publikation (Nr.) |
 EGU/EGU2015-12203.pdf |
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| Zusammenfassung |
| Interannual variability in the volumetric water-mass distribution within the North Atlantic
subtropical gyre (STG) is described in relation to the recent reported changes in the Atlantic
Meridional Overturning Circulation (AMOC). Using an Argo based gridded climatology and
a high-resolution ocean state estimate (ECCO), we project the ocean into thermohaline
coordinates as volumes of water defined by their temperature and salinity. We compare
monthly time-series of the volumetric distribution to the volume changes implied by the
water mass transformations due to air/sea fluxes of heat and freshwater over the STG, and the
divergence of advective transports across the latitudinal boundaries of the STG.
Coinciding with the reported AMOC changes during the winters of 2009/10 and
2010/11, in both the observations and the state estimate, the total STG volume
above the thermocline decreases while the volume below increases in compensation.
During the winter of 2009/10, this redistribution is equivalent to a transport of 25 Sv
(1 Sv==106 m3s-1) over 3 months. A comparison to two air-sea flux re-analyses
products shows that this variability cannot be explained by anomalous cooling over
the STG, which suggests the volumetric redistribution is caused by changes in the
transport divergence between 26 and 45°N. In ECCO, we see a reduction in the zonal
circulation of the STG and divergence of transport above the thermocline. Below the
thermocline we see an increase in the southward transport at 45°N and a decrease
at 26°N. Using two wind-stress products, we present evidence that the observed
changes are a barotropic response to anomalous wind-stress curl over the STG. |
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