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| Titel |
Southern Ocean Deep Convection Forcing of North Atlantic Centennial Variability |
| VerfasserIn |
Torge Martin, Wonsun Park, Mojib Latif |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093301
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| Publikation (Nr.) |
 EGU/EGU2014-7907.pdf |
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| Zusammenfassung |
| We present an oceanic teleconnection associated with the Southern Ocean Centennial
Variability (SOCV). The SOCV is driven by internal multi-centennial variability of open
ocean deep convection in the Atlantic sector of the Southern Ocean, which forces significant
variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC) in
control simulations with the Kiel Climate Model employing present climate greenhouse gas
concentrations. The deep convection is stimulated by a strong built–up of heat at mid–depth
and lasts until this heat reservoir is virtually depleted. The heat originates from relatively
warm deep water formed in the North Atlantic. The several decades lasting recharge process
sets a minimum time between convection events. Stochastically occurring, favorable sea
ice conditions as well as coincidental strong surface freshening are further factors
influencing the timing of convection onset and shutdown. The deep convection
flip–flop has intriguing similarities to the Weddell Polynya observed during the
1970s.
The state of Weddell Sea deep convection strongly influences the northward extent of
Antarctic Bottom Water (AABW). The retreat of AABW results in an enhanced meridional
density gradient that drives an increase in the strength and vertical extent of the North
Atlantic Deep Water (NADW) cell. This shows, for instance, as a peak in AMOC strength at
30°N about a century after Weddell Sea deep convection has ceased. The stronger southward
flow of NADW is compensated by an expansion of the North Atlantic subpolar gyre and an
acceleration of the North Atlantic Current, indicating greater deep water formation.
Contractions of the North Atlantic subpolar gyre enable anomalously warm water to penetrate
farther to the north, eventually weakening the AMOC and closing a quasi–centennial
cycle.
In our simulation the SOCV is associated with sea level variations in the order of 10 to
30cm/century in the North Atlantic and Southern Ocean, which is due to subpolar gyre
extent and oceanic heat content changes, respectively. This suggests that internal variability
on long time scales cannot be neglected a priori in assessments of 20th and 21st century
AMOC and regional sea level change. |
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