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| Titel |
Mechanism for potential strengthening of Atlantic overturning prior to collapse |
| VerfasserIn |
D. Ehlert, A. Levermann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-4979
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| Digitales Dokument |
URL |
| Erschienen |
In: Earth System Dynamics ; 5, no. 2 ; Nr. 5, no. 2 (2014-11-06), S.383-397 |
| Datensatznummer |
250115372
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| Publikation (Nr.) |
 copernicus.org/esd-5-383-2014.pdf |
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| Zusammenfassung |
| The Atlantic meridional overturning circulation (AMOC) carries large amounts
of heat into the North Atlantic influencing climate regionally as well as
globally. Palaeo-records and simulations with comprehensive climate models
suggest that the positive salt-advection feedback may yield a threshold
behaviour of the system. That is to say that beyond a certain amount of
freshwater flux into the North Atlantic, no meridional overturning
circulation can be sustained. Concepts of monitoring the AMOC and identifying
its vicinity to the threshold rely on the fact that the volume flux defining
the AMOC will be reduced when approaching the threshold. Here we advance
conceptual models that have been used in a paradigmatic way to understand the
AMOC, by introducing a density-dependent parameterization for the Southern
Ocean eddies. This additional degree of freedom uncovers a mechanism by which
the AMOC can increase with additional freshwater flux into the North
Atlantic, before it reaches the threshold and collapses: an AMOC that is
mainly wind-driven will have a constant upwelling as long as the Southern
Ocean winds do not change significantly. The downward transport of tracers
occurs either in the northern sinking regions or through Southern Ocean
eddies. If freshwater is transported, either atmospherically or via
horizontal gyres, from the low to high latitudes, this would reduce the eddy
transport and by continuity increase the northern sinking which defines the
AMOC until a threshold is reached at which the AMOC cannot be sustained. If
dominant in the real ocean this mechanism would have significant consequences
for monitoring the AMOC. |
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