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| Titel |
Different ocean states and transient characteristics in Last Glacial Maximum simulations and implications for deglaciation |
| VerfasserIn |
X. Zhang, G. Lohmann, G. Knorr, X. Xu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 9, no. 5 ; Nr. 9, no. 5 (2013-10-15), S.2319-2333 |
| Datensatznummer |
250085232
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| Publikation (Nr.) |
 copernicus.org/cp-9-2319-2013.pdf |
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| Zusammenfassung |
The last deglaciation is one of the best constrained global-scale climate
changes documented by climate archives. Nevertheless, understanding of the
underlying dynamics is still limited, especially with respect to abrupt
climate shifts and associated changes in the Atlantic meridional overturning
circulation (AMOC) during glacial and deglacial periods. A fundamental issue
is how to obtain an appropriate climate state at the Last Glacial Maximum
(LGM, 21 000 yr before present, 21 ka BP) that can be used as an initial
condition for deglaciation. With the aid of a comprehensive climate model,
we found that initial ocean states play an important role on the equilibrium
timescale of the simulated glacial ocean. Independent of the initialization,
the climatological surface characteristics are similar and quasi-stationary,
even when trends in the deep ocean are still significant, which provides an
explanation for the large spread of simulated LGM ocean states among the
Paleoclimate Modeling Intercomparison Project phase 2 (PMIP2) models.
Accordingly, we emphasize that caution must be taken when alleged
quasi-stationary states, inferred on the basis of surface properties, are used as a
reference for both model inter-comparison and data model comparison.
The simulated ocean state with the most realistic AMOC is characterized by a
pronounced vertical stratification, in line with reconstructions. Hosing
experiments further suggest that the response of the glacial ocean is
dependent on the ocean background state, i.e. only the state with robust
stratification shows an overshoot behavior in the North Atlantic. We propose
that the salinity stratification represents a key control on the AMOC
pattern and its transient response to perturbations. Furthermore, additional
experiments suggest that the stratified deep ocean formed prior to the LGM
during a time of minimum obliquity (~ 27 ka BP). This indicates
that changes in the glacial deep ocean already occur before the last
deglaciation. In combination, these findings represent a new paradigm for
the LGM and the last deglaciation, which challenges the conventional
evaluation of glacial and deglacial AMOC changes based on an ocean state
derived from 21 ka BP boundary conditions. |
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