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| Titel |
Bipolar seesaw control of glacial Atlantic overturning |
| VerfasserIn |
Rubén Banderas Carreño, Marisa Montoya |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055519
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| Zusammenfassung |
| The last glacial period was characterised by abrupt climate and environmental changes on
millennial time scales. Two types of events dominate this variability: Dansgaard-Oeschger
(DO) events, which involve decadal-scale warming by more than 10 K, and Heinrich events,
consisting of massive iceberg discharges from the Laurentide Ice Sheet during peak
glacial conditions. Both DO and Heinrich events are associated with widespread
climatic changes, including a synchronous temperature response over the North
Atlantic and an anti-phase temperature relationship over Antarctica and most of
the Southern Ocean. During the past decades important progress has been made
regarding the description and understanding of glacial abrupt climate changes,
leading to the prevalent paradigm that these were caused by reorganisations of North
Atlantic deep water formation (NADW) and the Atlantic meridional overturning
circulation (AMOC). However, important questions remain open. Most notably, the
ultimate causes for the ocean circulation reorganisations remain unknown. Recent
studies have suggested CO2 increases during deglaciation, as well as during glacial
abrupt climate changes, were preceded by increases of Southern Ocean upwelling in
response to an enhancement and/or shift of surface winds over that region. The
proposed hypothesis is that periods of halted or reduced NADW formation resulted
in warming of the Southern Ocean through the bipolar seesaw effect leading to
a reorganisation of Southern Hemisphere surface winds, and thereby enhanced
upwelling and atmospheric CO2 concentrations. Here, a coupled climate model of
intermediate complexity is used to assess the relevance of the aforementioned relationship
between CO2, Southern Ocean winds and AMOC variations for glacial abrupt climate
changes. Starting from a background glacial climate, a suite of simulations has
been performed by linearly increasing CO2, Southern Ocean winds, and both. Our
results confirm the possibility of triggering an abrupt warming in Greenland by
forcing the system with CO2 and/or wind. Preliminary results indicate the underlying
mechanism is related to a change in the North Atlantic freshwater balance, involving
mainly changes in southward sea-ice advection from the Arctic. Our results thus
point to a mechanism in which glacial abrupt climate changes are the result of an
internal oscillation which involves changes in CO2, surface winds and AMOC. |
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