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| Titel |
Potential impacts of the Agulhas Leakage on the Atlantic Meridional Overturning Circulation during glacial, deglacial, and interglacial times |
| VerfasserIn |
Gianluca Marino, Rainer Zahn, Patrizia Ziveri, Jung-Hyun Kim, Ian R. Hall, Laura Rodríguez-Sanz, P. Graham Mortyn |
| 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 |
250053815
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| Zusammenfassung |
| Freshwater injection to the northern North Atlantic derived from the demise of continental ice
is a prime factor in weakening the Atlantic Meridional Overturning Circulation (AMOC).
The degree to which the effects of freshwater perturbation in the north can be compensated
by buoyancy transports to the South Atlantic via the leakage of warm and salty thermocline
waters from the Indian Ocean, the so-called Agulhas Leakage (AL), remains a matter of
debate. Model simulations and proxy-based paleoceanographic reconstructions suggest that
the strength of the AL is sensitive to latitudinal migrations of the South Atlantic
Subtropical Front (STF) on decadal and glacial-to-interglacial timescales. Yet, a
comprehensive understanding of the potential impacts of the AL on the AMOC
under different boundary conditions has been hitherto inhibited by the dearth of
fine-scale, continuous, quantitative paleo-reconstructions of the AL changes and South
Atlantic STF meridional displacements during glacial, deglacial, and interglacial
periods.
We have generated a suite of multi-centennial-scale paleoceanographic records from the
Agulhas Corridor along IMAGES cores MD96-2080 (Agulhas Bank) and MD02-2588
(Agulhas Plateau), which are located in the path of the Agulhas Leakage and Agulhas Return
Current that straddles the South Atlantic STF on its return to the Indian Ocean. The records
document surface ocean variability throughout a full climatic cycle, from Marine Isotope
Stage (MIS) 7c (~225 ka BP) to MIS 5c (~90 ka BP). Paired planktonic foraminiferal
(Globigerinoides ruber, Globigerina bulloides) δ18O and Mg/Ca profiles at the core sites
reveal millennial sea surface temperature and salinity variability. The most pronounced of
these events occurred during the penultimate deglaciation (Termination II), between ~134
and ~126 ka BP, and featured a 2º-3ºC warming and a marked salinity increase in the
Agulhas Corridor. This event was coincident with a southward displacement of the
STF.
When viewed in the context of contemporaneous records of interhemispheric climate and
ocean change from polar ice cores and eastern North Atlantic marine cores, the timing and
magnitude of several of the millennial events in the Agulhas Corridor are indicative of an
involvement of the Agulhas Leakage in abrupt AMOC reorganizations under glacial,
deglacial, and interglacial conditions. |
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