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| Titel |
Impact of the salt leakage through the Indian-Atlantic ocean gateway on the Atlantic MOC |
| VerfasserIn |
G. Marino, R. Zahn, P. Ziveri, M. Ziegler, I. R. Hall, H. Elderfield |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066544
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| Zusammenfassung |
| Freshwater perturbation in the northern North Atlantic exerts a strong influence
on the stability of the Atlantic meridional overturning circulation (AMOC) with
potentially severe impacts on the regional and global climates. The occurrence
of ice rafted detritus (IRD) in the glacial sediments of the North Atlantic testifies
to past episodes of Laurentide ice sheet surging that also coincided with AMOC
curtailments and prominent climate deterioration in the Northeast Atlantic and
Western Europe. The equally abrupt warming shifts observed in Greenland ice core
and North Atlantic sediment core records that characterize the end of each IRD
event have been related to the rapid resumption of AMOC and its associated heat
transport.
The hysteresis response, under glacial boundary conditions, of the AMOC to
freshwater forcing suggests that a reduction in this forcing may have been sufficient
to trigger the rapid AMOC resumptions revealed by several palaeoceanographic
records. But recent modelling studies allude to the potential importance of a salt
surplus, originating in the Indian Ocean and transported to the South Atlantic via
the Agulhas leakage, that may have acted as a positive feedback on the AMOC
strengthening. This possibility, however, has yet to be adequately tested with palaeoproxy
reconstructions.
We present a suite of multi-centennial-scale palaeoceanographic records spanning a full
glacial cycle from the Southwest African margin and Agulhas Plateau that have been
generated as part of the EU Marie Curie GATEWAYS project. The sediment cores are
positioned such that they monitor the leakage of Agulhas water into the Atlantic and the
Agulhas Return Current that straddles the South Atlantic subtropical front on its way to the
Indian Ocean. Paired Mg/Ca-δ18O analyses on the planktonic foraminifera Globigerinoides
ruber and Globigerina bulloides reveal millennial-scale surface ocean temperature and
salinity changes at the core sites that reflect recurrent oscillations of the Agulhas
Leakage. Coeval changes in the IRD record from the Agulhas Plateau allude to
pronounced latitudinal migrations of regional oceanic fronts during the Agulhas
leakage events. The timing of events in our records of surface ocean conditions
(temperature, salinity, IRD) are out-of-phase with similar events in the North Atlantic,
suggesting that the Agulhas leakage, via its impact on the AMOC activity, may be a
significant climate forcing on millennial timescales during the Late Pleistocene. |
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