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| Titel |
A major change in North Atlantic deep water circulation 1.6 million years ago |
| VerfasserIn |
N. Khélifi, M. Frank |
| 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 ; 10, no. 4 ; Nr. 10, no. 4 (2014-07-29), S.1441-1451 |
| Datensatznummer |
250117021
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| Publikation (Nr.) |
 copernicus.org/cp-10-1441-2014.pdf |
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| Zusammenfassung |
| The global ocean–climate system has been highly sensitive to the formation
and advection of deep overflow water from the Nordic Seas as integral part
of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution
over the Pliocene–Pleistocene global cooling is not fully understood. In
particular, changes in the sources and mixing of prevailing deep waters that
were involved in driving overturning throughout the Pliocene–Pleistocene climate
transitions are not well constrained. Here we investigate the evolution of a
substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic
neodymium isotope (ϵNd) variability obtained from three
sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths
between 2170 and 5050 m in the northeast Atlantic. We find that prior to
the onset of major Northern Hemisphere glaciation (NHG) ∼3 million years ago (Ma), ϵNd values primarily oscillated
between −9 and −11 at all sites, consistent with enhanced vertical mixing
and weak stratification of the water masses during the warmer-than-today
Pliocene period. From 2.7 Ma to ∼2.0 Ma, the ϵNd signatures of the water masses gradually became more distinct,
which documents a significant advection of Nordic Seas overflow deep water
coincident with the intensification of NHG. Most markedly, however, at
∼1.6 Ma the interglacial ϵNd signatures at
sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.)
synchronously and permanently shifted by 2 to 3 ϵNd units
to less radiogenic values, respectively. Since then the difference between
glacial and interglacial ϵNd values has been similar to
the Late Quaternary at each site. A decrease of ∼2ϵNd units at 1.6 Ma was also recorded for the deepest
water masses by site 900 (∼5050 m w.d.), which thereafter,
however, evolved to more radiogenic values again until the present. This
major ϵNd change across the 1.6 Ma transition reflects a
significant reorganization of the overturning circulation in the northeast
Atlantic paving the way for the more stratified water column with distinct
water masses prevailing thereafter. |
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