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| Titel |
North-south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses |
| VerfasserIn |
M. Magny, N. Combourieu-Nebout, J. L. Beaulieu, V. Bout-Roumazeilles, D. Colombaroli, S. Desprat, A. Francke, S. Joannin, E. Ortu, O. Peyron, M. Revel, L. Sadori, G. Siani, M. A. Sicre, S. Samartin, A. Simonneau, W. Tinner, B. Vanniere, B. Wagner, G. Zanchetta, F. Anselmetti, E. Brugiapaglia, E. Chapron, M. Debret, M. Desmet, J. Didier, L. Essallami, D. Galop, A. Gilli, J. N. Haas, N. Kallel, L. Millet, A. Stock, J. L. Turon, S. Wirth |
| 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 (2013-09-02), S.2043-2071 |
| Datensatznummer |
250085217
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| Publikation (Nr.) |
 copernicus.org/cp-9-2043-2013.pdf |
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| Zusammenfassung |
On the basis of a multi-proxy approach and a strategy combining lacustrine
and marine records along a north–south transect, data collected in the
central Mediterranean within the framework of a collaborative project have
led to reconstruction of high-resolution and well-dated palaeohydrological
records and to assessment of their spatial and temporal coherency.
Contrasting patterns of palaeohydrological changes have been evidenced in the
central Mediterranean: south (north) of around 40° N of latitude,
the middle part of the Holocene was characterised by lake-level maxima
(minima), during an interval dated to ca. 10 300–4500 cal BP to the south
and 9000–4500 cal BP to the north. Available data suggest that these
contrasting palaeohydrological patterns operated throughout the Holocene,
both on millennial and centennial scales. Regarding precipitation
seasonality, maximum humidity in the central Mediterranean during the middle
part of the Holocene was characterised by humid winters and dry summers north
of ca. 40° N, and humid winters and summers south of ca.
40° N. This may explain an apparent conflict between palaeoclimatic
records depending on the proxies used for reconstruction as well as the
synchronous expansion of tree species taxa with contrasting climatic
requirements. In addition, south of ca. 40° N, the first millennium
of the Holocene was characterised by very dry climatic conditions not only in
the eastern, but also in the central- and the western Mediterranean zones as
reflected by low lake levels and delayed reforestation. These results suggest
that, in addition to the influence of the Nile discharge reinforced by the
African monsoon, the deposition of Sapropel 1 has been favoured (1) by an
increase in winter precipitation in the northern Mediterranean borderlands,
and (2) by an increase in winter and summer precipitation in the southern
Mediterranean area. The climate reversal following the Holocene climate
optimum appears to have been punctuated by two major climate changes around
7500 and 4500 cal BP.
In the central Mediterranean, the Holocene palaeohydrological changes
developed in response to a combination of orbital, ice-sheet and solar
forcing factors. The maximum humidity interval in the south-central
Mediterranean started ca. 10 300 cal BP, in correlation with the
decline (1) of the possible blocking effects of the North Atlantic
anticyclone linked to maximum insolation, and/or (2) of the influence of the
remnant ice sheets and fresh water forcing in the North Atlantic Ocean. In
the north-central Mediterranean, the lake-level minimum interval began only
around 9000 cal BP when the Fennoscandian ice sheet disappeared and a
prevailing positive NAO-(North Atlantic Oscillation) type circulation developed in the North Atlantic
area. The major palaeohydrological oscillation around 4500–4000 cal BP may
be a non-linear response to the gradual decrease in insolation, with additional key
seasonal and interhemispheric changes. On a centennial
scale, the successive climatic events which punctuated the entire Holocene in
the central Mediterranean coincided with cooling events associated with
deglacial outbursts in the North Atlantic area and decreases in solar
activity during the interval 11 700–7000 cal BP, and to a possible
combination of NAO-type circulation and solar forcing since ca. 7000 cal BP
onwards. Thus, regarding the centennial-scale climatic oscillations, the
Mediterranean Basin appears to have been strongly linked to the North
Atlantic area and affected by solar activity over the entire Holocene.
In addition to model experiments, a better understanding of forcing factors
and past atmospheric circulation patterns behind the Holocene
palaeohydrological changes in the Mediterranean area will require further
investigation to establish additional high-resolution and well-dated records
in selected locations around the Mediterranean Basin and in adjacent regions.
Special attention should be paid to greater precision in the reconstruction,
on millennial and centennial timescales, of changes in the latitudinal
location of the limit between the northern and southern palaeohydrological
Mediterranean sectors, depending on (1) the intensity and/or characteristics
of climatic periods/oscillations (e.g. Holocene thermal maximum versus
Neoglacial, as well as, for instance, the 8.2 ka event versus the 4 ka
event or the Little Ice Age); and (2) on varying geographical conditions from
the western to the eastern Mediterranean areas (longitudinal gradients).
Finally, on the basis of projects using strategically located study sites,
there is a need to explore possible influences of other general atmospheric
circulation patterns than NAO, such as the East Atlantic–West Russian or
North Sea–Caspian patterns, in explaining the apparent complexity of
palaeoclimatic (palaeohydrological) Holocene records from the Mediterranean
area. |
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