Articles | Volume 9, issue 5
Clim. Past, 9, 2043–2071, 2013

Special issue: Holocene changes in environment and climate in the central...

Clim. Past, 9, 2043–2071, 2013

Research article 02 Sep 2013

Research article | 02 Sep 2013

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

M. Magny1, N. Combourieu-Nebout2, J. L. de Beaulieu3, V. Bout-Roumazeilles4, D. Colombaroli5, S. Desprat6, A. Francke7, S. Joannin8,1, E. Ortu1, O. Peyron1, M. Revel9, L. Sadori10, G. Siani11, M. A. Sicre2, S. Samartin5, A. Simonneau12, W. Tinner5, B. Vannière1, B. Wagner7, G. Zanchetta13, F. Anselmetti14,*, E. Brugiapaglia15, E. Chapron12, M. Debret16, M. Desmet17,12, J. Didier1, L. Essallami18, D. Galop19, A. Gilli20, J. N. Haas21, N. Kallel22, L. Millet1, A. Stock1, J. L. Turon6, and S. Wirth20 M. Magny et al.
  • 1CNRS-UMR6249, Laboratoire Chrono-Environnement, UFR des Sciences et Techniques, 16 Route de Gray, 25030, Besançon, France
  • 2CNRS-UMR8212, Laboratoire des Sciences du Climate et de l'Environnement (LSCE)-Gif-sur-Yvette, France
  • 3CNRS-UMR7263-IMBE, Université Paul Cézanne, Aix-en-Provence, France
  • 4CNRS-UMR8217, Géosystèmes, Université de Lille 1, 59655, Villeneuve d'Ascq, France
  • 5Oeschger Center for Climate Change Research and Insitute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland
  • 6CNRS-UMR5808-Ecole Pratique des Hautes Etudes, Environnements et Paléoenviuronements Océaniques, Université de Bordeaux 1, 33405 Talence, France
  • 7University of Cologne, Institute for Geology and Mineralogy, Cologne, Germany
  • 8CNRS-USR3124 Maison des Sciences de l'Homme et de l'Environnement (MSHE) Ledoux, Besançon, France
  • 9Géosciences Azur, Observatoire Océanologique, La Darse, BP 48, 06235 Villefranche/Mer, France
  • 10Dipartimento di Biologia Ambientale, Università di Roma "La Sapienza", Piazzale Aldo Moro 5, 00185 Roma, Italy
  • 11CNRS-UMR8148 IDES, Département des Sciences de la Terre, Université Paris Sud, 91405 Orsay, France
  • 12CNRS-UMR7327 ISTO, Université d'Orléans, BRGM, 1A Rue de la Férollerie, 45071 Orléans, France
  • 13Dipartimento di Scienze della Terra, Via S. Maria 53, 56126 Pisa, Italy
  • 14Eawag, Department of Surface Waters, Überlandstrasse 133, 8600 Dübendorf, Switzerland
  • 15Dipartimento di Scienze Animali, Vegetali e dell'Ambiente, Università degli Studi del Molise, Campobasso, Italy
  • 16CNRS-UMR 6143 M2C, Universités de Caen Basse-Normandie et Rouen, 14000 Caen, France
  • 17GéoHydrosystèmes Continentaux, EA6293, Université F. Rabelais de Tours, Département Géosciences-Environnement, Faculté des Sciences et Techniques, Parc de Grandmont, 37200 Tours, France
  • 18Université de Gabès, Faculté des Sciences de Gabès, Gabès, Tunisia
  • 19CNRS-UMR5602 GEODE, Maison de la Recherche de l'Université du Mirail, Toulouse, France
  • 20Geological Institute, ETH Zürich, Zürich, Switzerland
  • 21Insitut für Botanik, Universität Innsbruck, Innsbruck, Austria
  • 22Faculté des Sciences de Sfax, Unité GEOGLOB, Route de Soukra, BP 802, 3038 Sfax, Tunisia
  • *current address: Insitute of Geological Sciences, University of Bern, Baltzerstrasse 1–3, 3012 Bern, Switzerland

Abstract. 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.