The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison
Odile Peyron1, Nathalie Combourieu-Nebout2, David Brayshaw3, Simon Goring4, Valérie Andrieu-Ponel5, Stéphanie Desprat6,7, Will Fletcher8, Belinda Gambin9, Chryssanthi Ioakim10, Sébastien Joannin1, Ulrich Kotthoff11, Katerina Kouli12, Vincent Montade1, Jörg Pross13, Laura Sadori14, and Michel Magny151Institut des Sciences de l'Evolution (ISEM), Université de Montpellier, France 2UMR 7194 MNHN, Institut de Paléontologie Humaine 1, Paris, France 3University of Reading, Department of Meteorology, United Kingdom 4Department of Geography, Univ. of Wisconsin-Madison, Wisconsin, USA 5Institut Méditerranéen de Biodiversité et d’Ecologie marine et continentale (IMBE), Aix Marseille Université, Aix-en -Provence, France 6EPHE, PSL Research University, Laboratoire Paléoclimatologie et Paléoenvironnements Marins, Pessac, France 7Univ. Bordeaux, EPOC UMR 5805, Pessac, France 8Geography, School of Environment, Education and Development, University of Manchester, United Kingdom 9Institute of Earth Systems, University of Malta, Malta 10Institute of Geology and Mineral Exploration, Athens, Greece 11Center for Natural History and Institute of Geology, Hamburg University, Hamburg, Germany 12Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Greece 13Paleoenvironmental Dynamics Group, Institute of Earth Sciences, Heidelberg University, Germany 14Dipartimento di Biologia Ambientale, Università di Roma "La Sapienza", Roma, Italy 15UMR 6249 Chrono – Environnement, Université de Franche – Comté, Besançon, France
Received: 16 Jun 2016 – Accepted for review: 17 Jun 2016 – Discussion started: 28 Jun 2016
Abstract. Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evidence for (i) opposing northern and southern precipitation regimes during the Holocene across the Mediterranean basin, and (ii) an east-to-west precipitation gradient or dipole during the early Holocene, from a wet eastern Mediterranean to dry western Mediterranean. Using quantitative climate information from marine and terrestrial pollen archives, we focus on two key time intervals, the early to mid-Holocene (8000 to 6000 cal yrs BP) and the late Holocene (4000 to 2000 yrs BP), in order to test the above mentioned hypotheses on a Mediterranean-wide scale. Palynologically derived climate information is compared with the output of regional-scale climate-model simulations for the same time intervals.
Quantitative pollen-based precipitation estimates were generated along a longitudinal gradient from the Alboran (West) to the Aegean Sea (East); they are derived from terrestrial pollen records from Greece, Italy and Malta as well as from pollen records obtained from marine cores. Because seasonality represents a key parameter in Mediterranean climates, special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate a previously described north-south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south-central and eastern Mediterranean region, while drier conditions prevailed from 45° N northwards. These patterns reversed during the late Holocene, with a wetter northern Mediterranean region and drier conditions in the east and south. More sites from the northern part of the Mediterranean basin are needed to further substantiate these observations. With regard to the existence of a west-east precipitation dipole during the Holocene, our pollen-based climate data show that the strength of this dipole is strongly linked to the seasonal parameter reconstructed: Early Holocene summers show a clear east-to-west gradient, with summer precipitation having been highest in the central and eastern Mediterranean and lowest over the western Mediterranean. In contrast, winter precipitation signals are less spatially coherent. A general drying trend occurred from the early to the late Holocene; particularly in the central and eastern Mediterranean. However, summer precipitation in the east remained above modern values, even during the late Holocene interval.
Pollen-inferred precipitation estimates were compared to regional-scale climate modelling simulations based on the HadAM3 GCM coupled to the dynamic HadSM3 and the high-resolution regional HadRM3 models. Climate model outputs and pollen-inferred precipitation estimates show remarkably good overall correspondence, although many simulated patterns are of marginal statistical significance. Nevertheless, models weakly support an east to west division in summer precipitation and there are suggestions that the eastern Mediterranean experienced wetter summer and winter conditions during the early Holocene and wetter summer conditions during the late Holocene. The extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question; our model, consistent with other global models, does not suggest an extension of the African monsoon into the Mediterranean. Given the difficulty in modelling future climate change in Southern Europe, more simulations based on high resolution global models and very high resolution regional downscaling, perhaps even including transient simulations, are required to fully understand the patterns of change in winter and summer circulation patterns over the Mediterranean region
Peyron, O., Combourieu-Nebout, N., Brayshaw, D., Goring, S., Andrieu-Ponel, V., Desprat, S., Fletcher, W., Gambin, B., Ioakim, C., Joannin, S., Kotthoff, U., Kouli, K., Montade, V., Pross, J., Sadori, L., and Magny, M.: The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison, Clim. Past Discuss., doi:10.5194/cp-2016-65, in review, 2016.