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Messinian vegetation maps of the Mediterranean region using models and interpolated pollen data
Geobios 40 (2007) 433–443 http://france.elsevier.com/direct/GEOBIO
Original article
Messinian vegetation maps of the Mediterranean region using models and interpolated pollen data Cartes de ve´ge´tation de la re´gion me´diterrane´enne au Messinien d’apre`s les mode`les et les donne´es polliniques interpole´es Eric Favre a,*, Louis Franc¸ois b, Fre´de´ric Fluteau c, Rachid Cheddadi d, Lysiane The´venod a, Jean-Pierre Suc a a
UMR 5125 PEPS CNRS, France, universite´ Lyon 1, campus de La Doua, baˆtiment Ge´ode, 69622 Villeurbanne cedex, France b Laboratoire de physique atmosphe´rique et plane´taire (LPAP), universite´ de Lie`ge, alle´e du 6-Aouˆt, 4000 Lie`ge, Belgique c Institut de physique du Globe de Paris (UMR 7154 CNRS), universite´ Denis-Diderot – Paris 7, boıˆte 89, 4, Place Jussieu, 75252 Paris cedex 5, France d Institut des sciences de l’e´volution (UMR 5554 CNRS), e´quipe pale´oenvironnements, universite´ de Montpellier II, Place Euge`ne-Bataillon, 34095 Montpellier, France Received 10 September 2006; accepted 16 December 2006 Available online 23 March 2007
Abstract This study proposes to compare the outputs from the CARAIB vegetation model forced by results from the LMD General Circulation Model with interpolated pollen data (Kriging method) from the Mediterranean region during the Messinian. The vegetation maps that have been obtained represent distinct phases of the salinity crisis: before the crisis and during the marginal evaporitic phase (interpolated map), and during the complete desiccation phase (simulated map). However, they are comparable in terms of vegetation density and agree on a strong contrast between the Northern (forest vegetation) and Southern (open vegetation) Mediterranean regions. Main differences concern the type of forests in the northern Mediterranean region, which are explained by discrepancies between precipitation amount predicted by the model and that calculated by a transfer function using pollen records. The interpolation method has been successfully tested in France using interpolated current pollen records by comparison with the present-day potential vegetation map. The resulting Messinian map is useful to validate or improve model simulation which does not take into account the depth of the Mediterranean Basin when it dried up. The Southern Mediterranean landscapes were open, with a steppe-like vegetation to the West and a savannah-like vegetation to the East. Forests prevailed to the North, organized in a mosaic system mainly controlled by relief. Such a contrast provides some explanation of the large number of deep fluvial canyons cut on the Northern margin at opposed to the South during the Mediterranean desiccation. # 2007 Elsevier Masson SAS. All rights reserved. Re´sume´ Cette e´tude vise a` comparer les simulations du mode`le de ve´ge´tation CARAIB contraint par le mode`le climatique LMD aux interpolations de donne´es polliniques (me´thode du Kriegage) pour le Messinien de la re´gion me´diterrane´enne. Les cartes de ve´ge´tation ainsi obtenues repre´sentent des phases distinctes de la crise de salinite´ messinienne : avant la crise et pendant la phase de de´poˆt des e´vaporites marginales pour la carte interpole´e, et pendant la phase de dessiccation comple`te pour la simulation. Ces cartes sont toutefois comparables en termes de densite´ de ve´ge´tation et s’accordent sur un fort contraste entre le nord (couverture forestie`re) et le sud (ve´ge´tation ouverte) de la re´gion me´diterrane´enne. Les principales diffe´rences portent sur le type de foreˆts au nord, elles s’expliquent par les e´carts entre les quantite´s de pluie pre´dites par le mode`le et celles calcule´es par la fonction de transfert construite sur les donne´es polliniques. La me´thode d’interpolation a e´te´ teste´e avec succe`s sur la France par interpolation de donne´es polliniques actuelles compare´e avec la carte de ve´ge´tation potentielle. La carte de ve´ge´tation interpole´e pour le Messinien est utilise´e pour valider ou ame´liorer la simulation qui ne peut prendre en compte la profondeur du bassin me´diterrane´en lorsqu’il e´tait a` sec. Les paysages sud-me´diterrane´ens e´taient ouverts avec des formations steppiques a` l’Ouest et une ve´ge´tation de savane a` l’Est. Les foreˆts dominaient au nord avec une organisation en mosaı¨que controˆle´e par les reliefs. Un tel contraste contribue a` expliquer l’abondance des canyons * Corresponding author. E-mail address: [email protected] (E. Favre). 0016-6995/$ – see front matter # 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2006.12.002
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fluviatiles creuse´s pendant le paroxysme de la crise sur les rives septentrionales de la Me´diterrane´e et leur relative rarete´ sur ses rives me´ridionales. # 2007 Elsevier Masson SAS. All rights reserved. Keywords: Palaeovegetation mapping; Messinian; Mediterranean region Mots cle´s : Cartes de pale´ove´ge´tation ; Messinien ; Re´gion me´diterrane´enne
1. Introduction The desiccation of the Mediterranean Sea during the Messinian is one of the most studied phenomenons concerning the Late Cenozoic, and is especially characterized by thick deposits of evaporites (Hsu¨ et al., 1973; Rouchy, 1982) and cutting of fluvial canyons (Clauzon, 1999) resulting from a severe drop in sea-level (about 1500 m: Clauzon et al., 1996). The knowledge of the vegetation cover before and during the crisis is crucial for clarifying how the climate context contributed to the Mediterranean desiccation (Suc and Bessais, 1990; Fauquette et al., 2006). It is also crucial for estimating the relative proportion of forests versus open vegetation. Indeed, the density of the vegetation cover is critical to evaluate the intensity of runoff and subaerial erosion not only within the fluvial networks (Clauzon, 1999), but also over the entire margin (Gorini et al., 2005). First attempts were carried out by Franc¸ois et al. (2006) using climate and vegetation models, and Kovar-Eder et al. (2006) using plant macroremain records. The former study provides a vegetation biome distribution resulting from outputs of the climate ECHAM4/ML used as inputs to the vegetation CARAIB global models for the Tortonian period, that is about four million years before the Messinian salinity crisis, however, without a detailed comparison with the fossil plant records at the scale of the Mediterranean region. The latter reconstruction uses a taxonomic physiognomic method able to express the variability in woody vegetation on geographic maps, considering each ecosystem separately. But, this reconstruction concerns a relatively long time-interval (7–4 Ma) with respect to the Messinian event itself, the almost complete desiccation of the Mediterranean Sea being restricted to the time-span 5.6–5.33 Ma whatever the referred scenario (Clauzon et al., 1996, 2005; Krijgsman et al., 1999). In this paper, we propose to compare (1) vegetation biome maps calculated by the CARAIB model forced with a Messinian-like climate (derived from a sensitivity test of the LMD model, in which the Mediterranean Sea and the Black Sea have been desiccated) with (2) the result of the Kriging interpolation (Krige, 1951; Matheron, 1963) of thirty pollen records from the Mediterranean region just preceding the salinity crisis or coeval with the onset of this event for some of them (covered time-interval: 6.7–5.4 Ma). 2. Climate and vegetation from model simulation The ‘‘Laboratoire de Me´te´orologie Dynamique’’ (LMD) General Circulation Model (GCM) (for further information see http://www.lmd.jussieu.fr/(lmdz/homepage.html; Pe´ron et al., 2005) and the CARAIB vegetation models (Otto et al., 2002;
Franc¸ois et al., 2006) have been used to study the impacts on climate and vegetation of a complete desiccation of the Mediterranean Sea and the Black Sea basins. The spatial resolution of the LMD model, and consequently for CARAIB one is 3.758 2.538 in longitude and latitude. The control GCM experiment corresponds to a present-day simulation, while the desiccation experiment is forced by boundary conditions representative of desiccated Mediterranean and Black seas with present-day values for the other boundary conditions (sea surface temperature, CO2, orbital parameters, solar constant). As it was not possible to use negative elevations in the LMD GCM, grid cells corresponding to the desiccated basins were assumed to have elevations of 0 m, and so, should be colder and wetter than in the actual desiccated basin. The climatic anomalies between the desiccation and control experiments are added to a presentday climatology (Cramer and Leemans, unpublished data, an updated version of the IIASA database: Leemans and Cramer, 1991) averaged at the spatial resolution of the GCM, before being used in the CARAIB vegetation model. CARAIB predicts the relative abundances and primary productivities of 15 plant functional types (2 herbaceous types, 4 needle-leaved boreal/ temperate trees, 4 broadleaved boreal/temperate trees, 3 subtropical trees and 2 tropical trees) on each model grid cell. A scheme is then used to produce a biome map of potential vegetation, from the simulated assemblage of PFTs calculated for each grid cell. Climate and vegetation simulations are performed over the entire earth, but the results presented in the current study are restricted to Western/Central Europe and the Mediterranean area. Fig. 1 compares the annual mean surface temperature and precipitation in the control and desiccation experiments, reconstructed by adding the LMD anomalies to the presentday climatology. In the desiccation experiment, mean annual temperature ranges between 12 and 188 C in the Northern edge of the former Mediterranean and between 16 and 228 C in the Southern edge, that is about 28 C higher than today (Fig. 1(A)). The Mediterranean region appears to be moderately drier than currently in this experiment with a precipitation range of 300– 600 mm/yr in its previous Northern edge and 0–150 mm/yr (0–400 mm/yr) in its previous Southern edge (Fig. 1(B)). The mean annual temperature values in the desiccation experiment are on the whole significantly lower than those obtained by transfer function from pollen data which focus on the marginal desiccation episode which occurred at the beginning of the crisis (Fauquette et al., 2006). Annual rainfall appears considerably more underestimated (difference of 400–700 mm for the North, 300–400 mm for the South) with respect to the same episode according to the pollen transfer function (Fauquette et al., 2006). Such relatively important differences in temperature and
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Fig. 1. Simulated climatic maps from the LMD GCM for Europe and the Mediterranean region: 1. Present-day climatology (an update of Leemans and Cramer, 1991) averaged over the model grid cells; 2. Reconstructed climate in the desiccation experiment obtained by combining the present-day climatology with the LMD model anomalies. A. Mean annual temperature (expressed in 8C); B. Annual precipitation (expressed in mm). Fig. 1. Cartes climatiques simule´es par le mode`le LMD pour l’Europe et la re´gion me´diterrane´enne8: 1. Climatologie actuelle (mise a` jour de Leemans et Cramer, 1991) moyenne´e sur la grille du mode`le ; 2. Climat simule´ lors de l’expe´rience d’asse`chement obtenu en combinant la climatologie actuelle et les anomalies du mode`le LMD. A. Tempe´rature moyenne annuelle (en 8C) ; B. Pre´cipitation annuelle (en mm).
precipitation between the simulation and the transfer function probably result from: the method used for simulating the climate of the salinity crisis in only removing the Mediterranean Sea and the Black Sea, without modifying any other boundary condition (referring for instance to atmospheric CO2, palaeogeography and palaeorelief, Atlantic sea surface temperature, etc.) and without considering the negative elevations in the desiccated basins;
the dissimilarity in climatic conditions at the beginning of desiccation (quantified using the transfer function) and during the desiccation itself (quantified using model simulation). In addition, consideration of uncertainties on climate quantification using the transfer function should also reduce discrepancies between the two approaches. Using the outputs from the LMD climate model, the CARAIB vegetation model (Otto et al., 2002; Franc¸ois et al.,
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Fig. 2. Potential vegetation maps obtained by a CARAIB model simulation for Europe and the Mediterranean region: 1. Present-day; 2. Desiccation experiment. A. Biome distribution; B. Net primary productivity of herbs (gram of carbon/m2/year). Fig. 2. Carte de la ve´ge´tation potentielle simule´e par le mode`le CARAIB pour l’Europe et la re´gion me´diterrane´enne : 1. Pre´sent ; 2. Expe´rience d’asse`chement. A. Distribution des biomes ; B. Productivite´ primaire des herbes (gramme de carbone/m2/an).
2006) reconstructs the potential vegetation biomes for each grid cell at the same resolution as for the LMD climate model (Fig. 2(A)). In Europe and the peri-Mediterranean region, vegetation spreads over 12 categories from desert to cooltemperate conifer forest. It is to be mentioned that open vegetation types and deserts cover the major part of the potential vegetation map during the Mediterranean desiccation (73%) and are particularly well-expressed on the Southern and Eastern edges of the desiccated Mediterranean. Other areas are occupied by forests (27%). Another observation is that forest environments are only represented above a West-East oriented line, which clearly separates Europe occupied by forests from the Mediterranean realm characterized by open landscapes. The level of forest opening is also well indicated in the model by the calculated net primary productivity of herbaceous vegetation (Fig. 2(B)). Indeed, in the model, herbs and trees grow in two different vegetation storeys, so that the amount of light available for the photosynthesis of herbs decreases as the
abundance of trees increases in the over-storey. The desiccation of the Mediterranean and the Black Sea basins appears to generate a very significant opening of the forest cover in Central and Eastern Europe. 3. Vegetation map from interpolated pollen data Interpolating pollen records for reconstructing past potential vegetation maps requires a present-day validation. We have carried out such a task using pollen samples of moss cushions (generally rich in pollen grains) from 129 localities in France. These moss cushions were collected in representative natural plant ecosystems (for example, protected restricted forests within large agricultural regions) in order to reduce biases caused by anthropogenic activity. The geographic distribution of the studied localities takes into account the high variability in the vegetation linked to the existence of several seashores, the presence of the meso-Mediterranean vegetation belt in the
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South, and the rapid succession of vegetation belts related to reliefs as the Alps or Pyrenees (Fig. 3(A)). The vegetation map presented in Fig. 3(B) was obtained for practically all the vegetation groups using the universal Kriging interpolation method in which the altitudinal component is considered. Only the aquatic plants are interpolated using the common Kriging since they have an azonal distribution. The Kriging method (Krige, 1951; Matheron, 1963) is considered as one of the most efficient interpolation method from the statistical point of view. This approach, unlike others, is based on an overall spatial study of the documented localities to estimate data variations. Thus, each locality, according to its characteristics (value of the considered variable, geographic position), contributes to the interpolation through a semi-variogram and the most appropriate model that was chosen. Some areas in France are not interpolated (white areas) because the error is greater than the average of all the errors on the entire map. In addition, various thresholds have been applied according to each plant group; this also reduces the interpolated surface area. Finally, it results in an interpolated surface area, which offers a minimum of uncertainty whatever the spatial distribution of the considered pollen localities. Most of the interpolated vegetation map is covered by warmtemperate deciduous forests. This assessment is in agreement with the present-day potential vegetation map (Fig. 3(A): Noirfalise et al., 1987; Bohn et al., 2004). Ecological or floristic subdivisions of these forests are indicated on the potential vegetation map. It is unrealistic to reach such a degree of precision on the interpolated map because of the impossibility to generally identify tree pollen grains more accurately than the genus level. As expected, variability in vegetation types is enhanced near the Mediterranean seashore and relief. Coastal halophytic ecosystems appear along the West shoreline of the Cotentin Peninsula and in the Rhoˆne Delta, as they are mostly recorded all along the Mediterranean coastline on the potential vegetation map. Boreal conifer forest is concentrated on the Northern Alps in the interpolated map, which suffers of lack of these forests on the Pyrenees with respect to the potential vegetation map. The Mediterranean xerophytic vegetation is drawn around the Mediterranean seashore reaching far up in the Rhoˆne Valley, and also a little bit on the Atlantic coastline (the Vende´e region). Distribution of the latter ecosystems almost completely fits with the present-day potential vegetation (Noirfalise et al., 1987; Bohn et al., 2004). Aquatic plants are abundant in the Channel region and in the Massif Central and Dombes (Northward Lyon). Such ecosystems are well known today in these regions but are insufficiently represented on the potential vegetation map where forests are often considered as prevalent. Finally, white spaces are related to a too much imprecise interpolation and do not refer to any plant ecosystem. As they contribute to all the plant ecosystems, their drawing is difficult to realize in a forest prevailing potential vegetation, herbs have been also considered specifically in interpolating their density (Fig. 3(C)). Indeed, they are mostly distributed on reliefs (meadows, Alpine vegetation belt), in some humid areas such as the Dombes and Sologne regions, and some coastal plains such as the Cotentin Peninsula. These
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results are fully satisfactory and show a relatively high consistency with the present-day potential vegetation map (Fig. 3(A)). Accordingly, it is substantially reliable to use the Kriging interpolation method for the Messinian period. Thirty Messinian pollen localities widely distributed around the Mediterranean (Fig. 3(D)) have been considered and, more specifically, their pollen spectra belonging to the time-interval 6.7–5.4 Ma. These sites have an accurate age according to combined (or not) approaches (biostratigraphy, magnetostratigraphy, isotope stratigraphy, radiometric age). The target is not to show and discuss their relative chronostratigraphic position, already done for most of them by Bertini (2002), Clauzon et al. (2005), Fauquette et al. (2006) and Jime´nez-Moreno et al. (in press), but to pay attention that they belong to a relatively restricted time-window for reconstructing the vegetation on a large space at the time of the salinity crisis with a maximum of reliability. According to the scenario of Clauzon et al. (1996, 2005), field observations or seismic profiles indicate that: some localities just predate the Messinian salinity crisis (Carmona D, Douiet 1, Andaluccia G1, MSD1, Habibas 1, Can Vilella, Tarragona E2, Garraf 1, Velona, Capodarso, Chomateri 2, Nestos 2, Drevonets C1, Site DSDP 380A, Naf 2); some others refer to the first (i.e. marginal) evaporitic phase covering the 5.96–5.52 Ma time-span (Clauzon et al., 1996) (Chabet bou Seter, Sahaouria, Cava Serredi, Al Pazzo, Borgo Tossignano, Eraclea Minoa, Racalmuto, Zinga); three localities (Sioneri, Monticino 87, Maccarone) belong to the second evaporitic phase (5.52–5.4 Ma) (the Adriatic-Po realm was a perched basin fed by freshwaters during the almost complete desiccation of the Mediterranean: Clauzon et al., 2005; Popescu et al., 2007 in this volume); one Atlantic locality (Bou Regreg) covers this entire timespan in which only the pollen spectra preceding the period of the entire desiccation of the Mediterranean have been considered. Accordingly, it is allowed to regard the interpolated vegetation map as representative of the onset of the Messinian salinity crisis (i.e. about 5.96–5.60 Ma). However, the large consistency of pollen records from the floral viewpoint and the demonstration that no significant climatic change occurred between 7 and 5 Ma (Suc and Bessais, 1990; Fauquette et al., 2006) led us to consider this interpolated map although established for a relatively long period (6.7–5.4 Ma) as representative of vegetation around the Mediterranean at the beginning of the Messinian salinity crisis. For each locality, identified taxa have been grouped into nine categories according to their respective climatic-ecological significance (Suc, 1984, 1989; Jime´nez-Moreno and Suc, in press). Among them, four are dedicated to strict forest ecosystems: the subtropical evergreen forests including Engelhardia, Hamamelidaceae, Taxodiaceae with some tropical elements (Euphorbiaceae, Mimosaceae) and Cathaya; the warm-temperate deciduous forests (Quercus, Carya, Carpinus, etc.); the temperate conifer forests composed of Cedrus and
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Fig. 3. Potential vegetation maps obtained by interpolation of pollen data. A. Present-day pollen localities (moss cushions: black points) situated on the natural vegetation map of France (Bohn et al., 2004). Legend of the main vegetation types in France: 1. Snow belt; 2. Alpine herbaceous belt; 3. Subalpine coniferous forest (Abies, Picea, Larix); 4. Subalpine Pinus forest; 5. Mountain Fagus forest; 6. Atlantic oak grove; 7. Sub-Mediterranean oak forest (deciduous Quercus); 8. Atlantic Pinus forest; 9. Evergreen meso-Mediterranean vegetation (forest and garrigue); 10. Riparian forest; 11. Halophytic coastal ecosystem; 12. Aquatic freshwater ecosystem. B. Present-day potential vegetation map of France obtained by interpolation of pollen records. C. Present-day density in herbs (expressed in increased darkness of brown with respect to their relative percentage) from interpolation of pollen records. D. Messinian ante-crisis paleogeographic map of the Mediterranean region and pollen localities. Deep marine basins are in dark blue, shallow marine basins in light blue, freshwater basins in light green. Pollen localities: 1. Bou Regreg
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Tsuga, which is replaced in higher altitude by the boreal conifer forest with Abies and Picea. The Mediterranean xerophytic vegetation is constituted by evergreen trees (Olea, Quercus, Ceratonia) and shrubs (Pistacia, Phillyrea). The Avicennia mangrove is an impoverished coastal vegetation made of shrubs and bushes of two species, A. marina mostly and A. alba, as observable today along the Red Sea and the Persian Gulf. This vegetation type was not considered by the interpolation method because it is represented by very few pollen grains. Hence, it was placed manually on the palaeovegetation map. In contrast to the present-day interpolated vegetation for France, it is difficult to specify the significance of halophytic ecosystems. Indeed, their presence is exaggerated in localities corresponding to evaporite deposition on the Mediterranean margins. Accordingly, it has been preferred to group them with all the other herbs in only one open vegetation type. Density of herbs has also been considered separately. The interpolation method is applied for each vegetation group (the Avicennia mangrove excepted) and for each grid cell, only the prevalent group is retained and associated to the respective area. In this way, it is possible to produce a synthetic map of the potential palaeovegetation (Fig. 3(E)) and density in herbs (Fig. 3(F)) at the resolution 0.28 0.28. The main character of these reconstructions is the relatively abrupt juxtaposition of forests Northwards and open vegetation southwards, except along the Iberian Peninsula and North Africa where the Mediterranean xerophytic vegetation developed as a transition. Such a contrast between the North and South of the Western Mediterranean is already known according to pollen records from the Mid-Miocene (Jime´nez-Moreno and Suc, in press), the Messinian (Fauquette et al., 2006) and the Zanclean (Suc et al., 1995a), but it receives now a
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cartographic expression for the entire Mediterranean region. The subtropical forests covered most of the North Mediterranean landscapes: it was more probably a mixed forest because the evergreen elements are often associated to deciduous ones which can represent up to 50% of the pollen content in some localities. Deciduous warm-temperate forests developed in Western Europe and in Southern Anatolia. The Avicennia mangrove inhabited some residual coastal places such as the Rifian Corridor, southern Sicily and northern Turkey. Interpolation points out a concentration of altitudinal conifer forests in the Northeastern Mediterranean region, suggesting that relief in Balkans, Dinarides and Apennines was at that time more elevated than in the Southern Alps. The Southern Mediterranean was mostly occupied by a steppic to subdesertic vegetation. Such an organization of the vegetation (Fig. 3(E)) is not absolutely different from the present one (Lalande et al., 1968; Que´zel and Me´dail, 2003) at a higher level in temperature for the whole Mediterranean region and a considerably higher amount of rainfall in the Northern Mediterranean, considering also the forthcoming Alpine uplifting. Interpolated density of herbs represented in a brown gradation (Fig. 3(F)) shows maxima of open landscapes in Southern Iberian Peninsula, North Africa and Middle East. 4. Comparison between the two achieved potential palaeovegetation maps This comparison is difficult because these maps are successive in time, the interpolated map from pollen data (Fig. 3(E)) might be understood as a stage immediately preceding the complete desiccation of the Mediterranean Sea, while the simulated map (Fig. 2(A2)) corresponds to a sensitivity test of the
(Warny, 1999); 2. Carmona D (Suc unpublished); 3. MSD 1 (Bachiri Taoufiq, 2000); 4. Andaluccia G1 (Bessais unpublished); 5. Douiet 1 (Bachiri Taoufiq, 2000); 6. Habibas 1 (Suc unpublished); 7. Chabet bou Seter (Chikhi, 1992); 8. Sahaouria (Chikhi, 1992); 9. Can Vilella (Agustı´ et al., 2006); 10. Tarragona E2 (Bessais and Cravatte, 1988); 11. Garraf 1 (Suc and Cravatte, 1982); 12. Sioneri (Bertini and Suc unpublished); 13. Cava Serredi (Suc unpublished); 14. Al Pazzo (Suc unpublished); 15. Velona (Bertini unpublished, Ghetti et al., 2002); 16. Monticino 87 (Bertini, 1994, 2006); 17. Borgo Tossignano (Bertini, 1994, 2006); 18. Maccarone (Bertini, 1994, 2006); 19. Zinga (Suc unpublished); 20. Eraclea Minoa (Suc unpublished); 21. Racalmuto (Bertini et al., 1998); 22. Capodarso (Suc et al., 1995b); 23. Chomateri 2 (Mettos et al., 2000); 24. Prosilio (Biltekin unpublished); 25. Nestos 2 (Drivaliari, 1993; Jime´nez-Moreno et al., in press); 26. Ravno´ Pole (Drivaliari, 1993; Jime´nez-Moreno et al., in press); 27. Drevonets C1 (Ivanov et al., 2002; Jime´nez-Moreno et al., in press); 28. DSDP Site 380A (Popescu, 2006); 29. Gan Yavne 5 (Drivaliari, 1993); 30. Naf 1 (Drivaliari, 1993; Fauquette et al., 2006). E. Messinian potential vegetation map obtained from interpolation of pollen records (halophytic ecosystems have been grouped within the open herbaceous vegetation). F. Density in herbs for the Messinian period (expressed in increased darkness of brown with respect to their relative percentage) from interpolation of pollen records. Fig. 3. Cartes de ve´ge´tation potentielle par interpolation des donne´es polliniques. A. Localite´s a` flore pollinique actuelle fournie par des coussinets de mousses (points noirs) situe´es sur la carte de ve´ge´tation naturelle de la France (Bohn et al., 2004). Le´gende des principaux types de ve´ge´tation existant en France : 1. E´tage nival ; 2. E´tage herbace´ alpin ; 3. E´tage forestier subalpin a` conife`res (Abies, Picea, Larix) ; 4. E´tage forestier subalpin a` Pinus ; 5. E´tage forestier montagnard a` Fagus ; 6. Bosquets atlantiques a` Cheˆne ; 7. E´tage suprame´diterrane´en a` Cheˆne a` feuillage caduc ; 8. Foreˆt atlantique a` Pinus ; 9. Ve´ge´tation sempervirente me´some´diterrane´enne (foreˆt et garrigue) ; 10. Ripisilve ; 11. Ecosyste`me littoral a` halophytes ; 12. Ecosyste`me d’eau douce. B. Carte actuelle de ve´ge´tation potentielle de la France obtenue par interpolation des donne´es polliniques. C. Densite´ actuelle en herbace´es obtenue par interpolation des donne´es polliniques (exprime´e dans une gamme de tons bruns clairs a` sombres selon le pourcentage relatif des herbes). D. Carte pale´oge´ographique de la Me´diterrane´e au Messinien avant la crise de salinite´ et localisation des sites polliniques. Les bassins marins profonds sont en bleu fonce´, les bassins marins peu profonds en bleu clair, les bassins d’eau douce en vert clair. Sites polliniques : 1. Bou Regreg (Warny, 1999) ; 2. Carmona D (Suc ine´dit) ; 3. MSD 1 (Bachiri Taoufiq, 2000) ; 4. Andaluccia G1 (Bessais ine´dit) ; 5. Douiet 1 (Bachiri Taoufiq, 2000) ; 6. Habibas 1 (Suc ine´dit) ; 7. Chabet bou Seter (Chikhi, 1992) ; 8. Sahaouria (Chikhi, 1992) ; 9. Can Vilella (Agustı´ et al., 2006) ; 10. Tarragona E2 (Bessais et Cravatte, 1988) ; 11. Garraf 1 (Suc et Cravatte, 1982) ; 12. Sioneri (Bertini et Suc, ine´dit) ; 13. Cava Serredi (Suc ine´dit) ; 14. Al Pazzo (Suc ine´dit) ; 15. Velona (Bertini, ine´dit ; Ghetti et al., 2002) ; 16. Monticino 87 (Bertini, 1994, 2006) ; 17. Borgo Tossignano (Bertini, 1994, 2006) ; 18. Maccarone (Bertini, 1994, 2006) ; 19. Zinga (Suc ine´dit) ; 20. Eraclea Minoa (Suc ine´dit) ; 21. Racalmuto (Bertini et al., 1998) ; 22. Capodarso (Suc et al., 1995b) ; 23. Chomateri 2 (Mettos et al., 2000) ; 24. Prosilio (Biltekin, ine´dit) ; 25. Nestos 2 (Drivaliari, 1993 ; Jime´nez-Moreno et al., sous presse) ; 26. Ravno´ Pole (Drivaliari, 1993 ; Jime´nez-Moreno et al., sous presse) ; 27. Drevonets C1 (Ivanov et al., 2002 ; Jime´nez-Moreno et al., sous presse) ; 28. DSDP Site 380A (Popescu, 2006) ; 29. Gan Yavne 5 (Drivaliari, 1993) ; 30. Naf 1 (Drivaliari, 1993; Fauquette et al., 2006). E. Carte de ve´ge´tation potentielle pour le Messinien obtenue par interpolation des donne´es polliniques (les e´cosyste`mes a` halophytes ont e´te´ inte´gre´s dans les e´cosyste`mes herbace´s). F. Densite´ en herbace´es pour le Messinien obtenue par interpolation des donne´es polliniques (exprime´e dans une gamme de tons bruns clairs a` sombres selon le pourcentage relatif des herbes).
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impact of a complete desiccation under the present-day other boundary conditions. The discrepancy between the northern part with forests and the Southern one with open landscapes is striking, either in the potential palaeovegetation map simulated by CARAIB (Fig. 2(A2)) or in that provided by the interpolation method (Fig. 3(E)). In both maps, tree vegetation is mostly present Northward from the septentrional Mediterranean shoreline. The Southern part of the studied area is largely dominated by xerophytes including open landscapes, especially steppes except in the Nile hinterland where it was a savannah-type vegetation (Fauquette et al., 2006). These more humid open plant ecosystems in the Southeastern Mediterranean region are consistent with some forest cover in Israel probably because of some influence of the Asian monsoon transferring intensified moisture over the Southeastern Mediterranean area (Griffin, 2002). On these points, pollen results agree with the CARAIB simulation for Northwestern Africa but disagree for Northeastern Africa where semi-desertic conditions are predicted. However, a quite large agreement concerns the Northwestern Mediterranean, which was covered by subtropical to warm-temperate forests as also supported by macrofloras such as that of Murviel-le`s-Be´ziers (Roiron and Ambert, 1990). In addition, some details are very consistent like the presence of mid- to high-altitude vegetation in the Balkans region.
5. Discussion The CARAIB simulation as the interpolation method display palaeovegetation maps where homogeneity prevails to the South and a mosaic vegetation-type to the North (especially in the Northeastern Mediterranean) as today. Probably the relief distribution forced such an organization as much as the climate. As the CARAIB potential palaeovegetation map (Fig. 2(A2)) produces only one subtropical forest grid cell on the Northwestern part of the desiccated Mediterranean, it demonstrates that the water amount is insufficient to install subtropical trees in the Northern part although temperature conditions are attested. The water parameter considers among others, precipitations, soil water and runoff. In the model, soil water is the most important water parameter influencing vegetation distribution. It is calculated from a hydrological budget based on the precipitation amount and the evaporative conditions. Concerning the North Mediterranean side, the temperature range may reveal selectively such subtropical vegetation, but soil water becomes the limiting factor. Northwards, when precipitation amount is sufficient, temperature level is failing. Around the desiccated Mediterranean, the most representative vegetations produced by CARAIB are warm-temperate mixed forests. This kind of vegetation is close to the Mediterranean xerophytic one. This is in agreement for the Western part with the interpolated vegetation map where Mediterranean xerophytes are present from Spain to the North Africa coastline.
Finally, the CARAIB potential palaeovegetation map produces also only one cool-temperate conifer forest grid cell located in the Balkans in agreement with the interpolated vegetation map. The latitudinal severe (and less drastic in longitude in the Southern Mediterranean) contrast in climate and the observed vegetation could contribute to explain why many deep and long fluvial canyons were cut all around the North Mediterranean margin during the desiccation phase at the difference of the Southwestern margin where only a more widespread and relatively less intense erosion occurred (Corne´e et al., 2005). In the North, the humid climatic conditions and the extensive forest cover benefited channelled water transport through river streams. On the contrary, in the Southwestern Mediterranean, steppe vegetation advantaged a spread runoff, considerably reduced because of the xeric climatic conditions. However, in the Southeastern Mediterranean region, intense channelled fluvial erosion again occurred because of long drainage basin in latitude reaching Central Africa (Sahabi canyon: Barr and Walker, 1973; Griffin, 2002; Nile canyon: Chumakov, 1973; Barber, 1980) where more humid conditions existed (Griffin, 2002), as also attested by a savannah-like relatively more dense vegetation cover (Fauquette et al., 2006). The Messinian evidences of the Avicennia mangrove are among the last ones in the Mediterranean region. This coastal ecosystem persisted in the Black Sea area up to at least 4 Ma (Popescu, 2006). In the Rifian Corridor and in Sicily, this residual mangrove coexisted with a very xeric and scattered vegetation as it is today along the Red Sea and the Persian Gulf under subdesertic conditions. Along the Black Sea, the ultimate refuge of the Avicennia mangrove is at such high latitude, the land is also covered by a relatively open vegetation surrounded by forests. The Tortonian vegetation simulated by Franc¸ois et al. (2006) using the CARAIB model based on climate reconstruction by the ECHAM4/ML atmospheric general circulation model shows a similar latitudinal contrast in vegetation (forests to the North, open vegetation to the South), but at a higher level in humidity for both environments. Two simulations were proposed, testing low and high level in CO2, respectively. The first condition shows the development of temperate mixed forests to the North in opposition to grasslands and semi-desert to the South. The second condition proceeds in advantaging strengthening of tropical vegetation (seasonal forest Northwards and savannah Southwards). The first situation (low CO2 level) appears more consistent with the Tortonian pollen records from the Western Mediterranean and the related palaeoclimate quantification (Fauquette et al., in press). It is also in better agreement with climate quantification for Southeastern Europe according to macro- and pollen floras (Bruch et al., 2006). In addition, this CARAIB Tortonian simulation does not display important discrepancies with the Messinian one that is reported in this paper (Fig. 2(A2)) and which appears as resulting from the previous situation if the Mediterranean Sea disappeared. We conclude that the Messinian interpolated vegetation map from pollen records (Fig. 3(E)) should be considered as an intermediate situation between the Tortonian
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simulated vegetation at low CO2 level and the simulated vegetation during the almost complete desiccation of the Mediterranean Sea. However, this last step is to be considered with caution, since the model has neglected the negative elevations that would have resulted from the desiccation of the Mediterranean Sea, This situation, corresponding to a very shallow sea, is in conflict with the palaeobiological records (Hsu¨ et al., 1973, 1978) and the depths of canyons cut during the desiccation phase (Clauzon, 1973; Chumakov, 1973). The desiccation of such a deep sea should have produced very dry and warm environments in its deeper parts where salt deposited. Several similarities exist with the palaeoecosystem maps drawn by Kovar-Eder et al. (2006) even if they focus on the Northeastern Mediterranean region and consider only plant macroremains for a relatively long time-interval (7–4 Ma): broad-leaved evergreen forests developed in the Northeastern Mediterranean, broad-leaved deciduous ecosystems extended more Northwards, and sclerophyllous vegetation grew in the Southernmost Greek Peninsula. Unfortunately, the comparison cannot be extended to the mountainous ecosystems, which are not considered in Kovar-Eder et al.’s study (2006). 6. Conclusion During the Messinian, temperature was on the whole 28 C higher than the present-day, allowing subtropical and warmtemperate vegetation types in the North Mediterranean region. The simulated and interpolated palaeovegetation maps are in good agreement concerning the high contrast between the North (forest vegetation) and South (open vegetation) Mediterranean region. However, the interpolated vegetation map and the simulated one represent two successive steps within the Messinian salinity crisis: the first one may illustrate the period just preceding the complete desiccation phase which includes the marginal evaporitic event; the second one illustrates somewhat the complete desiccation reduced to that of a shallow sea. Because it is validated by a present-day assessment at the scale of France, that is a highly diversified territory from the vegetation viewpoint, the interpolated palaeovegetation map can be used to validate or improve simulations provided by the CARAIB model, taking into account the discrepancies pointed out between the LMD simulation and the ‘‘Climatic Amplitude’’ transfer function about the level in moisture. As the Southern Mediterranean appears covered by an almost homogenous open vegetation (steppe to the West, savannah to the East), the Northern Mediterranean landscapes were, as today, significantly influenced by relief resulting in a mosaic organization of the vegetation. The transition from forest to open vegetation seems progressive in the Iberian Peninsula, while it appears rather sharp in the other peninsulas. Relief is suggested to have been at that time more elevated in the Dinarides–Balkans Chain than in the Southern Alps. Finally, the larger number of Messinian fluvial canyons along the Northern Mediterranean shoreline than in the Southern one may have some explanation in the density of the vegetation cover which favoured channelled water flow in the septentrional forest environments at the
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difference of the widespread runoff in the Southern region, a phenomenon also emphasized by the contrast in precipitation. The interpolated Messinian vegetation map may appear as an intermediate step between the Tortonian simulated vegetation and the map simulated for the Mediterranean desiccation step, with uncertainties related to the depth of the desiccated basin which has not been considered for modelling. Acknowledgements The authors are indebted to palynologists who provided their Messinian pollen data (A. Bertini, N. Bachiri Taoufiq, S. Warny, M.-J. Perez Villa, S.-M. Popescu and D. Biltekin). Some colleagues helped us in collecting mosses (C. Poumot, L. Londeix, A. Lefort, S. Joannin, A. Schnitzler, V. Fernandez), some others offered present-day pollen spectra (V. Vergne, M. Clet, A.-M. Le´zine). Several present-day pollen spectra come from the European Pollen Database (author of most of them: J.L. de Beaulieu). The first author benefited from a grant provided by the EEDEN (ESF) Programme to develop the modelling approach. This paper is a contribution to the ECLIPSE (CNRS) Projects on the Messinian salinity crisis and the EGEO Project from the French ANR Programme. LF is research associate at the Belgian National Foundation for Scientific Research (FNRS). Part of this work was carried out while LF was visiting the ‘‘Centre de Recherches Pe´trographiques et Ge´ochimiques’’ (CRPG) in Nancy, France, under a research grant from CNRS and Re´gion Lorraine. A research grant from FNRS (‘‘Cre´dit aux chercheurs’’) is also gratefully acknowledged. Reviewers (P. Roiron and S. Klotz) are acknowledged for significantly improving the manuscript. Contribution UMR5125-07.011 and UMR 5554 n82007-0014. References Agustı´, J., Oms, O., Furio´, M., Pe´rez-Vila, M.-J., Roca, E., 2006. The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin). In: Agustı´, J., Oms, O., Meulenkamp, J.E. (Eds.), Late Miocene to Early Pliocene environment and climate change in the Mediterranean area, Palaeogeography, Palaeoclimatology, Palaeoecology 238, 129–189. Bachiri Taoufiq, N., 2000. Les environnements marins et continentaux du corridor rifain au Mioce`ne supe´rieur d’apre`s la palynologie. Thesis, University of Casablanca, Casablanca. Barber, P.M., 1980. Palaeogeographic evolution of the Proto-Nile delta during the Messinian salinity crisis. Ge´ologie Me´diterrane´enne 7, 13–18. Barr, F.T., Walker, B.R., 1973. Late Tertiary channel system in Northern Lybia and its implications on Mediterranean sea level changes. Initial Reports of the Deep Sea Drilling Project 13, U. S. Government Printing Office, Washington, 1244–1250. Bertini, A., 1994. Messinian-Zanclean vegetation and climate in North-Central Italy. Historical Biology 9, 3–10. Bertini, A., 2002. Palynological evidence of upper Neogene environments in Italy. Acta Universitatis Carolinae Geologica 46, 15–25. Bertini, A., 2006. The northern Apennines palynological record as a contribute for the reconstruction of the Messinian palaeoenvironments. Sedimentary Geology 188/189, 235–258. Bertini, A., Londeix, L., Maniscalco, R., Di Stefano, A., Suc, J.-P., Clauzon, G., Gautier, F., Grasso, M., 1998. Paleobiological evidence of depositional conditions in the Salt member, Gessoso-Solfifera Formation (Messinian Upper Miocene) of Sicily. Micropaleontology 44, 413–433.
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Original article
Messinian vegetation maps of the Mediterranean region using models and interpolated pollen data Cartes de ve´ge´tation de la re´gion me´diterrane´enne au Messinien d’apre`s les mode`les et les donne´es polliniques interpole´es Eric Favre a,*, Louis Franc¸ois b, Fre´de´ric Fluteau c, Rachid Cheddadi d, Lysiane The´venod a, Jean-Pierre Suc a a
UMR 5125 PEPS CNRS, France, universite´ Lyon 1, campus de La Doua, baˆtiment Ge´ode, 69622 Villeurbanne cedex, France b Laboratoire de physique atmosphe´rique et plane´taire (LPAP), universite´ de Lie`ge, alle´e du 6-Aouˆt, 4000 Lie`ge, Belgique c Institut de physique du Globe de Paris (UMR 7154 CNRS), universite´ Denis-Diderot – Paris 7, boıˆte 89, 4, Place Jussieu, 75252 Paris cedex 5, France d Institut des sciences de l’e´volution (UMR 5554 CNRS), e´quipe pale´oenvironnements, universite´ de Montpellier II, Place Euge`ne-Bataillon, 34095 Montpellier, France Received 10 September 2006; accepted 16 December 2006 Available online 23 March 2007
Abstract This study proposes to compare the outputs from the CARAIB vegetation model forced by results from the LMD General Circulation Model with interpolated pollen data (Kriging method) from the Mediterranean region during the Messinian. The vegetation maps that have been obtained represent distinct phases of the salinity crisis: before the crisis and during the marginal evaporitic phase (interpolated map), and during the complete desiccation phase (simulated map). However, they are comparable in terms of vegetation density and agree on a strong contrast between the Northern (forest vegetation) and Southern (open vegetation) Mediterranean regions. Main differences concern the type of forests in the northern Mediterranean region, which are explained by discrepancies between precipitation amount predicted by the model and that calculated by a transfer function using pollen records. The interpolation method has been successfully tested in France using interpolated current pollen records by comparison with the present-day potential vegetation map. The resulting Messinian map is useful to validate or improve model simulation which does not take into account the depth of the Mediterranean Basin when it dried up. The Southern Mediterranean landscapes were open, with a steppe-like vegetation to the West and a savannah-like vegetation to the East. Forests prevailed to the North, organized in a mosaic system mainly controlled by relief. Such a contrast provides some explanation of the large number of deep fluvial canyons cut on the Northern margin at opposed to the South during the Mediterranean desiccation. # 2007 Elsevier Masson SAS. All rights reserved. Re´sume´ Cette e´tude vise a` comparer les simulations du mode`le de ve´ge´tation CARAIB contraint par le mode`le climatique LMD aux interpolations de donne´es polliniques (me´thode du Kriegage) pour le Messinien de la re´gion me´diterrane´enne. Les cartes de ve´ge´tation ainsi obtenues repre´sentent des phases distinctes de la crise de salinite´ messinienne : avant la crise et pendant la phase de de´poˆt des e´vaporites marginales pour la carte interpole´e, et pendant la phase de dessiccation comple`te pour la simulation. Ces cartes sont toutefois comparables en termes de densite´ de ve´ge´tation et s’accordent sur un fort contraste entre le nord (couverture forestie`re) et le sud (ve´ge´tation ouverte) de la re´gion me´diterrane´enne. Les principales diffe´rences portent sur le type de foreˆts au nord, elles s’expliquent par les e´carts entre les quantite´s de pluie pre´dites par le mode`le et celles calcule´es par la fonction de transfert construite sur les donne´es polliniques. La me´thode d’interpolation a e´te´ teste´e avec succe`s sur la France par interpolation de donne´es polliniques actuelles compare´e avec la carte de ve´ge´tation potentielle. La carte de ve´ge´tation interpole´e pour le Messinien est utilise´e pour valider ou ame´liorer la simulation qui ne peut prendre en compte la profondeur du bassin me´diterrane´en lorsqu’il e´tait a` sec. Les paysages sud-me´diterrane´ens e´taient ouverts avec des formations steppiques a` l’Ouest et une ve´ge´tation de savane a` l’Est. Les foreˆts dominaient au nord avec une organisation en mosaı¨que controˆle´e par les reliefs. Un tel contraste contribue a` expliquer l’abondance des canyons * Corresponding author. E-mail address: [email protected] (E. Favre). 0016-6995/$ – see front matter # 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2006.12.002
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fluviatiles creuse´s pendant le paroxysme de la crise sur les rives septentrionales de la Me´diterrane´e et leur relative rarete´ sur ses rives me´ridionales. # 2007 Elsevier Masson SAS. All rights reserved. Keywords: Palaeovegetation mapping; Messinian; Mediterranean region Mots cle´s : Cartes de pale´ove´ge´tation ; Messinien ; Re´gion me´diterrane´enne
1. Introduction The desiccation of the Mediterranean Sea during the Messinian is one of the most studied phenomenons concerning the Late Cenozoic, and is especially characterized by thick deposits of evaporites (Hsu¨ et al., 1973; Rouchy, 1982) and cutting of fluvial canyons (Clauzon, 1999) resulting from a severe drop in sea-level (about 1500 m: Clauzon et al., 1996). The knowledge of the vegetation cover before and during the crisis is crucial for clarifying how the climate context contributed to the Mediterranean desiccation (Suc and Bessais, 1990; Fauquette et al., 2006). It is also crucial for estimating the relative proportion of forests versus open vegetation. Indeed, the density of the vegetation cover is critical to evaluate the intensity of runoff and subaerial erosion not only within the fluvial networks (Clauzon, 1999), but also over the entire margin (Gorini et al., 2005). First attempts were carried out by Franc¸ois et al. (2006) using climate and vegetation models, and Kovar-Eder et al. (2006) using plant macroremain records. The former study provides a vegetation biome distribution resulting from outputs of the climate ECHAM4/ML used as inputs to the vegetation CARAIB global models for the Tortonian period, that is about four million years before the Messinian salinity crisis, however, without a detailed comparison with the fossil plant records at the scale of the Mediterranean region. The latter reconstruction uses a taxonomic physiognomic method able to express the variability in woody vegetation on geographic maps, considering each ecosystem separately. But, this reconstruction concerns a relatively long time-interval (7–4 Ma) with respect to the Messinian event itself, the almost complete desiccation of the Mediterranean Sea being restricted to the time-span 5.6–5.33 Ma whatever the referred scenario (Clauzon et al., 1996, 2005; Krijgsman et al., 1999). In this paper, we propose to compare (1) vegetation biome maps calculated by the CARAIB model forced with a Messinian-like climate (derived from a sensitivity test of the LMD model, in which the Mediterranean Sea and the Black Sea have been desiccated) with (2) the result of the Kriging interpolation (Krige, 1951; Matheron, 1963) of thirty pollen records from the Mediterranean region just preceding the salinity crisis or coeval with the onset of this event for some of them (covered time-interval: 6.7–5.4 Ma). 2. Climate and vegetation from model simulation The ‘‘Laboratoire de Me´te´orologie Dynamique’’ (LMD) General Circulation Model (GCM) (for further information see http://www.lmd.jussieu.fr/(lmdz/homepage.html; Pe´ron et al., 2005) and the CARAIB vegetation models (Otto et al., 2002;
Franc¸ois et al., 2006) have been used to study the impacts on climate and vegetation of a complete desiccation of the Mediterranean Sea and the Black Sea basins. The spatial resolution of the LMD model, and consequently for CARAIB one is 3.758 2.538 in longitude and latitude. The control GCM experiment corresponds to a present-day simulation, while the desiccation experiment is forced by boundary conditions representative of desiccated Mediterranean and Black seas with present-day values for the other boundary conditions (sea surface temperature, CO2, orbital parameters, solar constant). As it was not possible to use negative elevations in the LMD GCM, grid cells corresponding to the desiccated basins were assumed to have elevations of 0 m, and so, should be colder and wetter than in the actual desiccated basin. The climatic anomalies between the desiccation and control experiments are added to a presentday climatology (Cramer and Leemans, unpublished data, an updated version of the IIASA database: Leemans and Cramer, 1991) averaged at the spatial resolution of the GCM, before being used in the CARAIB vegetation model. CARAIB predicts the relative abundances and primary productivities of 15 plant functional types (2 herbaceous types, 4 needle-leaved boreal/ temperate trees, 4 broadleaved boreal/temperate trees, 3 subtropical trees and 2 tropical trees) on each model grid cell. A scheme is then used to produce a biome map of potential vegetation, from the simulated assemblage of PFTs calculated for each grid cell. Climate and vegetation simulations are performed over the entire earth, but the results presented in the current study are restricted to Western/Central Europe and the Mediterranean area. Fig. 1 compares the annual mean surface temperature and precipitation in the control and desiccation experiments, reconstructed by adding the LMD anomalies to the presentday climatology. In the desiccation experiment, mean annual temperature ranges between 12 and 188 C in the Northern edge of the former Mediterranean and between 16 and 228 C in the Southern edge, that is about 28 C higher than today (Fig. 1(A)). The Mediterranean region appears to be moderately drier than currently in this experiment with a precipitation range of 300– 600 mm/yr in its previous Northern edge and 0–150 mm/yr (0–400 mm/yr) in its previous Southern edge (Fig. 1(B)). The mean annual temperature values in the desiccation experiment are on the whole significantly lower than those obtained by transfer function from pollen data which focus on the marginal desiccation episode which occurred at the beginning of the crisis (Fauquette et al., 2006). Annual rainfall appears considerably more underestimated (difference of 400–700 mm for the North, 300–400 mm for the South) with respect to the same episode according to the pollen transfer function (Fauquette et al., 2006). Such relatively important differences in temperature and
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Fig. 1. Simulated climatic maps from the LMD GCM for Europe and the Mediterranean region: 1. Present-day climatology (an update of Leemans and Cramer, 1991) averaged over the model grid cells; 2. Reconstructed climate in the desiccation experiment obtained by combining the present-day climatology with the LMD model anomalies. A. Mean annual temperature (expressed in 8C); B. Annual precipitation (expressed in mm). Fig. 1. Cartes climatiques simule´es par le mode`le LMD pour l’Europe et la re´gion me´diterrane´enne8: 1. Climatologie actuelle (mise a` jour de Leemans et Cramer, 1991) moyenne´e sur la grille du mode`le ; 2. Climat simule´ lors de l’expe´rience d’asse`chement obtenu en combinant la climatologie actuelle et les anomalies du mode`le LMD. A. Tempe´rature moyenne annuelle (en 8C) ; B. Pre´cipitation annuelle (en mm).
precipitation between the simulation and the transfer function probably result from: the method used for simulating the climate of the salinity crisis in only removing the Mediterranean Sea and the Black Sea, without modifying any other boundary condition (referring for instance to atmospheric CO2, palaeogeography and palaeorelief, Atlantic sea surface temperature, etc.) and without considering the negative elevations in the desiccated basins;
the dissimilarity in climatic conditions at the beginning of desiccation (quantified using the transfer function) and during the desiccation itself (quantified using model simulation). In addition, consideration of uncertainties on climate quantification using the transfer function should also reduce discrepancies between the two approaches. Using the outputs from the LMD climate model, the CARAIB vegetation model (Otto et al., 2002; Franc¸ois et al.,
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Fig. 2. Potential vegetation maps obtained by a CARAIB model simulation for Europe and the Mediterranean region: 1. Present-day; 2. Desiccation experiment. A. Biome distribution; B. Net primary productivity of herbs (gram of carbon/m2/year). Fig. 2. Carte de la ve´ge´tation potentielle simule´e par le mode`le CARAIB pour l’Europe et la re´gion me´diterrane´enne : 1. Pre´sent ; 2. Expe´rience d’asse`chement. A. Distribution des biomes ; B. Productivite´ primaire des herbes (gramme de carbone/m2/an).
2006) reconstructs the potential vegetation biomes for each grid cell at the same resolution as for the LMD climate model (Fig. 2(A)). In Europe and the peri-Mediterranean region, vegetation spreads over 12 categories from desert to cooltemperate conifer forest. It is to be mentioned that open vegetation types and deserts cover the major part of the potential vegetation map during the Mediterranean desiccation (73%) and are particularly well-expressed on the Southern and Eastern edges of the desiccated Mediterranean. Other areas are occupied by forests (27%). Another observation is that forest environments are only represented above a West-East oriented line, which clearly separates Europe occupied by forests from the Mediterranean realm characterized by open landscapes. The level of forest opening is also well indicated in the model by the calculated net primary productivity of herbaceous vegetation (Fig. 2(B)). Indeed, in the model, herbs and trees grow in two different vegetation storeys, so that the amount of light available for the photosynthesis of herbs decreases as the
abundance of trees increases in the over-storey. The desiccation of the Mediterranean and the Black Sea basins appears to generate a very significant opening of the forest cover in Central and Eastern Europe. 3. Vegetation map from interpolated pollen data Interpolating pollen records for reconstructing past potential vegetation maps requires a present-day validation. We have carried out such a task using pollen samples of moss cushions (generally rich in pollen grains) from 129 localities in France. These moss cushions were collected in representative natural plant ecosystems (for example, protected restricted forests within large agricultural regions) in order to reduce biases caused by anthropogenic activity. The geographic distribution of the studied localities takes into account the high variability in the vegetation linked to the existence of several seashores, the presence of the meso-Mediterranean vegetation belt in the
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South, and the rapid succession of vegetation belts related to reliefs as the Alps or Pyrenees (Fig. 3(A)). The vegetation map presented in Fig. 3(B) was obtained for practically all the vegetation groups using the universal Kriging interpolation method in which the altitudinal component is considered. Only the aquatic plants are interpolated using the common Kriging since they have an azonal distribution. The Kriging method (Krige, 1951; Matheron, 1963) is considered as one of the most efficient interpolation method from the statistical point of view. This approach, unlike others, is based on an overall spatial study of the documented localities to estimate data variations. Thus, each locality, according to its characteristics (value of the considered variable, geographic position), contributes to the interpolation through a semi-variogram and the most appropriate model that was chosen. Some areas in France are not interpolated (white areas) because the error is greater than the average of all the errors on the entire map. In addition, various thresholds have been applied according to each plant group; this also reduces the interpolated surface area. Finally, it results in an interpolated surface area, which offers a minimum of uncertainty whatever the spatial distribution of the considered pollen localities. Most of the interpolated vegetation map is covered by warmtemperate deciduous forests. This assessment is in agreement with the present-day potential vegetation map (Fig. 3(A): Noirfalise et al., 1987; Bohn et al., 2004). Ecological or floristic subdivisions of these forests are indicated on the potential vegetation map. It is unrealistic to reach such a degree of precision on the interpolated map because of the impossibility to generally identify tree pollen grains more accurately than the genus level. As expected, variability in vegetation types is enhanced near the Mediterranean seashore and relief. Coastal halophytic ecosystems appear along the West shoreline of the Cotentin Peninsula and in the Rhoˆne Delta, as they are mostly recorded all along the Mediterranean coastline on the potential vegetation map. Boreal conifer forest is concentrated on the Northern Alps in the interpolated map, which suffers of lack of these forests on the Pyrenees with respect to the potential vegetation map. The Mediterranean xerophytic vegetation is drawn around the Mediterranean seashore reaching far up in the Rhoˆne Valley, and also a little bit on the Atlantic coastline (the Vende´e region). Distribution of the latter ecosystems almost completely fits with the present-day potential vegetation (Noirfalise et al., 1987; Bohn et al., 2004). Aquatic plants are abundant in the Channel region and in the Massif Central and Dombes (Northward Lyon). Such ecosystems are well known today in these regions but are insufficiently represented on the potential vegetation map where forests are often considered as prevalent. Finally, white spaces are related to a too much imprecise interpolation and do not refer to any plant ecosystem. As they contribute to all the plant ecosystems, their drawing is difficult to realize in a forest prevailing potential vegetation, herbs have been also considered specifically in interpolating their density (Fig. 3(C)). Indeed, they are mostly distributed on reliefs (meadows, Alpine vegetation belt), in some humid areas such as the Dombes and Sologne regions, and some coastal plains such as the Cotentin Peninsula. These
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results are fully satisfactory and show a relatively high consistency with the present-day potential vegetation map (Fig. 3(A)). Accordingly, it is substantially reliable to use the Kriging interpolation method for the Messinian period. Thirty Messinian pollen localities widely distributed around the Mediterranean (Fig. 3(D)) have been considered and, more specifically, their pollen spectra belonging to the time-interval 6.7–5.4 Ma. These sites have an accurate age according to combined (or not) approaches (biostratigraphy, magnetostratigraphy, isotope stratigraphy, radiometric age). The target is not to show and discuss their relative chronostratigraphic position, already done for most of them by Bertini (2002), Clauzon et al. (2005), Fauquette et al. (2006) and Jime´nez-Moreno et al. (in press), but to pay attention that they belong to a relatively restricted time-window for reconstructing the vegetation on a large space at the time of the salinity crisis with a maximum of reliability. According to the scenario of Clauzon et al. (1996, 2005), field observations or seismic profiles indicate that: some localities just predate the Messinian salinity crisis (Carmona D, Douiet 1, Andaluccia G1, MSD1, Habibas 1, Can Vilella, Tarragona E2, Garraf 1, Velona, Capodarso, Chomateri 2, Nestos 2, Drevonets C1, Site DSDP 380A, Naf 2); some others refer to the first (i.e. marginal) evaporitic phase covering the 5.96–5.52 Ma time-span (Clauzon et al., 1996) (Chabet bou Seter, Sahaouria, Cava Serredi, Al Pazzo, Borgo Tossignano, Eraclea Minoa, Racalmuto, Zinga); three localities (Sioneri, Monticino 87, Maccarone) belong to the second evaporitic phase (5.52–5.4 Ma) (the Adriatic-Po realm was a perched basin fed by freshwaters during the almost complete desiccation of the Mediterranean: Clauzon et al., 2005; Popescu et al., 2007 in this volume); one Atlantic locality (Bou Regreg) covers this entire timespan in which only the pollen spectra preceding the period of the entire desiccation of the Mediterranean have been considered. Accordingly, it is allowed to regard the interpolated vegetation map as representative of the onset of the Messinian salinity crisis (i.e. about 5.96–5.60 Ma). However, the large consistency of pollen records from the floral viewpoint and the demonstration that no significant climatic change occurred between 7 and 5 Ma (Suc and Bessais, 1990; Fauquette et al., 2006) led us to consider this interpolated map although established for a relatively long period (6.7–5.4 Ma) as representative of vegetation around the Mediterranean at the beginning of the Messinian salinity crisis. For each locality, identified taxa have been grouped into nine categories according to their respective climatic-ecological significance (Suc, 1984, 1989; Jime´nez-Moreno and Suc, in press). Among them, four are dedicated to strict forest ecosystems: the subtropical evergreen forests including Engelhardia, Hamamelidaceae, Taxodiaceae with some tropical elements (Euphorbiaceae, Mimosaceae) and Cathaya; the warm-temperate deciduous forests (Quercus, Carya, Carpinus, etc.); the temperate conifer forests composed of Cedrus and
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Fig. 3. Potential vegetation maps obtained by interpolation of pollen data. A. Present-day pollen localities (moss cushions: black points) situated on the natural vegetation map of France (Bohn et al., 2004). Legend of the main vegetation types in France: 1. Snow belt; 2. Alpine herbaceous belt; 3. Subalpine coniferous forest (Abies, Picea, Larix); 4. Subalpine Pinus forest; 5. Mountain Fagus forest; 6. Atlantic oak grove; 7. Sub-Mediterranean oak forest (deciduous Quercus); 8. Atlantic Pinus forest; 9. Evergreen meso-Mediterranean vegetation (forest and garrigue); 10. Riparian forest; 11. Halophytic coastal ecosystem; 12. Aquatic freshwater ecosystem. B. Present-day potential vegetation map of France obtained by interpolation of pollen records. C. Present-day density in herbs (expressed in increased darkness of brown with respect to their relative percentage) from interpolation of pollen records. D. Messinian ante-crisis paleogeographic map of the Mediterranean region and pollen localities. Deep marine basins are in dark blue, shallow marine basins in light blue, freshwater basins in light green. Pollen localities: 1. Bou Regreg
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Tsuga, which is replaced in higher altitude by the boreal conifer forest with Abies and Picea. The Mediterranean xerophytic vegetation is constituted by evergreen trees (Olea, Quercus, Ceratonia) and shrubs (Pistacia, Phillyrea). The Avicennia mangrove is an impoverished coastal vegetation made of shrubs and bushes of two species, A. marina mostly and A. alba, as observable today along the Red Sea and the Persian Gulf. This vegetation type was not considered by the interpolation method because it is represented by very few pollen grains. Hence, it was placed manually on the palaeovegetation map. In contrast to the present-day interpolated vegetation for France, it is difficult to specify the significance of halophytic ecosystems. Indeed, their presence is exaggerated in localities corresponding to evaporite deposition on the Mediterranean margins. Accordingly, it has been preferred to group them with all the other herbs in only one open vegetation type. Density of herbs has also been considered separately. The interpolation method is applied for each vegetation group (the Avicennia mangrove excepted) and for each grid cell, only the prevalent group is retained and associated to the respective area. In this way, it is possible to produce a synthetic map of the potential palaeovegetation (Fig. 3(E)) and density in herbs (Fig. 3(F)) at the resolution 0.28 0.28. The main character of these reconstructions is the relatively abrupt juxtaposition of forests Northwards and open vegetation southwards, except along the Iberian Peninsula and North Africa where the Mediterranean xerophytic vegetation developed as a transition. Such a contrast between the North and South of the Western Mediterranean is already known according to pollen records from the Mid-Miocene (Jime´nez-Moreno and Suc, in press), the Messinian (Fauquette et al., 2006) and the Zanclean (Suc et al., 1995a), but it receives now a
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cartographic expression for the entire Mediterranean region. The subtropical forests covered most of the North Mediterranean landscapes: it was more probably a mixed forest because the evergreen elements are often associated to deciduous ones which can represent up to 50% of the pollen content in some localities. Deciduous warm-temperate forests developed in Western Europe and in Southern Anatolia. The Avicennia mangrove inhabited some residual coastal places such as the Rifian Corridor, southern Sicily and northern Turkey. Interpolation points out a concentration of altitudinal conifer forests in the Northeastern Mediterranean region, suggesting that relief in Balkans, Dinarides and Apennines was at that time more elevated than in the Southern Alps. The Southern Mediterranean was mostly occupied by a steppic to subdesertic vegetation. Such an organization of the vegetation (Fig. 3(E)) is not absolutely different from the present one (Lalande et al., 1968; Que´zel and Me´dail, 2003) at a higher level in temperature for the whole Mediterranean region and a considerably higher amount of rainfall in the Northern Mediterranean, considering also the forthcoming Alpine uplifting. Interpolated density of herbs represented in a brown gradation (Fig. 3(F)) shows maxima of open landscapes in Southern Iberian Peninsula, North Africa and Middle East. 4. Comparison between the two achieved potential palaeovegetation maps This comparison is difficult because these maps are successive in time, the interpolated map from pollen data (Fig. 3(E)) might be understood as a stage immediately preceding the complete desiccation of the Mediterranean Sea, while the simulated map (Fig. 2(A2)) corresponds to a sensitivity test of the
(Warny, 1999); 2. Carmona D (Suc unpublished); 3. MSD 1 (Bachiri Taoufiq, 2000); 4. Andaluccia G1 (Bessais unpublished); 5. Douiet 1 (Bachiri Taoufiq, 2000); 6. Habibas 1 (Suc unpublished); 7. Chabet bou Seter (Chikhi, 1992); 8. Sahaouria (Chikhi, 1992); 9. Can Vilella (Agustı´ et al., 2006); 10. Tarragona E2 (Bessais and Cravatte, 1988); 11. Garraf 1 (Suc and Cravatte, 1982); 12. Sioneri (Bertini and Suc unpublished); 13. Cava Serredi (Suc unpublished); 14. Al Pazzo (Suc unpublished); 15. Velona (Bertini unpublished, Ghetti et al., 2002); 16. Monticino 87 (Bertini, 1994, 2006); 17. Borgo Tossignano (Bertini, 1994, 2006); 18. Maccarone (Bertini, 1994, 2006); 19. Zinga (Suc unpublished); 20. Eraclea Minoa (Suc unpublished); 21. Racalmuto (Bertini et al., 1998); 22. Capodarso (Suc et al., 1995b); 23. Chomateri 2 (Mettos et al., 2000); 24. Prosilio (Biltekin unpublished); 25. Nestos 2 (Drivaliari, 1993; Jime´nez-Moreno et al., in press); 26. Ravno´ Pole (Drivaliari, 1993; Jime´nez-Moreno et al., in press); 27. Drevonets C1 (Ivanov et al., 2002; Jime´nez-Moreno et al., in press); 28. DSDP Site 380A (Popescu, 2006); 29. Gan Yavne 5 (Drivaliari, 1993); 30. Naf 1 (Drivaliari, 1993; Fauquette et al., 2006). E. Messinian potential vegetation map obtained from interpolation of pollen records (halophytic ecosystems have been grouped within the open herbaceous vegetation). F. Density in herbs for the Messinian period (expressed in increased darkness of brown with respect to their relative percentage) from interpolation of pollen records. Fig. 3. Cartes de ve´ge´tation potentielle par interpolation des donne´es polliniques. A. Localite´s a` flore pollinique actuelle fournie par des coussinets de mousses (points noirs) situe´es sur la carte de ve´ge´tation naturelle de la France (Bohn et al., 2004). Le´gende des principaux types de ve´ge´tation existant en France : 1. E´tage nival ; 2. E´tage herbace´ alpin ; 3. E´tage forestier subalpin a` conife`res (Abies, Picea, Larix) ; 4. E´tage forestier subalpin a` Pinus ; 5. E´tage forestier montagnard a` Fagus ; 6. Bosquets atlantiques a` Cheˆne ; 7. E´tage suprame´diterrane´en a` Cheˆne a` feuillage caduc ; 8. Foreˆt atlantique a` Pinus ; 9. Ve´ge´tation sempervirente me´some´diterrane´enne (foreˆt et garrigue) ; 10. Ripisilve ; 11. Ecosyste`me littoral a` halophytes ; 12. Ecosyste`me d’eau douce. B. Carte actuelle de ve´ge´tation potentielle de la France obtenue par interpolation des donne´es polliniques. C. Densite´ actuelle en herbace´es obtenue par interpolation des donne´es polliniques (exprime´e dans une gamme de tons bruns clairs a` sombres selon le pourcentage relatif des herbes). D. Carte pale´oge´ographique de la Me´diterrane´e au Messinien avant la crise de salinite´ et localisation des sites polliniques. Les bassins marins profonds sont en bleu fonce´, les bassins marins peu profonds en bleu clair, les bassins d’eau douce en vert clair. Sites polliniques : 1. Bou Regreg (Warny, 1999) ; 2. Carmona D (Suc ine´dit) ; 3. MSD 1 (Bachiri Taoufiq, 2000) ; 4. Andaluccia G1 (Bessais ine´dit) ; 5. Douiet 1 (Bachiri Taoufiq, 2000) ; 6. Habibas 1 (Suc ine´dit) ; 7. Chabet bou Seter (Chikhi, 1992) ; 8. Sahaouria (Chikhi, 1992) ; 9. Can Vilella (Agustı´ et al., 2006) ; 10. Tarragona E2 (Bessais et Cravatte, 1988) ; 11. Garraf 1 (Suc et Cravatte, 1982) ; 12. Sioneri (Bertini et Suc, ine´dit) ; 13. Cava Serredi (Suc ine´dit) ; 14. Al Pazzo (Suc ine´dit) ; 15. Velona (Bertini, ine´dit ; Ghetti et al., 2002) ; 16. Monticino 87 (Bertini, 1994, 2006) ; 17. Borgo Tossignano (Bertini, 1994, 2006) ; 18. Maccarone (Bertini, 1994, 2006) ; 19. Zinga (Suc ine´dit) ; 20. Eraclea Minoa (Suc ine´dit) ; 21. Racalmuto (Bertini et al., 1998) ; 22. Capodarso (Suc et al., 1995b) ; 23. Chomateri 2 (Mettos et al., 2000) ; 24. Prosilio (Biltekin, ine´dit) ; 25. Nestos 2 (Drivaliari, 1993 ; Jime´nez-Moreno et al., sous presse) ; 26. Ravno´ Pole (Drivaliari, 1993 ; Jime´nez-Moreno et al., sous presse) ; 27. Drevonets C1 (Ivanov et al., 2002 ; Jime´nez-Moreno et al., sous presse) ; 28. DSDP Site 380A (Popescu, 2006) ; 29. Gan Yavne 5 (Drivaliari, 1993) ; 30. Naf 1 (Drivaliari, 1993; Fauquette et al., 2006). E. Carte de ve´ge´tation potentielle pour le Messinien obtenue par interpolation des donne´es polliniques (les e´cosyste`mes a` halophytes ont e´te´ inte´gre´s dans les e´cosyste`mes herbace´s). F. Densite´ en herbace´es pour le Messinien obtenue par interpolation des donne´es polliniques (exprime´e dans une gamme de tons bruns clairs a` sombres selon le pourcentage relatif des herbes).
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impact of a complete desiccation under the present-day other boundary conditions. The discrepancy between the northern part with forests and the Southern one with open landscapes is striking, either in the potential palaeovegetation map simulated by CARAIB (Fig. 2(A2)) or in that provided by the interpolation method (Fig. 3(E)). In both maps, tree vegetation is mostly present Northward from the septentrional Mediterranean shoreline. The Southern part of the studied area is largely dominated by xerophytes including open landscapes, especially steppes except in the Nile hinterland where it was a savannah-type vegetation (Fauquette et al., 2006). These more humid open plant ecosystems in the Southeastern Mediterranean region are consistent with some forest cover in Israel probably because of some influence of the Asian monsoon transferring intensified moisture over the Southeastern Mediterranean area (Griffin, 2002). On these points, pollen results agree with the CARAIB simulation for Northwestern Africa but disagree for Northeastern Africa where semi-desertic conditions are predicted. However, a quite large agreement concerns the Northwestern Mediterranean, which was covered by subtropical to warm-temperate forests as also supported by macrofloras such as that of Murviel-le`s-Be´ziers (Roiron and Ambert, 1990). In addition, some details are very consistent like the presence of mid- to high-altitude vegetation in the Balkans region.
5. Discussion The CARAIB simulation as the interpolation method display palaeovegetation maps where homogeneity prevails to the South and a mosaic vegetation-type to the North (especially in the Northeastern Mediterranean) as today. Probably the relief distribution forced such an organization as much as the climate. As the CARAIB potential palaeovegetation map (Fig. 2(A2)) produces only one subtropical forest grid cell on the Northwestern part of the desiccated Mediterranean, it demonstrates that the water amount is insufficient to install subtropical trees in the Northern part although temperature conditions are attested. The water parameter considers among others, precipitations, soil water and runoff. In the model, soil water is the most important water parameter influencing vegetation distribution. It is calculated from a hydrological budget based on the precipitation amount and the evaporative conditions. Concerning the North Mediterranean side, the temperature range may reveal selectively such subtropical vegetation, but soil water becomes the limiting factor. Northwards, when precipitation amount is sufficient, temperature level is failing. Around the desiccated Mediterranean, the most representative vegetations produced by CARAIB are warm-temperate mixed forests. This kind of vegetation is close to the Mediterranean xerophytic one. This is in agreement for the Western part with the interpolated vegetation map where Mediterranean xerophytes are present from Spain to the North Africa coastline.
Finally, the CARAIB potential palaeovegetation map produces also only one cool-temperate conifer forest grid cell located in the Balkans in agreement with the interpolated vegetation map. The latitudinal severe (and less drastic in longitude in the Southern Mediterranean) contrast in climate and the observed vegetation could contribute to explain why many deep and long fluvial canyons were cut all around the North Mediterranean margin during the desiccation phase at the difference of the Southwestern margin where only a more widespread and relatively less intense erosion occurred (Corne´e et al., 2005). In the North, the humid climatic conditions and the extensive forest cover benefited channelled water transport through river streams. On the contrary, in the Southwestern Mediterranean, steppe vegetation advantaged a spread runoff, considerably reduced because of the xeric climatic conditions. However, in the Southeastern Mediterranean region, intense channelled fluvial erosion again occurred because of long drainage basin in latitude reaching Central Africa (Sahabi canyon: Barr and Walker, 1973; Griffin, 2002; Nile canyon: Chumakov, 1973; Barber, 1980) where more humid conditions existed (Griffin, 2002), as also attested by a savannah-like relatively more dense vegetation cover (Fauquette et al., 2006). The Messinian evidences of the Avicennia mangrove are among the last ones in the Mediterranean region. This coastal ecosystem persisted in the Black Sea area up to at least 4 Ma (Popescu, 2006). In the Rifian Corridor and in Sicily, this residual mangrove coexisted with a very xeric and scattered vegetation as it is today along the Red Sea and the Persian Gulf under subdesertic conditions. Along the Black Sea, the ultimate refuge of the Avicennia mangrove is at such high latitude, the land is also covered by a relatively open vegetation surrounded by forests. The Tortonian vegetation simulated by Franc¸ois et al. (2006) using the CARAIB model based on climate reconstruction by the ECHAM4/ML atmospheric general circulation model shows a similar latitudinal contrast in vegetation (forests to the North, open vegetation to the South), but at a higher level in humidity for both environments. Two simulations were proposed, testing low and high level in CO2, respectively. The first condition shows the development of temperate mixed forests to the North in opposition to grasslands and semi-desert to the South. The second condition proceeds in advantaging strengthening of tropical vegetation (seasonal forest Northwards and savannah Southwards). The first situation (low CO2 level) appears more consistent with the Tortonian pollen records from the Western Mediterranean and the related palaeoclimate quantification (Fauquette et al., in press). It is also in better agreement with climate quantification for Southeastern Europe according to macro- and pollen floras (Bruch et al., 2006). In addition, this CARAIB Tortonian simulation does not display important discrepancies with the Messinian one that is reported in this paper (Fig. 2(A2)) and which appears as resulting from the previous situation if the Mediterranean Sea disappeared. We conclude that the Messinian interpolated vegetation map from pollen records (Fig. 3(E)) should be considered as an intermediate situation between the Tortonian
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simulated vegetation at low CO2 level and the simulated vegetation during the almost complete desiccation of the Mediterranean Sea. However, this last step is to be considered with caution, since the model has neglected the negative elevations that would have resulted from the desiccation of the Mediterranean Sea, This situation, corresponding to a very shallow sea, is in conflict with the palaeobiological records (Hsu¨ et al., 1973, 1978) and the depths of canyons cut during the desiccation phase (Clauzon, 1973; Chumakov, 1973). The desiccation of such a deep sea should have produced very dry and warm environments in its deeper parts where salt deposited. Several similarities exist with the palaeoecosystem maps drawn by Kovar-Eder et al. (2006) even if they focus on the Northeastern Mediterranean region and consider only plant macroremains for a relatively long time-interval (7–4 Ma): broad-leaved evergreen forests developed in the Northeastern Mediterranean, broad-leaved deciduous ecosystems extended more Northwards, and sclerophyllous vegetation grew in the Southernmost Greek Peninsula. Unfortunately, the comparison cannot be extended to the mountainous ecosystems, which are not considered in Kovar-Eder et al.’s study (2006). 6. Conclusion During the Messinian, temperature was on the whole 28 C higher than the present-day, allowing subtropical and warmtemperate vegetation types in the North Mediterranean region. The simulated and interpolated palaeovegetation maps are in good agreement concerning the high contrast between the North (forest vegetation) and South (open vegetation) Mediterranean region. However, the interpolated vegetation map and the simulated one represent two successive steps within the Messinian salinity crisis: the first one may illustrate the period just preceding the complete desiccation phase which includes the marginal evaporitic event; the second one illustrates somewhat the complete desiccation reduced to that of a shallow sea. Because it is validated by a present-day assessment at the scale of France, that is a highly diversified territory from the vegetation viewpoint, the interpolated palaeovegetation map can be used to validate or improve simulations provided by the CARAIB model, taking into account the discrepancies pointed out between the LMD simulation and the ‘‘Climatic Amplitude’’ transfer function about the level in moisture. As the Southern Mediterranean appears covered by an almost homogenous open vegetation (steppe to the West, savannah to the East), the Northern Mediterranean landscapes were, as today, significantly influenced by relief resulting in a mosaic organization of the vegetation. The transition from forest to open vegetation seems progressive in the Iberian Peninsula, while it appears rather sharp in the other peninsulas. Relief is suggested to have been at that time more elevated in the Dinarides–Balkans Chain than in the Southern Alps. Finally, the larger number of Messinian fluvial canyons along the Northern Mediterranean shoreline than in the Southern one may have some explanation in the density of the vegetation cover which favoured channelled water flow in the septentrional forest environments at the
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difference of the widespread runoff in the Southern region, a phenomenon also emphasized by the contrast in precipitation. The interpolated Messinian vegetation map may appear as an intermediate step between the Tortonian simulated vegetation and the map simulated for the Mediterranean desiccation step, with uncertainties related to the depth of the desiccated basin which has not been considered for modelling. Acknowledgements The authors are indebted to palynologists who provided their Messinian pollen data (A. Bertini, N. Bachiri Taoufiq, S. Warny, M.-J. Perez Villa, S.-M. Popescu and D. Biltekin). Some colleagues helped us in collecting mosses (C. Poumot, L. Londeix, A. Lefort, S. Joannin, A. Schnitzler, V. Fernandez), some others offered present-day pollen spectra (V. Vergne, M. Clet, A.-M. Le´zine). Several present-day pollen spectra come from the European Pollen Database (author of most of them: J.L. de Beaulieu). The first author benefited from a grant provided by the EEDEN (ESF) Programme to develop the modelling approach. This paper is a contribution to the ECLIPSE (CNRS) Projects on the Messinian salinity crisis and the EGEO Project from the French ANR Programme. LF is research associate at the Belgian National Foundation for Scientific Research (FNRS). Part of this work was carried out while LF was visiting the ‘‘Centre de Recherches Pe´trographiques et Ge´ochimiques’’ (CRPG) in Nancy, France, under a research grant from CNRS and Re´gion Lorraine. A research grant from FNRS (‘‘Cre´dit aux chercheurs’’) is also gratefully acknowledged. Reviewers (P. Roiron and S. Klotz) are acknowledged for significantly improving the manuscript. Contribution UMR5125-07.011 and UMR 5554 n82007-0014. References Agustı´, J., Oms, O., Furio´, M., Pe´rez-Vila, M.-J., Roca, E., 2006. The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin). In: Agustı´, J., Oms, O., Meulenkamp, J.E. (Eds.), Late Miocene to Early Pliocene environment and climate change in the Mediterranean area, Palaeogeography, Palaeoclimatology, Palaeoecology 238, 129–189. Bachiri Taoufiq, N., 2000. Les environnements marins et continentaux du corridor rifain au Mioce`ne supe´rieur d’apre`s la palynologie. Thesis, University of Casablanca, Casablanca. Barber, P.M., 1980. Palaeogeographic evolution of the Proto-Nile delta during the Messinian salinity crisis. Ge´ologie Me´diterrane´enne 7, 13–18. Barr, F.T., Walker, B.R., 1973. Late Tertiary channel system in Northern Lybia and its implications on Mediterranean sea level changes. Initial Reports of the Deep Sea Drilling Project 13, U. S. Government Printing Office, Washington, 1244–1250. Bertini, A., 1994. Messinian-Zanclean vegetation and climate in North-Central Italy. Historical Biology 9, 3–10. Bertini, A., 2002. Palynological evidence of upper Neogene environments in Italy. Acta Universitatis Carolinae Geologica 46, 15–25. Bertini, A., 2006. The northern Apennines palynological record as a contribute for the reconstruction of the Messinian palaeoenvironments. Sedimentary Geology 188/189, 235–258. Bertini, A., Londeix, L., Maniscalco, R., Di Stefano, A., Suc, J.-P., Clauzon, G., Gautier, F., Grasso, M., 1998. Paleobiological evidence of depositional conditions in the Salt member, Gessoso-Solfifera Formation (Messinian Upper Miocene) of Sicily. Micropaleontology 44, 413–433.
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