Poster:
Abstracts book of 13th Congress RCMNS, 2-6 September 2009, Naples, Italy “Earth System Evolution and the Mediterranean Area”, 2-6 September 2009, Naples, Italy, Acta Naturalia de “L’Ateneo Parmense”, Parma: 45 (1): p.135.
Authors:
Speranta-Maria Popescu, Gonzalo Jiménez-Moreno, Jean-Pierre Suc.
Abstract:
The beginning of the Neogene coincides with a transient cooler climate event (Mi-1) as response to the intermittent expansion on the East Antarctic Ice Sheets (EAIS). The Miocene is characterized by warm and humid climate that implied the development of forest environments in Europe. The vegetation was composed mainly by tropical, subtropical and warm-temperate plants, which attempted the maximum of diversity during the Miocene Climate Optimum event (17-15 Ma). Reconstruction of climatic parameters, applied to our pollen records, indicates for the Northeastern Spain a Mean Annual Temperature (MAT) of about 19°C, a Mean Temperature of the Warmest month (MTW) around 24.5°C, a Mean Temperature of the Coldest month (MTC) around 7.5 °C, and Mean Annual Precipitations (MAP) between 900 and 1700 mm. Similar results were obtained from the Lower Miocene flora in Germany (MAT~14.1-20.8°C, MTW ~25.7 -28.1°C, MTC~4.7 -13.3 °C, and MAP ~897-1281 mm). Several cooling events (Mi-1 to Mi-7) related to the EAIS expansion are responsible for a progressive impoverishment in tropical and subtropical plants, which will be replaced by warm-temperate ones. The most important cooling event during the Miocene was the Monterey Cooling Event, responsible for the disappearance of the Avicennia mangrove from the Northwestern Mediterranean coastline. Paleoclimate reconstruction indicates a decrease in MAT of about 2-4°C during this event. However, Serravallian and Tortonian were characterized by relatively warm climate. Our pollen records point out the development of open vegetation in Southern Spain and Northern Africa, suggesting warm and dry regional conditions. In Central and Southern Europe, the vegetation is characterized by forest development, indicating a warm and humid climate in the region. Vegetation reconstruction during the Messinian is incomplete because of the lack of sediments during the peak of the Messinian Salinity Crisis (MSC). Ones must notice the persistence of some tropical elements at the Southern Mediterranean latitude before the peak of MSC, then the northward migration of subdesertic herbs and shrubs during the almost complete desiccation phase. The N–S gradient in temperature and xericity was pronounced during the Late Miocene. Open vegetation growing under warm and dry conditions developed in Southwestern Europe and North Africa, whatever the longitude while forests flourished northward under warm and humid conditions. Paleoclimatic reconstruction for the Late Miocene indicates warmer climate characterized by MAT between15 and 24°C, with a strong seasonality correlated with high precipitation values (1100 -1550 mm) in North Europe and respectively low seasonality and low precipitation values (320-680 mm) in Southwestern Europe and North Africa. Similar values of MAT and MAP were obtained using plant macroremains. The West Antarctic glaciations at 6 Ma probably caused the disappearance of the Avicennia mangrove from Southern Mediterranean coastlines. During the Early Pliocene (5.332 – 3.6 Ma), the climate was relatively warmer (MAT higher of about 1-5°C than today). Increases in humidity characterize the Central and Eastern Europe (MAP higher of about 400 -1000 mm than today), that promoted the development of forest vegetation in this area. This warm climate was interrupted by cooling events between (4.7 – 4.5 Ma) related to small fluctuations of EAIS. The pollen floras from the European Early Pliocene allow a refined geographic specification of the different kinds of reconstructed vegetation. The Northern Mediterranean area is characterized by dominance of arboreal pollen, suggesting a dense forest cover, on contrary to the South Mediterranean where herbs were prevalent. Such a contrast in landscape between the North and South Mediterranean regions is to be related to the latitudinal gradient in humidity. In the North Mediterranean area, the vegetation organization was also closely linked to the relief. Coastal plains were inhabited by Taxodiaceae swamps (Glyptostrobus) replaced in some places by marshes (herbs and shrubs). Several plant ecosystems can be distinguished according to the geographic location: “salt marshes” along the Atlantic coastline up to Northwestern Europe; marshes mostly composed of Cyperaceae (with some discontinuous Glyptostrobus swamps) evidenced along the Mediterranean coastline and in the Dacic and Euxinian basins. Peculiar mediterranean-like vegetation assemblages characterized the North Mediterranean coastal plains but Mediterranean xerophytes were only significantly represented in Catalunya and Sicily, where their assemblage resembles the modern thermo-mediterranean belt. In the Southeastern Mediterranean region, the open vegetation was composed of herbs including subdesertic elements. Close to mountains, vegetation was organized with respect to a wellmarked altitudinal gradient. The low altitude vegetation was composed of Taxodiaceae (Sequoia) while Cathaya and Cedrus dominated the mid-altitude belt. Abies and Picea developed in higher altitude. The Eastern Europe vegetation was characterized by coexistent warm-temperate forests and open ecosystems. Some tropical and subtropical elements were persisting. Mediterranean xerophytes were indentified in few amounts in the Dacic and Euxinian basins, showing a slight increase according to the latitudinal gradient. DSDP Site 380A (southwestern Black Sea) provides relatively high percentages of Artemisia growing in Anatolia, which increased again during the cooler periods. Anatolia probably represents the origin of the repeated steppe expansions which occurred in Europe at each glacial phase. Finally, the Nile region documents the presence of savannah including some subdesertic taxa while riparian forests preserved several tropical-subtropical elements. The Late Pliocene (3.6 – 2.558 Ma) is still too much poorly-documented and needs more attention as it represents the key-moment of the progressive transition from the “greenhouse” climatic context to the “icehouse” one. Finally, this is also a crucial time-window because it includes the warming centred at around 3.1 Ma which is generally pointed out as the best past analogue of the present-day warming up. During this time-interval, contrast in vegetation between the North and South European regions exaggerated while the thermic latitudinal gradient increased up to approximately reach the present-day value (0.6°C/° in latitude). The Late Pliocene Optimum Climatic (3.1 Ma) is characterized by MAT higher of 3°C as today. This warm episode could be explained by: (1) reduced terrestrial ice-sheets in the polar zones and sea-ice cover that caused a strong ice-albedo feedback, (2) changes in thermohaline circulation caused by the closure of the Panama Seaway, and/or (3) reduced albedo and increased atmospheric water vapour as a consequence of a permanent El Niño. The onset of the North Hemisphere Glaciations which marks the beginning of Pleistocene (2.558 Ma) is well- and completely documented by pollen data from the DSDP Site 380 which, in addition, provides a continuous record of all the glacial-interglacial cycles up to the Present. The transition from 41 to 100 kyr climatic cycles is here particularly welldocumented. This long pollen sequence also specifies the chronologic succession of extinctions of thermophilous plants in the Northeastern Mediterranean region.