Séverine Fauquette

Climate and biomes in the West Mediterranean area during the Pliocene

A new pollen-derived method of climatic quantification, based on the mutual climatic range of plant taxa, has been applied to 17 Pliocene pollen sequences in the West Mediterranean area. The latitudinal gradient observed in the pollen data was confirmed by the climatic reconstructions: there is a gradient from north to south both for temperatures and precipitation. At the beginning of the Pliocene (5.32–5 Ma), the climate in the North Mediterranean area was, on average, warmer and more humid than today (respectively 1–4oC and 400–700 mm). In the South Mediterranean region, the climate was both warmer and drier than today (respectively equal to or 5oC higher and drier or equal humidity). The pollen-based climate estimates were then used to reconstruct biomes for the region. The results show the occurrence of three biomes: the broad-leaved evergreen=warm mixed forest, the xerophytic woods/scrub biome and the warm grass/shrub biome. These biomes are still represented today in the Mediterranean region despite different thermic and water conditions.

A method for climatic reconstruction of the Mediterranean Pliocene using pollen data

Pollen data from numerous sites around the Mediterranean Sea indicate that several important vegetation and climatic changes occurred during the Pliocene. These data are in good agreement with pollen records from northwest Europe and with δ18O curves from Mediterranean and Atlantic deep-sea cores. Quantitative palaeoclimatic reconstructions from Pliocene pollen data of the Mediterranean region cannot be based on conventional modern analogue techniques, as individual Pliocene pollen spectra contain taxa representing temperate, warm-temperate and subtropical plants that do not grow together today. Instead, we propose a new method that uses a climatic amplitude method modified to take partially into account the relative abundances of the taxa. We applied this method to the Pliocene Garraf 1 palynological sequence from Catalonia, which provides a long continuous record of climatic change from 5.3 Ma to the Early Pleistocene. We estimate that annual temperatures were 1 to 5°C higher than today and the annual precipitation 400 to 1000 mm higher than today prior to the beginning of the late Cenozoic glacial–interglacial cycles. In contrast, temperature and precipitation both fell sharply during the glacial phases of the earliest glacial–interglacial cycles.

40Ar/39Ar dating of a tephra layer in the Pliocene Senèze maar lacustrine sequence (French Massif Central): constraint on the age of the Réunion–Matuyama transition and implications on paleoenvironmental archives

Abstract The sedimentary sequence cored in the Seneze maar (Velay, France) is very favourable for magnetostratigraphy of the Late Pliocene and for studying the paleoenvironmental changes that occurred during that period. The magnetostratigraphic studies revealed that the sediments from this lacustrine sequence were deposited during the Matuyama reverse period, except for the upper part where a short normal polarity episode was recorded. A tephra layer interbedded in the sediments contemporaneous with this normal polarity event is dated at 2.10±0.01 Ma by the 40 Ar/ 39 Ar method. Using this chronological marker, it can be inferred that the normal polarity episode recorded in the Seneze sequence corresponds to the Reunion event and that the age of the normal–reverse transition closing this event is ca. 2.09 Ma. These chronological constraints also permit to (1) demonstrate that the ‘Villafranchian’ mammal fauna found in the Seneze maar is younger than 2.09 Ma and (2) correlate the climatic events recorded in the Seneze sequence to the marine δ 18 O records. This suggests that the Seneze pollen sequence (5–120 m depth) ranges from isotopic stage 85 to 76.

Vegetation and climate since the last interglacial in the Vienne area (France)

Biomes and climate reconstructions are based on variations of the pollen content of the sediments. Pollen analysis was conducted on sediment deposits sampled at Chantemerle site (Vienne department, France). The pollen diagram covered only the last 7200 years BP. Consequently, additional pollen sequences, derived from the European Pollen Database, have been used to provide a first climate and biome reconstruction on a longer period, from the Riss (ca 140 ka BP) to the present-day. These pollen sequences show that the succession of the biomes and of the climate has been similar throughout a large part of France since about 140 000 years BP. However it is noteworthy that near the Atlantic coast, a warmer biome is recorded during the temperate periods: the warm mixed biome. This homogeneity allows us to extrapolate the results obtained from all these sequences to the Vienne region. The climate was warmer and more humid than today, or equivalent, during the Eemian, Saint-Germain I and Saint-Germain II. These periods were characterised by temperate deciduous or mixed forests with warmer episodes of warm mixed forests. On the other hand, climate was colder and dryer than today during the glacial phases (Melisey I, Melisey II, Wurm, Late Glacial) which were characterised by cold steppes andror tundra.

A new approach for palaeoaltitude estimates based on pollen records: example of the Mercantour Massif (southeastern France) at the earliest Pliocene

Abstract The altitude of the Mercantour Massif (Southern Alps, France) during the earliest Pliocene has been estimated using a new quantification method. Instead of classical methods using geomorphologic criteria, our method uses biogeographic and climatologic criteria: composition of the modern vegetation belts in the European and peri-Mediterranean mountains, and Pliocene annual temperature estimates obtained from fossil pollen data. The climatic transfer function indicates for the coastal earliest Pliocene of the studied area a mean annual temperature of 16.5°C. Such a temperature today occurs at 38.5°N latitude in the Mediterranean region. The relation established by Ozenda between the present-day vertical and latitudinal vegetation assemblages evidences a shift of, on average in Western Europe, 110 m in altitude per degree in latitude. As a consequence, it is possible, taking into account that the Pliocene lapse rate was almost similar to the modern one, to estimate the minimum altitude of the massif at the earliest Pliocene. The so-obtained palaeoaltitude estimate is close to that obtained with the geomorphological method: the Mercantour Massif was almost 2000 meters high at the earliest Pliocene.

What was the late Pliocene Mediterranean climate like; a preliminary quantification from vegetation

Reconstruction of the composition and organisation of the late Pliocene vegetation in central Mediterranean and quantification of the climatic requirements of its main representatives allow temperature and precipitation estimates during the late Pliocene glacial/interglacial cycles, at ca 2.4 Ma. The late Pliocene climatic glacial and interglacial conditions are illustrated on a bioclimagram which correlates the mean annual temperature and precipitation criteria. Comparison between modern and late Pliocene vegetation indicates that late Pliocene interglacial climate was approximately 4 degrees C warmer, with more higher amount of precipitation than today, and that conditions similar to modern ones prevailed during late Pliocene glacials.

High resolution climate and vegetation simulations of the Mid-Pliocene, a model-data comparison over western Europe and the Mediterranean region

Here we perform a detailed comparison between climate model results and climate reconstructions in western Europe and the Mediterranean area for the mid-Piacenzian warm interval ( ca 3 Myr ago) of the Late Pliocene epoch. This region is particularly well suited for such a comparison as several quantitative climate estimates from local pollen records are available. They show evidence for temperatures significantly warmer than today over the whole area, mean annual precipitation higher in northwestern Europe and equivalent to modern values in its southwestern part. To improve our comparison, we have performed high resolution simulations of the mid-Piacenzian climate using the LMDz atmospheric general circulation model (AGCM) with a stretched grid which allows a finer resolution over Europe. In a first step, we applied the PRISM2 (Pliocene Research, Interpretation, and Synoptic Mapping) boundary conditions except that we used modern terrestrial vegetation. Second, we simulated the vegetation for this period by forcing the ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems) dynamic global vegetation model (DGVM) with the climatic outputs from the AGCM. We then supplied this simulated terrestrial vegetation cover as an additional boundary condition in a second AGCM run. This gives us the opportunity to investigate the model’s sensitivity to the simulated vegetation changes in a global warming context. Correspondence to: A. Jost (anne.jost@upmc.fr) Model results and data show a great consistency for mean annual temperatures, indicating increases by up to 4 C in the study area, and some disparities, in particular in the northern Mediterranean sector, as regards winter and summer temperatures. Similar continental mean annual precipitation and moisture patterns are predicted by the model, which broadly underestimates the wetter conditions indicated by the data in northwestern Europe. The biogeophysical effects due to the changes in vegetation simulated by ORCHIDEE are weak, both in terms of the hydrological cycle and of the temperatures, at the regional scale of the European and Mediterranean mid-latitudes. In particular, they do not contribute to improve the model-data comparison. Their main influence concerns seasonal temperatures, with a decrease of the temperatures of the warmest month, and an overall reduction of the intensity of the continental hydrological cycle.

Subtropical climate conditions and mangrove growth in Arctic Siberia during the early Eocene

The early Eocene (ca. 56–47.8 Ma) was an interval of exceptional warmth with reduced pole-to-equator temperature gradients. Climate proxies indicate mean annual air temperatures (MATs) and sea-surface temperatures (SSTs) exceeding 8–18 °C and frost-free, mild winters in polar areas, features that have proven difficult to reproduce with the most elaborate climate models. A full appraisal of the early Eocene polar climate has been, however, limited by possible seasonal biases associated with geochemical proxies and the lack of data from the vast Eurasian Arctic. Here we present multiproxy data from lower-middle Eocene coastal plain sediments of the New Siberian Islands (Russia) showing that taxodioid Cupressaceae, palms, and the mangrove Avicennia grew in Arctic Siberia above 72°N under air temperatures averaging 16–21 °C annually and 5.5–14 °C in winter. Kaolinite contents are exceptionally high (up to 60% of clay assemblages) and comparable to those found in present-day subtropical soils formed under high mean annual precipitation (MAP >1000 mm) and warm (MAT >15 °C) conditions. The Avicennia pollen records the northernmost mangrove growth ever documented and indicates early Eocene SSTs exceeding 13 °C in winter and 18 °C in summer. Considering the high MAP estimated for Arctic Siberia and other pan-Arctic landmasses, we propose that the heat from warm river waters draining into the Arctic might have amplified early Eocene polar warmth. Our results provide the first climate constraints for the early Eocene of Arctic Siberia and support the view that most climate models underestimate polar warming in greenhouse conditions.

Reconstruction of the abiotic characteristics of past biomes: an example from the last glacial-interglacial cycle in France.

Abstract The abiotic conditions (soil properties, water balance) associated with terrestrial biomes in France during the last climatic cycle have been quantified using an indirect method. A set of potential modern climatic analogues across the world was first selected for each biome type. The edaphic features corresponding to the chosen analogue vegetation were then taken from a global soil database and attributed to the biomes. Finally, the hydrological parameters were simulated for these analogues using a vegetation model. We have identified five groups of modern analogues with either higher latitudes or higher elevations than the average present environment of France. From these five groups of analogues, the first two represent boreal forest, two others are steppic, and the last one represents tundra. The first group of analogues represents boreal forests at high latitudes (averaged latitude: 61° N, average elevation: 300 m) with mainly sandy podzolized soils and intermittent permafrost, high precipitation and rapid drainage. The second group of analogues represents boreal forests at higher elevations and lower latitudes (44° N, 2100 m) with stony soil and lower precipitation as well as poorer drainage. The first group of steppes at low elevations and high latitudes (64° N, 500 m) is characterized by cambisol or gleysol soils. The second group of steppes at high elevations and relatively low latitudes (41° N, 2900 m) has a hydrological regime with high evapotranspiration and poor drainage that is compatible with presence of xerosols and yermosols. The tundra group (57° N, 1400 m) has lithosolic, cambisolic and gleysolic soils. The approach used here can be applied on a global scale and could provide useful boundary conditions for simulating past climate with general circulation models.