ELSEVIER Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336

Climatic interpretation of terrestrial malacofaunas of the last interglacial in southeastern France

Denis-Didier Rousseau a,b,Ł, Jean-Jacques PuisseÂgur 1 a PaleÂoenvironnements et Palynologie, UMR CNRS 5554, Institut des Sciences de l'Evolution, Universite Montpellier II, place E. Bataillon, case 61, 34095 Montpellier cedex 5, France b Lamont-Doherty Earth Observatory of Columbia University, Palisades NY 10964, USA Received 25 September 1997; accepted 24 November 1998

Abstract

The sequence of the Ruisseau de l'Amourette, in the French Alps, covering the isotope stages 5e, 5d, 5c, and part of 5a and 6, was studied for terrestrial mollusks. Correspondence analysis of the mollusk assemblages permits reconstruction of temperature and moisture trends using knowledge of the modern ecology of the recognized . The classic environmental succession of the last Interglacial±Early Glacial (WuÈrmian) is recognized. The Eemian (Sub-stage 5e) suggests warm and moist conditions. It is followed by the cold Melisey I (Sub-stage 5d) showing moisture variation, from dry in the lower part to moist in the upper part. The mollusk equivalent of St. Germain I and II also indicates warm and moist conditions. The Melisey II stadial (Sub-stage 5b) is missing but may be re¯ected by the deposition of barren gravel layers. All these environmental oscillations agree with the ¯uctuations described in the literature. However, Stage 5e indicates a particular trend as the mollusks recorded two well individual cool events which seem to correspond to variations identi®ed in various west-European continental records. However, as no particular cold indicator species were identi®ed, these events cannot be related to strong climatic ¯uctuations as emphasized in the early studies of the Greenland GRIP ice-core or in North Atlantic and western European records.  1999 Elsevier Science B.V. All rights reserved.

Keywords: Eemian; terrestrial mollusks; paleoclimates; Alps; France

1. Introduction 1981; Alexandrowicz et al., 1984; Meijer, 1984; Alexandrowicz, 1985; Neck, 1985, 1989; Good- Previous analyses of mollusks in Holocene sec- friend, 1988, 1991; Nyilas and SuÈmegi, 1989; tions (Lozek, 1972, 1985; Piechocki, 1977; Keen, Limondin and Rousseau, 1991; Rousseau et al., 1993, 1994, 1998; Somme et al., 1994; Limondin, Ł Corresponding author. Fax: C33 67 042032; E-mail: 1995) yielded paleoclimatic information that could [email protected] be related to other paleoclimatic records. Older inter- 1 Before the completion of this paper, Dr. Jean-Jacques Puis- glacial materials are dif®cult to ®nd mainly because seÂgur died. All the material described in this paper is deposited soil pedogenesis generally dissolves the shells. How- at Montpellier, but is accessible upon request to DDR (denis @dstu.univ-montp2.fr). The coded data are archived in Boul- ever, in some particular cases, individuals can be pre- der on line at ftp:==.ngdc.gov=paleo=contributions_by_author= served, and provide enough material for paleocolog- rousseau1998= ical interpretations. This is the case in slope deposits

0031-0182/99/$ ± see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0031-0182(99)00021-8 322 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 323 as described by Lozek (1964) and PuisseÂgur (1976), determined assemblage. Such an index allows char- or in carbonate deposits such as tufa (Kerney et acterization of the structure of a given assemblage al., 1980; Alexandrowicz, 1985; Preece et al., 1986; and permits us to detect any changes affecting the as- Rousseau et al., 1992). Records that can be studied semblages. Additionally, the analysis of the species for the last interglacial are rare as the time resolution diversity allows us to de®ne assemblages relevant for is not generally as good as for the Holocene. environmental interpretations. The aim of this paper is to present results of Each count was also coded for multivariate analy- the statistical analysis of terrestrial malacofaunas, sis by transforming the values into abundance classes yielded by a well developed Quaternary sequence in on a logarithmic scale, following the method de- the French Alps. This record was not affected by scribed by Rousseau (1987). Such a coding retains erosion due to the glacier advance. The results will information on representative variations, while sup- be interpreted in relation to the recent published data pressing the differences between the well represented from both continental and marine records. and the poorly represented species. Correspondence analysis (Benzecri and Benzecri, 1980) applied to the mollusk data (see Rousseau, 1991; Rousseau et al., 2. Material and methods 1993) allows simultaneous study of mollusk assem- blages (represented by rows) and mollusk species The `Ruisseau de l'Amourette' section is located (represented by columns). This allows statistical in- in the TrieÁves basin (Fig. 1), a large depression terpretation of species behaviour in terms of eco- bordered by the Vercors Mountain to the west, the logical niches. Consequently, results from rows and Oisans Mountain to the east, the Devoluy Mountain columns can be plotted in a single diagram, fa- to the south and opens north to the Drac valley. cilitating environmental interpretation. This method This area was not affected by WuÈrmian glaciers has already been successfully applied to Quaternary (Montjuvent, 1978, 1980). However, an ice dam mollusk assemblages (Rousseau, 1986, 1987, 1991; blocked the valley behind which a lake formed and Rousseau and PuisseÂgur, 1989, 1990; Limondin and laminated clays were deposited. Rousseau, 1991; Rousseau et al., 1993; Rousseau 131 samples from a 46 m deep section composed and Kukla, 1994). The environmental interpretation of clays and silts were analyzed for pollen and mol- of the Ruisseau de l'Amourette mollusk assemblages lusks (Gremmen et al., 1984). All mollusk species is based on information on the current ecological were counted, and broken shells were included fol- tolerance of individual living species (thermal and lowing the method developed by Lozek (1964). For moisture requirements, and vegetation association) each mollusk assemblage, from one stratigraphical (Kerney and Cameron, 1979; Kerney et al., 1983). layer, the number of species was counted and the Indeed, all the recognized fossil species have modern Shannon index H 0 computed. The Shannon index counterparts exhibiting the same ecological charac- describes the diversity of a biological community teristics (Rousseau, 1989). using the formula: Both mollusk and pollen studies show two warm Xn intervals separated by a cold interval (Gremmen et 0 H D pk log2 pk al., 1984) (Fig. 2). This interpretation was accepted 1 later by de Beaulieu et al. (1992) when taking into where pk is the frequency of one species in one account the succession of the reconstructed vegeta-

Fig. 1. Ruisseau de l'Amourette sequence. (a) Map showing the location of the Ruisseau de l'Amourette sequence. (b) Detail of the geological area of the Ruisseau de l'Amourette sequence: 1 D substratum; 2 D Les Serres gravels; 3 D L'Amourette formation; 4 D glacio-lacustrine clays (WuÈrmian); 5 D lower terraces gravels (WuÈrmian); 6 D valley bottom in®lling (Holocene); 7 D WuÈrmian front moraines; 8 D area of ice-dammed lakes; Dev D Devoluy Mountain (modi®ed from de Beaulieu et al., 1992). (c) The Ruisseau de l'Amourette sequence. Numbering of the samples, and of the corresponding sections studied. Description of the lithology: 1 D calcareous gravels and pebbles; 2 D clay with macro-remains of plants and mollusks; 3 D sandy loam; 4 D shaly lignites with occurrence of lacustrine chalk and wood; 5 D dark shale (after Gremmen et al., 1984 modi®ed). 324 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 325 tion. Although they support the earlier chronology of diversity values. The high diversity is related to nu- Eemian to St. Germain I de®ned for the Ruisseau de merous ecological opportunities present in a forest l'Amourette sequence, de Beaulieu et al. (1992) state environment. On the contrary, open environments, that the ªpollen diagram is atypical leading to a veg- and especially those in northern Europe, or at high etation history peculiar to the southern Alpsº. This elevations offer fewer niches, resulting in a lower assumption is based on the high percentages of Pinus species diversity. In this case, the index values are (pine) during the early temperate phases of the Inter- low, between 1.5 and 2.5. However, low values are glacial and by the signi®cant role of Fagus (beech) also characteristic of assemblages that are affected associated with Carpinus (hornbeam) and Abies (®r) by problems in sediment deposition (Rousseau et al., during the late temperate phase of the Interglacial (de 1993). In ¯uvial deposits mollusk shells are gener- Beaulieu et al., 1992). Preliminary results of oxygen ally broken or dominated by aquatic taxa. isotope studies of mollusk shells from the Ruisseau de Several assemblages indicate a low diversity, as l'Amourette support this interpretation (Ch. Hannss, well as a low number of individuals, suggesting that oral commun.). Eight mollusk zones were recognized deposition conditions disturbed the distribution of (Figs. 3 and 4) according to the species composition the species among the assemblages (Fig. 4). This im- (Gremmen et al., 1984). The ®rst three are interpreted plies that such assemblages cannot be considered for as corresponding to the previous glacial period of a further ecological interpretations. On the other hand, Riss age. The fourth is a warm interval correlated with assemblages that show a low number of individuals the Eemian interglacial. This agrees with the pollen coupled with diversity values related to assemblages record (Fig. 2). A relatively cold phase (zones E and in natural conditions will be used for ecological F) overlies the Eemian, and in turn is followed by analyses. another warm interval, zone G, assumed to be the Following this procedure, the majority of sam- equivalent of St Germain I. This also is in agreement ples show a diversity index varying between 2.8 and with pollen data (Fig. 2). Gravel layers interrupt the 4.3. There are, however, three assemblages which sequence. They are overlain by sediments indicating show low values (0.63, 1.6 and 1.8) (Fig. 4). Such another warm interval, zone H, showing a truncated a distribution is in agreement with the occurrence upper part by early WuÈrm deposits. of environments ranging from cool (values tending to 2) to warm climate conditions (values tending to 4.3). Assemblages allocated to warm periods in 3. Results the earlier biostratigraphic study present the highest diversity values, although the lowest value of the Mollusk assemblages from the Ruisseau de whole sequence is recorded in mollusk zone G. One l'Amourette sequence reveal relatively high values can notice also that warm intervals show assem- of the Shannon index that seem to be in agreement blages with diversity values ¯uctuating between 1.8 with the earlier biostratigraphical interpretation for and 4. Cold assemblages also vary between 1.5 and interglacial assemblages (Rousseau et al., 1993). The 4 (Fig. 4). The correspondence analysis of the set of values vary between 0.5 and 4.5, indicating that sev- selected assemblages permits interpretation of these eral environmental variations occurred in the fossil variations (Figs. 5 and 6). sequence. The ®rst two axes explain 21.4% of the total vari- An earlier survey of modern mollusk assemblages ance, based on 98 samples containing 46 taxa recog- (Rousseau et al., 1993) indicates that mollusk assem- nized. If each taxon had a contribution equivalent to blages from forest environments show the highest the general variability, the theoretical value would be 1=46 D 0.022. Each taxon indicating higher values than this threshold is used for the interpretation of the results. Fig. 2. Simpli®ed pollen diagram of the Ruisseau de l'Amourette sequence (modi®ed from Gremmen et al., 1984). Plot of the The ®rst axis discriminates secale, Clausilia main arboreal taxa against depth. The non-arboreal taxa are not parvula, Pupilla muscorum, Vallonia costata, Punc- represented here. tum pygmaeum, Vertigo pygmaea, Vallonia pulchella, 326 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 iate analysis. The Âgur in Gremmen et al. (1984). Fig. 3. Simpli®ed mollusk diagram of the Ruisseau de l'Amourette against depth. The abundance scale used is a logarithmic one applied for the multivar mollusk zones are from Puisse D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 327

Fig. 4. Variation of the diversity index H 0 for the terrestrial assemblages plotted against depth. Mollusk zones and pollen biostratigraphy are from Gremmen et al. (1984). In temperate forest conditions, the values are generally varying above 3 (Rousseau et al., 1993).

Trichia hispida,andCochlicopa lubrica on the pos- The second axis discriminates on the positive side itive side (Table 1). These species mainly indicate Vertigo angustior, Vallonia enniensis, Succinea pu- open environment conditions. Species with high con- tris, Vallonia pulchella, Clausilia pumila, Vertigo an- tributions on the negative side of the ®rst axis corre- tivertigo, Carychium minimum, Cochlicopa lubrica, spond to Helicodonta obvoluta, Cochlostoma septem- Euconulus fulvus, Zonitoides nitidus, Acicula polita, spirale, Discus rotundatus, Azeca goodalli, Cepaea Vertigo genesii, Vitrina sp.(Table1).Thesediffer- sp., Aegopinella nitidula, Acicula polita, Aegopinella ent species indicate moist conditions. Vertigo genesii pura, Ena montana,andAcanthinula aculeata (Ta- that represents moist environments, also indicates ble 1). This second set groups together species that cold conditions when associated with Columella col- require a forest cover, or at least shading from trees umella or Pupilla alpicola. The negative side of the or bushes. Such discrimination is characteristic in the second axis groups Abida secale, Discus rotunda- multivariate analysis of assemblages of land snails. tus, Cochlostoma septemspirale, Helicodonta obvo- However, in the particular case of the Ruisseau de luta, Cepaea sp., Ena montana, Aegopinella nitidula, l'Amourette sequence, the open environment species Aegopinella pura, Azeca goodalli, Achantinula ac- do not include numerous so-called cold species, those uleata. (Table 1). The highest contribution is due to that now live in the Arctic tundra, or at high elevations Abida secale. All these taxa characterize dry environ- above the tree-line. ments. In the study of Quaternary snail assemblages 328 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336

Fig. 5. Correspondence analysis of the Ruisseau de l'Amourette malacofaunas. Plot of the species on the ®rst factor plane (axes 1±2). The arrows indicate how the species explain the variability of the general data set. Black arrows indicate the highest contributions while white arrows show high values. Determination of temperature and moisture gradients by 40ë rotation of the factors. The codes of the species correspond to those indicated in Table 1. from northern France, PuisseÂgur (1976) indicated the boundary conditions are represented among the that particular mollusk assemblages occurred during mollusk assemblages of a given fossil sequence, the transitional times, i.e. Late Glacial, that were mainly ®rst axis opposes cold (i.e. arctic or steppe environ- characterized by substantial numbers of individuals ments) and temperate (i.e. forests) conditions, while of Abida secale. the second axis opposes xeric (i.e. dry grasslands) The distribution of the different species on the and damp (i.e. swamp) conditions (Rousseau, 1987). ®rst factor plane (Fig. 5) shows that the forest or Thus, the lack of one boundary condition leads to the open-forest species are plotted together in the third interpretation of the multivariate analysis in terms of quadrant (1 2). The other taxa indicating open climatic gradients, both `temperature' and moisture environmental conditions are plotted following a fan after a rotation of the ®rst two axes. shape with moist species on one hand opposed to dry We took the forest pole as a reference point for ones on the other hand. the rotation by 40ë because it is best expressed in The distribution of the mollusk assemblages in the the analysis (Fig. 6). Species characteristic of for- correspondence analysis (Table 2) resembles that of est environment are also well grouped on the third the species (Fig. 6). However, it presents an L-shape, quadrant (1 2). Subsequently, we calculated the characteristic of the Guttman effect indicating a re- coordinates of the assemblages (Table 2) and by lationship between the two axes. Such a distribu- taking into account both their stratigraphic position tion has already been described for other mollusk and diversity index value, we extracted two relation- sequences in which either extreme temperature or ships, one representing `temperature' changes and moisture conditions were lacking. Indeed, when all the other the moisture trend. The temperature label D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 329

Fig. 6. Correspondence analysis of the Ruisseau de l'Amourette malacofaunas. Plot of the mollusk assemblages on the ®rst factor plane (axes 1±2). Determination of temperature and moisture gradients by 40ë rotation of the factors. is used better as an indication of climatic changes a warming trend appears. This is in agreement with as the mollusk trend in this case has been shown to the interpretation of the pollen samples of this inter- compare well to the marine δ18O record (Rousseau val as an equivalent of Melisey I according to the and PuisseÂgur, 1990). pollen stratigraphy, and corresponds to isotope Sub- The interpreted temperature values show marked stage 5d. The interval from 14 to 5 m depth, mollusk variations from temperate to cold conditions (Fig. 7). zone G, shows marked variations, ranging from cold The lower part of the sequence (between 46 and 38 to temperate, similar to the `Eemian' mollusk zone m; mollusk zones A, B and C) represents cold condi- D. The temperate conditions are preceded and fol- tions, which would agree with the assumption of its lowed by cold and cool peaks. This mollusk zone late Riss age. The Eemian interval (between 38 and was interpreted as corresponding to the equivalent of 28 m; mollusk zone D) shows overall temperate con- St Germain I in the pollen Grande Pile stratigraphy ditions which are interrupted by two cool episodes or marine isotope Sub-stage 5c. The uppermost mol- named C1 and C2 (Fig. 7). These cool intervals are lusk zone H, between 4 and the top of the sequence, suf®ciently marked to be considered in the discus- once again shows particularly temperate conditions sion. They were named C for cool and numbered 1 similar in magnitude to those indicated during the and 2 according to their occurrence in the chronol- mollusk zones D (Eemian) and G (St Germain I). In ogy of the sequence. They apparently are not related the earlier biostratigraphical study, PuisseÂgur (Grem- to any other record because of the lack of reliable men et al., 1984) interpreted this zone as being the absolute dates. The following interval (between 28 mollusk equivalent of the Grande Pile St Germain and 14 m; mollusk zones E and F) indicates cold II. The gravels separating zones G and H would cor- conditions with minor ¯uctuations. Towards the top respond in this case to marine Sub-stage 5b (or to 330 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336

Table 1 the Melisey II interval in the Grande Pile chronol- Correspondence analysis of the malacological samples from the ogy). Ruisseau de l'Amourette The moisture variations in biozones A, B and Species Code Factor 1 Factor 2 C relate to dry conditions with minor ¯uctuations species (Fig. 7). On the contrary, mollusk zone D, of Eemian Acicula polita s002 0.142 0.152 age, shows a moister environment. However, one can Carychium minimum s004 0.251 note that the two cool episodes recognized in the Carychium tridentatum s005 `temperature' curve are different. The ®rst one, C1, Succinea oblonga s009 0.025 is drier than the second one, C2, which presents the Succinea putris s010 0.468 Azeca goodalli s015 0.302 0.141 moistest values of the sequence (Fig. 7). The follow- Cochlicopa lubrica s016 0.113 0.225 ing cold interval, mollusk zones E and F, suggests Vertigo antivertigo s022 0.383 the driest conditions of the sequence with the occur- Vertigo substriata s023 0.095 rence of mollusks characteristic of steppe conditions. Vertigo pygmaea s024 0.213 0.048 This is in agreement with the general interpretation Vertigo moulinsiana s025 Vertigo genesii s026 0.118 of marine Sub-stage 5d. The second part of this in- Vertigo angustior s028 0.024 0.701 terval sees a return to intermediate (from a statistical Orcula doliolum s030 point of view, i.e., centre of the axis) conditions. Abida secale s032 3.387 1.075 The `temperate' intervals corresponding to mollusk Pupilla muscorum s033 0.341 zones G and H are mainly corresponding to moist Vallonia costata s038 0.328 Vallonia pulchella s039 0.171 0.442 conditions presenting some minor ¯uctuations. Vallonia enniensis s040 0.033 0.524 Acanthinula aculeata s043 0.108 0.101 Ena montana s045 0.121 0.288 4. Discussion Ena obscura s046 Punctum pygmaeum s047 0.329 Discus rotundatus s049 0.435 0.813 The results of the multivariate analysis support Vitrina sp. s051 0.042 0.121 the biostratigraphic interpretation of the mollusk as- Vitrea subrimata s054 0.035 0.083 semblages. Biozones A, B, and C correspond to the Vitrea contracta s056 0.027 upper part of the penultimate glaciation. Mollusk Nesovitrea hammonis s058 zone D is the mollusk equivalent of the Eemian ac- Aegopinella pura s059 0.138 0.180 Aegopinella nitidula s060 0.230 0.274 cording to pollen data, or marine isotope Sub-stage Oxychilus sp. s067 5e. Mollusk zones E and F are indicative of cold con- Zonitoides nitidus s068 0.180 ditions and are interpreted as the mollusk equivalent Euconulus fulvus s069 0.036 0.207 of pollen zone Melisey I, or marine isotope Sub- Clausilia parvula s079 1.456 0.815 stage 5d. Mollusk zone G is the mollusk equivalent Clausilia bidentata s080 Clausilia pimila s082 0.036 0.388 of the St Germain I or Sub-stage 5c. Perforatella bidentata s094 0.030 0.025 Finding a mollusk sequence which relates to the Trichia hispida s097 0.150 0.093 pollen stratigraphy during marine isotope Stage 5 is Euomphalia strigella s099 0.049 0.073 of great importance as no similar record has been Helicodonta obvoluta s100 0.653 0.450 found in western Europe. However, mollusk data Arianta arbustorum s101 Helicigona lapicida s102 0.090 0.058 render additional information of interest. Capaea sp. s104 0.302 0.341 First, the Eemian interval, which was recognized Cochlostoma septemspirale s121 0.526 0.681 also by the pollen content (Gremmen et al., 1984), Limax sp. s136 shows a particular and complex trend with the occur- Monacha sp. s173 0.034 0.022 rence of two cool episodes with a different climatic Percentage of variance 12.15 9.24 signature. This is also expressed in the pollen dia- Signi®cant contributions (higher than the theoretical threshold D gram through the percentages of arboreal taxa. C1 is 1=46) of species to the explanation of the variability of the data expressed by a decrease in Alnus and Quercus and set according to the ®rst two factors. Positive and negative signs the appearance of Abies whereas C2 shows a strong indicate the location on the axes. Codes of the species used in the factor plane diagram. D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 331

Fig. 7. Time series of mollusk assemblages from the Ruisseau de l'Amourette sequence on the temperature and moisture gradients against depth. The values correspond to the variability of the general data set along the gradients. C1 and C2 indicate the occurrence of the two recognized cool Eemian events. decrease in Alnus, Quercus, Corylus, Carpinus by et al. (1994) also indicate the occurrence of two high values of Abies (Fig. 2). The ®rst one, C1, at the environmental variations during the Eemian in the base of the interval is cool and dry. The second peak, French Massif Central. They are both recorded in C2, is cool and moist. The recognition of these two the magnetic susceptibility and in the pollen signals cold episodes is of particular importance as similar and are interpreted as related to the GRIP record. events were described from the GRIP Greenland ice- Finally, when calibrating the pollen record of La core as cold events, and named 5e4 and 5e2 (GRIP Grande Pile sequence with both the beetles and the members, 1993). New analyses of the CH4 record organic matter studied in parallel, Guiot et al. (1993) of the GRIP ice-core indicate that these events are indicated the occurrence of a cold spell in the early related to older ice inserted into the Eemian interval, Eemian temperature estimates by including Taxus in implying that these cold spells are invalid (Chappel- the considered taxa for transfer function. Moreover, laz et al., 1997). The discussion nevertheless remains the deciduous percentages during the Eemian at La open as North Atlantic DSDP 609 (Broecker et al., Grande Pile indicate a ®rst cold spell in the lower 1990), NA87-25 (Cortijo et al., 1994), Norwegian part due to the development of the Taxus forest. This Sea V27-60 (Cortijo et al., 1994) also indicate one or is in agreement with the last temperature reconstruc- two cooling events during Sub-stage 5e in the North tion by Guiot et al. (1993). On top of the Grande Pile Atlantic. Lauritzen (1995) also described an unsta- Eemian, the deciduous trees drastically and quickly ble isotope record from Stage 5e from Norwegian recede (Woillard, 1979) during a second cold and speleothems. He recognized two sharp variations rapid event described by Woillard and known in the in the isotopic signal that he interpreted as related literature as the `Woillard event' (Kukla et al., 1997). to the GRIP Eemian events. In northern Denmark, It is not the purpose of this paper to discuss the Seidenkrantz and Knudsen (1997) indicate the evi- reliability of the Greenland ice-core and the other dence of two major environmental and hydrological marine and western European continental records changes during the Eemian from both benthic fora- which indicate cold events during the Eemian. How- minifera and stable isotopes. Southwards, Thouveny ever, if these events did in fact occur, it is truly 332 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336

Table 2 Correspondence analysis of the malacological samples from the Ruisseau de l'Amourette

Sample Depth (m) CTR1 CTR2 F1 F2 rF1 rF2 M058 0.69 0.023 0.041 0.754 0.878 1.157 0.013 M059 1.11 0.079 0.108 1.214 1.240 1.730 0.133 M060 1.29 0.201 0.356 0.867 1.008 1.329 0.016 M061 2.44 0.068 0.353 0.314 0.175 M062 2.69 0.168 0.151 0.773 0.640 0.987 0.181 M065 4.02 0.030 0.064 0.472 0.603 0.765 0.026 M066 4.30 0.039 0.046 0.476 0.449 0.650 0.076 M067 4.47 0.028 0.066 0.288 0.388 0.482 0.029 M068 5.21 0.018 0.161 0.579 0.340 0.495 M069 5.45 0.053 0.008 0.314 0.246 0.196 M070 5.70 0.112 0.015 0.528 0.395 0.351 M071 5.98 0.034 0.011 0.440 0.218 0.450 0.197 M072 6.50 0.094 0.089 0.562 0.373 0.429 M073 6.75 0.023 0.024 0.153 0.133 0.080 M074 7.03 0.188 0.040 0.090 0.170 M075 7.27 0.011 0.028 0.133 0.182 0.225 0.015 M076 7.58 0.023 0.129 0.196 0.067 0.225 M077 7.87 0.300 0.012 0.680 0.529 0.428 M078 8.11 0.013 0.059 0.157 0.082 0.146 M079 8.43 0.068 0.188 0.656 0.623 0.278 M080 8.67 0.050 0.017 0.469 0.236 0.482 0.208 M081 8.98 0.260 0.123 0.673 0.404 0.742 0.256 M082 9.27 0.307 0.162 0.615 0.389 0.693 0.221 M083 9.55 0.225 0.701 0.684 1.054 1.247 0.154 M084 9.86 0.102 0.033 0.554 0.273 0.565 0.249 M087 10.70 0.187 0.734 0.036 0.444 0.585 M088 10.98 0.011 0.204 0.154 0.584 0.348 0.493 M089 11.19 0.091 0.119 0.374 0.210 0.332 M091 11.64 0.028 0.029 0.418 0.372 0.016 0.559 M092 11.75 0.195 0.027 0.877 0.285 0.782 0.489 M093 11.99 0.164 0.094 0.568 0.496 0.293 M094 12.27 0.457 0.117 0.817 0.701 0.436 M095 12.59 0.226 0.019 0.732 0.549 0.485 M096 12.94 0.283 0.027 0.877 0.654 0.584 M097 13.25 0.426 0.158 0.885 0.576 0.690 M098 13.53 0.019 0.156 0.263 0.651 0.330 0.620 M099 13.88 0.038 0.056 0.466 0.321 0.342 M100 14.23 0.029 0.301 0.645 0.301 0.645 M101 14.62 0.013 0.029 0.112 0.145 0.039 0.179 M102 14.86 0.018 0.177 0.042 0.146 0.109 M103 15.18 0.014 0.117 0.519 0.473 0.244 M106 15.77 0.065 0.677 0.290 0.816 0.812 0.302 M107 16.09 0.071 0.138 0.515 0.626 0.811 0.008 M108 16.40 0.110 0.085 0.516 0.396 0.635 0.141 R648 19.20 0.039 0.047 0.610 0.498 0.356 R650 19.69 0.056 0.241 0.594 0.610 0.197 R651 20.01 0.037 0.043 0.433 0.404 0.588 0.072 R652 20.29 0.050 0.253 0.535 0.572 0.150 R653 20.60 0.039 0.015 0.406 0.218 0.428 0.171 R654 20.81 0.319 0.019 1.153 0.245 0.553 1.041 R655 21.09 1.083 0.452 2.717 1.531 0.574 3.065 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 333

Table 2 (continued)

Sample Depth (m) CTR1 CTR2 F1 F2 rF1 rF2 R656 21.41 0.420 0.038 1.557 0.407 0.689 1.454 R657 21.58 0.607 0.146 2.753 1.180 0.866 2.867 R529 25.25 0.171 0.957 0.001 0.614 0.734 R530 25.46 0.454 0.114 1.844 0.805 0.569 1.930 R531 26.97 1.221 0.404 1.953 0.980 0.505 2.126 R532 27.28 0.821 0.261 1.570 0.772 0.418 1.699 R533 27.56 0.146 0.026 0.585 0.215 0.211 0.586 R534 27.88 0.086 0.499 0.020 0.305 0.395 R535 28.12 0.064 0.021 1.268 0.636 0.328 1.380 R536 28.40 0.031 0.686 0.040 0.410 0.551 R537 28.72 0.192 0.184 0.730 0.624 0.947 0.158 R538 29.03 0.200 0.171 0.559 0.450 0.704 0.139 R539 29.28 0.059 0.109 0.582 0.693 0.905 0.000 R540 29.56 0.059 0.109 0.582 0.693 0.905 0.000 R541 29.80 0.069 0.196 0.700 0.410 0.600 R547 31.41 0.018 0.081 0.335 0.620 0.260 0.655 R410 31.52 0.053 0.097 0.426 0.500 0.109 0.648 R415 32.74 0.186 0.213 0.941 0.584 0.768 R417 33.06 0.036 0.033 0.457 0.379 0.003 0.594 R419 33.47 0.081 0.070 0.525 0.426 0.664 0.128 R420 33.65 0.100 0.269 0.142 0.250 R421 34.00 0.038 0.021 0.566 0.367 0.645 0.198 R422 34.17 0.090 0.113 0.748 0.733 1.042 0.102 R424 34.59 0.227 0.251 0.880 0.806 1.183 0.156 R425 34.77 0.062 0.175 0.481 0.707 0.851 0.086 R301 36.52 0.063 0.263 0.669 0.682 0.229 R302 36.83 0.039 0.073 0.384 0.455 0.595 0.002 R303 37.11 0.017 0.310 0.023 0.182 0.252 R305 37.46 0.098 0.316 1.367 0.844 1.121 R307 37.99 0.092 0.181 0.540 0.297 0.486 R308 38.16 0.046 0.076 0.448 0.392 0.230 R208 38.34 0.275 0.119 0.268 0.134 R207 38.65 0.079 0.016 0.531 0.206 0.499 0.274 R206 38.93 0.036 0.014 0.816 0.449 0.868 0.336 R205 39.25 0.048 0.245 0.738 0.723 0.287 R204 39.56 0.024 0.123 0.339 0.339 0.124 R203 39.84 0.162 0.166 0.932 0.822 0.031 1.242 R202 40.12 0.121 0.054 0.674 0.391 0.134 0.768 R201 40.44 0.107 0.556 0.014 0.347 0.435 R101 42.05 0.020 0.011 0.245 0.157 0.037 0.289 R102 42.36 0.091 0.615 0.084 0.460 0.417 R103 42.68 0.068 0.055 0.919 0.723 0.037 1.169 R104 43.06 0.035 0.808 0.236 0.339 0.771 R105 43.41 0.065 0.013 0.904 0.348 0.314 0.916 R107 44.57 0.014 0.042 0.322 0.491 0.583 0.069 R108 44.81 0.070 0.105 0.448 0.480 0.656 0.035 R109 45.27 0.067 0.023 1.001 0.510 0.253 1.095

Signi®cant contributions (higher than the theoretical threshold D 1=98) of the terrestrial assemblages to the explanation of the variability of the data set according to the ®rst two factors (CTR1, CTR2). Positive and negative signs indicate the location on the axes. Coordinates of the assemblages on the ®rst two factors (F1, F2), and on the two climatic gradients (rF1, rF2) after a rotation of 40ë of the axes. 334 D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 amazing that they would seem to have a reduced dis- 5. Conclusions tribution limited to the North Atlantic and western Europe. Recent investigations from the Nordic Seas The multivariate analysis of the mollusk record (Norwegian, Iceland and Greenland seas) by Fron- from the Ruisseau de l'Amourette sequence indi- val and Jansen (1997) support such interpretation cates several major oscillations, in agreement with indicating that the sea-surface temperature of the the pollen record, that do not correspond to local Norwegian±Iceland Sea was less stable during the changes. However, during isotope Sub-stage 5e, two Eemian interglacial indicating marked shifts. Con- cool events are characterized. The moisture analysis cerning the Ruisseau de l'Amourette record, the lack shows that these two cool Eemian events were dif- of species indicating cold environments, i.e. Col- ferent, with the ®rst one dry and the second moister. umella columella, Vertigo genesii, Pupilla alpicola, These events could be interpreted as the equivalent which occur presently at high elevations in the Alps of cold events recognized in other continental se- (Kerney and Cameron, 1979), leads us to better in- quences corresponding to different locations: in the terpret the cool events recognized in the Alps as GRIP ice-core and in western European records. regional variations. Such interpretation is reinforced The lack of any cold indicator species during these by the lack of any physical dates and would agree particular events suggests that may re¯ect local envi- with the Southern Alps signi®cance of the pollen ronmental ¯uctuations. Despite the lack of any abso- diagram as noticed by de Beaulieu et al. (1992). lute time scale, the Ruisseau de l'Amourette section Recent reconstructions from mollusk assemblages in nevertheless shows a climatic sequence which is in a British late glacial-Holocene sequence also indi- agreement with the general interpretation of marine cated a signi®cant cooling event although the typical isotope Stage 5. cold indicator species did not occur (Rousseau et Similar events have been recorded in both high al., 1998). In that case, as in the Amourette se- and middle latitudes in Europe, from different envi- quence, the general composition of the assemblage ronmental contexts and biological and non-biologi- and the ratios between the different species counts cal proxy data. This suggests that these new results contribute to such reconstructions. Then the plac- from mollusk assemblages are mainly responses to ing of these particular events within the chronology changes in the macro-climate over Europe during the of the interglacial needs to be improved. The present past 130,000 years and subsequently further investi- results allow only hypothetical correlations with sim- gations are needed in this region. ilar events reported elsewhere as it was proposed for those characterized at the Lac du Bouchet (Thouveny et al., 1994). Acknowledgements The bipartition of the Melisey I interval is inter- esting because it resembles the succession described We would like to thank V. Lozek, R. Preece and from the GRIP Greenland δ18O record (GRIP mem- an anonymous reviewer for comments and criticisms bers, 1993). In that case, however, mollusk zone E about this paper, and Sonia and Greg Hamilton for would last three times longer than zone F. The fact improving the English. This work was supported by that the lower part of mollusk zone E is colder than the the CEC-EPOCH programme and an NSF-CNRS fel- upper part concurs with both marine and ice-core iso- lowship (DDR). This is ISEM (Institut des Sciences tope studies. Not surprisingly, Vertigo genesii, an Arc- de l'Evolution de Montpellier) contribution 98-051. tic indicator species (Kerney et al., 1983), only occurs during that peculiar interval. Mollusk zone G shows a simpler pattern of a temperate episode bracketed Appendix A by cold and cool intervals. This also agrees with the classical interpretation of marine isotope Sub-stage Coded values used for the correspondence analysis. Code of the 5c. Finally the marked warming at the end of mol- assemblages and depth (in metres) lusk zone H is in agreement with the climatic trend m1: Acicula polita; m24: Discus rotundatus; expressed at the base of marine isotope Stage 5a. m2: Carychium minimum; m25: Vitrina sp.; D.-D. Rousseau, J.-J. PuisseÂgur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321±336 335

m3: C. tridentatum; m26: Vitrea subrimata; Desert from 13C of shell organic matter. Nature 333, m4: Succinea oblonga; m27: Vitrina contracta; 757±760. m5: S. putris; m28: Nesovitrea hammonis; Goodfriend, G.A., 1991. Holocene trends in δ18Olandsnail m6: Azeca goodalli; m29: Aegopinella pura; shells from the Negev Desert and their implications for m7: Cochlicopa lubrica; m30: A. nitidula; changes in rainfall source areas. Quat. Res. 35, 417±426. m8: Vertigo antivertigo; m31: Oxychilus sp.; Gremmen, W., Hannss, Ch., PuisseÂgur, J.J., 1984. Die warmzeit- m9: V. substriata; m32: Zonitoides nitidus; lichen Ablagerungen am Ruisseau de l'Amourette (TrieÁves, m10: V. pygmaea; m33: Euconulus fulvus; franzoÈsiche Alpen). Eiszeitalter Gegw. 34, 87±103. m11: V. moulinsiana; m34: Clausilia parvula; GRIP members, 1993. Climate instability during the last inter- m12: V. genesii; m35: Cl. bidentata; glacial period recorded in the GRIP ice core. Nature 364, m13: V. angustior; m36: Cl pumila; 203±207. m14: Orcula doliolum; m37: Perforatella bidentata; Guiot, J., de Beaulieu, J.L., Cheddadi, R., David, F., Ponel, P., m15: Abida secale; m38: Trichia hispida; Reille, M., 1993. The climate in Western Europe during the m16: Pupilla muscorum; m39: Euomphalia strigella; last Glacial=Interglacial cycle derived from pollen and insect m17: Vallonia costata; m40: Helicodonta obvoluta; remains. Palaeogeogr., Palaeoclimatol., Palaeoecol. 103, 73± m18: V. pulchella; m41: Arianta arbustorum; 93. m19: V. enniensis; m42: Helicigona lapicida; Keen, D.H., 1981. The Holocene deposits of the Channel Islands. m20: Acanthinula aculeata; m43: Cepaea sp.; Rep. Inst. Geol. Sci. 81=10, 1±13. m21: Ena montana; m44: Cochlostoma septemspirale; Kerney, M.P., Cameron, R.A.D., 1979. A Field Guide to the Land m22: E. obscura; m45: Limax sp.; Snails of Britain and north west Europe. 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