Maurice Reille

Comparison of terrestrial and marine records of changing climate of the last 500,000 years

A broad correspondence between long pollen sequences and the deep-sea oxygen isotope record has been noted for some time, but there has been little effort to explore just how similar the two types of evidence are in terms of their overall structure on glacial-interglacial timescales and also how they may differ. These questions have profound importance both for how we view the stratigraphic record of changing climate in different regions and for our understanding of the climate system. Here we link the four longest European pollen records and derive a terrestrial sequence of vegetation events and a coherent stratigraphic scheme for the last 500,000 years. Comparison of the terrestrial and marine records shows good agreement, but it also reveals that the pollen sequences contain a higher degree of climate sensitivity than the oxygen isotope record. In addition, it suggests that neither an oxygen isotope record nor a Milankovitch-forced ice volume model may provide an appropriate template for fine-tuning the terrestrial record and that better chronologies will depend on an improved understanding of controls on sedimentation rates in individual sedimentary basins

The last climatic cycle at La Grande Pile (Vosges, France) a new pollen profile

A new pollen diagram has been made from an old unanalyzed core from La Grande Pile (GP XX). Correlations with the previous work of Woillard (1975–1978) leads to the following conclusions: the end of the Eemian was marked by a minor climatic change prior to the Melisey I stadial; the Ognon II and Ognon III interstadials are not consistent, and correspond to the level of reworking of mesophilous taxa during the last Pleniglacial; the limitations of the botanical interpretation of pollen spectra from the last Pleniglacial are underlined; lastly, Bruckenthalia and Larix are identified for the first time at La Grande Pile. The respective roles of these taxa following the Eemian are additional arguments for correlating the St-Germain I and II with the Early Weichsel interstadials in the north of middle Europe.

The climate in Western Europe during the last Glacial/Interglacial cycle derived from pollen and insect remains

Using the pollen sequence of La Grande Pile XX (France), we review problems with the application of transfer functions in paleoclimatic reconstructions. One of them is to find modern analogues for the herbaceous vegetation of the cold periods. We propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods. Another method to solve these problems is based on constraining by insect remains. The two methods provide coherent reconstructions. The results are also compared with other paleodata. There is a good correlation with the six cold Heinrich events between 70 and 15 ka B.P. A cooling event during the Eemian period (marked by high percentages of Taxas) at about 125 ka B.P. needs still to be correlated with high resolution ocean and ice cores.

An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe

Abstract Long continuous lacustrine sequences constitute on the continent a precious tool for coupling the long term continental environmental changes with deep sea and ice core records, using the ‘count from the top’ method. Moreover, they can contribute to long distance correlation on the continent itself and thus help to classify discontinuous sedimentary records. Palynostratigraphical correlation is proposed here between the Velay long sequence and the late Middle Pleistocene series from Central Europe with special attention to temperate episodes. The similarities between the Praclaux and the Holsteinian Interglacial suggest that they are both contemporaneous with marine isotopic stage (MIS) 11, even if absolute dates are still divergent. The evidence of two major warm periods with an interglacial type of vegetation between the Holsteinian and the Eemian is confirmed by the Velay record.

Establishing a terrestrial chronological framework as a basis for biostratigraphical comparisons.

The palynological signature of interglacial deposits in the fragmentary European terrestrial record has often been used as the basis for determining their chronostratigraphical position and ultimately their age. This has placed emphasis on the presence/absence and abundance of certain characteristic taxa, but given the lack of continuous stratigraphies and independent chronologies, it has been difficult to assess the extent to which this strategy has produced reliable schemes. Here, an alternative approach is adopted whereby a chronological framework is developed for long and continuous pollen sequences from southern Europe. This in turn allows the emergence of a complete stratigraphical scheme of major vegetation events for the last 430 thousand years (ka) and the evaluation of the stage record of different taxa and their potential diagnostic value for biostratigraphical correlation. The comparison shows distinct similarities among some temperate stages of the terrestrial equivalent complexes of Marine Isotope Stages (MIS) 5 and 7 and also of MIS 9 and 11, but examination of combined records of taxa provides a possibility to differentiate between individual stages. A numerically-derived dichotomous key for the terrestrial stages based on the palynological records of 10 taxa is presented. Carpinus, Fagus, Abies, Pterocarya and Buxus emerge as the best ‘indicator pollen types’ because of their variable behaviour from one stage to the next, possibly a result of their late expansion within a temperate stage or reduced genetic variability. The analysis shows that the palynological signature of a temperate deposit can constrain the range of chronostratigraphical possibilities, but vegetation and palynological variability arising from local factors could result in difficulties in making a definite assignment at individual sites.

High-resolution record of climate stability in France during the last interglacial period

The last interglacial period (127–110 kyr ago) has been considered to be an analogue to the present interglacial period, the Holocene, which may help us to understand present climate evolution. But whereas Holocene climate has been essentially stable in Europe, variability in climate during the last interglacial period has remained unresolved, because climate reconstructions from ice cores, continental records and marine sediment cores give conflicting results for this period. Here we present a high-resolution multi-proxy lacustrine record of climate change during the last interglacial period, based on oxygen isotopes in diatom silica, diatom assemblages and pollen–climate transfer functions from the Ribains maar in France. Contrary to a previous study, our data do not show a cold event interrupting the warm interglacial climate. Instead, we find an early temperature maximum with a transition to a colder climate about halfway through the sequence. The end of the interglacial period is clearly marked by an abrupt change in all proxy records. Our study confirms that in southwestern Europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate.

A re-evaluation of the vegetation history of the eastern Pyrenees (France) from the end of the last glacial to the present

Abstract Fourteen pollen records obtained from 10 sites in the eastern Pyrenees are presented along with the results of 40 new radiocarbon dates of samples obtained from these sites. The data (784 pollen spectra) provide a more comprehensive evaluation of the vegetation history of the region than has hitherto been possible. The salient elements of the regional plant succession are described in the light of a study of regional pollen rain/vegetation relationships. Vegetational developments during the last glacial-interglacial transition and the Holocene are compared with those of other regions in France and the western Mediterranean. This approach therefore provides a new synthesis of published and unpublished information over a large area. A consistent and coherent pattern emerges and the new evidence indicates a number of previously-held views on the vegetation history of the Pyrenees to be erroneous.

The late Pleistocene and Holocene in the Lourdes Basin, Western Pyrenees, France: new pollen analytical and chronological data

In the Lourdes Basin, pollen analytical results and 41 14C dates from three sites (four profiles, 538 spectra) have enabled a coherent biostratigraphy to be established from the last Pleniglacial to the present. The end of the Würm Pleniglacial is characterised by a long phase dominated by Poaceae that extended from ca. 20 000 to ca. 15 000 B.P. Another phase with Poaceae, in the context of a treeless environment, is recorded during the late-glacial between the Juniperus optimum (ca. 13 000 B.P.) and the Betula optimum (after ca. 12 500 B.P.). A marked decline in Betula and a rise in Artemisia values suggest a significant cooling of the climate during the Younger Dryas, an event which is now clearly recorded at several sites in southern Europe. The beginning of the Holocene is characterized by the minor role of Pinus and the early arrival of Quercus which achieves an absolute maximum before the arrival of Ulmus and Corylus. A critical assessment of previously published data is made in the light of these new results.

Recent contributions to the climatology of the last glacial-interglacial cycle based on French pollen sequences

Abstract New pollen data derived from three long French sequences and methodological improvements in the methods used to reconstruct past climates are summarized here, after a short presentation of the study sites and pollen diagrams. Estimated climate parameters during the major episodes of the last 140,000 years are shown to be coherent between sites. Analysis of the seasonality variations provides much additional information. In particular it is shown that the advection from the ocean has governed the last climatic cycle on the European continent.

The transition from temperate phases to stadials in the long upper Pleistocene sequence from Les Echets (France)

Abstract From two sections of the long sequence of Les Echets, corresponding to the end of the Eemian and to the end of St-Germain II interstadial respectively, detailed pollen diagrams have been established which provide information about the climatic conditions prevailing during the transitions from very temperate periods to the following cold stadials.