P.C. Tzedakis

Palaeolithic landscapes of Europe and environs, 150,000-25,000 years ago: An overview

Abstract When considering the evolution and migrations of Neandertalers and early modem human beings, the harsh conditions of the last glacial maximum are often implicitly or explicitly assumed as their environmental background. This perception is false: the conditions of the high glacial apply to a small fraction of late Pleistocene time. Here we review the palaeoenvironmental history of Europe from 150,000 to 25,000 years ago with the aid of data from long cores of ice and marine and continental sediments. The results are displayed in four sketch maps that illustrate the landscapes of an interglacial-glacial cycle. The maps, connected by palaeoenvironmental histories, show that especially between 60,000 and 25,000 years ago, a critical part of the Palaeolithic, the glacial landscapes were for much of the time less barren than is generally assumed, but numerous climate changes on a scale of several millennia are evident, placing a premium on accurate dating of the co-evolution of humans and landscape. Moreover, during the glacial interval abrupt climatic changes lasting from a century to a few millennia were common. Their importance for landscape changes and their impact on human activity remain to be ascertained.

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

Cryptic or mystic? Glacial tree refugia in northern Europe.

Here, we examine the evidence for tree refugia in northern Europe during the Late Pleniglacial (LPG) interval of maximum tree-range contraction. Our review highlights the often equivocal nature of genetic data and a tendency to overestimate potential tree distributions due to warm climate-model bias, and also reveals a convergence of macrofossil and pollen evidence. What emerges is the absence of temperate trees north of 45°N and a west-east (W-E) asymmetry in boreal tree distribution, with a treeless Western Europe north of 46°N, while restricted boreal populations persisted in Eastern Europe up to 49°N, and higher latitudes east of the Fennoscandian ice-sheet. These results have implications for current thinking on European genetic diversity patterns, species migration capacity, and conservation strategies.

Ecological thresholds and patterns of millennial-scale climate variability: The response of vegetation in Greece during the last glacial period

The regional expression of millennial-scale climate variability during the last glacial is examined with particular reference to the vegetation response in Greece. Inspection of three pollen records from contrasting bioclimatic areas suggests that differences in the magnitude of cold events as recognized in the North Atlantic and western Mediterranean are expressed in terms of tree population changes only in areas with a range of favorable habitats. By contrast, records from sites where populations approach their tolerance threshold do not appear to resolve differences in the amplitude of the climate oscillations. Understanding the importance of local factors in modulating the biological response to climate change is critical when attempting to establish the spatial pattern of millennial variability.

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.

Comparison of changes in vegetation in northeast Greece with records of climate variability on orbital and suborbital frequencies over the last 450 000 years

Abstract A new direct pollen–orbital tuning procedure, based on a correspondence between changes in certain vegetation elements and March and June perihelion configurations, is applied to the Tenaghi Philippon record, northeast Greece. The development of a refined chronological scheme allows comparisons to be made with records of climate variability from the North Atlantic as well as of global sea level/ice volume and atmospheric CO2 content. On orbital frequencies, the comparison reveals a close correspondence between relative ice volume extent and tree population size during glacial intervals. During interglacial and interstadial periods the degree of forest development is more closely associated with high-latitude insolation and related climate regimes rather than extent of residual ice volume. On suborbital frequencies, the Greek record shows similar repeat times in peaks of steppe vegetation with North Atlantic ice-rafting events, but the amplitude of this variability in the two records is not always proportional. Overall, what emerges is that the major shifts in the relative abundance of forest v. open vegetation communities at Tenaghi Philippon on orbital and suborbital frequencies over the last 450 000 years are coherent with high-latitude changes affecting atmospheric and oceanic circulation. Glacial decreases in atmospheric CO2 content contributed to the elimination of tree populations by exacerbating water stress conditions during arid intervals, but do not appear to be the primary driver of the observed vegetation changes at this latitude. Variations in CO2 levels (in the order of 40 ppmv) between different interglacial/interstadials periods with adequate moisture availability appear to have had a limited effect on the nature and size of tree populations.

Volcanic ash layers illuminate the resilience of Neanderthals and early modern humans to natural hazards

Marked changes in human dispersal and development during the Middle to Upper Paleolithic transition have been attributed to massive volcanic eruption and/or severe climatic deterioration. We test this concept using records of volcanic ash layers of the Campanian Ignimbrite eruption dated to ca. 40,000 y ago (40 ka B.P.). The distribution of the Campanian Ignimbrite has been enhanced by the discovery of cryptotephra deposits (volcanic ash layers that are not visible to the naked eye) in archaeological cave sequences. They enable us to synchronize archaeological and paleoclimatic records through the period of transition from Neanderthal to the earliest anatomically modern human populations in Europe. Our results confirm that the combined effects of a major volcanic eruption and severe climatic cooling failed to have lasting impacts on Neanderthals or early modern humans in Europe. We infer that modern humans proved a greater competitive threat to indigenous populations than natural disasters.

The last climatic cycle at Kopais, central Greece

Thick lacustrine sequences from southern Europe provide an opportunity to derive continuous records where the chronostratigraphical position of pre-Holocene stages can be determined with increased confidence. Here, high-resolution sediment and pollen analytical results from a 60 m core recovered from the Kopais basin, central Greece, spanning the interval from the last interglacial to the early Holocene are presented. The record shows distinct shifts between open vegetation periods of increased erosion with sediment inwashing and forest periods associated with calcite precipitation in the lake. The sequence of major events of the last climatic cycle contained at Kopais bears strong similarities to other records in Greece, but also reveals the presence of high-frequency oscillations with higher amplitudes than previously seen at other sites.

Last interglacial conditions in southern Europe: evidence from Ioannina, northwest Greece

A new record combining isotopic and palynological results over the interval 133-111 ka BP at 100-200 year resolution from a long lacustrine sequence at Ioannina, northwest Greece is presented. The sequence provides an opportunity to examine the nature of climate variability during the Last Interglacial in southern Europe where information has hitherto been relatively limited. The record shows that the frequency and amplitude of changes during the transitional late glacial and late interglacial phases were markedly higher than that of the full interglacial interval. These differences are probably a reflection of the relative size of ice sheets in the circum-North Atlantic and associated ice-rafting events and climatic perturbations during these periods. During intervals of increased ice volume, it appears that North Atlantic variability has a significant downstream impact, dominating the climate signal in northwest Greece. During intervals of minimum ice volume there may be a decoupling between the North Atlantic system and continental climates with other factors, such as insolation changes, becoming more important. The length of the Last Interglacial at Ioannina defined by the presence of forest is here estimated to be c. 15 ka, in agreement with recent results from Portugal, but in conflict with estimates of c. 10 ka for the duration of the Eemian in northwest Europe. In the absence of independent confirmation for these estimates, however, these differences and associated implications remain unresolved.

European vegetation during Marine Oxygen Isotope Stage-3

European vegetation during representative “warm” and “cold” intervals of stage-3 was inferred from pollen analytical data. The inferred vegetation differs in character and spatial pattern from that of both fully glacial and fully interglacial conditions and exhibits contrasts between warm and cold intervals, consistent with other evidence for stage-3 palaeoenvironmental fluctuations. European vegetation thus appears to have been an integral component of millennial environmental fluctuations during stage-3; vegetation responded to this scale of environmental change and through feedback mechanisms may have had effects upon the environment. The pollen-inferred vegetation was compared with vegetation simulated using the BIOME 3.5 vegetation model for climatic conditions simulated using a regional climate model (RegCM2) nested within a coupled global climate and vegetation model (GENESIS-BIOME). Despite some discrepancies in detail, both approaches capture the principal features of the present vegetation of Europe. The simulated vegetation for stage-3 differs markedly from that inferred from pollen analytical data, implying substantial discrepancy between the simulated climate and that actually prevailing. Sensitivity analyses indicate that the simulated climate is too warm and probably has too short a winter season. These discrepancies may reflect incorrect specification of sea surface temperature or sea-ice conditions and may be exacerbated by vegetation–climate feedback in the coupled global model.