Bp

10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000

Figure 2.11 Estimated mid-summer sea-surface temperatures in the north Atlantic region over the past 130,000 years, based on analyses of the varying frequencies of temperature-sensitive surface-living organisms in deep-sea core V23-82. After Sancetta et al. 1973.

the different regions of Europe. In the northern zones of the Netherlands, Britain, Denmark and northern Germany, for example, both of these interstadials (the Amersfoort/ Brorup and Odderade) were characterized by the migration of dense pine and birch woodland into areas which had previously been

420 440 46o 48o 500 520 540 560 530 g0° 62°N RE5 34 V23 84 RE5 36 V23 83 V23 82 V23 81 RC9 225 V23 47

420 440 46o 48o 500 520 540 560 530 g0° 62°N RE5 34 V23 84 RE5 36 V23 83 V23 82 V23 81 RC9 225 V23 47

Figure 2.12 Reconstructed patterns of fluctuations of cold and warm sea-water currents in the north Atlantic region, based onfaunal evidence from eight deep-sea cores at latitudes ranging from 42°N to 62°N. During the coldest glacial phases currents of'polar' sea water extended southwards along the European coastline to ca 44°N - i.e. to the latitude of northern Spain. During the last inter glacial, 'subtropical' currents extended northwards as far as the southern coast of Britain. After Mclntyre et al. 1972.

Figure 2.12 Reconstructed patterns of fluctuations of cold and warm sea-water currents in the north Atlantic region, based onfaunal evidence from eight deep-sea cores at latitudes ranging from 42°N to 62°N. During the coldest glacial phases currents of'polar' sea water extended southwards along the European coastline to ca 44°N - i.e. to the latitude of northern Spain. During the last inter glacial, 'subtropical' currents extended northwards as far as the southern coast of Britain. After Mclntyre et al. 1972.

occupied by open or shrub-tundra communities. Further to the south in the Rhone valley and the western flanks of the Alps, however, the same episodes were characterized by a succession of more warmth-demanding deciduous species, which shows an overall pattern of ecological succession remarkably similar in many respects to that recorded in the same areas during the different stages of the last interglacial - i.e. a succession from birch and pine, through to elm, oak, hazel and hornbeam forests and then back to pine, spruce and other cold-tolerant species (Woillard 1978; de Beaulieu & Reille 1984). Both Zagwijn and Behre see this as a further indication of the very steep climatic and ecological gradients which existed over northern, western and central Europe during the earlier stages of the last glaciation, resulting partly from the continuing presence of some land ice in Scandinavia, partly from the presence of extremely cold sub-polar waters in the northern parts of the Atlantic ocean and partly from the increased level of continentality of the climate in northwestern Europe caused by the general reduction in world-wide sea levels.

The climatic reconstruction provided by Zagwijn (1990) for these periods is illustrated in Fig. 2.5. He suggests that July temperatures ranged from around 12°C (approximately 6°C below present-day values) in southern Scandinavia and northern Germany, to around 18-20°C (1-2°C below present values) in the southern parts of France and along the Atlantic coast. Essentially the same patterns are confirmed by the recent multivariate analyses of climatic and vegeta-tional patterns proposed by Guiot et al. (1989, 1993) for the pollen sequences at La Grande Pile and Les Echets (Fig. 2.8). In the case of Les Echets, the peak of warm conditions during both the St Germain I and II episodes are calculated as being ca 1-2°C cooler than the present day, whilst at La Grande Pile, 250 km to the north-east of Les Echets in the foothills of the Vosges mountains, it would seem that average annual temperatures could have been almost identical to those of the present in the same region (Sejrup & Larsen 1991).

One of the intriguing details to emerge from the study of these early interstadial deposits in Europe is the evidence for a bipartite climatic sequence during the earlier of the two interstadials, St Germain I. In the pollen diagrams from both Grande Pile and Les Echets (Figs 2.6, 2.7) this is marked by a very short episode, perhaps only 1,000-2,000 years in length, during which overall tree-pollen frequencies were sharply reduced and there was a temporary re-establishment of essentially open vegetation clearly implying a major climatic cooling (Woillard 1978; de Beaulieu & Reille 1984). The same episode is probably indicated by the similar reduction in tree-pollen ratios which separates the twin peaks of the Amersfoort and Brorup interstadials in northern Europe (Figs 2.9, 2.10) and in similar fluctuations recorded in many other contemporaneous pollen sequences extending as far to the south and east as Grenada in Spain and Tenaghi Phillipon in Greece (Zagwijn 1990; Behre 1990). Taking all the relevant data into account, Zagwijn (1990) suggests that during this interval overall climatic conditions in Europe may have fallen to levels similar to those experienced during the glacial episodes of isotope stages 5d and 5b. The explanation for this brief but very sharp climatic oscillation remains uncertain. For the human groups who were occupying the various regions of Europe, however, the impact of this climatic event must have been just as significant as that of the more long-term climatic and ecological deteriorations which characterized stages 5d and 5b of the isotope records.

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