Lúcia Abreu

Similar orbital geometry and greenhouse gas concentrations during marine isotope stage 11 (MIS 11) and the Holocene make stage 11 perhaps the best geological analogue period for the natural development of the present interglacial climate. Results of a detailed study of core MD01-2443 from the Iberian margin suggest that sea surface conditions during stage 11 were not significantly different from those observed during the elapsed portion of the Holocene. Peak interglacial conditions during stage 11 lasted nearly 18 kyr, indicating a Holocene unperturbed by human activity might last an additional 6-7 kyr. A comparison of sea surface temperatures (SST) derived from planktonic foraminifera for all interglacial intervals of the last million years reveals that warm temperatures during peak interglacials MIS 1, 5e, and 11 were higher on the Iberian margin than during substage 7e and most of 9e. The SST results are supported by heavier δ18O values, particularly during 7e, indicating colder SSTs and a larger residual ice volume. Benthic δ13C results provide evidence of a strong influence of North Atlantic Deep Water at greater depths than present during MIS 11. The progressive ocean climate deterioration into the following glaciation is associated with an increase in local upwelling intensity, interspersed by periodic cold episodes due to ice-rafting events occurring in the North Atlantic.

ABSTRACT A marine pollen record from the Portuguese margin provides the means of correlating vegetation changes in southern Europe with North Atlantic sea-surface temperature and the marine isotope stratigraphy for the interval 180 to 345 kyr (marine isotope stages 7, 8 and 9). It reveals close correspondence between the patterns and timing of forest expansion and contraction and changes in North Atlantic sea-surface temperatures, but pronounced offsets between marine isotopic warm stage boundaries and forested intervals. Our study confirms the previous tentative observation that the latter vary in length from one stage to another and also highlights floristic differences between sites resulting from local climatic, geological and biogeographical factors.

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.