| Summary: | Tese de mestrado em Ciências do Mar, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2012 Understanding past climate variability, especially abrupt climate events, is essential for predicting future climate, as they may provide crucial information about the climate system’s sensitivity to perturbations. Accordingly, this research is focused on documenting the vegetation response to the natural evolution of the current interglacial period, the Holocene, and on evaluating the anthropogenic contribution to it. Also, we intend to identify the nature, timing and causes of Holocene climate variability at orbital and suborbital time scales in a key region of the North Atlantic region. The present study reveals the vegetation and climate changes in southwestern France and northern Spain for the last ca. 9000 cal. yr BP in a well dated shelf core, KS05-10, retrieved in the southwestern margin of the Bay of Biscay (Basque country). The continuous high resolution pollen record shows orbital and suborbital climate fluctuations contemporaneous with those noticed for the North Atlantic region, Greenland and Europe. The gradual decline of pine and oak trees and the general increase of herbaceous plants, reflecting a gradual cooling between 9000 and 1000 yr cal. BP, follows the cooling in Greenland as well as the decrease of mid-latitude summer insolation. The gradual replacement of the oak forest by beech also reveal the reduction of seasonality, probably triggered by the gradual increase of the precession, and the increase of moisture conditions in mid- to late Holocene. Superimposed on the orbitally induced long-term cooling, KS05 10 pollen record detects an abrupt millennial scale climatic event between 8.3 and 8.1 ka in the southwestern Bay of Biscay, which is related to the well-known 8.2 ka event. The vegetation changes (reduction of temperate and humid trees, particularly Corylus, increase of ubiquist plants, principally Cyperaceae, and the presence of Carpinus) point to a cold and wet episode. ...
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