Present-day and past (last 25 000 years) marine pollen signal off western Iberia

Abstract

The comparison between modern terrestrial and marine pollen signals in and off western Iberia shows that marine pollen assemblages give an integrated image of the regional vegetation colonising the adjacent continent. Present-day Mediterranean and Atlantic forest communities of Iberia are well discriminated by south and north marine pollen spectra, respectively. Results from Total Pollen Concentration together with recognized conceptual models of fine particle dynamics in the Iberian margin have allowed us to establish the present-day pattern of pollen dispersion in this region. The 25 000 year-long record of continental (pollen) and marine ( δ 18O of Globigerina bulloides, Ice-rafted detritus—IRD and Neogloboquadrina pachyderma s.) proxies, from the Galician margin composite core (MD99-2331 and MD03-2697), show that vegetation cover in north-western Iberia has responded contemporaneously to the climate variability of the North-Atlantic. The vegetation response to the well known North Atlantic Heinrich events 2 and 1 (H2 and H1) is however complex and characterised by two vegetation phases at low and mid-altitudes of north-western Iberia. The beginning of each Heinrich event is marked on land by an important pine forest reduction and the expansion of heathers which are synchronous with the heaviest planktic δ 18O values and the maxima of N. pachyderma (s.) suggesting that these first phases were cold and wet. Pinus forest expansion characterising the second phase of each Heinrich event indicates a less cold episode associated, during H1, with an increase of dryness as suggested by the development of semi-desert associations. The comparison of our Galician margin multi-proxy record with several pollen sequences from in and off Iberia allows us to demonstrate that H1 event is the marine equivalent of the Oldest Dryas on the continent. The occurrence of temperate trees during the last glacial maximum (LGM) and the rapid expansion of deciduous Quercus during the Bölling-Allerød period in our Galician margin composite sequence show that not only the southern but also north-western Iberia was a refugium zone for deciduous trees during the last glacial period, especially at low and mid-altitude zones. Furthermore, the comparison between southern and northern marine and terrestrial sequences allows us to confirm that vegetation responded to the Bölling-Allerød warming, the Younger Dryas cold event and the Holocene more quickly in low and mid-altitudes of north-western Iberia and in the south than in the high altitude northern region most likely as the result of the higher density of refugia for temperate trees in these zones during the LGM.