Increasing vegetation and climate gradient in Western Europe over the Last Glacial Inception (122-110 ka):: data-model comparison

High-resolution terrestrial (pollen) and marine (planktic and benthic isotopes, coarse fraction, and N. pachyderma (s)) analyses have been performed in the Marine Isotope Stage (MIS) 5 interval of IMAGES core MD99-2331 retrieved in the northwestern Iberian margin. This study shows the occurrence of a Zeifen Interstadial/Stadial succession on land and in the ocean during the first part of MIS 5e. In northwestern Iberia, the Eemian is marked from 126 to 122 ka by the development of deciduous Quercus forest at the same time as Mediterranean forest colonised southern Iberia, and deciduous Quercus-Corylus forest occupied northernmost European regions. From 121 to 115 ka Carpinus betulus forest developed in NW Iberia indicating a winter cooling by 2degreesC on land and an increase in annual precipitation by 100-200 min along with a Sea Surface Temperature (SST) decreasing trend off Iberia. A similar cooling has been documented at the same time in northern Germany (52degreesN) by the replacement of deciduous forest by coniferous (Abies-Picea) formations, implying a southward displacement of the deciduous tree line between similar to60degreesN and 50degreesN as early as 120 ka. The southward migration of the tree line between 72degreesN and 58degreesN simulated by the Earth Model of Intermediate Complexity MoBidiC from 122 and 120 ka and considered as a major process to initiate the last glaciation is, therefore, compatible with data. Between 115 and 110 ka, the substantial ice accumulation in northern high latitudes (MIS 5e/5d transition) was synchronous with successive drops, C26 and C25, in northeastern Atlantic SST. In northwestern Iberia Abies-Pinus trees developed at the expense of Quercus-Carpinus forest. A tundra-like environment occupied northern Germany, marking the end of the interglacial in northwestern Europe at 115 ka, and boreal forest likely colonised northeastern France. The first displacement of the vegetation belts at 121 ka was enhanced at 115 ka indicating an amplification of the vegetation and climate gradients in northeastern Atlantic and European borderlands probably related with the well-developed ice caps at that time. The comparison between the general trend in the estimated and simulated MoBidiC winter and summer temperatures for latitudes between 35 and 45degreesN, shows that both follow quite straightforwardly the precession signal although the simulated and reconstructed temperatures agree better in the South than North of 40degreesN. Annual precipitation is exhibiting opposite trend in the data and in the model. This contradiction is likely the fact that the zonal climate simulated by the model may not accurately represent the regional climate features, as reconstructed from the pollen. (C) 2004 Elsevier B.V All rights reserved.