Reviewing the Lateglacial–Holocene transition in NW Iberia: A palaeoecological approach based on the comparison between dissimilar regions

Isotopic records from Greenland ice cores have revealed a number of centennial to millennial-scale climatic fluctuations affecting the eastern North Atlantic during the Lateglacial/Holocene transition. Most of them appear directly correlated with quantitative temperature changes reconstructed for a very climate-sensitive locality in NW Iberia, Laguna de La Roya (LR). The chironomid-inferred LR temperature record was used as a reference to update the chronologies and improve the interpretations of 16 different key pollen sites from NW Iberia. Botanical and zoological macroremains from archaeological sites and natural deposits were also reviewed in order to check if they support the changing environments predicted by pollen data. Pollen evidence corresponding to the less intense Lateglacial and Early Holocene cold phases identified in LR was found at all sites. Nevertheless, only minor vegetation changes occurred during the Older Dryas, La Roya-I (13,600–13,350 cal BP), La Roya-II (13,300–12,900 cal BP), the 11.4 ka and the 9.3 ka event at very sensitive sites located close to ecotonal situations. We conclude that the LR chironomid inferred-temperature curve is able to explain the main tree-line oscillations and also the major local/regional vegetation changes that occurred over the whole of NW Iberia during the Lateglacial and Early Holocene. During this period, the most relevant landscape modifications occurred at the onset of the Lateglacial, at the transition to the YD, and at the onset of the Holocene. However, noticeable changes also occurred during the 8.2 ka event, which mostly affected the hyperoceanic coastal mountain ranges and some continental depressions inland. The rapid succession of changes registered during the Early Holocene affected the different co-existing biocoenoses in an unequal way and resulted in a diversity of plant and animal resources available for human populations. This may explain that the hunter–gatherer groups even persisted in some areas of NW Iberia until the Mid Holocene.