Holocene environmental change on the Atlantic coast of NW Iberia as inferred from the Ponzos wetland sequence

Abstract

The intertidal environment of the Ponzos beach (NW Iberian Peninsula) hosts a sedimentary sequence (including large wood fragments) deposited during the first half of the Holocene in a hygrophilous continental wetland. Pollen and macrofossil data alongside radiocarbon dating allow reconstruction of the changes that occurred during the Early and Middle Holocene in the landscape of the NW Iberia coastal lowlands, as well as the local wetland plant communities, in response to the climate variations and the eustatic sea-level oscillations. The sequence represents the evolution of a coastal wetland from its initial phases as a hygrophilous wetland towards the subsequent installation of a freshwater lagoon. Pollen data show the dominant role of Atlantic (mainly deciduous) woody taxa, the scarcity of conifers and the lack of Mediterranean elements in the coastal landscapes around the Ponzos site. The presence and abundance of some taxa such as deciduous Quercus, Castanea, Fagus, Tilia and Ulmus during the Early Holocene provides further support for the occurrence of glacial refuges in the Cantabrian-Atlantic area during the Last Glaciation. The diverse vegetation that characterizes the modern landscapes in this territory established later, spreading from these glacial reservoirs of biodiversity. In this sense, the notable and early presence of Fagus at the beginning of the Holocene, a tree also previously recorded during several phases of the Last Glacial Cycle on the NW Iberia coasts, is noteworthy. In addition, during the Early and Middle Holocene are recorded other trees that are currently extirpated as natural taxa in the area, such as Pinus, Tilia and Carpinus