First high-resolution multi-proxy palaeoenvironmental record of the Late Glacial to Early Holocene transition in the Ría de Arousa (Atlantic margin of NW Iberia)

A 322-cm-long sedimentary sequence obtained in the shallow marine basin of the Ría de Arousa—a submerged unglaciated river valley on the Atlantic margin of northwestern Iberia—was analysed using a multi-proxy approach to study how climatic and sea level changes affected the coastal ecosystems during the Last Glacial–Interglacial Transition. Past sedimentation, vegetation and marine productivities were inferred from palynological, radiocarbon, seismic and lithological data. A substantial reduction in the pollen and dinoflagellate cyst accumulation rates is observed at ∼12,700 to 11,700 cal a BP, suggesting lower marine and vegetation productivities likely as a response to the Younger Dryas cooling event. Overall, the regional vegetation changed from cold-tolerant open woodlands (Pinus sylvestris/P. nigra and Betula) dominating before ∼10,200 cal a BP to coastal wetlands and the regional spread of Quercus-dominated forests after ∼9800 cal a BP. Cluster analysis and principal component analysis allowed the identification of several small environmental oscillations, such as the 11.4 ka and 10.5 ka cooling events. After that, a conspicuous heath expansion was likely favoured by the palaeotopography, the increased precipitation and the relative sea level rise, which might have caused a profound change in the coastal configuration. Concurrently, both the dinoflagellate cyst and non-pollen palynomorph records reveal variations in the marine productivity and coastal hydrodynamics that also agree with a period of marked marine transgression, warming and increasing river flow. New sedimentary data highlight the high sensitivity of the ria's ecosystems to environmental oscillations and show a close temporal correspondence between terrestrial and marine responses to climate change.