| Summary: | Poster.-- AGU 100 Fall Meeting Ecological resistance and resilience of freshwater coastal back-barrier perched lakes are intimately linked to the stability of the sand-barrier enclosing them, which controls the inflow of seawater. We address the long-term ecological changes (2,700 cal yr BP to present) in one of these systems in NW Spain (Doniños, A Coruña) from a multi-proxy paleoecological reconstruction based on biological, physical, and chemical analyses of its lacustrine sedimentary record, as well as on GPR surveys of the sand barrier. Although human intervention cannot be completely disregarded, AMS 14C and OSL datings show that ecological changes were synchronous with the main climatic periods of the studied interval. The ancient freshwater lake was catastrophically emptied due to barrier breaching coinciding with the increase of storms within the Dark Ages (350-750 CE) and the Little Ice Age (LIA, 1500-1930 CE), the latter characterized by an active retrograding sand barrier. Erosion induced by storms and increased rainfall generated two hiatuses which left no record of the ecological recovery of the system. By contrast, the transition from the Medieval Climate Anomaly to the LIA (1100-1500 CE) shows a gradual ecological transformation from an isolated lake towards a transitional shallow choked lagoon and, finally, an intermittent tidal lagoon, which lasted approx. 200 yr. Although determining whether an observed ecosystem change represents a regime shift in the framework of the Alternative Stable States Hypothesis is difficult in highly variable systems, this gradual change is here not ascribed as a sudden non-linear ecological regime shift. A 210Pb age-model for the upper sediments shows that the current freshwater lake was established c. 1945 CE, after the dune fields stabilized in the region associated to the known decrease in storm and wind intensities. Changes in the main North Atlantic atmospheric patterns in the last decades are considered the ultimate agents of the complete isolation of the lake from the sea. This work stresses the need of a detailed knowledge of the stratigraphy of the sand-barrier and the lacustrine infilling for reliable reconstructions of the long-term ecological trajectories of coastal perched lakes This research was funded by projects RapidNAO (CGL2013-40608R) and PaleoModes (CGL2016-75281-C2) Peer reviewed
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