The last millenium of natural and anthropogenic disturbances on a remote island on the edge of Europe: a diatom-based paleolimnological approach

Previous studies show that climate variability and volcanism along with the arrival of humans played a significant role in the recent evolution of insular Azorean ecosystems. However, the timing and rate of anthropogenic impacts are poorly understood. Paleolimnological research allows us to reconstruct ecological conditions prior to and after human settlement on oceanic islands, to understand how species and island ecosystems responded to both natural and anthropogenic disturbances. Here, we present the first high-resolution reconstruction of ecological changes in Lake Funda (Flores Island, Azores) over the last millennium based on diatom analysis from a 993 cm-long sediment core retrieved in June 2017. The chronology of the reconstructed paleoenvironmental events has been established with a preliminary radiocarbon-based age model. The three main ecological periods were mostly related to human disturbance. (1) During the pre-human arrival period (AD 950 to 1330), the sediment record has a diverse benthic and tychoplanktonic diatom assemblage dominated by Staurosirella pinnata and Pseudostaurosira elliptica, representing the baseline conditions of Lake Funda. (2) Upon human arrival in Flores, around AD 1330, human disturbances in the catchment area (e.g., livestock release and gradual forest clearance) and climate fluctuations led to changes in the diatom assemblage. Several climate fluctuations from AD 1330 to 1560 and the onset of human-driven deforestation (ca. 1380 AD) led to an abrupt drop in diatom diversity and the dominance of eutrophic Aulacoseira spp.. (3) Finally, the most recent period (AD 1560 to 2008) corresponds to the well-established Portuguese settlement in Flores Island. Complete forest clearance led to a second ecological perturbation characterized by a highly productive lake with an anoxic hypolimnion and enhanced in-lake nutrient recycling. From 1980, changes in diatom assemblages suggest prolonged periods of summer stratification and increase i