Late Holocene ecological shifts and chironomid-inferred summer temperature changes reconstructed from Lake Uddelermeer, the Netherlands

This paper presents a late Holocene chironomid-inferred record of July air temperature from a core obtained from Lake Uddelermeer in the Netherlands. The core interval, which dates from 2500 to 400 cal. yr. BP, was analysed at multi-decadal resolution for organic content, pollen, spores and NPPs (Non Pollen Palynomorphs), and chironomid head capsules. These proxies indicate that, from 2500 to 1140 cal. yr. BP, the lake was mesotrophic and sustained a Littorellion community, while the chironomid assemblage was dominated by littoral species associated with macrophytes. At 1140 cal. yr. BP, a shift in the lake ecology occurred from low-nutrient to high-nutrient conditions dominated by algae. This shift might be linked to a concurrent increase in human impact and is reflected in the chironomid assemblage by increases in eurytopic taxa, which are resistant to disturbances. Shifts in the chironomid record between 2500 and 1140 cal. yr. BP do not coincide with changes in lake ecology and are presumably driven by climate change. Using a Norwegian-Swiss calibration dataset as a modern analogue, we produced a chironomid-inferred temperature (C-IT) reconstruction. This reconstruction compares well to other regional temperature reconstructions in timing and duration showing a Roman Warm Period between 2240 and 1760 cal. yr. BP, a Dark Age Cold Period starting at 1760 cal. yr. BP and the Medieval Climate Anomaly beginning at 1280 cal. yr. BP. The C-IT record indicates a temperature drop of 1.5 °C from the Roman Warm Period to the Dark Age Cold Period. Findings improve knowledge of the first millennium AD in NW Europe, which was characterised by changes in landscape, vegetation, society and climate.