A 14 500-year multi-proxy reconstruction of climate and environmental change in Eastern Baltics

This study presents a 14 500-year high-resolution multi-proxy reconstruction of past climate and environmental changes from Lake Nakri in Southern Estonia. Estonia's geographical position at the intersection of maritime and continental climate zones and boreal and nemoral biomes makes it a highly suitable location for studying even relatively small past fluctuations in climate. We used Chironomidae, Cladocera, pollen, and loss-on-ignition analyses to reconstruct mean July air temperatures, to explore changes in continentality expressed as annual temperature range (ATR), and track environmental changes in the catchment (land cover, land use) and in the lake (trophy, pH, etc.), throughout the late glacial and Holocene. Chironomidae and pollen analysis were used to reconstruct July air temperatures. The reconstruction curves are coherent and consistently reveal climate events, apparent around the 9.0–8.0 ka, 7.5–7.0 ka, 6.0–5.5 ka, 1.0–0.5 ka cal BP in the temperature records. The exception to the otherwise consistent proxy pattern is that Chironomidae reveal an earlier onset of Early Holocene warming compared with the pollen record. This discrepancy may be attributed to low local pollen productivity and delayed postglacial vegetation development. The chironomid-based reconstructions show that the Younger Dryas climate was marked by a 3 °C drop in summer temperature and increased ATR. Although the chironomid-based continentality (difference in summer and winter temperatures) reconstruction approach is still under development, we present a first tentative chironomid-inferred ATR reconstruction, which revealed a major decreasing trend throughout the postglacial. Cladocera remains were used to evaluate past changes in nutrient status and we found no evidence of significant shifts in trophic state and in-lake productivity. Therefore, we conclude that the chironomid-based reconstruction was not biased by such changes. The resulting reconstructions provide critical insights into past regional climate variability and ecosystem responses in eastern temperate-boreal ecotones. Our new palaeotemperature curves can serve as a reference for future regional climate studies.