NOAA/WDS Paleoclimatology - Eastern Finland Late Holocene Lake Level Reconstructions

Long-term paleoclimatic records are needed for understanding natural variability in the context of climate change. Two lake sediment cores were collected from eastern Finland from sites considered sensitive for precipitation and temperature, respectively, over the last ~3000 yr. The paleoclimatic reconstructions based on fossil Chironomidae (Insecta: Diptera) assemblages were considered against a North Atlantic Oscillation (NAO) reconstruction to disentangle possible forcing mechanisms. Generally low effective precipitation was reconstructed between ~3000 and 1500 cal yr BP (calibrated years before present). A distinct stream flow event occurred between ~2400 and 2200 cal yr BP, and the highest effective precipitation occurred ~1300 cal yr BP. The Medieval Climate Anomaly (MCA) between ~1200 and 800 cal yr BP was dry, but the Little Ice Age (LIA) between ~700 and 200 cal yr BP had fluctuating precipitation. The temperature reconstruction depicted a late Holocene cooling trend, which ended at ~1300 cal yr BP when the warm MCA began. The MCA was followed by the cold LIA and the last 100 yr have been characterized by rapid warming. Present temperatures are higher than during any time period of the late Holocene. A general trend of positive NAO mode with elevated summer temperatures and dry hydroclimatic conditions prevailed during the MCA and a negative mode with reduced temperatures during the LIA. However, the NAO-hydroclimate relationship over eastern Scandinavia was not straightforward during the LIA, which varied in moisture dynamics. The records from this present study provide a unique climate archive from the crossing point of southern and northern and eastern and western air masses.