| Summary: | A long-term perspective of past hydroclimate variability for the Baltic region provides important context for evaluating the potential impacts of Northern Hemisphere temperature changes and shifting ocean-atmospheric interactions on northern European climate. Lake Nuudsaku is an open-basin lake in south-central Estonia with seasonal overflow fed by active springs and groundwater. Stable isotope analyses of surface water samples from regional lakes, rivers, wetlands, and precipitation indicate that Lake Nuudsaku water δ 18 O values are consistent with the isotopic composition of inflowing meteoric water. The isotopic composition of fine-grained (<63 μm) endogenic CaCO3 (δ 18 O calcite ) samples from Lake Nuudsaku vary between ∼14 to -9‰ (VPBD) over the last ∼9400 years. Based on sensitivity tests, we interpret the δ 18 O calcite variations from Lake Nuudsaku as a record of meteoric inputs; principally reflecting variations in the seasonality of precipitation, with temperature changes as a secondary influence. The δ 18 O calcite record indicates the early Holocene at ∼9400 calendar years before present (cal yr BP) was characterized by a high proportion of cold season (November through April) precipitation and lower temperatures, followed by waning cold season precipitation and higher temperatures until ∼8200 cal yr BP. The middle Holocene (8200–4200 cal yr BP) was likely a period of overall reduced cold season precipitation and higher temperatures, and/or increased warm season (May through October) precipitation. The late Holocene transition at ∼4200 cal yr BP generally marks a shift to lower δ 18 O calcite values that we interpret largely the result of increased cold season precipitation amounts. This was followed by the onset of more variable precipitation amounts and temperatures after ∼3600 cal yr BP, which gave way to less variable conditions during the last ∼2600 years. The Medieval Climate Anomaly (MCA) is marked by δ 18 O calcite values that are near the Holocene and present-day averages. The period ...
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