Evaluating North-Atlantic-driven variations in precipitation sources throughout the Holocene using oxygen isotopes from Lake Nuudsaku in Southern Estonia

Oxygen isotopes derived from authigenic carbonates from finely laminated, open lake systems record variations in precipitation source. This study focuses on the radiocarbon and ²¹⁰Pb dated sediment record from Lake Nuudsaku in southern Estonia in order to evaluate how northerly versus southerly moisture sources have changed throughout the Holocene as a result of fluctuating North Atlantic Ocean conditions, primarily the North Atlantic Oscillation (NAO). Modern water samples from Lake Nuudsaku and regional precipitation samples have been collected from the winter and summer months, indicating that during the winter Estonia receives precipitation with a more negative δ¹⁸O value from the north (North Atlantic and Baltic Sea). In contrast, during the summer months precipitation is transported from a southern source (Mediterranean and Black Seas), with more positive δ¹⁸O values. The modern surface water is depleted in δ¹⁸O relative to summer precipitation, indicating that the lake receives a substantial amount of winter precipitation. We thus interpret lower δ¹⁸O values in the sediment record as periods of time in which there were increases in the amount of winter precipitation. Isotope data indicate an increasing trend toward decreasing winter precipitation amounts during the first half of the Holocene (9.5-5 ka) and an increase of winter precipitation after 5ka. Winter precipitation decreased from 4 to 3 ka, and then increased until ~0.7 ka. The upper ~700 years of the record shows a general decrease in winter precipitation.