Here we present δ18Odiatom data from two high-latitude lakes; one has short residence time and a water isotopic composition (δ18Olake) that fluctuate due to seasonal variations in precipitation and temperature, and the other has δ18Olake that is influenced by longer lake water residence times and evaporation. The δ18Odiatom records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from δ18Odiatom between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation.