Holocene fluctuations of lake levels in the French Jura and sub-Alpine ranges,and their implications for past general circulation patterns

Temperature and precipitation variations reflected in lake-level fluctuations in the French Jura and Pre-Alps during the last nine millennia are qualitatively assessed by reference to: (1) climatic oscillations reconstructed in the Alps; and (2) modern processes behind Alpine tree-limit variations. The summer season - and mainly the late summer - appears to have a deterministic impact on the Holocene environment. Correlations between palaeoclimatic proxy data recorded in the north Atlantic area from high and middle latitudes, and climatic dynamics illustrated by the 'Little Ice Age' and the recent warming, suggest: (1) the existence of climatic oscillations due to varying solar activity superimposed on larger plurimillennial climatic trends; and (2) that these minor climatic phases correspond with two main types of general circulation pattern alternating over western Europe during the last six millennia. The climatic deteriorations correspond with cooling at high latitudes inducing a stronger thermal gradient and an enhanced cyclonicity over western Europe (and vice versa during climate improvement phases).