Abstract. Causal explanations for the 4.2 ka BP event are based on the
amalgamation of seasonal and annual records of climate variability that was
manifest across global regions dominated by different climatic regimes.
However, instrumental and paleoclimate data indicate that seasonal climate
variability is not always sequential in some regions. The present study
investigates the spatial manifestation of the 4.2 ka BP event during the boreal
winter season in Eurasia, where climate variability is a function of the
spatiotemporal dynamics of the westerly winds. We present a multi-proxy
reconstruction of winter climate conditions in Europe, west Asia, and
northern Africa between 4.3 and 3.8 ka. Our results show that, while winter
temperatures were cold throughout the region, precipitation amounts had a
heterogeneous distribution, with regionally significant low values in W Asia,
SE Europe, and N Europe and local high values in the N Balkan Peninsula, the
Carpathian Mountains, and E and NE Europe. Further, strong northerly winds
were dominating in the Middle East and E and NE Europe. Analyzing the
relationships between these climatic conditions, we hypothesize that in the
extratropical Northern Hemisphere, the 4.2 ka BP event was caused by the
strengthening and expansion of the Siberian High, which effectively blocked
the moisture-carrying westerlies from reaching W Asia and enhanced outbreaks
of cold and dry winds in that region. The behavior of the winter and summer
monsoons suggests that when parts of Asia and Europe were experiencing winter
droughts, SE Asia was experiencing similar summer droughts, resulting from
failed and/or reduced monsoons. Thus, while in the extratropical regions of
Eurasia the 4.2 ka BP event was a century-scale winter phenomenon, in the
monsoon-dominated regions it may have been a feature of summer climate
conditions.
Age- and sex-specific strategies of spring migration in the masked shrike are reflected in a differential response to winter climate conditions
