Windiness spells in SW Europe since the last glacial maximum

Abstract Dunefields have a great potential to unravel past regimes of atmospheric circulation as they record direct traces of this component of the climate system. Along the Portuguese coast, transgressive dunefields represent relict features originated by intense and frequent westerly winds that largely contrast with present conditions, clearly dominated by weaker northwesterly winds. Optical dating and subsurface stratigraphy document three age clusters indicating main episodes of dune mobilization during: the last termination (20–11.6 ka), Middle Holocene (5.6 ka), and Late Holocene (1.2–0.98 and 0.4–0.15 ka). We find reconstructed windfields to be analogous during all episodes and dominated by strong westerlies. Yet, larger grain size diameters and dune volumes documented for the last termination support amplified patterns compatible with a southward shift and intensification of the North Atlantic westerlies during winters. Conversely, dunes deposited after the Middle Holocene are compatible with more variable windfields and weakened patterns controlled by interannual shifts towards low values of the North Atlantic Oscillation (NAO). This work demonstrates that present windfield regimes in southern Europe are not compatible with past aeolian activity. Indeed, present day analogs indicate that wind intensities compatible with past aeolian activity are rare at present (sediment transport potentials below estimates in the aeolian record), but can occur if the jet stream is diverted to the south (i.e. 30°N with negative NAO index) or if very deep cyclones anchor around 50°N, extending their influence to the western Portuguese coast (relatively low NAO index). However, these conditions represent temporary patterns lasting around one day, while we suggest that the identified episodes of aeolian activity may represent semi-permanent conditions.