Sand invasion along the Portuguese coast forced by westerly shifts during cold climate events

Abstract

Phases of higher aeolian activity are responsible for the formation and movement of large transgressive dunefields. Well-reported phases of aeolian activity in northwest Europe are coincident with global cooling events and were related to enhanced westerly winds and storminess. However, the extent to which these climatic episodes influenced dunefield dynamics in southwest Europe remains an open question. Ground penetrating radar (GPR) was used to image the stratigraphy of a cliff-top coastal transgressive dunefield in Portugal and reconstruct former windfield regimes. Using optically stimulated luminescence (OSL) five major phases of aeolian activity were dated at 12.6, 5.6, 1.2, 0.4 and 0.3 ka, and related to coastal instability and enhanced westerlies. These phases were later reconciled to favorable patterns of atmospheric circulation simulated by global and regional climate models at both synoptic and local scales, respectively. The results prove that major phases of aeolian activity in southwest Europe are associated with the onset of cold climate events of global distribution coinciding with aeolian accumulation in northwest Europe. This implies the dominance of zonal westerlies along the western coast of Europe from Denmark to Portugal during the onset of cold climate events. Model simulations suggest that the pattern of atmospheric circulation during periods of enhanced aeolian activity is compatible with prolonged negative phases of the North Atlantic Oscillation (NAO).