Dunes in the Gibraltar Strait Realm

This chapter examines the origin, evolution and present state of the coastal dunes along the South Atlantic Spanish coast around the Strait of Gibraltar. Wind regime in the zone is strongly affected by the North Atlantic Oscillation (NAO). Low or negative NAO index values give rise to the prevalence of westerly humid winds, while during periods with a positive NAO index easterly, dry winds prevail. Several Holocene and historical aeolian phases have been identified in the zone, represented by different aeolian deposits, many of them containing archaeological remains. The oldest one dates to shortly after the mid-Holocene eustatic maximum. During historical times dune-building episodes were associated with a higher frequency and persistence of easterly winds. During the 20th century, and especially in the last few decades, the prevalence of positive values of the NAO index has favoured the growth and advance of mobile dunes in the vicinity of the Strait of Gibraltar. In contrast, dune ridges associated with westerly winds are much less mobile or stable and form shore-parallel ridges covered by vegetation. In the Atlantic side of the Strait, environmental health of coastal dunes is satisfactory, especially those included in the Strait of Gibraltar Natural Park, where more effective protection measures are applied. The Mediterranean side is characterized by a dense population and intense human interventions, leading to erosion problems. Climate change predictions for the next decades suggest an increase in the frequency and intensity of easterly-Levante winds in the Strait. This situation would favour the reinforcement and growth of the Levante-derived dunes around the Strait, and perhaps recovery of the small dunes existing in the Mediterranean side.