Morphological and temporal variations of transgressive dunefields of the northern and mid-littoral Rio Grande do Sul coast, Southern Brazil

Transgressive dunefields are present along the entire stretch of the Rio Grande do Sul (RS) coast, from Rondinha to Mostardas. These dunefields change their morphology and size along the coast and through time. The aim of this paper is to describe the spatial and temporal variations of the dunefields and analyze the main agents that control these variations. The dunefields at the northern littoral are narrow (1300 to 1400 m wide) due to the local higher precipitation, lower wind drift potential (DP) and smaller sand supply. Southwards, the dunefields increase their width (reaching 6900 m), as the precipitation decreases and the wind DP and the sand supply increase in the area. The RS dunefields have changed through time. Since 1948, the dunefields have experienced increases in the deflation area, in the vegetation cover and in the moist areas. These processes of dunefield stabilization are probably the result of the historical increase in precipitation and decrease in wind DP. As the northern dunefields are smaller, they have less sand, thus they were more susceptible to stabilization processes. In the southern dunefields, the larger amount of sand and the ongoing coastline erosion have retarded the stabilization processes.