Relationships and Function of Coastal and Marine Environments

The coastal dunes of southern Brazil are remarkably similar because Holocene sea-level changes have influenced their genesis (Pfadenhauer 1980; Schwarzbold and Schafer 1984), resulting in the sequential formation of depressions and dune ridges parallel to the shore. The most recent transgression-regression events moulded the 300–1000 m wide foredunes, with seasonally flooded freshwater marshes immediately interior of them. The flat marine terrace supplies a considerable amount of fine quartz sand to the beach (Pfadenhauer 1980), and the sandy substrate of windblown foredunes contains a high proportion of shell fragments but little organic matter (Cordazzo and Seeliger 1987). Since the tidal ranges are low (<50 cm), the dominant southeasterly and northeasterly onshore winds in the winter and summer, respectively, control seawater flooding of the beaches and shore profiles (Pfadenhauer 1980; Costa et al. 1984, 1991; Bernardi et al. 1987). Different orientations of the coast north and south of 33° S imply variations in onshore wind approach angles and impact. On the northern coast, NE onshore winds induce considerable beach-dune sand transport. In contrast, along the southern coast beach-dune sandflow is reduced because NE winds blow parallel to the shore, whilst SE winds blow directly onshore and cause inundation of beaches and landward erosion of backshore and foredune sands. Additionally, winter cold front passages lead to severe beach overwash and differentially affect sand dynamics along the northern and southern coasts.