Regional wind fields and dunefield migration, southern Brazil

Abstract

This paper examines a seemingly anomalous situation in southern Brazil where the dunefields on Santa Catarina Island (e.g. Joaquina Beach) migrate to the NNW, almost completely the opposite direction (c. 160°) to the dunefields immediately to the south (e.g. Pinheira Beach), and some much further to the north (e.g. Cabo Frio) which migrate to the SSW. A variety of mechanisms are examined to explain the differences in dunefield migration including grain size variations, topographic effects on local winds, shoreline orientation, and regional wind field changes. The mean grain sizes of the two beaches, Pinheira and Joaquina, are not sufficiently different to restrict aeolian sediment transport in either place, nor to account for a lack of transport from the NNE to the SSW in the case of Joaquina. Some topographic steering of the wind is likely but could not account for the long-term average difference in migration trends of the island dunefields compared to the mainland dunefields. While the orientation of the shoreline to prevailing winds is an important control on beach and dune sediment transport, it is not the dominant controlling mechanism. An analysis of the regional wind patterns demonstrates that there is a major shift in the regional wind field near the island such that the dominant island winds blow from the SW/SSW while those further south blow from the NE. It is concluded that this is the predominant reason for the divergence in the direction of migration of the dunefields. Figure 2. Satellite image of the Joaquina Beach and Lagoa transgressive dunefield. 564 P. Hesp et al.Figure 3. Vertical aerial photograph of the Pinheira complex barrier. Suites of relict foredunes alternate with discrete foredune/ blowout complexes and parabolic dunes.dunefield in the north. The transgressive dunefield comprises an extensive, largely vegetated deflation plain covered by a chaotic mix of nebkha, blowouts and parabolic dunes (Bigarella, 1975), an active dunefield of reversing transverse dunes and two marginal precipitation ridges flanking each side of the dunefield (Figure 2). The transgressive dunefields at Praia do Moçambique and Praia do Ingleses to the north are similar. PinheiraPinheira lies immediately to the southwest of the southern tip of Florianopolis and generally faces east (Figures 1 and 3). It is approximately 25 km SW of Joaquina in a direct line. It is a symmetrical, arcuate embayment which extends through 180° of curvature. The Holocene sediments form a wide (c. ~5·0 km) complex, prograded barrier comprising suites of relict foredune ridges interspersed in the southern half with discrete sets of parabolic dunes or, less commonly, foredune/blowout complexes. The modern foredune is low and stable in the south, and higher, more complex and cut by north-trending blowouts in the northern (i.e. south-facing) portion. The active and vegetated parabolic dunes migrate, or have migrated, respectively, to the south and SSW; that is, c. 140° to 160° in the opposite direction to the Florianopolis dunefields (Figur...

Coastline orientation, aeolian sediment transport and foredune and dunefield dynamics of Moçambique Beach, Southern Brazil

“…The mean tidal range is microtidal at 0.8 m, with a maximum of 1.2 m Schettini et al, 1996;Trucolo, 1998;Hesp et al, 2009). The prevailing and dominant winds in the Santa Catarina island area are generally southerlies (Hesp et al, 2007).…”

“…These increase in size and merge northwards into a small transgressive dunefield originally comprising transverse dunes and a precipitation ridge (now wholly vegetated). With distance northwards, the dunefield widens and becomes an extensive transgressive dunefield and headland bypass system comprising deflation plain, double precipitation ridges and large transverse dunes (Miot da Silva, 2006;Miot da Silva et al, 2008;Hesp et al, 2007Hesp et al, , 2009see Figs. 2 and 13).…”

Caracterização geológica, geomorfológica e evolutiva holocênica do litoral sul de Jaguaruna, SC, Brasil

“…Segundo Hesp (2000), o entendimento dos mecanismos ou fatores responsáveis pela inicialização dessas fases/ pulsos de desenvolvimento de dunas ainda são extremamente limitados. Entretanto, Hesp et al (2007) discorrem teorias sobre a formação dessas feições, a qual associa essas fases a três hipóteses: mudanças do nível de base, mudanças climatológi-cas e alterações no aporte de sedimento.…”

Interaction of alongshore sediment transport and habitat conditions at Laguna La Mancha, Veracruz, Mexico

“…Parts of the west coast of South Africa (Tinley 1985) and southern Brazil (Hesp et al 2007) have been described as having substantial eolian transport from one embayment to another across intervening headlands. Tinley (1985) has named these areas "headland bypass dune fields" and has noted the importance of these dune fields in the regional and local sediment budget.…”