Late Holocene intensification of colds fronts in southern Brazil as indicated by dune development and provenance changes in the São Francisco do Sul coastal barrier

Holocene coastal barriers from southern Brazil present great geomorphological changes during their late stages of development. In this study, we investigate the Holocene evolution of the São Francisco do Sul (SFS) barrier through geomorphological, heavy minerals and grain size analyses constrained by Optically Stimulated Luminescence (OSL) dating. The SFS barrier stands out among the southern Brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion. The progradation of the SFS barrier started at least 4914 ± 478 years ago and had a pronounced morphodynamic shift around 1891 ± 155 years ago. This shift is characterized by episodic development of parabolic dunes migrating to NNW associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the SFS barrier. This morphodynamic-provenance shift resulted from the strengthening of SSE winds and associated wave systems responsible for the northward alongshore drift, implying intensification of cold fronts coupled with higher precipitation since 1891 ± 155 years ago. OSL dating combined with grain size, heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the Late Holocene. Reconstruction of the Late Holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes.

► Sediment decoupling between beach ridges and superimposed dunes in S Brazil.
► Grain-size, heavy minerals analysis and OSL dating showed different provenance.
► Holocene Westerlies displacement & ENSO strengthening caused morphodynamic shift.