Influências das flutuações do nível do mar e mudanças climáticas na dinâmica dos manguezais do litoral Sul de Santa Catarina durante o Holoceno.

Abstract

The objective of this work was to identify the main factors controlling the mangrove dynamics in the southern limit of this ecosystem in the South American continent, in the Laguna - Santa Catarina region. This study was based on the integration of sedimentary facies, isotopes (δ13C and δ15N), elementary organic matter (C/N), and pollen data with 14C dates obtained from core RP4 (S 28°29'18.41 " and W 48°50'47.01) with 2 meters depth sampled from a tidal flat near the Santo Antônio Lagoon, 8 km away from the present coastline, west of the town of Laguna. Three facies associations were identified: facies Herbaceous Floodplain, Fluvial channel and tidal flat with Spartina. The Herbaceous Floodplain is characterized by massive mud with benthic tubes, fragments of shells and roots. The facies association of Fluvial Channel presents sand with crossed stratification and massive. The top of the studied core presents the facies association Tidal Flat with Spartina represented by mud silt with roots fragments. The integration of these data suggests an increase in the relative sea-level during the Holocene, when the low river courses were flooded and it favored the formation of lagoon systems that are well represented along the Santa Catarina littoral, especially in the study area. A gradual Holocene marine transgression would have favored the mangrove expansion on tidal flat flats. Considering the physicochemical and hydrodynamic, probably the sedimentary environment was favorable for the establishment and expansion of mangroves over the last centuries, when occurs a strong contribution of organic matter sourced from estuary in the study site and development of tidal flats. The absence of mangrove pollen grains along the studied core (<9000 years AP) indicates, besides the low relative sea-level stand, another factor must have prevented mangrove establishment in the study area. The presence of Laguncularia and Avicennia shrubs/trees nowadays in the study area and the absence of mangrove pollen grains in the studied stratigraphic profile indicates that these genus were established only during the last decades. Probably, the temperatures during the Holocene winters on the modern austral limit of the South American mangroves prevented the mangrove establishment during that period the sediments of the core RP4 were accumulated. Probably, the increase in minimum winter temperatures during the last decades has allowed the expansion of the southern limit of the southern American mangroves into temperate zones.