Os efeitos das oscilações climáticas e variações do nível do mar sobre o manguezal de Laguna (SC) - limite sul americano

Abstract

A mangrove ecosystem located in the Santo Antônio Lagoon, Laguna (SC), Southern Brazil is considered to be the southern limit of mangroves occurrence in South America has been chosen as the study site for this work. Our major goal was to study the dynamic of this mangrove regarding climatic changes during the mid- to late-Holocene. The study has been carried out based on one sediment core, RP-01 (4.75 m depth) sampled using a Peat Sampler set. A multiproxy analysis that links geochemistry (ie. Total C, Total N, C/N, C/S, δ13C and δ15N), sedimentology and palynology have been used in order to achieve the main goal. These data were temporally synchronized with six radiocarbon ages. Five facies were described considering their geometry, sediment composition, texture, grain size and geochemistry. They were grouped into two facies associations: i) lagoon and ii) distributary mouth bar. A transition from marine to terrestrial influence on the organic matter source during the mid-late Holocene has been proposed for the area. The increase in the terrestrial organic matter, especially occurred from the late Holocene on, just as the bigger contribution of the Sambaqui and Tubarão Rivers towards the lagoon has favored the development of the distributary mouth. The vegetation has also changed during this time. Pollen data indicated that over the mid-Holocene herbaceous plants dominated the area suggesting a less humid climate than the present one. The enhancement in the pollen grains of trees, shrubs, palms and the appearance of the mangrove towards the late Holocene it is interpreted as a sign of more humid and warm climate conditions than the later one in this region. This is probably related to the shifting of the ITCZ southwards and the intensification of the SAMS causing higher precipitation rates. The development of the studied mangrove site has occurred mainly during the past centuries, highlighting changes on the climate in the Laguna (SC) region and showing a sett up of a warmer and more humid climate than that observed during the mid-Holocene.