Late Quaternary vegetation and coastal environmental changes at Ilha do Cardoso mangrove, southeastern Brazil

Abstract

A 190cm mangrove sediment core from the Ilha do Cardoso State Park, State of São Paulo, southeastern Brazil was analyzed for pollen, diatoms as well as carbon and nitrogen isotopes. The goal was to determine the dynamics of the coastal terrestrial/aquatic ecosystems, vegetation history and climate change in this region of the Brazilian Atlantic rainforest, during the Late Pleistocene and Holocene.The values for total organic carbon—TOC (from ~3 up to 40%), C/N ratios (from ~10 up to 130), and δ15N (~0 to >8) are associated with well preserved aquatic and terrestrial organic matter and possibly influenced by nitrogen cycling (e.g., denitrification) that caused 15N enrichment between >40,000calyrB.P. and ~23,000calyrB.P. Depleted δ13C values (~ -28.0‰) are also observed and indicate the predominance of C3 plants. During this time interval, the pollen analysis reveals the presence of the genera Ilex, Alchornea, Weinmannia, Myrsine, Symplocos, Drimys and Podocarpus on a site currently occupied by mangrove vegetation. These data suggest that in the past prevailed a colder and more humid climate than today, with a low relative sea-level. From ~23,000calyrB.P. to ~2200calyrB.P. a sedimentary hiatus likely occurred, related to an erosive event associated to the post glacial sea-level rise. Since at least ~2200calyrB.P., sediments are marked by relatively low C/N ratios (from 2 to 27), exhibit more enriched δ13C (from ~-26.0‰ to −24.0‰) and δ15N (up to ~7) values and are characterized by the presence of marine diatoms. This indicates the return of the marine coastal line to its current position, and consequently the development of mangrove.