Relative Sea Level Variations and Climatic Evolutuion in Southeastern and Southern Brazil During the Late Holocene
Palavras-chave:Paleoenvironment, Sea Level variations, Late Holocene.
Analysis of organic sediments from a swamp forest on the coastal plain of São Paulo State (southeastern Brazil) has been carried out. Diatom and pollen contents from the same samples were analysed. This study allowed reconstruction of the regional paleoenvironment during the Late Holocene. From at least 4400 to 3250 yr BP the site was a lagoon surrounded by a relatively open forest. At ca. 3250 yr BP, after the retreat of the sea, a swamp forest occupied the area. This swamp forest remains until the present day. It was locally altered during a short period between ca. 1400 and 775 yr BP when, due to a rise in groundwater, a fresh water lake or marsh was formed. The climate was similar to the present during the whole Late Holocene, except for three slightly more humid episodes: 3250-2600, around 2000, and 1400-775 yr BP. No human impact on the vegetation was recorded during the Late Holocene. Our results show that sea level was higher than the present zero level from 4400 to 3250 yr BP, contradicting a widely accepted relative sea level trend that suggests that at least two important negative sea level oscillations occurred during the Holocene (4100-3800 and 3000-2700 yr BP). Conversely, these results tend to confirm more recent studies that propose a continuously declining relative sea level trend. Comparison of our data with those from 24 sites situated in southeastern, southern and central Brazil show that the more humid episodes recorded at Cananéia-Iguape might be correlated with El Niño like events. Trends in climatic evolution during the Late Holocene are opposite at north and south of 20ºS latitude.