Past and current mangrove dynamics on the Bragança Peninsula, Northern Brazil

Abstract

A wide mangrove belt of about 350 km occurs along the coast between the Amazon estuary and the Gurupi River (North Brazil). The main objective of this work was to identify and analyze the present effect of inundation frequency on system structure and of past changes in relative sea-level and climate, using tools such as palynology, radiocarbon dating, remote sensing and the Geographic Information Systems (GIS).The combination of topography and tidal regime data allowed, together with GIS tools, to determine frequencies and the extent of flooded areas. This allowed the association between the topographical characteristics of the peninsula and the main vegetation types. The current mangrove dynamics, specially gain and lost of vegetation coverage at the coastline, suggest a relative sea-level (RSL) rise.The examined sediment cores from Bragança recorded at least two transgressive events, which defined the spatial distribution of the mangroves on that area during the Holocene. The study area was flooded by a rapidly rising sea-level during the postglacial. The stabilization of sea-level near modern level was found around 5100 14C yr BP. Probably, between 1800 and 1400 14C yr BP occurred a maximum decrease of about 1 m below the modern RSL, following a gradual RSL rise until 1000 14C yr BP, when the RSL was re-established close to the current RSL. The integration of stratigraphic and palynological data indicate two dry periods with relatively low inundation frequency during the last 1000 years. The first event probably extended over a period of 500 years and took place between 860 and 370 14C yr BP. The second one started 200 14C yr BP and probably finished about 100 years ago. These two dry events occurred during the so called Little Ice Age period, characterized by dry periods in South America and glacier advances.