Late Holocene development of a mangrove ecosystem in southeastern Brazil (Itanhaém, state of São Paulo)
Abstract Most palynological studies of mangroves have been carried out in the Indo-Pacific region, but few have investigated these ecosystems along the southern Atlantic coast. This paper provides information on the palynology of a mangrove at Itanhaem, state of Sao Paulo, on the southeastern Brazilian coast. This mangrove occurs on microtidal flats adjacent to a fluvial-tidal channel mouth (Itanhaem River), part of an estuarine lagoon system established in the mid-Holocene. Pollen samples were collected from the surface and from bromeliad water in order to define the composition of modern pollen rain in the study area. The results show a strong presence of rain forest taxa in the mangrove pollen spectra, which differ from those obtained from northern Brazilian mangroves, which are characterized by higher percentages of the mangrove taxa Rhizophora and Avicennia . Based on palynological and 14 C chronological analysis of a shallow core measuring 135 cm in depth, the Itanhaem mangrove already existed by 1300 years BP and began expanding about 1000 years BP, reaching its present extent sometime after 300 years BP. Its evolution is related to the sedimentary filling of the estuarine–lagoonal depositional system. Two factors may have controlled the development of this mangrove: the relative increase of intertidal areas due to this sedimentary filling and the decrease in wave action and increase in pelitic deposition in the intertidal zone related to the partial closing of the estuarine–lagoonal inlets. These processes were favored by the advance of bayhead deltas and by the development of sand spits as a part of the regression of the Holocene strandplain.