Impactos das mudanças do nível do mar nos manguezais do sudeste do brasil durante o holoceno e antropoceno usando uma abordagem multi-proxy

Abstract

Mangroves are intertidal forests, susceptible to changes in tidal flooding frequency. Then, its dynamics along the topographic gradients of a coastal plain may be used as an indicator of sea-level changes. This work aims to identify the mangrove dynamics during the Holocene and Anthropocene and infer relative sea-level (RSL) changes based on satellite/drone images and pollen, isotopes (δ13C, δ15N), elemental (C\N), X-ray fluorescence (XRF), and sedimentary data, as well as C-14 dating along three cores sampled along a mangrove and a transition mangrove/herbaceous zone following a topographical gradient of a coastal plain in the southeastern Brazilian coast. These multi-proxy data indicated a change from a flat occupied by herbs, palms, tree/shrubs to a lagoon surrounded by mangroves with an increase of sedimentary organic matter sourced from estuarine waters between ~6300 and ~4650 cal yr BP. The RSL rise caused a landward mangrove migration during the early-middle Holocene, widely recorded along the Brazilian coast. The RSL fall converted that lagoon with mangroves into a flat occupied by herbs, palms, and trees/shrubs during the middle-late Holocene. The last thousand years were characterized by a significant decrease in the mangrove pollen occurrence on highest tidal flats occupied by modern mangroves between 390 cal yr BP (1560 AD) and 77 cal yr BP (1873 AD), probably caused by a RSL fall associated with the Little Ice Age (LIA). The core G-4, sampled from the lowest tidal flats and mainly occupied by Rhizophora, revealed an increased trend in Rhizophora pollen percentage since 77 cal yr BP (1873 AD). However, cores sampled from the highest mangrove tidal flats, in the ecotone mangrove/ herbaceous vegetation, indicated an increase of pollen percentages of Rhizophora, Avicennia, and Laguncularia, suggesting a mangrove migration into the highest tidal flats previously occupied by herbs, palms, and trees/shrubs since 1958 (core G-3) and 1955 AD (core RBN-2). These trends must be related to the increase in estuarine influence by a RSL rise since the end of the Little Ice Age and intensified during the last decades.