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Projections of the impacts of modern Relative Sea Level (RSL) rise on estuarine mangroves should be supported by coastal topographic data and records of mangrove dynamics under past RSL change. This work identified inland and seaward mangrove migrations along the Jucuruçu River (Bahia, Northeastern Brazil), during the Holocene based on sedimentary features, palynological and geochemical (δ 13 C, δ 15 N, C/N) data integrated with digital elevation models. During the Middle Holocene, in response to RSL rise, the estuary saw mangrove forest establish up to~37 km inland. RSL stood between -1.4 (+0.36/-2.2 m) and +1 (2.19/0.2 m) around 7400 cal yr BP, and rose to a highest position of +3.25 (4.22/2.45 m) reached around 5350 cal yr BP. That marine incursion caused the inland replacement of freshwater vegetation by mangroves on tidal flats. Since then, the estuary experienced RSL fall, reducing inland tidal water salinity towards the Late Holocene, making that the mangroves were replaced by freshwater floodplain vegetation. Today, in the seaward part of the estuary near its mouth, mangroves occupy an area of~10 km 2 along tidal channels. Considering a RSL rise of 98 cm up to the end of the 21 st century, at a rate significantly higher than that of Middle Holocene RSL rise (1.5 mm/yr) and fall (0.6 mm/yr), the current mangrove substrates are expected to drown and/or eroded near the coast, while new mangroves may establish inland, at topographically higher tidal flats in nowadays freshwater-tidal zones. Mangrove area could expand over 13 km 2 of coastal and flood plain. Following the same interaction between RSL/climate changes and Holocene mangrove dynamics, such upstream mangrove migration may be attenuated or intensified by changes in fluvial discharge.

This work aims to study the impacts of climate change in the subtropical mangroves during the late-Holocene on a southern Brazilian coastal plain and discuss the environmental conditions to the mangrove establishment near the austral limit of South America mangroves. Samples were collected to study palynological groups, sedimentary facies, and geochemistry analyses (δ13C, δ15N, TOC, TN, C:N ratio, TS, and C:S ratio), synchronized with four radiocarbon ages. The main result of this research was the mangrove succession, divided into three palynological zones composing two facies association: (1) herbaceous tidal flat and (2) mangrove tidal flat. The first zone between at least ~1815 and ~1629 cal. yr BP was marked by the mangrove absence with marine particulate organic carbon, C3 terrestrial plants, and macrophytes organic matter influence with δ13C values between −26.7‰ and −20‰, δ15N values x̅ = 3.5‰ and C:N around 21.8. The second zone between ~1629 and ~853 cal. yr BP was marked by the mangrove establishment represented only by Laguncularia pollen under influence of estuarine organic matter (δ13C x̅ = −26.5‰; δ15N x̅ = 3.2‰, and C:N around 16.4). The third zone reveals an increase of Laguncularia and presence of Avicennia pollen since ~853 cal. yr BP. Near the surface (<10 cm) occurs Rhizophora pollen, indicating the establishment of this genus during the past decades, under the modern environmental condition (δ13C x̅ = −27.02‰; δ15N x̅ = 3.12‰, and C:N around 17.42). This mangrove vertical succession may be associated with the low-temperature tolerance, where the sequence Rhizophora, Avicennia, and Laguncularia occurs from the northern to the southern limits of Santa Catarina coast, respectively, reflecting the temperature gradient. Therefore, probably, the establishment of the mangrove assemblage identified along the studied pollen profile was influenced by a temperature increase of air and water during the late-Holocene and, considering the Rhizophora genus, only during the past decades.

The aim of this paper is to evaluate the compatibility between the Holocene relative sea-level (RSL) curves proposed for the Brazilian littoral and mangrove dynamics along a fluvial valley in the state of southern Bahia. This was done integrating geomorphological, sedimentological, palynological, and stable isotopic data from two cores collected at the mouth of the Jucuruçu River and at a site 23 km inland, near the city of Prado, northeastern Brazil. Core PR07, sampled from a fluvial plain at about 4.5±1 m above the RSL, reveals mangrove pollen (5–20%) and estuarine/terrestrial organic matter (δ13C=~–25‰, C/N=7.3–67) between 4.5 m (~7400 cal yr BP) and 1.75 m depth (~5350 cal yr BP). Core PR11, sampled from a mangrove tidal flat, also revealed mangrove pollen taxa (5-28%) since 660 cal yr BP. Core PR07 indicated absence of mangrove pollen and increase of sedimentary organic matter sourced from terrestrial C3 plants (δ13C=~–27‰, C/N=22–159) during the last 5350 cal yr BP. Probably, the changes in vegetation and sedimentary organic matter identified in core PR07 were caused by the combined effects of the RSL fluctuations, with a highstand at about 5350 cal yr BP of 2.7±1.35 m, and changes in fluvial discharge.

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