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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 (δ13C, δ15N, 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 km2 along tidal channels. Considering a RSL rise of 98 cm up to the end of the 21st 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 km2 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. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Generally, palaeoenvironmental interpretations consider only allogenic processes, when autogenic factors may have a strong influence on proxies of stratigraphic sequences. For instance, the Holocene history of the vegetation along the southern littoral of the State of Bahia in north-eastern Brazil is characterized by mangrove dynamics controlled by allogenic processes. However, over smaller timescales (~700 years), autogenic processes may have controlled vegetation dynamics and hence observed pollen distribution. This work proposes tidal channel dynamics as one of the main cause for changes in pollen assemblage along the studied stratigraphic profiles during the last centuries, based on sedimentology, pollen and elemental analysis (δ13C, δ15N and C/N) and radiocarbon dating of sedimentary organic matter from two cores sampled from an abandoned meander and a tidal flat at the mouth of the Jucuruçu River. One core was sampled from a mangrove formed during the past ~550 cal yr bp. Another core recorded sediments in a várzea forest (swamp seasonally and permanently inundated by freshwater) located ~2.7 km from the current shoreline, which displayed a maximum age of ~680 cal yr bp. Two facies associations were identified: tidal channel (A) and tidal flat/oxbow lake (B). This work proposes allogenic processes as the main driving forces controlling the wetlands dynamics at the studied site during the Holocene. However, our data also reveal that part of the changes in vegetation over the last ~700 years reflect tidal channels and tidal flats development, which represent autogenic processes. The change in timescale analysis from the Holocene to recent centuries may have weakened the influence of allogenic factors. However, this needs interpretation with reference to the spatial scale of the depositional environment as the larger the depositional system analyzed, the stronger the influence of autogenic processes on stratigraphic sequences over longer timescales. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution sedimentological, geochemical and pollen analysis on sediment core from the coastal plain of the Doce River, southeastern Brazil, revealed changes in the depositional system and vegetation caused by combined action of oscillations in relative sea-level (RSL) and sedimentary supply during the Holocene. Two main phases were discerned using sedimentary features, δ13C, δ15N, total organic carbon (TOC), total nitrogen (N), C/N and cluster analysis of pollen data, temporally synchronized with radiocarbon age dating. The data indicates the presence of a lagoon system surrounded by a tidal plain colonized by mangroves and its sedimentary organic matter sourced from C4 plants between ~8050 and ~7115calyrBP. However, during the mid- and late-Holocene the mangroves shrank and freshwater vegetation expanded (C3 plants), probably, due to a marine regression. During this phase, the development of a lacustrine environment was followed by the colonization of herbs, trees and shrubs. The continuous sediment infilling into the lake allowed the expansion of a herbaceous plain as seen today. This geomorphologic and vegetation evolution is in agreement with the mid-Holocene RSL maximum above present RSL and subsequent fall to the present time. [Copyright &y& Elsevier]

Winter temperature and sea-level position are critical factors affecting the global distribution of mangroves and saltmarshes. The replacement of saltmarshes by mangroves is expected due to global warming, reflecting the long-term natural trends in the Holocene and anthropogenic impacts since the 20th century. We documented the Holocene history of wetlands dynamics in the boreal limits of the American mangroves, located at Bay Champagne, Louisiana (USA), by integrating sedimentological, palynological, geochemical (δ13C and C\N), X-ray fluorescence (XRF) data, and radiocarbon chronology from two sediment cores. The results indicated a freshwater lake environment with herbs and wetland ferns, as well as C 3 terrestrial plants, between ~8100 and ~6500 cal yr BP. This environment shifted into a lagoon and saltmarshes having sedimentary organic matter sourced from marine algae between ~6500 and ~1500 cal yr BP. In the final stage, washover sediments were deposited in the lagoon during the last ~1500 cal yr BP. Despite the increased marine influence over the last ~6500 cal yr BP, mangrove pollen were not recorded between ~8100 and ~1500 cal yr BP, suggesting that mangroves were absent in the study area during that time interval. Historical evidence and a comparative analysis of our multi-proxy data with other mangrove studies from the Gulf of Mexico, Caribbean, and eastern South America revealed a gradual mangrove expansion from tropical to subtropical coasts of South and North America during the mid-late Holocene. The mangrove colonies at their current boreal (29° 09′ N) and austral (28° 29′ S) limits were established in the early and mid-20th century, respectively. This mangrove dynamics on a continental scale suggests that the poleward mangrove migration was likely caused by the warming climate during the Holocene. More importantly, the industrial-era warming has likely accelerated the mangrove expansion, but it was not the primary force that drove the mangrove migration into temperate zones. • Subtropical mangroves were studied by pollen, facies, isotopes and X-ray fluorescence. • Lake shifted into a lagoon with saltmarsh and marine organic matter at 6.5 k cal yr BP. • Mangroves did not occur between ~8100 and ~1500 cal yr BP in the study area. • Gradual warming caused poleward mangrove migration during the mid-late Holocene. • The industrial-era warming has likely accelerated the mangrove expansion. [ABSTRACT FROM AUTHOR]

Abstract: The dynamics, over the last 7500years, of a mangrove at Marajó Island in northern Brazil were studied by pollen and sedimentary facies analyses using sediment cores. This island, located at the mouth of the Amazon River, is influenced by riverine inflow combined with tidal fluctuations of the equatorial Atlantic Ocean. Herbaceous vegetation intermingled with rainforest dominates the central area of the island, while várzea is the main vegetation type along the littoral. In particular, the modern northeastern coastal zone is covered by a mosaic of dense rainforest, herbaceous vegetation, mangroves, várzea, and restinga. The integration of pollen data and facies descriptions indicates a tidal mud flat colonized by mangroves in the interior of Marajó Island between ~7500calyr BP and ~3200calyr BP. During the late Holocene, mangroves retracted to a small area (100–700m in width) along the northeastern coastal plain. Mangrove expansion during the early and mid Holocene was likely caused by the post-glacial sea-level rise which, combined with tectonic subsidence, led to a rise in tidal water salinity. Salinity must have further increased due to low river discharge resulting from increased aridity during the early and mid Holocene. The shrinking of the area covered by mangrove vegetation during the late Holocene was likely caused by the increase in river discharge during the late Holocene, which has maintained relatively low tidal water salinity in Marajó Island. Tidal water salinity is relatively higher in the northeastern part of the island than in others, due to the southeast–northwest trending current along the littoral. The mixing of marine and riverine freshwater inflows has provided a refuge for mangroves in this area. The increase in flow energy during the last century is related to landward sand migration, which explains the current retraction of mangroves. These changes may indicate an increased exposure to tidal influence driven by the relative sea-level rise, either associated with global fluctuations or tectonic subsidence, and/or by an increase in river water discharge. [Copyright &y& Elsevier]

The Atlantic Forest and mangrove dynamics along the Brazilian coast have been affected by climate, relative sea-level (RSL), and anthropogenic forces. Individualizing the effects of these drivers on paleoecological records is a challenge. This was addressed by pollen analysis along three cores sampled from lakes on a coastal plateau, primarily influenced by rainfall, and from a fluvial valley, influenced by sea-level and fluvial discharge, in northeastern Brazil. Pollen records from the fluvial valley indicated the presence of mangroves along an estuary in the mid-Holocene. During the past ~5800 cal yr BP, mangroves, adapted to brackish water, were replaced by herbaceous vegetation adapted to freshwater in the fluvial valley. Concurrently (~5680–240 cal yr BP), expansion of Atlantic Forest and contraction of herbaceous vegetation occurred on the coastal plateau. This divergence of pollen records between two distinct sedimentary environments (lakes on a coastal plateau and fluvial valleys) was attributed to RSL and climate effects. The combination of RSL fall and higher fluvial discharge favored seaward mangrove migration and expansion of herbaceous vegetation along the fluvial valley during the mid-late Holocene. However, the increase in rainfall on the coastal plateau favored the expansion of arboreal vegetation and contraction of herbaceous vegetation. At ~1700 CE, an abrupt shift from arboreal to herbaceous vegetation occurred on the coastal plateau. This vegetation change is likely attributed to European colonization on the southern coast of the state of Bahia, which was colonized by Portuguese navigators ~1500 CE. Part of the Atlantic Forest has naturally regenerated and was preserved as a national park in recent decades. This study showed that although the sampling sites are close, pollen assemblages can differ considerably depending on the depositional environment. Therefore, pollen analyses in different depositional environments are necessary to assess individually driving forces impacts on coastal vegetation dynamics during the Holocene. • Atlantic Forest and mangrove in the Brazilian coast were studied by pollen analysis. • Mangroves along fluvial valley were replaced by herbs after 5800 cal yr BP. • Atlantic Forest expanded and herbs area shrank on coastal plateau (5700–240 cal yr BP). • Abrupt shift from arboreal to herbs occurred on coastal plateau at ~1700 CE. • Climate, sea-level, and European colonization effects on vegetation were identified. [ABSTRACT FROM AUTHOR]