The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods.T he extreme biological diversity of tropical forests has inspired and puzzled naturalists and scientists for centuries, and the forest refuge hypothesis (FRH) has long been one of the major paradigms to explain it. According to the FRH, forest retraction and fragmentation during glacial periods would have promoted isolation and consequently allopatric speciation in forest patches, or ecological refuges, surrounded by open habitats in the Amazon (1). Although originally based on climate fluctuations in the Pleistocene, the FRH was subsequently invoked for climate changes irrespective of the time period (2). The FRH was also applied to South America's Atlantic Forest (3), one of the topfive biodiversity hotspots on Earth (4). The FRH gained broad acceptance during the 1980s when empirical paleoecological data from neotropical rainforests were still lacking. Nevertheless, heavy criticism came upon the FRH because some paleobotanical data showed that forests had persisted throughout glacial cycles (5). As paleoclimatic models of species and habitats became widely used, recent studies revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity and endemism are associated with historically stable Atlantic Forest areas (6).This hypothesis is ba...
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. accommodation regime. The interpretation shows that the entire study area can be 57 defined as a mixed sedimentation shelf, showing supply and accommodation regimes. 58
M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPTShelf morphology worked as an indicator of these changes. Carbonate/terrigenous 59 deposition during a highstand/regressive phase coeval along the eastern Brazilian shelf, 60 either laterally and across shelf. This lateral/along coast variation in sediment supply 61 and carbonate production leads to distinct lateral facies and geometry. These spatial 62 changes in morphology and facies, with coexistence of carbonate and siliciclastic 63 sedimentation, are very important for the correlation and interpretation of the geological 64 record, especially stratigraphic surfaces and sequence units. 65 66
ABSTRACT:In areas of the continental shelf where sediment supply is greater than the sediment dispersion capacity, an extensive terrigenous deposits and consequently submerged deltas can be formed. The Eastern Brazilian shelf is characterized by the occurrence of river-feed deltas in between starving coasts. Herein, modern sedimentary processes acting along the Doce river adjacent continental shelf are investigated. The main objective was to understand the shelf sediment distribution, recognizing distinct sedimentary patterns and the major influence of river sediment discharge in the formation of shelf deposits. The study used 98 surficial samples that were analyzed for grain size, composition and bulk density. Results revealed 3 distinct sectors: south -dominated by mud fraction with a recent deposition from riverine input until 30 m deep and from this depth bioclastic sands dominate; central--north -sand-mud dominated, been recognized as a bypass zone of resuspended sediment during high energy events; and north -relict sands with high carbonate content. The modern sedimentation processes along the Doce river continental shelf is dominated by distinct sedimentary regimes, showing a strong fluvial influence associated with wave/wind-induced sediment dispersion and a carbonate regime along the outer shelf. These regimes seem to be controlled by the distance from the river mouth and bathymetric gradients.
KEYWORDS:
A correlação de dados geofísicos (sonar de varredura lateral e perfilador de subfundo -3,5 e 7,0 kHz) permitiu a caracterização da distribuição de sedimentos de fundo na porção sul da Baía de Guanabara. Foram reconhecidos quatro tipos de ecocaráteres: o tipo 1, onde não ocorre penetração do sinal acústico e está relacionado a um fundo arenoso e a um padrão de reflexão do sonar homogêneo cinza claro com sand wave e mega-ripples; o tipo 2A, onde é observada a penetração do sinal com refletores do embasamento acústico e um fundo predominantemente lamoso com alto teor de areia fina a muito fina e padrão homogêneo cinza claro de sonar; o tipo 2B, com penetração do sinal com refletores sendo observados junto a um fundo predominantemente arenoso, com alto teor de lama e padrões de sonar homogêneos cinza escuros; e o último ecocaráter observado, o tipo 3, com penetração do sinal com uma série de refletores múltiplos, observando-se um fundo lamoso com alto teor de areia fina a muito fina e reflexão homogênea cinza escuro nos sonogramas.Palavras-chave: Baía de Guanabara; Sísmica de alta freqüência; Sonar de varredura lateral; Sedimentos de fundo.
CHARACTERIZATION OF SIDE-SCAN SONAR AND HIGH RESOLUTION SEISMIC (3.5 -7.0 kHZ) REFLECTION PATTERNS ALONG THE SOUTHERN MARGIN OF THE GUANABARA BAY -RJ -The correlation of geophysical data
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.