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The study of disarticulated ossicles of recent sea cucumbers from Campos Basin, Rio de Janeiro, Brazil, from various Holocene strata, obtained by micropaleontological methods, resulted in the identification of at least eight holothurian taxa, belonging to the five of the seven orders of Holothuroidea: Apodida (Synaptidae, Chiridotidae), Dendrochirotida (Psolidae and Cucumariidae), Holothuriida (Holothuria), and Molpadiida (Molpadiidae, Eupyrgidae). Our paper endorses the importance of studies of recent fauna based on isolated ossicles for taxonomy, biostratigraphy, and ecology. This study represents the first effort at the study of recent fauna of sea cucumbers based on the analysis of preserved ossicles in marine sediments. [ABSTRACT FROM AUTHOR]

This paper discusses data from the pioneering and the latest research in Serranópolis, Goiás, Brazil. It focuses on subjects such as landscape, mobility, territoriality, distribution of rock art sites, lithic material, anthropic action, and natural processes as elements that impact archaeological sites. The approach includes the hunter-gathering groups from the Itaparica (Paranaíba Phase) and Serranópolis (Serranópolis Phase) Traditions from Upper to Middle Holocene, which are characterized by their set of lithic artifacts. Therefore, some data resulting from research that took place between 2000 and 2020 by several researches were included in the previous study from 1980 to 2000 by Schmitz and his crew. The key element is the landscape analysed within a multidsciplinary approach through the Landscape Archaeology. This paper emphasizes some subjects that must be reanalyzed through current techniques and sustains that new excavations need to take place with a special attention to the relation between the landscape and the data developed under a geoarqueological point of view. [ABSTRACT FROM AUTHOR]

Northeastern Brazil has thousands of wetland fossiliferous deposits with megafauna and, in some cases, associated lithic artifacts. The timing of the arrival of humans in South America and the extinction of megafauna is still debated and these sites contribute both to this discussion and to the reconstruction of the Late Pleistocene and Holocene paleoenvironment. Lagoa do Quari, 40 km south of São Raimundo Nonato, Piauí state, is a marsh deposit in the present semiarid caatinga environment, excavated by an interdisciplinary team in 2002–2003. This paper presents the archaeological, palaeontological, geological, chronological, stratigraphical and palynological results and their implications for the Quaternary of northeastern Brazil. The site has a rich megafaunal bonebed at the bottom, dominated by Eremotherium giant sloth remains with poor biodiversity, and a sandy‐silty deposit at the top; two 14C dates constrain this latter layer to 9,944–9,557 and 6,308–6,177 cal. years BP and the associated rich lithic industry of quartz and chert shows a technical continuity throughout the Holocene in the region. Palynology describes an open landscape with periodic wet phases, which could explain the richness of the archaeological occurrences in Holocenic Brazilian prehistory. This study offers a model of interdisciplinary enquiry into the paleoenvironment and prehistory of lowland South America. [ABSTRACT FROM AUTHOR]

This paper presents carbon isotope data on soil organic matter (SOM) collected along an ecosystem transect that includes a wooded savannah (cerrado), a tropical semideciduous forest (cerradão), a forest transition type and a tropical forest. The study area is located in the Rondonia state, southwestern Brazilian Amazon region. 14 C data of total soil organic matter and charcoal indicate that the organic matter in these soils is at least Holocene in age. The forest and forest transition sites are characterized by d 13 C soil depth profiles generated typically by C3 plants, indicating no major changes in plant communities have occurred in this region during the time period represented by the isotope data. In contrast, the cerrado and cerradão have experienced significant vegetation changes during the Holocene. The d 13 C data (-30‰ to -27‰) obtained in the deepest part of the profile at the cerradão site show the expansion of the C3 forest vegetation into this region during early Holocene. A vegetation change consisting of increased C4 plant influence is reflected in the 13 C-enriched values (-19‰ to -16.0‰) at both sites during the middle Holocene. The recent part of the 13 C record shows a clear expansion of C3 vegetation, particularly at the cerradão site. The regression/expansion of the forest and savannah vegetation documented at the cerradão and cerrado sites is probably related to changes from a humid to a drier climate and a return to more humid conditions and is in agreement with palaeoclimatic information reported for Brazil and the Bolivian Altiplano. This study suggests that large areas in the Amazon basin have been affected by vegetation changes during the Holocene and that soil organic matter in the transition areas between savannah and forest ecotones contains a valuable palaeorecord of vegetation changes in the Amazon region. [ABSTRACT FROM AUTHOR]

The aim of this paper is to reconstruct an 11,000-year history of depositional environmental change in southeastern Brazil, based upon the integration of particulate organic matter and stable isotope (C and N) data from a 136-cm sediment core from Lake Canto Grande. These proxies are used to explore the evolution of terrestrial and marine influence on the lake. Isotopic (δ 13 C: −27.87‰ to −31.9‰; δ 15 N: −0.07‰–4.9‰) and elemental (total organic carbon - TOC: 0.58%–37.19%; total nitrogen - TN: 0.08%–1.73%; C/N: 0.3 to 54.7) values recorded in Lake Canto Grande suggest that the sedimentary organic matter was derived from mostly C 3 land plants and freshwater phytoplankton. Particulate organic matter and cluster analyses distinguished four associations characterized by the predominance of amorphous organic matter, followed by phytoclasts and palynomorphs. These results indicate two different phases of lake evolution. The first phase (136 - 65 cm; ∼10,943 cal yr. B.P. to ∼8529 cal yr. B.P.) is recorded by sand layers interbedded with mud, which contain amorphous organic matter (AOM, 45–59%) and phytoclasts (opaques - OP: 6–18%; non-opaques – NOP: 17–23%) which indicate a floodplain area. The second phase (65–0 cm; ∼8529 cal yr. B.P. to ∼662 cal yr. B.P.) comprises mud, AOM (68–86%) and palynomorphs (PAL, 8–16%) related to lake establishment comparable to modern conditions. Thus, characterizing particulate organic matter, in combination with stable isotopes, proved to be invaluable proxies for lacustrine paleoenvironmental change through the Holocene. [ABSTRACT FROM AUTHOR]

This paper presents the geological and morphological evolution of the prograded Cassino barrier during the middle and late Holocene. A special focus is given on the presentation and discussion of records of environmental changes that occurred during barrier progradation. The results demonstrated that variable rates of progradation were produced by environmental changes that affected the coastal sediment budget, such as changes in the wave climate. The total progradation of 18 km recorded for the Cassino barrier is probably the highest extension of progradation registered for a ridge plain associated with a coastal barrier. Sea-level changes during barrier progradation were accessed by the high difference between the degree of compaction of the foredune and backshore/foreshore deposits detected by the drilling system applied in this study and were confirmed by the limit of those deposits, which were also revealed by GPR records. During most of the time of barrier progradation, an overall sea-level fall of approximately 2 ± 1 m occurred. Six sets of relict foredune ridges were identified, and the limits between them were well marked by ridge truncations and the formation of transgressive dune sheets (TDS). Optically stimulated luminescence ages show that the TDS were formed under the driest climate conditions, with age periods very close to 3.8, 3.5, 1.9, 1.5, 0.22 and 0.09 ka ago, interspersed with ages of known wetter conditions in southern Brazil. The modern phases of TDS formation, with ages varying from 0.25 to 0.22 ka ago, were coincident with the time period of the younger pulse of the Little Ice Age (LIA), which was characterized by arid and cold conditions in southern South America. A comparison with prograded barriers located 350 to 600 km to the north suggests the existence of teleconnections, with phases of TDS and parabolic dunes that formed with a time interval of approximately 405 to 583 years. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an evolutionary model for a coastal barrier in the southernmost coastal sector of Brazil during the Holocene. The dataset is based on 15–20 m drill cores and ground-penetrating radar (GPR) records. The model barrier evolution has two main steps. The first step is the transgression of the barrier controlled by sea-level rise during the Postglacial Marine Transgression, which ended at approximately 6–5 cal ka. Radiocarbon dating indicates that the coastal plain began to be flooded by lagoonal waters between ∼10 and 6.7 cal ka. The second step comprises a barrier transgression controlled by a negative sediment budget of the beach system during the last 6–5 cal ka in a period of an overall slow sea-level fall of approximately 2 m. During the second step, the transgressive barrier migrated because of coastal erosion (the negative sediment budget) and the landward transference of sand by wind and lagoonal delta washout. [Copyright &y& Elsevier]

The coastal plain of southern Brazil documents several environmental changes mainly related to sea-level fluctuation and climatic variations during the Quaternary. Comprehensive studies have been carried out, of local and regional scope, in order to improve the knowledge about the geological evolution of this portion of the South American. In this paper we present the results of stable isotope, palynological and palynofaciological analysis of the PSC-03 core (7744 cal yr BP – Modern) was performed to provide the sedimentary evolution of the Santa Catarina coastal plain. Palynological and palynofacies analyses revealed abundant and diversified palynological associations, including terrestrial palynomorphs (spores, pollen grains, fungi, and freshwater algae), marine elements (dinoflagellate cysts and foraminiferal linings), besides abundant phytoclasts and amorphous organic matter. Based on the combined analysis of δ13C isotopes (−20.7 ‰ to −29.6 ‰) and the C/N ratio (15.5–68) of the selected samples, we deduce that the organic matter is derived from marine phytoplankton and terrestrial C 3 plants. The integrated approach of palynofacies and stable isotopes (δ13C and C/N) analyses revealed three distinct intervals, which characterize the environmental evolution of this portion of the coastal plain. The Interval I (7744 to 2844 cal yr BP) is related to a marginal marine environment, followed by the Interval II (2857 to 2276 cal yr BP), which indicates shallow water conditions, with wetland or soggy soils, while the Interval III (2124 cal yr BP to Modern) shows a subaerial scenario, strongly influenced by arboreal forms of the Atlantic Forest. Comparisons with other sites in southeastern South America were carried out, especially from Uruguay and Argentina, showing similarities in the palynological succession, as response to broader climatic conditions. • Stable isotopes (δ13C and C/N) and palynofacies analyses are used for understanding coastal evolution of southern Brazil. • Three paleoenvironmental phases are identified within the last 7744 cal years BP. • The marine influence is evidenced between 7744 and 2884 cal years BP. • Major development of the Atlantic Forest in the area from 2124 cal years BP onwards. [ABSTRACT FROM AUTHOR]

In the southern tropical Andes, previous studies performed on lacustrine basins display large water-level fluctuations due to changes in the precipitation minus evaporation balance during the Holocene. Significant changes in groundwater levels were also inferred from river paleowetland deposits in northern Chile and the northern Bolivian Altiplano but the discrepancies which appeared in the data from paleolakes and paleowetlands are still not understood. In this paper we present stratigraphy and diatom analyses in new paleowetland records from non-glacial valleys. These data, compared with previous results, show that non-stormy precipitation (recorded by fine and/or organic sedimentation) dominated continuously from ∼11 200 to ∼1500 cal yr BP and that convective rainfall (recorded by strong erosion) occurred only episodically in the northern Altiplano. Convective rainfall was similar to the type of precipitation which nowadays occurs during the rainy season (austral summer) when the tropical easterlies from the Atlantic reach the Bolivian Andes. Non-stormy precipitation is interpreted as a result of an intensification of cold-air incursions from southern polar regions, in good agreement with data from Brazil. The maximum intensity in cold-air incursions occurred during the Early Holocene and coincided with a climatic optimum in Antarctica and a considerably reduced El Nin˜o Southern Oscillation (ENSO). During the Middle and Late Holocene, cold-air incursions decreased and the ENSO frequency increased. We suggest that the interactions between the southern high and low latitudes, by means of cold-air incursions and associated changes in the west wind flow, have been the main mechanisms involved in climatic changes at the latitudes of Bolivia. [Copyright &y& Elsevier]

Deltaic systems possess singular morphology and represent a portion of the Brazilian large fluvial systems, with complex dynamics and mouths located at the Atlantic Ocean. Landscapes generated are occupied by diverse human activities over the coast and depend on a certain degree of dynamic equilibrium to its maintenance. The mouth of Jequitinhonha River, located at the extreme South of Bahia state, has suffered great transformations over the last decades, causing coastal erosion processes due to fluvial discharge reduction, thus changing the local dynamic. So, to understand the preterit deltaic dynamic and the possible agents of the current changes, we proposed an approach utilizing grain size and Optically Stimulated Luminescence (OSL) of the deposits by the river mouth, with the processes currently demonstrated. The main results point to mixed depositional environment over the sampling points and additionally in depths, demonstrating cyclicity of depositional agents and energy. Depositional ages obtained were 2.72 ± 0.23 (Ky) for the left riverbank, 1.1 ± 0.15 (Ky) for the right riverbank, and the youngest deposit located at the front island, with absolute dating of 0.555 ± 0.065 (Ky). The results evidence a tendency of coastal progradation during the last thousands of years, prior to anthropic interventions which diminished and regulated fluvial discharge of Jequitinhonha River, resulting in advancement of local coastal erosive processes. [ABSTRACT FROM AUTHOR]

Modern precipitation over northeastern (NE) South America is strongly controlled by the seasonal meridional migration of the Intertropical Convergence Zone (ITCZ). Ample evidence from the Northern Hemisphere suggests a mid‐ to late Holocene southward migration of the ITCZ. Such a shift would be expected to increase precipitation over semi‐arid northern NE Brazil (Southern Hemisphere). However, the most robust precipitation record from northern NE Brazil shows a drying trend throughout the Holocene. Here, we address this issue presenting a high‐temporal resolution reconstruction of precipitation over northern NE Brazil based on data from a marine sediment core, together with analyses of mid‐ and late Holocene simulations performed with the fully coupled climate model FGOALS‐s2. Both, our data and the climate model simulations show a decrease in precipitation over northern NE Brazil from the mid‐ to the late Holocene. The model outputs further indicate a latitudinal contraction of the seasonal migration range of the ITCZ that, together with an intensification of the regional Walker circulation, were responsible for the mid‐ to late Holocene changes in precipitation over NE South America. Our results reconcile apparently conflicting precipitation records and climate mechanisms used to explain changes in precipitation over NE South America. Plain Language Summary: The tropical rainbelt impacts food and water security for 1 billion people. Knowing its dynamics is of utmost importance. The suggestion of a southward migration of the tropical rainbelt through the Holocene (last 11,700 years) has influenced paleoclimatology for two decades. However, most of the available evidence supporting this suggestion comes from tropical Northern Hemisphere precipitation reconstructions like northernmost South America. They systematically show a decrease in precipitation through the Holocene. In the tropical Southern Hemisphere like northeastern Brazil, at the opposite side of the tropical rainbelt, precipitation reconstructions are, however, rare. We reconstructed mid‐ to late Holocene (last 5,200 years) changes in precipitation over northeastern Brazil (tropical Southern Hemisphere), where modern precipitation is associated with the southern border of the tropical rainbelt. We analyzed three independent indicators of changes in precipitation recorded in marine sediments collected off northeastern Brazil. All indicators suggest a decrease in precipitation over northeastern Brazil from the mid‐ to the late Holocene. Together with climate model simulations, our results indicate a latitudinal contraction of the tropical rainbelt. A Holocene contraction of the rainbelt, in contrast to a southward migration, reconciles apparently conflicting precipitation reconstructions and provides valuable insights into the dynamics of the tropical rainbelt. Key Points: Precipitation over northern northeastern Brazil decreased from the mid‐ to the late HoloceneThe meridional migration range of the Intertropical Convergence Zone contracted from the mid‐ to the late HoloceneTogether with the intensification of the regional Walker circulation, our results reconcile previously conflicting records [ABSTRACT FROM AUTHOR]

Shell concentrations are one of the most distinctive features of the Holocene coastal stratigraphy in the southern portion of Santa Catarina State, southern Brazil. In this paper, we integrated stratigraphic, geochronological, geophysical, and taphonomic data to discuss the processes involved in the genesis of shell concentrations in a siliciclastic and subtropical setting, a useful analogy for ancient shell concentrations in semi-closed environments affected by storms. The data indicated the succession of three facies associations (FA): bay, lagoon, and back-barrier. This succession implies a grain size fining-upward trend that is representative of a gradual shallowing. Interpretation of GPR sections revealed that the passage from the bay to lagoonal deposits occurred by forming a laterally continuous, high-amplitude surface overlain by sigmoidal reflections, which characterized the progressive basinward backstepping of the lagoonal margin. Shell concentrations in bay deposits are an allochthonous product of storm flows in shallow waters. In contrast, accumulations of the bivalve Anomalocardia brasiliana had their valves reworked in the lagoonal margins and transported to the bottom, characterizing a parautochthonous accumulation. In this study, the correlation of taphonomy and grain size indicates that in bay FA, the loss of periostracum is correlated with increased gradients of fine sand, and part of the shell samples correlates to corrosion and abrasion in increased gradients of medium sand and decreased ones of fine sand. Additionally, in the lagoon FA, the loss of periostracum depends on the decrease in mud-enriched sediments and the increase in fine and medium sand, whereas brightness loss and color alteration are related to the increase in fine and medium sand, as well as margin modification. Corrosion was positively correlated to the mud-dominated fraction. • Dense concentrations of bivalve shells occur in the bay and lagoon facies association. • Allochthonous and parautochthonous bivalve shell concentrations were differentiated. • In bay FA, the loss of periostracum positively correlates to fine sand. • In the lagoon FA, corrosion was positively correlated to mud-dominated sediments. • Gradients of medium sand and fine sand correlated to corrosion and abrasion. [ABSTRACT FROM AUTHOR]

The Brazil-Falklands/Malvinas Confluence (BFMC), a highly energetic convergence of surface currents in the western South Atlantic, has shifted southward in recent years and this shift is projected to progress in the future. Palaeoecological insights documenting past changes of these currents may help in anticipating future impacts on the environment. We used dinoflagellate cyst analyses from a marine sediment core to reconstruct environmental changes in the Argentine continental margin, western South Atlantic, during the last ca. 12,600 years. The dynamics of the BFMC were reconstructed using the relative frequency of warm-water indicators for the Brazil Current (BC) versus cold-water taxa thriving in the Falklands/Malvinas Current (FMC). We found that the latitudinal position of the BFMC was relatively stable with only minor amplitude migrations between 12.6 and 8.7 cal kyr BP, followed by periods with stronger shifts to the south and the north until 0.66 cal kyr BP. After that, the BFMC shifted continuously to the south. The increase in freshwater algae abundance after ca. 5.7 cal kyr BP suggests an increase in precipitation over the adjacent Rio de la Plata drainage basin in south-eastern South America. As previously documented, such an increase in precipitation was probably related to a higher El Niño-Southern Oscillation frequency and longer, stronger El Niño events since the mid-Holocene. The dinoflagellate cyst record indicates a phase of the enhanced presence of nutrient-rich waters over the core site between ca. 6.3 and 5.7 cal kyr BP, as well as from 0.66 cal kyr BP to the recent. The highest eutrophication in the ocean surface occurred during the last ca. 100 years, most probably due to stronger human impact in the area of the Rio de la Plata drainage basin. [ABSTRACT FROM AUTHOR]

A paleoenvironmental reconstruction was performed in a Riparian Forest near Campinas to improve knowledge of paleoclimate and paleoenvironment in the State of São Paulo, Brazil. A sediment core of 182 cm depth was collected in a swamp located within a Cerrado/Seasonal Semi-deciduous ecotone forest. The chronological frame is given by eight radiocarbon dating methods. Pollen and stable isotope analyses (d 13C and d 15N) were performed all along the core. Modern pollen rain is based on five surface samples collected along the Riparian Forest. Results show a sequence of changes in vegetation and climate between 25 and 13 cal kyr before present (BP), and from 4 cal kyr BP to the present time, with a hiatus between 11 and 4 kyr cal BP. Drier climatic conditions characterized the late Pleistocene and early Holocene, although they had moisture peaks able to maintain an open forest. The Riparian Forest became fully installed from 4 cal kyr BP onward. Our results are in agreement with other regional studies and contribute to build a regional frame for past climatic conditions at the latitude of São Paulo. [ABSTRACT FROM AUTHOR]

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A large area in northeastern Marajó Island, northern Brazil, has been characterized geomorphologically, applying information acquired from Landsat imagery. This study was combined with detailed sedimentologic analysis of continuous cores, which provided a record of depositional settings developed in this area through the Holocene. The results revealed well-preserved, meandering to anastomosed drainage networks of wide palaeochannels that were superimposed by a narrower palaeochannel system. In both cases, the sedimentary record consists of sands, heterolithic deposits and muds, locally rich in plant debris. The strata are organized into fining upward successions that reach approximately 18 m thick in the wide channels and 4 m thick in the narrow channels. Sedimentary features suggestive of a coastal location for the wider palaeochannels and reworking of sediments by tidal currents include the prevalence of well to moderately sorted, rounded to subrounded, fine- to medium-grained sands displaying foreset packages separated by mud couplets, suggestive of tidal cycles. The data presented herein point to a rise in relative sea level reaching the Lake Arari area during the early to late/mid Holocene. This event was followed by a relative sea level drop. Tectonics seem to have contributed to an overall lowering in relative sea level in the study area since the mid-Holocene, which does not follow the same pattern recorded in other areas along the northern Brazilian coast. [ABSTRACT FROM AUTHOR]

Aim We aim to propose validated, spatially explicit hypotheses for the late Quaternary distribution of the Brazilian Atlantic forest, and thereby provide a framework for integrating analyses of species and genetic diversity in the region. Location The Atlantic forest, stretching along the Brazilian coast. Methods We model the spatial range of the forest under three climatic scenarios (current climate, 6000 and 21,000 years ago) with BIOCLIM and MAXENT. Historically stable areas or refugia are identified as the set of grid cells for which forest presence is inferred in all models and time projections. To validate inferred refugia, we test whether our models are matched by the current distribution of the forest and by fossil pollen data. We then investigate whether the location of inferred forest refugia is consistent with current patterns of species endemism and existing phylogeographical data. Results Forest models agree with pollen records and predict a large area of historical forest stability in the central corridor (Bahia), as well as a smaller refuge (Pernambuco) along the Brazilian coast, matching current centres of endemism in multiple taxa and mtDNA diversity patterns in a subset of the species examined. Less historical stability is predicted in coastal areas south of the Doce river, which agrees with most phylogeographical studies in that region. Yet some widely distributed taxa show high endemism in the southern Atlantic forest. This may be due to limitations of the modelling approach, differences in ecology and dispersal capability, historical processes not contemplated by the current study or inadequacy of the available test data sets. Main conclusions Palaeoclimatic models predict the presence of historical forest refugia in the Atlantic rain forest and suggest spatial variation in persistence of forests through the Pleistocene, predicting patterns of biodiversity in several local taxa. The results point to the need for further studies to document genetic and species endemism in the relatively poorly known and highly impacted areas of Atlantic rain forests of north-eastern Brazil. [ABSTRACT FROM AUTHOR]

An examination of the late Holocene environmental and cultural sequences of the southern Brazilian highlands indicates that the colonisation of this region by the Taquara/Itararé people is associated with the expansion of Araucaria forest resulting from the onset of wetter climatic conditions in the region, which started between around 1410 and 900 cal. yr BP. The more intense and permanent human occupation of this region is associated with the advance of Araucaria forest, which provided Taquara/Itararé groups with a newly abundant and reliable resource: Araucaria seeds. In addition, we review the evidence for landscape transformation associated with the beginning of food-production in the region. Charcoal records show that local populations may have practiced slash-and-burn agriculture at lower elevations since the beginning of the late Holocene around 4320 cal. yr BP, and continued this practice during the second part of the late Holocene. [ABSTRACT FROM AUTHOR]

Soils in the Barreirinhas region, Maranhão State, were sampled for δ13C analysis and buried charcoal fragments in the soils were radiocarbon dated. Three soil profiles collected in forested areas around the Lagoa do Caçó and one in a woody savanna (mixture of non-arboreal and arboreal species) located approximately 10 km southeast of the Lagoa were studied. A high-resolution pollen record was obtained from lake sediments, showing that forest vegetation was predominant in the area in the early Holocene. From approximately 10 000 14C yr BP the pollen spectrum gradually changed, suggesting the dominance of open savanna communities, these were transformed to a more forested landscape (woody savanna) from approximately 7500 yr BP. The lake sediments also record evidence of fire (indicated by buried charcoal particles at several soil depths) during the Holocene. The δ13C analysis of soil organic matter (SOM) indicates that from between approximately 10 000 yr BP and 9000 yr BP to ~4000 yr BP, a woody savanna prevailed at two sites around the lake, probably reflecting a drier climate. From ~ 4000-3000 yr BP to the present, the results indicate a moderate and progressive increase in arboreal vegetation around the lake as a result of the return to more humid climate conditions probably similar to the present-day. The carbon isotope results from the site located 10 km from the lake indicate the presence of an open vegetation from the early Holocene. In general, there is agreement between the palaeovegetation patterns inferred from the pollen and carbon isotope data. However, a much less uniform landscape, with a mosaic of different ecosystems at any given time, is inferred from the carbon isotope record. [ABSTRACT FROM AUTHOR]

From west to east, the Fluminense coastline, composed of two series of lagoons, presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south Atlantic. The physico-chemical conditions of the lagoons are controlled by the duration of the dry season. They are characterized by hypersaline conditions with organic-carbonate sedimentation in the upwelling-influenced area, and by hyposaline conditions with organic-detrital sedimentation out of the upwelling-influenced area. On a core collected in the Brejo do Espinho hypersaline lagoon, diatom analysis supported by sedimentological data revealed a varying high water level from 4500 to 2200 14C yr BP induced by successive freshwater inputs in to the lagoon. Two major dry events occurred during this period, probably related to relative sea-level fluctuations. At 2200 14C yr BP, a drastic change occurred, as indicated by a carbonate nodule, carbonate-dominated sediments and poly- to hypersaline diatoms, all suggesting arid conditions. The Brejo do Espinho record suggests that before 2200 14C yr BP, the central part of the Brazilian coast was mostly subjected to south to southeasterly winds and weaker trade winds, whereas after 2200 14C yr BP, trade winds dominated, implying drier conditions at the easternmost part of the Fluminense coastline. These results would also suggest a late Holocene increase in El Niño activity (after 2200 14C yr BP), consistent with several El Niño records from western South America. [ABSTRACT FROM AUTHOR]

Carbon isotope data on soil organic matter (SOM) were collected along an ecosystem transect 90 m in length that includes a tropical forest on the plateau, a transitional forest-savanna and savanna in a depression. Total organic carbon data show a significant increase in carbon content from sites representing forest ecosystem to sites representing savanna ecosystem. It was hypothesized that carbon accumulation in the depression is controlled by flooding conditions that slow down carbon decomposition and in part by carbon transport from the upper part of the transect (the savanna and the transition forest-savanna areas) into the depressions by water during the rainy season. The origin of the carbon was confirmed by using soil 13 C analysis. The savanna sites located in the depression showed d 13 C values between –19.5‰ and –22.5‰ indicating a mixture of C3 and C4 plants. The vegetation cover in the depression is predominantly C3 grasses with d 13 C values of about –27‰ and –26‰. In the site under savanna located at an elevation slightly higher, the d 13 C value was more enriched (–16‰) showing the predominance of C4 plants ( d 13 C of –13.6‰). At the forest-savanna transition and in the forest ecosystem the d 13 C values were characteristic of C3 plants (–25‰ and –28.1‰). 14 C and 13 C data indicate that the organic matter of mixed origin has been deposited for at least the last 7000 years in the savanna depressions. The 13 C pattern observed in the soil organic matter profiles indicate a predominance of C3 plants in the early part of the Holocene. About 7000 to 4000 years ago, the data show the influence of C4 plants, indicating forest regression associated with a drier climate than at present. The more recent 13 C records suggest forest expansion, and the return to a climate similar to the present. [ABSTRACT FROM AUTHOR]

Geomorphologic studies and palynological analysis of a core in the middle of Lagoa Santa, a lake in central Brazil (19°389S; 43°549W), have provided palaeoenvironmental information on the region and lake history during the Holocene. Prior to 5300 yr BP there is no pollen record in the sediments. The presence of spores of Lycopodium and algae (Phase I) between c. 6100 and 5400 yr BP indicate a gradual increase of moisture in the ancient valley. Between c. 5400 and c. 4600 yr BP the records of pollen, spores and algae indicate the presence of an intermittent marsh on the valley floor (Phase IIA) and a climate drier than at present; Gramineae pollen dominates the assemblages, followed by Compositae and Portulacaceae. At approximately 4600 yr BP pollen grains are abundant, percentage of arboreal pollen increases and Lycopodium spores are replaced by fern spores of a moist environment; the marsh was replaced by a permanent lake (Phase IIB). An ancient landslide scar was probably active shortly before this time and started to deposit debris at the basin outlet causing the formation of the permanent lake that has existed since then. A mosaic of forests and ‘cerrado’ (savannah-like vegetation) covered the region around the lake and the climate was warm semi-humid, similar to the present. The abundant archaeological sites dating from c. 5000 yr BP are coeval with the formation of the lake and of the change towards a more humid phase. From c. 3000 yr BP to the present, changes in the percentage of arboreal pollen indicate small oscillations in precipitation. The uppermost 20 cm of the sediment contains oxidized clay mixed with the lake sediment. Nevertheless, the well-preserved palynomorphs show that the oxidized material was transported to the lake as a result of human activities around the basin. The depletion of Stryphnodendron spp. trees in recent last centuries confirms human disturbance of the natural ecosystems. In general terms, the climatic variations detected at Lagoa Santa during the Holocene are in accordance with those in other parts of central Brazil. [ABSTRACT FROM AUTHOR]