Late Quaternary vegetation and climate dynamics in southeastern Amazonia inferred from Lagoa da Confusão in Tocantins State, northern Brazil

Late Quaternary vegetation and climate dynamics have been reconstructed by pollen analysis of a lacustrine sediment core from Lagoa da Confusão. The lake lies about 160 km southwest of Palmas, capital of Tocantins State. The study area is located in the cerrado (savanna) and cerrado/Amazon rain forest transition region of southeastern Amazonia. The record, dated by 4 AMS radiocarbon dates, provide insight into vegetation and climate dynamics of late Pleistocene and Holocene age. Pollen data indicate that the study region was dominated by cerrado (savanna), fìrst of the campo limpo type (grassland savanna) between 60,300-51,700 (chronology A) or 29,000-27,400 (14)C yr B.P. (chronology B) and than of the campo sujo type between 51,700-24,670 (chronology A) or 27,400-14,000 (14)C yr B.P. (chronology B). Existing small areas of gallery forests increased slightly during the second period. Amazon forest taxa occurred sparsely in the study region. The palaeovegetation infer a markedly drier climate (low precipitation and long annual dry season) during the glacial periods compared to the modern climate. A sedimentary gap probably occurred during the full glacial and/or Lateglacial period, suggesting drier climatic conditions than during the two earlier periods. During the early and mid Holocene the campo cerrado type (savanna woodland) was dominant and the landscape was more forested by the stronger presence of gallery forest and Amazon forest trees. Precipitation was higher, and the length of the annual dry season was shorter than during the late Pleistocene periods. After 5460 (14)C yr B.P. campo cerrado was still dominant, but forest cover increased markedly by the expansion Amazon forest populations and palm trees, reflecting the wettest climate period recorded. The results from Lagoa da Conlusão support the general trend of dry glacial conditions, as reported from other tropical South American lowland regions. The expansion of the Amazon rain forest since the mid Holocene in northwestern and southwestern Amazonia is now also confirmed for the southeastern Amazon region

Impact of the Holocene sea-level changes in coastal, eastern and Central Amazonia

Pollen records from six sites are summarised and compared to provide insights in Holocene changes in the Amazon coastal and lowland regions of northern Brazil. The hydrology of Amazonian wetlands, especially those in the eastern part of the Basin, is strongly influenced by the Atlantic sea-level. Rapid sea-level rise in the early Holocene stabilized at near modern levels at ca. 7500 (14)C yr B.P. Mangroves first occur in coastal sequences of northeastern Pará State about 7500 (14)C yr B.P. The arrival of the mangroves in the pollen sequences is taken as an indication of sea-level. The retreat of mangroves after about 6700 (14)C yr B.P. reflects a lower relative sea-level. The modern mangrovos developed mostly between 4000 and 3500 (14)C yr B.P. or somewhat later at the present-day coastline. First impact of early Holocene sea-level rise in the Amazon Basin is found by the change of active to passive river systems between at ca. 8300 and 8000 (14)C yr B.P. Later, local Mauritia palm swamps developed along river margins in central and eastern Amazonia. The timing and length of this period differs and is probably related to the different location and topography of the rivers. It is suggested that the Mauritia palm swamp stage is a regional phenomenon for the whole low lying Amazon Basin. First várzea and igapó forests (seasonally inundated forests) developed at that time as well, but the area of this seasonally inundated forests was still small. The modern large extension of várzea and igapó forest areas is relatively young in age. In eastern Amazonia, marked increase of várzea/igapó forests is documented since 3120 (14)C yr B.P., especially since 2470 (14)C yr B.P., and in central Amazonia since 4070 (14)C yr B.P. and especially since 2080 (14)C yr B.P. The development of huge seasonally inundated areas must have had an important influence on the Amazonian water and carbon cycle and the regional climate in Arnazonia

Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant

Corrigendum to "Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)" published in Clim. Past, 4, 107–124, 2008

No abstract available

Orbital and millenial-scale environmental changes between 64 and 25 ka BP recorded in Black Sea sediments

High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ~64–55 and 40–32 ka BP, and two major humid phases ~54–45 and 28–20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard–Oeschger (D–O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ~500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ~54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials

Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifcations to forest expansion, but generally lacked high resoltiuon proxies to measure these efects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profles confrm that in spite of climatic fuctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifcations were linked to demographic changes, the efects of which are still visible today

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide

Pre-Retirement Attitudes and Financial Preparedness: A Cross-Cultural and Gender Analysis

The purpose of this research was to examine the differences between males and females across three different cultures in terms of financial resources for retirement years and pre-retirement attitudes and intentions