Millenial-scale climatic and vegetation changes in a northern Cerrado (Northeast, Brazil) since the Last Glacial Maximum

In the Southern Hemisphere, lacustrine sediments started to be deposited with the beginning of the deglaciation at ca 19,000 cal yr BP. At this time the region of Lake Caço was dominated by sparse and shrubby vegetation with dominance of steppic grasses in a poor sandy soil. The landscape did not present any ecological characteristics of a modern Cerrado. However single pollen grains of two Cerrado indicators, Byrsonima and Mimosa, suggest that some Cerrado species were able to survive under the prevailing arid climate, probably as small shrubs. After 15,500 cal yr BP, a sudden increase in the moisture rates is evidenced with the progressive expansion of rainforest showing successive dominance of various associations of taxa. The development of the forest stopped abruptly at the end of the Pleistocene between 12,800 and 11,000 cal yr BP, as attested by strong fires and the expansion of Poaceae. In the early Holocene an open landscape with a relatively high level of water in the lake preceded the progressive expansion of Cerrado species towards a denser forested landscape; fires are recorded from then on, resulting in the physiognomy of the Cerrado we know today. Late Pleistocene paleoenvironmental records from northern Brazil reflect the interplay between insolation forcing of two hemispheres with the local components represented by the interannual shift of the Inter Tropical Convergence Zone and the influence of seasonal equatorwards polar air incursions. © 2005 Elsevier Ltd. All rights reserved.This research benefited from a CNPq (Brazil)–IRD (France) convention and is part of Paléotropique UR 55 at IRD.Peer reviewe

Overview of Quaternary pollen records in Central and South America, Caribbean and Mexico

For over a decade the general impression of research on past and present pollen– vegetation relationships has been incomplete in most of the Neotropics. Continental-scale synoptic studies often missed out on the vast majority of potentially available studies and data. Here we present an inventory of palaeoecological research in Central and South America, Caribbean and México, in terms of pollen records and modern rain samples. With a set of maps, we show that there are over 1400 cores and sections with palaeoecological data and more than 4800 modern samples. Some biomes and regions have a relatively high research density while the scarcity at others offer opportunities for future research. An increasing number of records are sustained by geochronological control points for age modelling, and multi-proxy studies are taking the lead over single proxy publications. This compilation of research shows the numerous innovative topics currently being explored to increase our understanding of palaeoenvironmental settings and modern vegetation-pollen relationships. To impulse divulgation and collaboration, we present the newly developed website and interactive map interface, where this inventory and corresponding reference database is publically available. Researchers and students are invited to pinpoint their new studies and publications, making interactive use of this platform for increased detectability and awareness on available publications

Climate variability and human impact on the environment in South America during the last 2000 years: synthesis and perspectives

An improved understanding of present-day climate variability and change relies on high-quality data sets from the past two millennia. Global efforts to reconstruct regional climate modes are in the process of validating and integrating paleo-proxies. For South America, however, the full potential of vegetation records for evaluating and improving climate models has hitherto not been sufficiently acknowledged due to its unknown spatial and temporal coverage. This paper therefore serves as a guide to high-quality pollen records that capture environmental variability during the last two millennia. We identify the pollen records with the required temporal characteristics for PAGES-2 ka climate modelling and we discuss their sensitivity to the spatial signature of climate modes throughout the continent. Diverse patterns of vegetation response to climate change are observed, with more similar patterns of change in the lowlands and varying intensity and direction of responses in the highlands. Pollen records display local scale responses to climate modes, thus it is necessary to understand how vegetation-climate interactions might diverge under variable settings. Additionally, pollen is an excellent indicator of human impact through time. Evidence for human land use in pollen records is useful for archaeological hypothesis testing and important in distinguishing natural from anthropogenically driven vegetation change. We stress the need for the palynological community to be more familiar with climate variability patterns to correctly attribute the potential causes of observed vegetation dynamics. The LOTRED-SA-2 k initiative provides the ideal framework for the integration of the various paleoclimatic sub-disciplines and paleo-science, thereby jumpstarting and fostering multi-disciplinary research into environmental change on centennial and millennial time scales