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Selected AbstractsPalaeoenvironmental context of the Late-glacial woolly mammoth (Mammuthus primigenius) discoveries at Condover, Shropshire, UKGEOLOGICAL JOURNAL, Issue 4 2009J. R. M. Allen Abstract In 1986/1987 the remains of several mammoths, Mammuthus primigenius (Blumenbach), were discovered on the spoil heap of an actively working gravel pit at Condover, Shropshire, England. The discovery of the remains posed two questions that could be addressed by analyses of biological proxies. First, as none of the bones was found in situ it was necessary to confirm the stratum in which the remains occurred. Second, what was the environment in which these animals lived and died? A range of biological indicators was used to address these questions, including pollen, spore and algal, plant macrofossil, invertebrate, anuran and biological mineral analyses. Multivariate statistical analyses of palynological and Pediastrum data, along with evidence from the Coleopteran assemblages, support the attribution of the mammoth bones to a unit of dark grey clayey sandy silt, although they may have lived at the time of the overlying green detritus mud. The palaeobiological data supports the correlation of these sediments to the Devensian Late-glacial. The mammoths entered this basin at the start of the Late-glacial Interstadial (Greenland Interstadial 1e) (ca. 14,830,3930 cal. year BP; 12,300,±,110 14C year BP) and became mired in soft cohesive sediments. Palaeotemperature reconstructions, based on the Coleopteran assemblages, from the time when the mammoths actually became mired, show that the climate was temperate with mean July temperatures between 15 and 19°C and mean January temperatures between ,13 and +6°C. Biological indicators from the sediments encasing the mammoths indicate that the landscape surrounding the basin was treeless and dry, contrasting with rich vegetation within the basin itself that had possibly attracted the mammoths to the site. Evidence of sedimentary disturbance suggests that the mammoths caused large-scale bioturbation of the deposits making palaeoenvironmental interpretations difficult. Fossils of terrestrial blowflies, carcass and dung beetles show that some of the decaying corpses must have lain exposed on the land surface for sufficient time for the soft parts to have rotted away and skin and bones to have become desiccated before many of them sank into the dark grey clayey sandy silt. Copyright © 2009 John Wiley & Sons, Ltd. [source] The millennial dynamics of a boreal forest stand from buried treesJOURNAL OF ECOLOGY, Issue 3 2004DOMINIQUE ARSENEAULT Summary 1We reconstructed the dynamics of a black spruce (Picea mariana) and jack pine (Pinus banksiana) forest stand in northern Québec using a continuous, 5200-year-long sequence of stem remains buried in adjacent peatland. Simulations of recruitment of such remains provided guidelines for inferring past ecosystem structure and composition at the stand scale. 2Compared with the late Holocene (4650,0 cal. year BP (CYBP)), the mid Holocene (5200,4650 CYBP) period was characterized by faster tree growth, larger stems and higher stem density, indicating higher forest productivity in association with a milder climate. 3The presence of stem remains of both species from 17 out of 20 contiguous 250-year time intervals suggests that the spruce-pine stand exhibited high compositional stability, with both species regenerating after fire from canopy-stored seed banks. 4Relative species abundance closely followed the duration of past fire intervals deduced from the number of tree rings in buried conifers. Time periods of long (4650,3950, 3400,1850 and 250,0 CYBP) and short fire intervals (4950,4650, 3950,3400 and 1850,250 CYBP) were associated, respectively, with decreasing and increasing pine abundance, probably reflecting faster juvenile growth, lower shade tolerance, earlier sexual maturity and shorter longevity in jack pine compared with black spruce. 5We conclude that both climate change and climate-induced fire disturbance have been driving long-term ecosystem dynamics. Our field evidence supports the idea that interactions between disturbances and the life-history traits of species modulate the impact of climate change at the scale of forest stands. At the same time, disturbances may result in long-term stability of disturbance-adapted ecosystems. [source] Two-step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1GLOBAL CHANGE BIOLOGY, Issue 6 2010LYDIE M. DUPONT Abstract High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6,14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change. [source] Sources for sedimentary bacteriohopanepolyols as revealed by 16S rDNA stratigraphyENVIRONMENTAL MICROBIOLOGY, Issue 7 2008Marco J. L. Coolen Summary Bacteriohopanoids are widespread lipid biomarkers in the sedimentary record. Many aerobic and anaerobic bacteria are potential sources of these lipids which sometimes complicates the use of these biomarkers as proxies for ecological and environmental changes. Therefore, we applied preserved 16S ribosomal RNA genes to identify likely Holocene biological sources of bacteriohopanepolyols (BHPs) in the sulfidic sediments of the permanently stratified postglacial Ace Lake, Antarctica. A suite of intact BHPs were identified, which revealed a variety of structural forms whose composition differed through the sediment core reflecting changes in bacterial populations induced by large changes in lake salinity. Stable isotopic compositions of the hopanols formed from periodic acid-cleaved BHPs, showed that some were substantially depleted in 13C, indicative of their methanotrophic origin. Using sensitive molecular tools, we found that Type I and II methanotrophic bacteria (respectively Methylomonas and Methylocystis) were unique to the oldest lacustrine sediments (> 9400 years BP), but quantification of fossil DNA revealed that the Type I methanotrophs, including methanotrophs related to methanotrophic gill symbionts of deep-sea cold-seep mussels, were the main precursors of the 35-amino BHPs (i.e. aminopentol, -tetrol and -triols). After isolation of the lake ,3000 years ago, one Type I methanotroph of the ,methanotrophic gill symbionts cluster' remained the most obvious source of aminotetrol and -triol. We, furthermore, identified a Synechococcus phylotype related to pelagic freshwater strains in the oldest lacustrine sediments as a putative source of 2-methylbacteriohopanetetrol (2-Me BHT). This combined application of advanced geochemical and paleogenomical tools further refined our knowledge about Holocene biogeochemical processes in Ace Lake. [source] A study of Holocene floodplain particle size characteristics with special reference to palaeochannel infills from the upper Severn basin, Wales, UKGEOLOGICAL JOURNAL, Issue 2 2001Mark Patrick Taylor Abstract Multiple sedimentary units from floodplain reaches at Welshpool on the upper River Severn and at the confluence of the Afon Tanat and Afon Vyrnwy (mid-Wales, UK) were examined to ascertain if they have distinctive particle size characteristics. Changes in particle size characteristics and their possible relationship to known human and climatic impacts are also discussed. Ellipse plots of particle size characteristics from the River Severn floodplain at Welshpool show that coarse-grained outwash deposits can be clearly discriminated from channel margin or palaeochannel sediments. In contrast, at the Afon Tanat,Vyrnwy study reach, this discrimination is not seen so clearly. The relationships between age and particle size characteristics from the most sampled sedimentary environment, palaeochannel infills, were also examined. The data from the River Severn floodplain at Welshpool show that palaeochannel sediments reveal a gradual but clear increase in particle size from the mid- to late Holocene towards the present day. Sediments deposited in the period 90,160 years BP are markedly coarser. It is suggested that these changes may be related to the combined effect of land-use changes, metal mining impacts and changes in flood frequency and magnitude that occurred at this time within the upper Severn basin. In contrast, the particle size characteristics of post Late Devensian/Early Holocene units from Tanat,Vyrnwy palaeochannels were random with no discernible age,size patterns. It is suggested that the non-systematic grain size distribution may be due to the steeper valley gradients of the Tanat,Vyrnwy system (and by inference higher stream powers) and its relatively narrow valley form enabling more effective coupling between coarser outwash deposits found on and at the edges of hillslopes and the valley floor. Although the two study reaches have undergone comparable environmental change during the Holocene and lie in the piedmont zone of their catchments, palaeochannel units of the same age possess distinctly different characteristics. Intrinsic reach-scale geomorphic factors would appear to preclude the uniform application of particle size characteristics to determine alluvial response to environmental change. Consequently, care needs to be applied to the use of such data for environmental discrimination because the phenomenon of equifinality means that a specific set of sediment characteristics is not necessarily exclusive to specific fluvial environments in either space or time. Copyright © 2001 John Wiley & Sons, Ltd. [source] Holocene pollen records from the central Arctic Foothills, northern Alaska: testing the role of substrate in the response of tundra to climate changeJOURNAL OF ECOLOGY, Issue 6 2003W. Wyatt Oswald Summary 1To explore the role of edaphic controls in the response of arctic tundra to climate change, we analysed Holocene pollen records from lakes in northern Alaska located on glaciated surfaces with contrasting soil texture, topography and tundra communities. Using indicator taxa, pollen accumulation rates (PARs) and multivariate comparison of fossil and modern pollen assemblages, we reconstructed the vegetational changes at Upper Capsule Lake (Sagavanirktok surface) and Red Green Lake (Itkillik II surface) in response to increased effective moisture between the early and middle Holocene. 2In the Red Green record, low PARs and the continuous presence of taxa indicative of prostrate-shrub tundra (PST; Equisetum, Polypodiaceae, Thalictrum and Rosaceae) indicate that the vegetation resembled PST throughout the Holocene. During the warm, dry early Holocene (11 300,10 000 cal years BP), PST also occurred on Sagavanirktok surfaces, as evidenced by PST indicators (Bryidae, Polypodiaceae, Equisetum and Rosaceae) in this interval of the Upper Capsule record. However, PARs increased, suggesting increased vegetation cover, PST taxa declined and taxa indicative of dwarf-shrub tundra (DST; Rubus chamaemorus and Lycopodium annotinum) increased between 10 000 and 7500 cal years BP. 3We hypothesize that between the early and middle Holocene the fine-textured soils and smooth topography of Sagavanirktok surfaces led to increased soil moisture, greater vegetation cover, permafrost aggradation, anoxic and acidic soil conditions, slower decomposition and the development of a thick organic layer. In contrast, soil moisture remained low on the better-drained Itkillik II surface, and vegetational changes were minor. 4Landscape-scale substrate variations have an effect on how tundra responds to climate change, suggesting that the response of arctic ecosystems to future variability may be spatially heterogeneous. [source] Climatic control of blanket mire development at Kentra Moss, north-west ScotlandJOURNAL OF ECOLOGY, Issue 5 2000Christopher J. Ellis Summary 1,Four peat cores were collected from Kentra Moss, north-west Scotland, and analysed for botanical macrofossils and peat humification. The pollen record was used as a template for the identification of synchronous levels between cores. 2,A non-random pattern of change in bryophyte macrofossils and humification was simultaneous between all four cores. Stratigraphic changes occurred independently of human land-use and were best interpreted as palaeoclimatic events. Remains of Racomitrium lanuginosum and Sphagnum papillosum, in conjunction with changes in peat humification, provided the clearest indication of past increases in climatic wetness (,wetshifts') to impact upon mire hydrology and ecology. 3,Eight wetshifts were identified and radiocarbon-dated, beginning at c. 3250, 2550, 2150, 1400, 1150, 875, 600 and 325 calibrated years BP (cal. BP). Seven of these wetshifts match closely with palaeoclimatic events from a range of mires previously examined in Britain and Ireland. We suggest that blanket mires may provide the best source of decade- to century-scale palaeoclimatic information in oceanic north-west Europe. 4,The proxy-climatic evidence indicates that: (i) the extinction of Sphagnum imbricatum at Kentra Moss (at c. 1400 cal. BP) was caused by an increase in climatic and mire surface wetness, when it was replaced first by Racomitrium lanuginosum and then by Sphagnum papillosum; and (ii) that increased climatic wetness and human land-use were responsible for the shift from an early minerotrophic peatland to ombrotrophic blanket mire at c. 4070 cal. BP. 5,Given the evidence for a prevailing climatic effect on the development of Kentra Moss, the effect of human-induced global warming on Britain's blanket mire resource will probably be significant. British blanket mires have international conservation status, and future changes in their ecology will challenge conservationists, academics and politicians. [source] Glacial refugia and the phylogeography of Steller's sea lion (Eumatopias jubatus) in the North PacificJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2006A. HARLIN-COGNATO Abstract Mitochondrial DNA sequence data were used to examine the phylogeographic history of Steller's sea lions (Eumetopias jubatus) in relation to the presence of Plio-Pleistocene insular refugia. Cytochrome b and control region sequences from 336 Steller's sea lions reveal phylogenetic lineages associated with continental refugia south of the ice sheets in North America and Eurasia. Phylogenetic analysis suggests the genetic structure of E. jubatus is the result of Pleistocene glacial geology, which caused the elimination and subsequent reappearance of suitable rookery habitat during glacial and interglacial periods. The cyclic nature of geological change produced a series of independent population expansions, contractions and isolations that had analogous results on Steller's sea lions and other marine and terrestrial species. Our data show evidence of four glacial refugia in which populations of Steller's sea lions diverged. These events occurred from approximately 60 000 to 180 000 years BP and thus preceded the last glacial maximum. [source] Comparison of 85Kr and 3H Apparent Ground-Water Ages for Source Water Vulnerability in the Collyer River Catchment, Maine,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2008William C. Sidle Abstract:, Apparent ground-water ages as determined by the noble gas isotope 85Kr and the water isotope 3H are compared. Refined gas extraction methodology at the wellhead permits efficient collection of Kr for 85Kr isotope enrichment. 85Kr isochrones elucidate areas of much younger ground-water ages than 3H. Declining 3H activities in the catchment prevent its correlation with the youngest measured 85Kr ages. Source water for most drinking water supplies in the Collyer River catchment is recharged within 40 years BP (2004). Mean-age (,) transport modeling suggests uncertainty of ground-water ages is greatest in the central basin area. [source] The lower limit of mountain permafrost in the Russian Altai MountainsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2007Kotaro Fukui Abstract Permafrost-indicator features, such as rock glaciers, pingos and ice-wedge polygons, exist at many locations in and around the South Chuyskiy Range of the Russian Altai Mountains (,50°N). The distribution of these features suggests that the altitudinal range of the sporadic/patchy permafrost zones and the widespread discontinuous/continuous permafrost zones are 1800,2000,m ASL and above 2000,m ASL, respectively. The lower limit of discontinuous permafrost is approximately 200,m lower than in the Mongolian Altai, which are at a similar latitude. Cold air drainage and/or temperature inversions during winter within U-shaped valleys together with a thin snow cover because of low precipitation during the same season likely cause the lower permafrost limit in the study area. The calibrated 14C ages of tree remnants found in a rock glacier front in the lower Akkol valley were 293,±,21 years BP and 548,±,21 years BP. Given the time of emergence from beneath the Sofiyskiy glacier, this rock glacier developed between 3800,2600 and 550 years BP. Copyright © 2007 John Wiley & Sons, Ltd. [source] Early Holocene human remains from the Argentinean Pampas: Additional evidence for distinctive cranial morphology of early South AmericansAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Héctor M. Pucciarelli Abstract The cranial morphology of Early Holocene American human samples is characterized by a long and narrow cranial vault, whereas more recent samples exhibit a shorter and wider cranial vault. Two hypotheses have been proposed to account for the morphological differences between early and late-American samples: (a) the migratory hypothesis that suggests that the morphological variation between early and late American samples was the result of a variable number of migratory waves; and (b) the local diversification hypothesis, that is, the morphological differences between early and late American samples were mainly generated by local, random (genetic drift), and nonrandom factors (selection and phenotypic plasticity). We present the first craniometric study of three early skulls from the Argentinean Pampas, dated ,8,000 cal. years BP (Arroyo Seco 2, Chocorí, and La Tigra), and one associated with mega-faunal remains (Fontezuelas skull). In addition, we studied several Late Holocene samples. We show that the skulls from the Argentinean Pampas are morphologically similar to other Early Holocene American skulls (i.e., Lagoa Santa from Brazil, Tequendama, Checua, and Aguazuque from Colombia, Lauricocha from Peru, and early Mexicans) that exhibit long and narrow cranial vaults. These samples differ from the Late Holocene American samples that exhibit a shorter and wider cranial vault. Our results underscore the important differences in cranial morphology between early and late-American samples. However, we emphasize the need for further studies to discuss alternative hypotheses regarding such differences. Am J Phys Anthropol 143:298,305, 2010. © 2010 Wiley-Liss, Inc. [source] Spatial patterns and evolutionary processes in southern South America: A study of dental morphometric variationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Valeria Bernal Abstract The purpose of this article is to examine the patterns of evolutionary relationships between human populations from the later Late Holocene (1,500,100 years BP) of southern South America on the basis of dental morphometric data. We tested the hypotheses that the variation observed in this region would be explained by the existence of populations with different phylogenetic origin or differential action of gene flow and genetic drift. In this study, we analyzed permanent teeth from 17 samples of male and female adult individuals from throughout southern South America. We measured mesiodistal and buccolingual diameters at the base of the crown, along the cement,enamel junction. The results of multiple regression analysis and a mantel correlogram indicate the existence of spatial structure in dental shape variation, as the D2 Mahalanobis distance between samples increases with increasing geographical distance between them. In addition, the correlation test results show a trend toward reduction of the internal variation of samples with increasing latitude. The detected pattern of dental variation agrees with the one expected as an outcome of founder serial effects related to an expansion of range during the initial occupation of southern South America. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Coalescent simulations of Yakut mtDNA variation suggest small founding populationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009Mark Zlojutro Abstract The Yakuts are a Turkic-speaking population from northeastern Siberia who are believed to have originated from ancient Turkic populations in South Siberia, based on archaeological and ethnohistorical evidence. In order to better understand Yakut origins, we modeled 25 demographic scenarios and tested by coalescent simulation whether any are consistent with the patterns of mtDNA diversity observed in present-day Yakuts. The models consist of either two simulated demes that represent Yakuts and a South Siberian ancestral population, or three demes that also include a regional Northeast Siberian population that served as a source of local gene flow into the Yakut deme. The model that produced the best fit to the observed data defined a founder group with an effective female population size of only 150 individuals that migrated northwards approximately 1,000 years BP and who experienced significant admixture with neighboring populations in Northeastern Siberia. These simulation results indicate a pronounced founder effect that was primarily kin-structured and reconcile reported discrepancies between Yakut mtDNA and Y chromosome diversity levels. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Role of wild plant foods among late Holocene hunter-gatherers from Central and North Patagonia (South America): An approach from dental evidenceAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2007Valeria Bernal Abstract This study evaluates the role of plant foods in the subsistence of hunter-gatherers that inhabited the Central East, Northwest, and Northeast Patagonia (Argentina) during the late Holocene (ca. 3,000,500 years BP). The goal of the present study is to assess the temporal variation of dental caries ratio and wear rate in skeletal samples to ascertain if the biological information supports the dietary shift toward greater consumption of wild plant foods around 1,500 years BP, suggested by other types of evidence. The authors registered caries, antemortem and postmortem tooth loss, and tooth wear from eight samples belonging to hunter-gatherers from Patagonia for which chronological sequences from early late Holocene (ca. 3,000,1,500 years BP) up to final late Holocene (ca. 1,500,500 years BP) are available. The results indicate that caries percentages in Patagonian samples fall within the range established for hunter-gatherers but there are significant geographical differences. In addition, caries ratio does not change significantly through time, so the amount of carbohydrates consumed seems to have remained fairly constant since 3,000 years BP. In contrast, there is a marked temporal trend toward the reduction of wear rates in the three areas, suggesting a faster rate in early late Holocene than in final late Holocene. These results would reflect a change to less hard and/or abrasive diets in the final late Holocene, probably owing to differences in food processing methods employed. Am J Phys Anthropol, 2007. © 2007 Wiley-Liss, Inc. [source] Community patterns generated by human harvesting on Chilean shores: a reviewAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2001Carlos A. MorenoArticle first published online: 21 FEB 200 Abstract 1.,The Chilean rocky coast has been exploited for food by coastal gatherers for at least 8500 years BP and probably was an important factor in how prehistoric people were able to colonize the South Americas Pacific Rim. The main species targeted in the past were the same as those today except that now the gatherers are resident and the fishing activity is more intense and persistent. 2.,With many pertinent studies from around the world having been published on this topic, mostly conducted in Marine Reserves, this review tries to identify the main patterns that can help us recognize, in the Chilean intertidal, the degree of exploitation on wave exposed and wave protected rocky shore habitats. 3.,Three clear patterns were identified depending on the trophic level adopted by the human gatherers in the food chain of the intertidal zone. First, when the humans act as herbivores, collecting the large laminarian Durvillaea antarctica, adult plants disappear from the accessible sites, especially the midlittoral, semi-exposed and exposed habitats. 4.,Second, when humans harvest the ecologically important herbivorous archeogastropoda Fissurella spp., this results in the red alga Mazzaella laminarioides covering almost 100% of the midlittoral rocks. Third, when humans become top predators by collecting the muricid carnivore Concholepas concholepas, then bivalves, mainly Perumytilus purpuratus, cover the rocks in multiple layers. 5.,These patterns contribute to the evaluation of the state of conservation of the Chilean rocky intertidal shores, especially because the north and the south are beginning to be connected by a new coastal road. Thus it is necessary to evaluate urgently, on a large spatial scale, the state of conservation of these communities, in order to help select the appropriate places for establishing Marine Reserves. Copyright © 2001 John Wiley & Sons, Ltd. [source] ROCK SURFACE HARDNESS AS AN INDICATION OF EXPOSURE AGE: AN ARCHAEOLOGICAL APPLICATION OF THE SCHMIDT HAMMER,ARCHAEOMETRY, Issue 1 2000M. W. BETTS A Schmidt Hammer was employed in evaluating the surface hardness of rocks which line ancient anthropogenic pit features, known as Pukaskwa pits, on the north shore of Lake Superior, Canada. This technique offers a possible new method of producing relative ana absolute dates for such exposed stone features Analysis of the data has provided a relative chronology for the pit features, representing two distinct construction phases. The range of absolute dates generated from the data indicates that the pits were likely constructed by Blackduck peoples c. 900 to 400 years BP. [source] Evidence of the final drainage of the Baltic Ice Lake and the brackish phase of the Yoldia Sea in glacial varves from the Baltic SeaBOREAS, Issue 3 2002THOMAS ANDRÉN A clay-varve chronology based on 14 cross-correlated varve graphs from the Baltic Sea and a mean varve thickness curve has been constructed. This chronology is correlated with the Swedish Time Scale and covers the time span 11 530 to 10250 varve years BP. Two cores have been analysed for grain size, chemistry, content of diatoms and changes in colour by digital colour analysis. The final drainage of the Baltic Ice Lake is dated to c. 10800 varve years BP and registered in the cores analysed as a decrease in the content of clay. This event can be correlated with atmospheric ,14C content and might have resulted in an increase in these values recorded between 11 565 and 11 545 years BP. The results of the correlation between the varve chronology from the Baltic Sea, the Greenland GRIP ice core and the atmospheric ,14C record indicate that c. 760 years are missing in the Swedish Time Scale in the part younger than c. 10250 varve years BP. A change in colour from a brownish to grey varved glacial clay recorded c. 10770 varve years BP is found to be the result of oxygen deficiency due to an increase in the rate of sedimentation in the early Preboreal. The first brackish influence is recorded c. 10540 varve years BP in the northwestern Baltic Sea and some 90 years later in the eastern Gotland Basin. [source] Late Weichselian pollen stratigraphy, clay varve chronology and palaeomagnetic secular variations in Lake Bolmen, Småland, south SwedenBOREAS, Issue 3 2001JONAS ISING Pollen analysis, glacial varve chronology and palaeomagnetic measurements were carried out on Late Weichselian lake sediments from southwestern Smaland, south Sweden. The sequence is correlated to the GRIP event stratigraphy, expressed in calendar years BP, and covers the period from the deglaciation at c. 14 400 to 11 300 calendar years BP. The series encompasses c. 930 varves and has been connected to the local varve chronology. Varve thickness increases markedly after the Older Dryas stadial, which indicates an accelerated deglaciation and melting of dead ice. The pollen diagram displays the vegetation development from the deglaciation at c. 14 400 calendar years BP to the transition to the Holocene. The vegetation succession starts with an arctic pioneer vegetation at the deglaciation, changes to a more stable tundra environment and displays a development which concurs with the traditional lateglacial pollen stratigraphy for southern Sweden. A palaeo-magnetic secular variation curve is presented displaying two westerly declination swings at 14200-13800 and 12 800-11 600 calendar years BP, respectively. The upper one can be recognized from other palaeomagnetic stratigraphies from southern Sweden and Estonia. [source] 10Be dating of Younger Dryas Salpausselkä I formation in FinlandBOREAS, Issue 4 2000SILVIO TSCHUDI Boulders of the Younger Dryas Salpausselkä I (Ss I) formation west of Lahti, southern Finland, were sampled for surface exposure dating. The 10Be concentrations, determined by accelerator mass spectrometry, yield minimum exposure ages of 11 930 ± 950, 11 220 ± 890, 11 050 ± 910 and 11 540 ± 990 years, using recently published production rates scaled for latitude and elevation. This includes a correction to the production rate resulting from postglacial uplift of the Fennoscandian lithosphere (i.e. changing elevation) during the time of exposure. The error-weighted mean exposure age of 11 420 ± 470 years of the analysed boulders agrees with previous varve dates of Ss I, which range from 11 680 to 11 430 calendar years BP. However, erosion has to be taken into account as a process affecting rock surfaces and therefore influencing exposure ages. Available information suggests an erosion rate of 5 mm/kyr, which increases the error-weighted mean exposure age to a value of 11 610 ± 470 years. Within the errors, the formation of Ss I in the Vesala area west of Lahti falls into the Younger Dryas time bracket, as defined by the GRIP and GISP 2 ice core (Greenland). [source] Amino acids in Quaternary soil horizons from southwest PolandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2003A. Szponar Summary Aminostratigraphy has proved to be a useful approach for dating fossils from the Quaternary. In these studies the amino acids in Quaternary soil formations were determined in an attempt to establish their stratigraphical relationships and relative ages. The sampling sites are in the southwest of Poland, in the Trzebnickie Hills. Three samples of fossil soils and two of recent soils were analysed. The absolute age of the soil samples was estimated by radiocarbon dating. We found that the total amount of amino acids decreased with the increasing age of soil. The smallest amounts of amino acids were found in the oldest fossil soil of Denekamp (Vistulian) age dated 29 600 ± 760 years bp. A sample of recent loess soil contained the most total amino acids, whereas the fossil soil of Lower Atlantic age, dated 3540 ± 230 years bp, was intermediate in respect of the total amount of amino acids, oxidation state and degree of biochemical transformation. Neutral amino acids formed a majority of all the amino acids studied. The method we describe could be useful in relative chronostratigraphical identification of fossil soils. [source] Late-glacial and Holocene vegetation, climate and fire dynamics in the Serra dos Órgãos, Rio de Janeiro State, southeastern BrazilGLOBAL CHANGE BIOLOGY, Issue 6 2010HERMANN BEHLING Abstract We present a high-resolution pollen and charcoal record of a 218 cm long sediment core from the Serra dos Órgãos, a subrange of the coastal Serra do Mar, located at 2130 m altitude in campos de altitude (high elevation grass- and shrubland) vegetation near Rio de Janeiro in southeastern Brazil to reconstruct past vegetation, climate and fire dynamics. Based on seven AMS 14C ages, the record represents at least the last 10 450 14C yr bp (12 380 cal years bp), The uppermost region was naturally covered by campos de altitude throughout the recorded period. Diverse montane Atlantic rain forest (ARF) occurred close to the studied peat bog at the end of the Late-glacial period. There is evidence of small Araucaria angustifolia populations in the study area as late as the early Holocene, after which point the species apparently became locally extinct. Between 10 380 and 10 170 14C yr bp (12 310,11 810 cal yr bp), the extent of campos de altitude was markedly reduced as montane ARF shifted rapidly upward to higher elevations, reflecting a very wet and warm period (temperatures similar to or warmer than present day) at the end of the Younger Dryas (YD) chronozone. This is in opposition to the broadly documented YD cooling in the northern Hemisphere. Reduced cross-equatorial heat transport and movement of the Intertropical Convergence Zone over northeastern Brazil may explain the YD warming. Markedly extended campos de altitude vegetation indicates dry climatic conditions until about 4910 14C yr bp (5640 cal yr bp). Later, wetter conditions are indicated by reduced high elevation grassland and the extension of ARF into higher elevation. Fire frequency was high during the early Holocene but decreased markedly after about 7020 14C yr bp (7850 cal yr bp). [source] Evidence of artificial cranial deformation from the later prehistory of the Acacus Mts. (southwestern Libya, Central Sahara)INTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 4 2008F. Ricci Abstract The 1999,2001 Italian,Libyan Archaeological Mission in the Acacus and Messak, southwestern Libya, resulted in the discovery of human specimens from the Wadi Tanezzuft Valley belonging to the Final Pastoral horizon (i.e. late Neolithic, about 3000 years bp). Some of these show clear traces of artificial cranial deformation. This practice, hitherto unrecorded in the central Sahara, is described and analysed in this paper. It represents an additional source of information about population movements and cultural connections in the area. It does not appear to be gender-related, and neither does it involve all individuals in the sample, suggesting some kind of social and/or cultural differentiation within the group. The pattern of cranial deformation described here is not directly related to types most commonly encountered among recent African populations and elsewhere. It may be considered a combination of antero-posterior and circumferential deformation and thus is referred to as a ,pseudo-circular type'. Archaeological and ethnographic literature related to Africa and southwestern Asia is investigated in order to identify a possible origin of such a custom and its pattern of diffusion. The evidence, according to other sources of information, contributes to interpret this area at the centre of the Sahara as a focal point of population movements and circulation of cultural traditions across North Africa in the latest phases of the Pastoral Neolithic. Copyright © 2008 John Wiley & Sons, Ltd. [source] Genetic divergence between sympatric Arctic charr Salvelinus alpinus morphs in Gander Lake, Newfoundland: roles of migration, mutation and unequal effective population sizesJOURNAL OF FISH BIOLOGY, Issue 8 2008D. Gomez-Uchida A suite of 10 microsatellite loci was used to examine genetic divergence between two sympatric morphs of Arctic charr Salvelinus alpinus (,dark' and ,pale') inhabiting Gander Lake, Newfoundland. Results can be summarized as follows: (1) the morphs are strongly reproductively isolated , gene flow,migration estimates were consistently low in long and short-term evolutionary timescales of analysis; (2) intermorph divergence based on allele size (RST) was significantly larger than those based on allele state (,) implying a cumulative effect of stepwise-like mutations; (3) historical (coalescent) and current (linkage disequilibrium) point estimates of effective population size (Ne) were consistently higher for dark than for pale S. alpinus. The first and second findings lend support to the hypothesis that divergence between forms may have preceded the last glacial period (ending c. 12 000 years bp). The third finding argues for significant differences in habitat quantity and quality between morphs, which were emphasized in a previous study. Overall, these analyses underscore the importance of genetic assessment and monitoring in the conservation of fish diversity, with emphasis on ,rare' or under-represented forms among temperate species pairs. [source] Ever deeper phylogeographies: trees retain the genetic imprint of Tertiary plate tectonicsMOLECULAR ECOLOGY, Issue 24 2007ARNDT HAMPE Changes in species distributions after the last glacial maximum (c. 18 000 years bp) are beginning to be understood, but information diminishes quickly as one moves further back in time. In this issue of Molecular Ecology, Magri et al. (2007) present the fascinating case of a Mediterranean tree species whose populations preserve the genetic imprints of plate tectonic events that took place between 25 million years and 15 million years ago. The study provides a unique insight into the pace of evolution of trees, which, despite interspecific gene flow, can retain a cohesive species identity over timescales long enough to allow the diversification of entire plant and animal genera. [source] Post-ice age recolonization and differentiation of Fucus serratus L. (Phaeophyceae; Fucaceae) populations in Northern EuropeMOLECULAR ECOLOGY, Issue 7 2003J. A. Coyer Abstract The seaweed Fucus serratus is hypothesized to have evolved in the North Atlantic and present populations are thought to reflect recolonization from a southern refugium since the last glacial maximum 18 000,20 000 years bp. We examined genetic structure across several spatial scales by analysing seven microsatellite loci in populations collected from 21 localities throughout the species' range. Spatial auto-correlation analysis of seven microsatellite loci revealed no evidence for spatial clustering of alleles on a scale of 100 m despite limited gamete dispersal in F. serratus of , 2 m from parental individuals. Pairwise , analysis suggested that the minimal panmictic unit for F. serratus was between 0.5 and 2 km. Isolation by distance was significant along some contiguous coastlines. Population differentiation was strong within the Skagerrak,Kattegat,Baltic Seas (SKB) (global ,= 0.17) despite a short history of , 7500 years. A neighbour-joining tree based on Reynold's distances computed from the microsatellite data revealed a central assemblage of populations on the Brittany Peninsula surrounded by four well-supported clusters consisting of the SKB, the North Sea (Ireland, Helgoland), and two populations from the northern Spanish coast. Samples from Iceland and Nova Scotia were most closely aligned with northwest Sweden and Brittany, respectively. When sample sizes were standardized (N = 41), allelic diversity was twofold higher for Brittany populations than for populations to the north and threefold higher than southern populations. The Brittany region may be a refugium or a recolonized area, whereas the Spanish populations most likely reflect present-day edge populations that have undergone repeated bottlenecks as a consequence of thermally induced cycles of recolonization and extinction. [source] Likely multiple origins of a diploid hybrid sunflower speciesMOLECULAR ECOLOGY, Issue 9 2002A. E. Schwarzbach Abstract The recurrent origin of diploid hybrid species is theoretically improbable because of the enormous diversity of hybrid genotypes generated by recombination. Recent greenhouse experiments, however, indicate that the genomic composition of hybrid lineages is shaped in part by deterministic forces, and that recurrent diploid hybrid speciation may be more feasible than previously believed. Here we use patterns of variation from chloroplast DNA (cpDNA), nuclear microsatellite loci, cross-viability and chromosome structure to assess whether a well-characterized diploid hybrid sunflower species, Helianthus anomalus, was derived on multiple occasions from its parental species, H. annuus and H. petiolaris. Chloroplast DNA and crossability data were most consistent with a scenario in which H. anomalus arose three times: three different H. anomalus fertility groups were discovered, each with a unique cpDNA haplotype. In contrast, there was no clear signature of multiple, independent origins from the microsatellite loci. Given the age of H. anomalus (> 100 000 years bp), it may be that microsatellite evidence for recurrent speciation has been eroded by mutation and gene flow through pollen. [source] Genetic variation and clonal diversity in four clonal sedges (Carex) along the Arctic coast of EurasiaMOLECULAR ECOLOGY, Issue 2 2001Anna Stenström Abstract We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. stans by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (HT) within populations and a small part of the diversity among populations (GST ranged 0.05,0.43). Carex bigelowii had genetic variation (HS = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (HS = 0.335), C. lugens (HS = 0.339) and C. stans (HS = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10 000 years bp compared to areas deglaciated 60 000 years bp or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. stans that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems. [source] | ||||||||||||||||