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LGM
Selected AbstractsPast and present potential distribution of the Iberian Abies species: a phytogeographic approach using fossil pollen data and species distribution modelsDIVERSITY AND DISTRIBUTIONS, Issue 2 2010Francisca Alba-Sánchez Abstract Aim, Quaternary palaeopalynological records collected throughout the Iberian Peninsula and species distribution models (SDMs) were integrated to gain a better understanding of the historical biogeography of the Iberian Abies species (i.e. Abies pinsapo and Abies alba). We hypothesize that SDMs and Abies palaeorecords are closely correlated, assuming a certain stasis in climatic and topographic ecological niche dimensions. In addition, the modelling results were used to assign the fossil records to A. alba or A. pinsapo, to identify environmental variables affecting their distribution, and to evaluate the ecological segregation between the two taxa. Location, The Iberian Peninsula. Methods, For the estimation of past Abies distributions, a hindcasting process was used. Abies pinsapo and A. alba were modelled individually, first calibrating the model for their current distributions in relation to the present climate, and then projecting it into the past,the last glacial maximum (LGM) and the Middle Holocene periods,in relation to palaeoclimate simulations. The resulting models were compared with Iberian-wide fossil pollen records to detect areas of overlap. Results, The overlap observed between past Abies refugia,inferred from fossil pollen records,and the SDMs helped to construct the Quaternary distribution of the Iberian Abies species. SDMs yielded two well-differentiated potential distributions: A. pinsapo throughout the Baetic mountain Range and A. alba along the Pyrenees and Cantabrian Range. These results propose that the two taxa remained isolated throughout the Quaternary, indicating a significant geographical and ecological segregation. In addition, no significant differences were detected comparing the three projections (present-day, Mid-Holocene and LGM), suggesting a relative climate stasis in the refuge areas during the Quaternary. Main conclusions, Our results confirm that SDM projections can provide a useful complement to palaeoecological studies, offering a less subjective and spatially explicit hypothesis concerning past geographic patterns of Iberian Abies species. The integration of ecological-niche characteristics from known occurrences of Abies species in conjunction with palaeoecological studies could constitute a suitable tool to define appropriate areas in which to focus proactive conservation strategies. [source] A new algorithm for reactive power management and pricing in an open access environmentEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2008G. Reza Yousefi Abstract In deregulated electricity markets, reactive power is one of the ancillary services that is provided by the Independent System Operator (ISO). In this paper we propose a new algorithm to ,tune' reactive power resources with the objectives of minimizing active power losses and optimizing system voltage profile and stability. In our solution, we assume that reactive power resources are either owned by or are under long-term contracts with the ISO. The optimization problem is solved as an Extended Multi-objective Optimal Power Flow (EMOPF) problem using Lexico Graphic Method (LGM). Thereafter, using the concept of Fair Resource Allocation (FRA), the cost of reactive power is allocated to existing transactions. The application of the algorithm to a test system is also presented. Copyright © 2007 John Wiley & Sons, Ltd. [source] Rockshelter sedimentation in a dynamic tropical landscape: Late Pleistocene,Early Holocene archaeological deposits in Kitulgala Beli-lena, southwestern Sri LankaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2009Nikos Kourampas Kitulgala Beli-lena, a rockshelter in gneiss in humid tropical southwestern Sri Lanka, was inhabited by Late Pleistocene,Early Holocene (>31,000,7880 B.P.) hunter-gatherers who made geometric microliths and exploited rainforest resources. Micromorphological analysis of a ca. 3-m-thick succession of diamictic loams, clays, and breccia with cultural content suggests that relative contribution of episodic colluviation and roof fall, water seepage through joints and diverse human activity varied through time. Facies changes across the profile reflect monsoon weakening ca. 20,000,16,000 cal B.P. and abrupt intensification ca. 15,700 cal B.P., on the wane of the global Last Glacial Maximum (LGM). Post-depositional modification included clay, sesquioxide, and minor phosphate translocation; termite and other arthropod bioturbation; and clast weathering on the rockshelter floor. Human input (tools and tool-making refuse, reworked charcoal and associated combustion by-products) is markedly higher in sediments younger than ca. 15,700 cal B.P., suggesting intensification of site use immediately after the LGM. © 2009 Wiley Periodicals, Inc. [source] Late Wisconsinan Port Eliza Cave deposits and their implications for human coastal migration, Vancouver Island, CanadaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2006M. Al-Suwaidi Sediments of Port Eliza Cave provide a record of the Last Glacial Maximum (LGM) on Vancouver Island that has important implications for human migration along the debated coastal migration route. Lithofacies changes from nonglacial diamict to glacial laminated silt and clay and till, then a return to nonglacial conditions with oxidized clay, colluvial block beds, and speleothems, along with radiocarbon and U/Th dates, define glacial,nonglacial transitions. Scanning electron microscope studies and clay mineralogy confirm that the laminated fines represent glaciation. Preglacial faunal evidence shows a diverse range from small species, including birds, fish, vole, and marmot, to larger species, such as mountain goat. Pollen data from the same unit show a cold, dry tundra environment with sparse trees. Deglaciation occurred prior to an age of 12.3 ka B.P. based on dated mountain goat bone. These data support the viability of the coastal migration route for humans prior to ,16 ka B.P. and then as early as ,13 ka B.P. © 2006 Wiley Periodicals, Inc. [source] Ancient transpacific voyaging to the new world via Pleistocene South Pacific IslandsGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2004Steve Wyatt How humans first arrived in America remains a mystery. Although the Beringian and coastal options have been discussed in detail, a transpacific route from the Old World to the New World via the islands of Oceania has been essentially ignored. Of the many factors involved in completing such a voyage, besides an adequate watercraft, landfall frequency and prevailing winds and currents were most important. A chain of islands in the landless eastern South Pacific, with its consequent and possibly favorable modifications of regional sea surface currents, would have been particularly beneficial to eastbound mariners. Comparing present-day bathymetry with estimated late Pleistocene glacially induced sea level fluctuations suggests that latent islands may actually exist, especially when the effects of other geological phenomena are also considered. If exposed during the last glacial maximum (LGM), such a chain of islands could have provided facilitating layover points for ancient eastbound seafaring explorers, thus making a transpacific journey more plausible. © 2004 Wiley Periodicals, Inc. [source] GLACIATION OF MT ALLEN, STEWART ISLAND (RAKIURA): THE SOUTHERN MARGIN OF LGM GLACIATION IN NEW ZEALANDGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2009MARTIN S. BROOK ABSTRACT. The origin of two ridges on the eastern slopes of Mt Allen, southern Stewart Island, has remained equivocal, with differences of opinion over the exact process-mechanisms of formation. A variety of approaches was used to test a number of possible hypotheses about the origin of the ridges. These include topographic and spatial positioning, geomorphology, sedimentology and palaeoclimatological extrapolations to reconstruct two small former cirque glaciers with equilibrium line altitudes (ELAs) of c. 600 m. It would appear the two ridges reflect a glacial origin, the glaciers interpreted as forming during the Last Glacial Maximum (LGM) in New Zealand. Whilst glaciation during this time (18,19 ka) was extensive in the Southern Alps, the restricted nature of glaciation on Mt Allen suggests the low altitude restricted glaciation to niche sites on the lee side of upland areas. [source] Sediment Distribution Around Glacially Abraded Bedrock Landforms (Whalebacks) at Lago Tranquilo, ChileGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2005Neil F. Glasser Whalebacks are convex landforms created by the smoothing of bedrock by glacial processes. Their formation is attributed to glacial abrasion either by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. This paper reports field measurements of sediment depth around two whaleback landforms in order to investigate the relationship between glacigenic deposits and whaleback formation. The study site, at Lago Tranquilo in Chilean Patagonia, is situated within the Last Glacial Maximum (LGM) ice limits. The two whalebacks are separated by intervening depressions in which sediment depths are generally 0.2 to 0.3 m. Two facies occur on and around the whalebacks. These facies are: (1) angular gravel found only on the surface of the whalebacks, interpreted as bedrock fracturing in response to unloading of the rock following pressure release after ice recession, and (2) sandy boulder-gravel in the sediment-filled depressions between the two whalebacks, interpreted as an ice-marginal deposit, with a mixture of sediment types including basal glacial and glaciofluvial sediment. Since the whalebacks have heavily abraded and striated surfaces but are surrounded by only a patchy and discontinuous layer of sediment, the implication is that surface abrasion of the whalebacks was achieved primarily by clasts entrained in basal ice, not by subglacial till sliding. [source] CHRONOLOGY OF THE LAST GLACIATION IN CENTRAL STRAIT OF MAGELLAN AND BAHÍA INÚTIL, SOUTHERNMOST SOUTH AMERICAGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2005R.D. McCULLOCH ABSTRACT. Glacier fluctuations in the Strait of Magellan tell of the climatic changes that affected southern latitudes at c. 53,55°S during the Last Glacial Maximum (LGM) and Late-glacial/Holocene transition. Here we present a revised chronology based on cosmogenic isotope analysis, 14C assays, amino acid racemisation and tephrochronology. We unpick the effect of bedrock-derived lignite which has affected many 14C dates in the past and synthesise new and revised dates that constrain five glacier advances (A to E). Advance A is prior to the LGM. LGM is represented by Advance B that reached and largely formed the arcuate peninsula Juan Mazia. Carbon-14and 10Be dating show it occurred after 31 250 cal yrs BP and culminated at 25 200,23 100 cal yrs BP and was then followed by the slightly less extensive advance C sometime before 22 400,20 300 cal yrs BP. This pattern of an early maximum is found elsewhere in South America and more widely. Stage D, considerably less extensive, culminated sometime before 17 700,17 600 cal yrs BP and was followed by rapid and widespread glacier retreat. Advance E, which dammed a lake, spanned 15 500,11770 cal yrs BP. This latter advance overlaps the Bølling-Allerød interstadials and the glacier retreat occurs during the peak of the Younger Dryas stadial in the northern hemisphere. However, the stage E advance coincides with the Antarctic Cold Reversal (c. 14800,12700 cal yrs BP) and may indicate that some millennial-scale climatic fluctuations in the Late-glacial period are out of phase between the northern and southern hemispheres. [source] Reconstruction of the Ross Ice Drainage System, Antarctica, at the Last Glacial MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2-3 2000George H. Denton We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface. [source] The Geologic Basis for a Reconstruction of a Grounded Ice Sheet in McMurdo Sound, Antarctica, at the Last Glacial MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2-3 2000George H. Denton A grounded ice sheet fed from the Ross Embayment filled McMurdo Sound at the last glacial maximum (LGM). This sheet deposited the little-weathered Ross Sea drift sheet, with far-traveled Transantarctic Mountains (TAM) erratics, on lower slopes of volcanic islands and peninsulas in the Sound, as well as on coastal forelands along the TAM front. The mapped upper limit of this drift, commonly marked by a distinctive moraine ridge, shows that the ice-sheet surface sloped landward across McMurdo Sound from 710 m elevation at Cape Crozier to 250 m in the eastern foothills of the Royal Society Range. Ice from the Ross Embayment flowed westward into the sound from both north and south of Ross Island. The northern flowlines were dominant, deflecting the southern flowlines toward the foothills of the southern Royal Society Range. Ice of the northern flowlines distributed distinctive kenyte erratics, derived from western Ross Island, in Ross Sea drift along the TAM front between Taylor and Miers Valleys. Lobes from grounded ice in McMurdo Sound blocked the mouths of TAM ice-free valleys, damming extensive proglacial lakes. A floating ice cover on each lake formed a conveyor that transported glacial debris from the grounded ice lobes deep into the valleys to deposit a unique glaciolacustrine facies of Ross Sea drift. The ice sheet in McMurdo Sound became grounded after 26,860 14C yr bp. It remained near its LGM position between 23,800 14C yr bp and 12,700 14C yr bp. Recession was then slow until sometime after 10,794 14C yr bp. Grounded ice lingered in New Harbor in the mouth of Taylor Valley until 8340 14C yr bp. The southward-retreating ice-sheet grounding line had penetrated deep into McMurdo Sound by 6500 14C yr bp. The existence of a thick ice sheet in McMurdo Sound is strong evidence for widespread grounding across the Ross Embayment at the LGM. Otherwise, the ice-sheet surface would not have sloped landward, nor could TAM erratics have been glacially transported westward into McMurdo Sound from farther offshore in the Ross Embayment. [source] Sediment sequences and paleosols in the Kyichu Valley, southern Tibet (China), indicating Late Quaternary environmental changesISLAND ARC, Issue 3 2009Knut Kaiser Abstract The Tibetan Plateau is highly sensitive to environmental changes and affects the settings of a far larger territory in Central Asia and beyond. Thus, knowledge on past environmental changes in that area is essential. Even though the Kyichu (Lhasa River) Valley and its tributaries is an easily accessible area, the Late Quaternary landscape evolution of southern Tibet is in general scarcely known. Therefore, 12 sedimentary sections in the middle and lower catchment were subjected to multidisciplinary analyses (sedimentology, paleopedology, AMS 14C and luminescence dating, and charcoal determination) aiming at results on regional paleoenvironmental changes. At the altitude studied (3600,4000 m above sealevel), no glacial relics could be detected, indicating that the valley positions have been unglaciated since the Last Interglacial. The lack of fluvial,lacustrine structures above the floodplain is due to the aggradational character of this tectonically (sub-)active valley, which caused an alluvial burying of older valley bottoms. During the Late Pleistocene the mouth area of the Kyichu was occupied by a lake which was part of a larger dam-lake in the superordinate Yarlung Zhangbo Valley. On the valley flanks, loesses were predominantly deposited before the Last Glacial Maximum (LGM), whereas eolian sands were predominantly deposited around and after the LGM. Paleosols of Last Interglacial, Last Glacial and Holocene ages regularly occur at terrestrial sites representing temperate to cool and humid to semiarid conditions during soil formation. Ages of colluvial sediments indicate that the widespread barren valley slopes were primarily formed by Late Pleistocene erosion followed by a secondary Holocene erosion phase. Charcoal spectra indicate a Late Holocene change from a forest environment to a pastoral environment with sparse grasses, herbs and dwarf shrubs. It is assumed that the Late Holocene environmental changes, such as loss of forests/woodlands and erosion, have at least been reinforced by humans, enhancing a regional climatic aridification and cooling trend. [source] From ice age to modern: a record of landscape change in an Andean cloud forestJOURNAL OF BIOGEOGRAPHY, Issue 9 2010B. G. Valencia Abstract Aim, To investigate the palaeoecological changes associated with the last ice age, subsequent deglaciation and human occupation of the central Andes. Location, Lake Pacucha, Peruvian Andes (13°36,26, S, 73°19,42, W; 3095 m elevation). Methods, Vegetation assemblages were reconstructed for the last 24 cal. kyr bp (thousand calibrated 14C years before present), based on pollen analysis of sediments from Lake Pacucha. An age model was established using 14C accelerator mass spectrometry dates on bulk sediment. Fossil pollen and sedimentological analyses followed standard methodologies. Results, Puna brava replaced the Andean forest at the elevation of Lake Pacucha at the Last Glacial Maximum (LGM). Deglaciation proceeded rapidly after 16 cal. kyr bp, and near-modern vegetation was established by c. 14 cal. kyr bp. The deglacial was marked by the range expansion of forest taxa as grassland taxa receded in importance. The mid-Holocene was marked by a lowered lake level but relatively unchanged vegetation. Quinoa and maize pollen were found in the latter half of the Holocene. Main conclusions, Temperatures were about 7,8 °C colder than present at this site during the LGM. The pattern of vegetation change was suggestive of microrefugial expansion rather than simple upslope migration. The mid-Holocene droughts were interrupted by rainfall events sufficiently frequent to allow vegetation to survive largely unchanged, despite lowering of the lake level. Human activity at the lake included a 5500-year history of quinoa cultivation and 3000 years of maize cultivation. [source] Subantarctic flowering plants: pre-glacial survivors or post-glacial immigrants?JOURNAL OF BIOGEOGRAPHY, Issue 3 2010Nathalie Van der Putten Abstract Aim, The aim here was to assess whether the present-day assemblage of subantarctic flowering plants is the result of a rapid post-Last Glacial Maximum (LGM) colonization or whether subantarctic flowering plants survived on the islands in glacial refugia throughout the LGM. Location, The circumpolar subantarctic region, comprising six remote islands and island groups between latitudes 46° and 55° S, including South Georgia in the South Atlantic Ocean, the Prince Edward Islands, Îles Crozet, Îles Kerguelen, the Heard Island group in the South Indian Ocean and Macquarie Island in the South Pacific Ocean. Methods, Floristic affinities between the subantarctic islands were assessed by cluster analysis applied to an up-to-date dataset of the phanerogamic flora in order to test for the existence of provincialism within the subantarctic. A review of the primary literature on the palaeobotany, geology and glacial history of the subantarctic islands was carried out and supplemented with additional palaeobotanical data and new field observations from South Georgia, Île de la Possession (Îles Crozet) and Îles Kerguelen. Results, First, a strong regionalism was observed, with different floras characterizing the islands in each of the ocean basins, and endemic species being present in the South Indian Ocean and South Pacific Ocean provinces. Second, the majority of the plant species were present at the onset of accumulation of post-glacial organic sediment and there is no evidence for the natural arrival of new immigrants during the subsequent period. Third, a review of geomorphological data suggested that the ice cover was incomplete during the LGM on the majority of the islands, and ice-free biological refugia were probably present even on the most glaciated islands. Main conclusions, Several independent lines of evidence favour the survival of a native subantarctic phanerogamic flora in local refugia during the LGM rather than a post-LGM colonization from more distant temperate landmasses in the Southern Hemisphere. [source] Phylogeography of the world's tallest angiosperm, Eucalyptus regnans: evidence for multiple isolated Quaternary refugiaJOURNAL OF BIOGEOGRAPHY, Issue 1 2010Paul G. Nevill Abstract Aim, There is a need for more Southern Hemisphere phylogeography studies, particularly in Australia, where, unlike much of Europe and North America, ice sheet cover was not extensive during the Last Glacial Maximum (LGM). This study examines the phylogeography of the south-east Australian montane tree species Eucalyptus regnans. The work aimed to identify any major evolutionary divergences or disjunctions across the species' range and to examine genetic signatures of past range contraction and expansion events. Location, South-eastern mainland Australia and the large island of Tasmania. Methods, We determined the chloroplast DNA haplotypes of 410 E. regnans individuals (41 locations) based on five chloroplast microsatellites. Genetic structure was examined using analysis of molecular variance (AMOVA), and a statistical parsimony tree was constructed showing the number of nucleotide differences between haplotypes. Geographic structure in population genetic diversity was examined with the calculation of diversity parameters for the mainland and Tasmania, and for 10 regions. Regional analysis was conducted to test hypotheses that some areas within the species' current distribution were refugia during the LGM and that other areas have been recolonized by E. regnans since the LGM. Results, Among the 410 E. regnans individuals analysed, 31 haplotypes were identified. The statistical parsimony tree shows that haplotypes divided into two distinct groups corresponding to mainland Australia and Tasmania. The distribution of haplotypes across the range of E. regnans shows strong geographic patterns, with many populations and even certain regions in which a particular haplotype is fixed. Many locations had unique haplotypes, particularly those in East Gippsland in south-eastern mainland Australia, north-eastern Tasmania and south-eastern Tasmania. Higher haplotype diversity was found in putative refugia, and lower haplotype diversity in areas likely to have been recolonized since the LGM. Main conclusions, The data are consistent with the long-term persistence of E. regnans in many regions and the recent recolonization of other regions, such as the Central Highlands of south-eastern mainland Australia. This suggests that, in spite of the narrow ecological tolerances of the species and the harsh environmental conditions during the LGM, E. regnans was able to persist locally or contracted to many near-coastal refugia, maintaining a diverse genetic structure. [source] Fossil evidence and phylogeography of temperate species: ,glacial refugia' and post-glacial recolonizationJOURNAL OF BIOGEOGRAPHY, Issue 11 2009Robert S. Sommer Abstract We present a short synthesis of the Pleistocene distribution dynamics and phylogeographic recolonization hypotheses for two temperate European mammal species, the red deer (Cervus elaphus) and the roe deer (Capreolus capreolus), for which high-resolution patterns of fossil evidence and genetic data sets are available. Such data are critical to an understanding of the role of hypothesized glacial refugia. Both species show a similar pattern: a relatively wide distribution in the southern part of Central Europe 60,000,25,000 years ago, and a strong restriction to areas in southern Europe for nearly 10,000 years during the Last Glacial Maximum (LGM) and the early Late Glacial (25,000,14,700 years ago). With the beginning of Greenland Interstadial 1 (Bølling/Allerød warming, c. 14,700,11,600 years ago) a sudden range expansion into Central Europe is visible, but the colonization of most of Central Europe, including the northern European Lowlands, only began in the early Holocene. In a European context, regions where the species were distributed during the LGM and early Late Glacial are most relevant as potential origins of recolonization processes, because during these c. 10,000 years distribution ranges were smaller than at any other time in the Late Quaternary. As far as the present distribution of temperate species and their genetic lineages is concerned, so-called ,cryptic refugia' are important only if the species are actually confirmed there during the LGM, as otherwise they could not possibly have contributed to the recolonization that eventually resulted in the present distribution ranges. [source] Glacial refugia for summer-green trees in Europe and south-west Asia as proposed by ECHAM3 time-slice atmospheric model simulationsJOURNAL OF BIOGEOGRAPHY, Issue 12 2007Suzanne A. G. Leroy Abstract Aim, To generate maps of potential refugia for summer-green trees during the Last Glacial Maximum (LGM). Locations, Southern Europe and south-western Asia. Methods, Time-slice simulations of the atmospheric climate with the ECHAM3 model are used for the LGM. Limiting factors beyond which cool and warm groups of deciduous trees cannot grow (such as temperature in growing degree days, minimum monthly temperature and precipitation in summer) are chosen. A limited validation by fossil pollen and charcoal records from LGM sites was done. Results, Two sets of maps extending from Europe to the Caspian region for cool and warm summer-green trees are presented. Three criteria are combined using contour lines to indicate confidence levels. Small areas within the three southern peninsulas of Europe (Spain, Italy and Greece) are highlighted as possible refugia for summer-green trees. Further, areas that have remained poorly known are now proposed as refugia, including the Sakarya,Kerempe region in northern Turkey, the east coast of the Black Sea and the area south of the Caspian Sea. Main conclusions, The maps produced in this study could be used to facilitate better long-term management for the protection of European and south-western Asian biodiversity. [source] Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial MaximumJOURNAL OF BIOGEOGRAPHY, Issue 7 2006Louise Cromer Abstract Aim, There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c. 130,000 yr bp, i.e. prior to the LGM. Location, Lake Reid, Larsemann Hills, East Antarctica (76°23, E; 69°23, S). Methods, Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c. 130,000 yr bp. Results, Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM. Main conclusion, The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent. [source] Pollen-based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 18,000 14C yr BPJOURNAL OF BIOGEOGRAPHY, Issue 9 2004Elizabeth J. Pickett Abstract Aim, This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid-Holocene and at the last glacial maximum (LGM). Methods, Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 14C yr bp. Results, 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad-scale patterns of vegetation distribution. The north,south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed-canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad-scale pattern emerges. 2. Differences between the modern and mid-Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south-eastern Australia some sites show a shift towards more moisture-stressed vegetation in the mid-Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm-temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture-demanding vegetation in the mid-Holocene than today. South-western Australia was slightly drier than today. The single site in north-western Australia also shows conditions drier than today in the mid-Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid-Holocene, in sites occupied today by cool-temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions, This study provides the first continental-scale reconstruction of mid-Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project. [source] Mid-Holocene and glacial-maximum vegetation geography of the northern continents and AfricaJOURNAL OF BIOGEOGRAPHY, Issue 3 2000I. Colin Prentice Abstract BIOME 6000 is an international project to map vegetation globally at mid-Holocene (6000 14C yr bp) and last glacial maximum (LGM, 18,000 14C yr bp), with a view to evaluating coupled climate-biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduces the second Special Feature on BIOME 6000. Site-based global biome maps are shown with data from North America, Eurasia (except South and Southeast Asia) and Africa at both time periods. A map based on surface samples shows the method's skill in reconstructing present-day biomes. Cold and dry conditions at LGM favoured extensive tundra and steppe. These biomes intergraded in northern Eurasia. Northern hemisphere forest biomes were displaced southward. Boreal evergreen forests (taiga) and temperate deciduous forests were fragmented, while European and East Asian steppes were greatly extended. Tropical moist forests (i.e. tropical rain forest and tropical seasonal forest) in Africa were reduced. In south-western North America, desert and steppe were replaced by open conifer woodland, opposite to the general arid trend but consistent with modelled southward displacement of the jet stream. The Arctic forest limit was shifted slighly north at 6000 14C yr bp in some sectors, but not in all. Northern temperate forest zones were generally shifted greater distances north. Warmer winters as well as summers in several regions are required to explain these shifts. Temperate deciduous forests in Europe were greatly extended, into the Mediterranean region as well as to the north. Steppe encroached on forest biomes in interior North America, but not in central Asia. Enhanced monsoons extended forest biomes in China inland and Sahelian vegetation into the Sahara while the African tropical rain forest was also reduced, consistent with a modelled northward shift of the ITCZ and a more seasonal climate in the equatorial zone. Palaeobiome maps show the outcome of separate, independent migrations of plant taxa in response to climate change. The average composition of biomes at LGM was often markedly different from today. Refugia for the temperate deciduous and tropical rain forest biomes may have existed offshore at LGM, but their characteristic taxa also persisted as components of other biomes. Examples include temperate deciduous trees that survived in cool mixed forest in eastern Europe, and tropical evergreen trees that survived in tropical seasonal forest in Africa. The sequence of biome shifts during a glacial-interglacial cycle may help account for some disjunct distributions of plant taxa. For example, the now-arid Saharan mountains may have linked Mediterranean and African tropical montane floras during enhanced monsoon regimes. Major changes in physical land-surface conditions, shown by the palaeobiome data, have implications for the global climate. The data can be used directly to evaluate the output of coupled atmosphere-biosphere models. The data could also be objectively generalized to yield realistic gridded land-surface maps, for use in sensitivity experiments with atmospheric models. Recent analyses of vegetation-climate feedbacks have focused on the hypothesized positive feedback effects of climate-induced vegetation changes in the Sahara/Sahel region and the Arctic during the mid-Holocene. However, a far wider spectrum of interactions potentially exists and could be investigated, using these data, both for 6000 14C yr bp and for the LGM. [source] Isozyme variation and recent biogeographical history of the long-lived conifer Fitzroya cupressoidesJOURNAL OF BIOGEOGRAPHY, Issue 2 2000A. C. Premoli Abstract Aim Palaeoenvironmental records of Pleistocene glaciation and associated vegetation changes in Patagonia have led to the hypothesis that during the last glacial maximum (LGM) tree species survived locally in favourable habitats. If present populations originated from spread from only one refugium, such as an ice-free area of coastal Chile (Single Refugium hypothesis), we would expect that eastern populations would be genetically depauperate and highly similar to western populations. In contrast, if the ice cap was not complete and tree species persisted in forest patches on both slopes of the Andes (Multiple Refugia hypothesis), we would expect a greater degree of genetic divergence between populations either on opposite sides of the Cordillera (Cordillera Effect scenario) or towards its present-day southern distributional limit where the ice sheet reached its maximum coverage (Extent-of-the-Ice scenario). Location We tested this refugia hypothesis using patterns of isozyme variation in populations sampled over the entire modern range of the endemic conifer Fitzroya cupressoides (Mol.) Johnst. (Cupressaceae) in temperate South America. Methods Fresh foliage was collected from twenty-four populations and analysed by horizontal electrophoresis on starch gels. Results Twenty-one putative loci were reliably scored and 52% were polymorphic in at least one population. Populations from the eastern slope of the Andes were genetically more variable than those from the western slope; the former had a greater mean number of alleles per locus, a larger total number of alleles and rare alleles, and higher polymorphism. Genetic identities within western populations were greater than within eastern populations. Discriminant analyses using allelic frequencies of different grouping schedules of populations were non significant when testing for the Single Refugium hypothesis whereas significant results were obtained for the Multiple Refugia hypothesis. Main conclusions Our results indicate that present Fitzroya populations are the result of spreading from at least two, but possibly more, glacial refugia located in Coastal Chile and on the southern flanks of the Andes in Argentina. [source] Glacial refugia of temperate trees in Europe: insights from species distribution modellingJOURNAL OF ECOLOGY, Issue 6 2008Jens-Christian Svenning Summary 1The Pleistocene is an important period for assessing the impact of climate change on biodiversity. During the Last Glacial Maximum (LGM; 21 000 years ago), large glaciers and permafrost reached far south in Europe. Trees are traditionally thought to have survived only in scattered Mediterranean refugia (southern refugia hypothesis), but a recent proposal suggests that trees may have been much more widely and northerly distributed (northern refugia hypothesis). 2In this study, the southern vs. northern refugia hypotheses were investigated by estimating the potential LGM distributions of 7 boreal and 15 nemoral widespread European tree species using species distribution modelling. The models were calibrated using data for modern species distributions and climate and projected onto two LGM climate simulations for Europe. Five modelling variants were implemented. 3Models with moderate to good predictive ability for current species range limits and species richness patterns were developed. 4Broadly consistent results were obtained irrespective of the climate simulation and modelling variant used. Our results indicate that LGM climatic conditions suitable for boreal species existed across Central and Eastern Europe and into the Russian Plain. In contrast, suitable climatic conditions for nemoral tree species were largely restricted to the Mediterranean and Black Sea regions. Large proportions of these northern and southern regions would have been suitable for a number of boreal or boreal plus nemoral tree species, respectively. 5These findings are consistent with recent palaeoecological and phylogeographic data regarding LGM distributions of trees and other boreal and nemoral taxa. 6Synthesis. It is clear that the view of the LGM landscape in Europe as largely treeless, especially north of the Alps, needs to be revised. Trees were probably much more widespread during the LGM than hitherto thought, although patchily distributed at low densities due to low atmospheric CO2 concentrations and high wind-speeds. The findings presented here help explain the occurrence of mammal assemblages with mixtures of forest, tundra and steppe species at many localities in southern Central and Eastern Europe during the LGM, as well as the phylogeographic evidence for the extra-Mediterranean persistence of many boreal species. [source] Quaternary tephra marker beds and their potential for palaeoenvironmental reconstruction on Chatham Island, east of New Zealand, southwest Pacific Ocean,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2010Katherine A. Holt Abstract Tephras provide one of the most reliable methods of time control and synchronisation within Quaternary sequences. We report on the identification of two widespread rhyolitic tephras , the Kawakawa and Rangitawa tephras , preserved in extensive peat deposits on Chatham Island ,900,km east of New Zealand. The tephras, both products of supereruptions from the Taupo Volcanic Zone, occur as pale, fine-ash dominated layers typically 10,150,mm thick. Mineralogically they are dominated by rhyolitic glass, together with subordinate amounts of quartz, feldspar, hypersthene, hornblende, Fe,Ti oxides and zircon. Phlogopite/biotite was identified additionally in Rangitawa Tephra. Ages for each tephra were obtained via mineralogical and major element glass composition-based correlation with well-dated equivalent deposits on mainland New Zealand, and we also obtained a new zircon fission-track age for Rangitawa Tephra (350,±,50,ka) on Chatham Island. Both tephras were erupted at critical times for palaeoenvironmental reconstructions in the New Zealand region: the Kawakawa at ca. 27 cal. ka, near the beginning of the ,extended' LGM early in marine isotope stage (MIS) 2; and the Rangitawa at ca. 350 ka near the end of MIS 10. The time constraints provided by the tephras demonstrate that Chatham Island peats contain long-distance pollen derived from mainland New Zealand, which provides a reliable proxy for identifying glacial,interglacial climate conditions, in this case during the MIS 11,10 and MIS 2,1 cycles. The two tephras thus provide important chronostratigraphic tie-points that facilitate correlation and synchronisation not only across the Quaternary deposits of the Chatham Islands group but also with climatically significant terrestrial and marine records in the wider New Zealand region. Copyright © 2010 John Wiley & Sons, Ltd. [source] Timing and style of Late Pleistocene glaciation in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2010Liubing Xu Abstract Glacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd. [source] Recognition and palaeoclimatic implications of late Quaternary niche glaciation in eastern Lesotho,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2009Stephanie C. Mills Abstract Geomorphic evidence of former glaciation in the high Drakensberg of southern Africa has proven controversial, with conflicting glacial and non-glacial interpretations suggested for many landforms. This paper presents new geomorphological, sedimentological and micromorphological data, and glacier mass-balance modelling for a site in the Leqooa Valley, eastern Lesotho, preserving what are considered to be moraines of a former niche glacier that existed during the Last Glacial Maximum (LGM). The geomorphology and macro-sedimentology of the deposits display characteristics of both active and passive transport by glacial processes. However, micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes. The application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude (ELA) of 3136,m a.s.l. and palaeoglacier mass balance characteristics comparable with modern analogues, reflecting viable, if marginal glaciation. Radiocarbon dates obtained from organic sediment within the moraines indicate that these are of LGM age. The reconstructed palaeoclimatic conditions during the LGM suggest that snow accumulation in the Drakensberg was significantly higher than considered by other studies, and has substantial relevance for tuning regional climate models for southern Africa during the last glacial cycle. Copyright © 2009 John Wiley & Sons, Ltd. [source] First cosmogenic 10Be constraints on LGM glaciation on New Zealand's North Island: Park Valley, Tararua Range,JOURNAL OF QUATERNARY SCIENCE, Issue 8 2008Martin S. Brook Abstract We report the first direct ages for late Quaternary glaciation on the North Island of New Zealand. Mt Ruapehu, the volcanic massif in the North Island's centre, is currently glaciated and probably sustained glaciers throughout the late Quaternary, yet no numeric ages have been reported for glacial advances anywhere on the North Island. Here, we describe cosmogenic 10Be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the Tararua Range, part of the axial ranges of the North Island. Results indicate that a limited valley glaciation occurred, culminating in recession at the end of the last glacial coldest period (LGCP, ca. 18,ka). This provides an initial age for deglaciation on the North Island during the last glacial,interglacial transition (LGIT). It appears that glaciation occurred in response to an equilibrium-line altitude (ELA) lowering of ,1400,m below the present-day mean summer freezing level. Ages for glaciation in the Tararua Range correspond closely to exposure ages for the last glacial maximum (LGM) from the lateral moraines of Cascade Valley in the South Island, and in Cobb Valley, in northern South Island. The corollary is that glaciation in the Tararua Range coincided with the phase of maximum cooling during MIS 2, prior to the Antarctic Cold Reversal (ACR), during the LGCP. Copyright © 2008 John Wiley & Sons, Ltd. [source] Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2008William M. Phillips Abstract The extent of the last British,Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23,19,ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5,ka. Copyright © 2008 John Wiley & Sons, Ltd. [source] The role of the Iceland Ice Sheet in the North Atlantic during the late Quaternary: a review and evidence from Denmark Strait,JOURNAL OF QUATERNARY SCIENCE, Issue 1 2008John T. Andrews Abstract Investigations indicate that the Iceland Ice Sheet was reduced in size during MIS 3 but readvanced to the shelf break at the LGM. Retreat occurred very rapidly around 15,k,16,k cal. yr BP. By contrast, the margin of the ice sheet on the East Greenland shelf, north of the Denmark Strait, was at or close to the shelf break during MIS 3 and 2 and retreat starting ,17,k cal. yr BP. Quantitative X-ray diffraction analysis of the <2,mm sediment fraction was undertaken on 161 samples from Iceland and East Greenland diamictons, and from cores on the slopes and margins of the Denmark Strait. Weight% mineralogical data are used in a principal component analysis to differentiate sediments derived from the two margins. The first two PC axes explain 52% of the variance. These associations are used to characterise sediments as being affiliated with (a) Iceland, (b) East Greenland or (c) mixed. The contribution from Iceland becomes prominent during MIS 2. The extensive outcrop of early Tertiary basalts on East Greenland between 68° and 71° N is an alternative source for basaltic clasts and North Atlantic sediments with ,Nd(0) values close to ±0. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evidence for regionally wet conditions before the LGM in southeast Australia: OSL ages from a large palaeochannel in the Lachlan Valley,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2007Justine Kemp Abstract Optically stimulated luminescence (OSL) techniques have been used to obtain the first ages on Late Pleistocene channels in the Lachlan Valley, southeastern Australia. Two OSL ages from channel sand and overlying source-bordering dune sand indicate that large sinuous channels, with bankfull discharges six to eight times greater than the present river, were fully established by 34,ka BP. This conclusion is consistent with regional lake level and geomorphic evidence of cool, pluvial conditions that preceded the last glacial maximum (LGM), providing new information on a long-standing palaeohydrological problem caused by the apparent synchroneity of large river systems and regional aridity. Copyright © 2007 John Wiley & Sons, Ltd. [source] The deglaciation of Clyde Inlet, northeastern Baffin Island, Arctic Canada,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2007Jason P. Briner Abstract The behaviour of ice sheets as they retreated from their Last Glacial Maximum (LGM) positions provides insights into Lateglacial and early Holocene ice-sheet dynamics and climate change. The pattern of deglaciation of the Laurentide Ice Sheet (LIS) in arctic fiord landscapes can now be well dated using cosmogenic exposure dating. We use cosmogenic exposure and radiocarbon ages to constrain the deglaciation history of Clyde Inlet, a 120,km long fiord on northeastern Baffin Island. The LIS reached the continental shelf during the LGM, retreated from the coastal lowlands by 12.5,±,0.7,ka (n,=,3), and from the fiord mouth by 11.7,±,2.2,ka (n,=,4). Rapid retreat from the outer fiord occurred 10.3,±,1.3,ka (n,=,6), with the terminus reaching the inner fiord shortly after 9.4,ka (n,=,2), where several moraine systems were deposited between ca. 9.4 and ca. 8.4,ka. These moraines represent fluctuations of the LIS during the warmest summers since the last interglaciation, and this suggests that the ice sheet was responding to increased snowfall. Before retreating from the head of Clyde Inlet, the LIS margin fluctuated at least twice between ca. 7.9 and ca. 8.5,ka, possibly in response to the 8.2,ka cold event. Copyright © 2006 John Wiley & Sons, Ltd. [source] Palaeohydrology of Laguna de Tagua Tagua (34° 30, S) and moisture fluctuations in Central Chile for the last 46,000,yr,JOURNAL OF QUATERNARY SCIENCE, Issue 7-8 2005Blas L. Valero-Garcés Abstract Central Chile (32,35° S) lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient. A new core from Laguna de Tagua Tagua (34° 30, S) provides a sedimentologic, geochemical and palynological record of regional hydrologic balance for the last 46,000,cal.,yr,BP. According to our age model, relatively humid conditions occurred during glacial times before 43,500,cal.,yr,BP and from 40,000 to 21,500,cal.,yr,BP. Reduced moisture conditions and likely lower temperatures occurred from 42,400,40,100,cal.,yr,BP. Higher lake levels, and pollen assemblages with Valdivian rainforest taxa, imply much higher precipitation during glacial times (40,100,21,000,cal.,yr,BP) compared to today and, therefore, enhanced westerly activity in northern Central Chile. Afterwards, the general decrease in moisture was punctuated by two abrupt arid periods at 21,000,19,500,cal.,yr,BP and 17,000,15,000,cal.,yr,BP, and two more humid intervals: 19,500,17,000 (almost coincident with the global Last Glacial Maximum, LGM) and 13,500,11,500,cal.,yr,BP. The early and mid-Holocene were the most arid periods in Central Chile for the studied time interval. Millennial-scale palaeohydrological reconstructions from Tagua Tagua are consistent with regional climatic records. Copyright © 2005 John Wiley & Sons, Ltd. [source] |