bluuebunny/crossref_metadata_2025_split huggingface dataset:
Holocene Changes in Tropical Wind Intensity and Rainfall: Evidence from Southeast Ghana
Authors: Talbot M. R. 
Published: July 2006

AbstractRemnants of a fixed aeolian dune ridge occur along the southeast coast of Ghana, just behind the present shoreline. Aeolian sands also cover extensive areas of the Accra Plains. No dunes are present here, the sands mainly occurring as sheets which blanket an early Holocene landscape. The sediments are of mid-Holocene age and were deposited during the interval 4500 B.P.–3800 yr B.P., when the southwesterly winds were stronger than they are at present and much of tropical Africa seems to have been subject to marked aridity. The onset of drier, windier conditions around 4500 yr B.P. brought to an end the more equable climates than had characterized much of West Africa during the earlier Holocene. Aridity, intensified winds, and desert expansion between 4500 and 3800 yr B.P. parallel environmental conditions in tropical continental areas at the height of the Late Pleistocene glaciation.
A Record of Late Quaternary Vegetation from Davis Lake, Southern Puget Lowland, Washington
Authors: Barnosky Cathy W. 
Published: July 2006

AbstractPollen and macrofossil analyses of a core spanning 26,000 yr from Davis Lake reveal late Pleistocene and Holocene vegetational patterns in the Puget Lowland. The core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units. The late Pleistocene pollen sequence records two intervals of tundra-parkland vegetation. The earlier of these has high percentages ofPicea, Gramineae, andArtemisiapollen and represents the vegetation during the Evans Creek Stade (Fraser Glaciation) (ca. 25,000–17,000 yr B.P.). The later parkland interval is dominated byPicea, Tsuga mertensiana, and Gramineae. It corresponds to the maximum ice advance in the Puget Lowland during the Vashon Stade (Fraser Glaciation) (ca. 14,000 yr B.P.). An increase inPinus ontortapollen between the two tundra-parkland intervals suggests a temporary rise in treeline during an unnamed interstade. After 13,500 yr B.P., a mixed woodland of subalpine and lowland conifers grew at Davis Lake during a period of rapid climatic amelioration. In the early Holocene, the prolonged expansion ofPseudotsugaandAlnuswoodland suggests dry, temperate conditions similar to those of present rainshadow sites in the Puget Lowland. More-mesic forests ofTsuga eterophylla, Thuja plicata, andPseudotsuga, similar to present lowland vegetation, appeared in the late Holocene (ca. 5500 yr B.P.).
Vegetation and Climate during the Last Glacial Maximum in Japan
Authors: Tsukada Matsuo 
Published: July 2006

AbstractThe Japanese Archipelago was almost entirely covered by coniferous forests during the last glacial maximum. Northern Hokkaido was distinguished by coniferous parkland and tundra vegetation, while southern Hokkaido and northernmost Honshu were covered by northern boreal coniferous forests consisting mainly of Picea jezoensis, Picea glehnii, Abies sachalinensis, and Larix gmelinii; Tsuga was missing from the forest. More diverse boreal forests including species from Sakhalin and northern Japan grew together in northeastern Honshu. Central Honshu and the mountains of southwestern Japan supported subalpine coniferous forests which are now mainly restricted in distribution to the central mountains. Temperate coniferous forests (Picea polita, Abies firma, and Tsuga sieboldii) existed principally in the modern mid-temperate and evergreen laurel-oak forest regions. Haploxylon pine and tree birch were also abundant in the boreal and cool-temperate zones, as was Diploxylon in the southern temperate zone. Significant populations of Fagus were found along the Pacific coasts of Kyushu and Shikoku, but they were too small to be defined as a beech forest zone. Quercetum mixtum (Quercus, Ulmus, and Tilia) was more common in the coastal lowlands of southwestern Japan than those of northeastern Honshu; it was completely eliminated from Hokkaido. The reduced mean August temperature inferred from the floral assemblages showed a latitudinal gradient 20,000 yr ago; it was 8–9°C in northern Hokkaido, 7.7–8.7°C in northernmost Honshu, 7.2–8.4°C in the central mountains, 6.5°C in the Chugoku District, and 5–6°C in Kyushu. The probable annual precipitation ranged from 1050 to 1300 mm along coasts in southwestern Japan during the culmination of the last glaciation.
Radiocarbon dating of Danube Delta Deposits
Authors: Panin Nicolae , Panin Stefana , Herz Norman , Noakes John E. 
Published: July 2006

AbstractThe Holocene history of the Danube Delta has been studied using 14C analyses of faunal material. The principal phases of development include: (1) initial Letea Caroarman spit, 11,700–9800 yr B.P. in its central part, 8800-5500 yr B.P. in its southern part; (2) Sf. Gheorghe I Delta, 8900-7200 yr B.P.; (3) Sulina Delta, 7200-2000 yr B.P., and (4) Sf. Gheorghe II Delta-Chilia Delta 2000 yr B.P.-present. Other smaller-scale features have also been dated, including secondary deltas (Coşna and Sinoe Deltas) and littoral bars. Age determinations carried out on whole samples were erratic and it was found that individual species had to be separated and dated. In all cases, the older dates were of transported material whereas the younger dates gave the true age of the formation.
Late Weichselian Environmental History in Southeastern Sweden during the Deglaciation of the Scandinavian Ice Sheet
Authors: Björck Svante , Möller Per 
Published: July 2006

AbstractLate Weichselian litho-, bio-, and chronostratigraphy (14C and varves) in southeastern Sweden provide a detailed picture of the deglaciation pattern and dynamics, shore displacement, late-glacial sedimentation, and history of the landscape, vegetation, and climate. Two plausible glacial models were tested against lithologic, chronologic, and climatic data. Permafrost at and outside the ice margin and topographic conditions beneath the ice apparently caused inward spread of frozen glacier-bed conditions. This led to a buildup of a large zone of debris-rich basal ice. A climatic amelioration about 12,700 yr B.P. changed the temperature profile in the ice sheet. Deposition of basal melt-out till began at the previously frozen glacier bed, and a rapid recession of the clean ice set in; thin exposed debris-rich basal ice which was separated from the active ice margin about 150 yr later. In this zone of stagnant ice there followed a 200– 300-yr period marked by subglacial and supraglacial melt-out and resedimentation, forming a large hummocky/transverse moraine. The mild climate favored rapid plant immigration, and a park-tundra was established. The gradual closing of the landscape was interrupted by a 100- to 150-yr period of tundra vegetation and a cool, dry climate, with local vegetational differences caused by differences in soil moisture. About 12,000 yr B.P. a second climatic amelioration set in, and during the next 1000 yr a birch (and pine) woodland gradually developed. Soils stabilized andEmpetrumheaths became abundant as the climate gradually deteriorated at the end of this period. By 11,000 yr B.P. the area had become a tundra again with scattered birch stands, dominated by herbs such asArtemisia, Chenopodiaceae, grasses, and sedges. Some 500 yr later a birch/pine woodland again succeeded, and within about 500 yr the vegetation changed to a rather closed woodland as the climate ameliorated further. However, the time lag between climatic and vegetation change was considerable.
Late Quaternary Evolution of the Northern Aegean Shelf
Authors: Perissoratis C. , Mitropoulos D. 
Published: July 2006

AbstractA dense network of 3.5 kHz and Uniboom seismic profiles revealed the geological evolution of the Ierissos-Alexandroupolis Shelf area of the northern Aegean during the latest sea-level rise. Near the end of the Pleistocene, ca. 14,000 yr B.P., the sea was at about − 120 m, and almost 5300 km2 of shelf was exposed to subaerial erosion. Two permanet lakes existed in the Ierissos and Kavalla Gulfs, as well as a number of ephemeral lakes scattered throughout the rest of the area. Kavalla Gulf was drained by the Nestos River which joined the Strymon River at the outer Strymonikos Plateau. On the flat Samothraki Plateau were dune fields, marshes, and a number of minor seasonal rivers, while the Evros River flowed east of the plateau. By ca. 13,000 yr B.P. the sea had risen to − 70 m and covered 30% of the previously exposed shelf. The lakes at Ierissos and Strymonikos Gulfs were shallower and the sea approached to within about 5 km of them. Kavalla Gulf and the adjacent eastern Strymonikos Plateau lay 10 m above sea level, while the sea intruded along river mouths at the Samothraki Plateau. During this transgression of the sea river-bed gravels and sands were covered by silts and clays. At the Pleistocene-Holocene transition, ca. 10,500 yr B.P., the sea lay at about − 50 m and in areas of steep slope the coast was close to its present position. At Kavalla Gulf, the sea advanced along the paleochannel of the Nestos River, and the island of Samothraki was separated from the mainland. By ca. 7500 yr B.P. the sea was only 15 m below its present level and the northeastern Aegean shelf assumed nearly its present morphology. The Nestos River changed course to the east and Thassos Island was separated from the mainland. Coarse sediment formed wedges nearshore, whereas fine-grained sediments were distributed widely by current action. In many areas, relict sediments are present.
Radiocarbon Dates on Deglaciation, Cordillera Central, Northern Peruvian Andes
Authors: Birkeland P.W. , Rodbell D.T. , Short S.K. 
Published: July 2006

AbstractThree radiocarbon dates along with relative-dating criteria place limits on the deglaciation history of Manachaque Valley, Cordillera Central. Ice retreated from the late-glacial maximum by at least 12,100 yr B.P. During ice retreat numerous moraines were deposited throughout the valley. Glacier cover was reduced to about half that of the last glacial maximum by at least 9700 yr B.P. and to less than a tenth by at least 6450 yr B.P. Because all dates are minimum, the dates and field data are consistent with little or no ice remaining by early Holocene. No unambiguous Younger Dryas moraines are present.
The Late Pleistocene Laurentide Glacier: Th/U Dating of its Major Fluctuations and δ18O Range of the Ice
Authors: Hillaire-Marcel Claude , Causse Christiane 
Published: July 2006

AbstractDirect information on the isotopic composition and timing of the now-vanished Laurentide glacier can be found in subglacial calcite or in early diagenetic concretions from glaciolacustrine deposits. Th/U isotopic measurements on early diagenetic concretions frome Lake Deschaillons varves (St. Lawrence Lowland, Québec) date the early Wisconsinan major ice advance at ca. 80,000 yr (isotopic stage 5a/4 transition). Significant retreat occurred at ca. 46,000 yr (isotopic stage 3) as indicated by Th/U isochrones on early diagenetic concretions from Lake Gayhurst varves in the Appalachian foothills of Québec. During the maximum extension of the ice, which is dated at ca. 22,000 yr by Th/U measurements on subglacial calcite at Cantley (northern margin of the St. Lawrence Lowland), δ18O values (vs PDB) ranging from −16/−19‰ (surficial ice) to ca. −30‰ (basal ice) are inferred for the Laurentide ice isotopic composition. Superimposition of two phases of carbonate precipitation does not prevent the establishment of their respective age and isotopic composition through correlation of independent parameters and calculation of mixing lines.
The Use of Total Lake-Surface Area as an Indicator of Climatic Change: Examples from the Lahontan Basin
Authors: Benson L.V. , Paillet F.L. 
Published: July 2006

AbstractVariation in the size of lakes in the Lahontan basin is topographically constrained. River diversion also has played a major role in regulating lake size in Lahontan subbasins. The proper gage of lake response to change in the hydrologic balance is neither lake depth (level) nor lake volume but instead lake-surface area. Normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies. To a first approximation, normalization can be accomplished by dividing the paleosurface area of a lake by its mean-historical, reconstructed surface area.
Quaternary Marine Transgressions and Paleoclimate in the Yangtze River Delta Region
Authors: Lin Jingxing , Zhang Shanlin , Qiu Jinbo , Wu Biaoyun , Huang Huanzhong , Huang Huizhen , Xi Jianguo , Tang Baogen , Cai Zuren , He Yubao 
Published: July 2006

AbstractEight marine transgressions have been recognized from more than 30 deep drill holes (ca. 300 m deep) through Quaternary sequences in the Yangtze River delta region. These are, in ascending order, the Rugao and Zhoupe transgressions (early Pleistocene); the Shanghai, Jiading, and Wangdian transgressions in the middle Pleistocene; the Jiangyin and Gehu transgressions in the late Pleistocene; and the Zhenjiang transgression in the Holocene. The transgressions correspond to warm periods and regressions to cold periods. The younger transgressions were not only of shorter duartion, but also of larger magnitude. The findings verify that there were five moderately warm periods during the early to middle Pleistocene and two very warm periods during the late Pleistocene in the Yangtze River delta region.
Dating Geomorphologic Surfaces Using Cosmogenic 3He
Authors: Cerling T. E. 
Published: July 2006

AbstractCosmogenically produced 3He in rocks can be used to date geomorphologic surfaces. Using the Late Pleistocene Bonneville flood event, the subsequent development of the Provo shoreline, and associated volcanic rocks, a production rate of 432 atoms/g/yr in olivine is determined for 38°56′ N latitude (present geomagnetic latitude 46.5°) at 1445 m altitude integrated over the last 14,400 years. Measurements of cosmogenic helium in flood deposits, on river-scoured surfaces, and lava flows show that it is possible to date directly large-scale events such as volcanic eruptions and catastrophic floods. Olivine and pyroxene are both satisfactory minerals for cosmogenic dating by the 3He method. However, in most cases, plagioclase and quartz are unsuitable because they do not quantitatively retain helium isotopes in their lattices.
Reconstruction of Past Erosional Force from Tree Ring Information around the Rokko Mountains, Japan
Authors: Kashiwaya Kenji , Okimura Takashi 
Published: July 2006

AbstractTorrential rainfalls in the Rokko Mountains have often triggered severe landslides and debris flows, but few such phenomena have occurred in the area just to the north of the mountains during the same rainfall events. The periodicity of 25–30 years in excess rainfall data (i.e., the annual summation of heavy rainfall of more than 100 mm/day during the past 100 years) around the mountains correlates with the increased frequency of landslides and debris flows. Analyses of tree-ring widths that span the past 50–240 years in samples taken from various areas in the mountains and the area just to the north indicate that most sequences have a dominant periodicity of about 25–30 years, the ring series in the mountain areas having a more conspicuous periodicity than those from the area just to the north. These results lead to the conclusion that excess rainfall may provide a first approximation of erosional force in areas affected by slope movement, and that tree-ring width may be used as a proxy for erosional force.
Paleoclimate Deduced from a Multidisciplinary Study of a Half-Million-Year-Old Stalagmite from Rana, Northern Norway
Authors: Lauritzen Stein-Erik , Løvlie Reidar , Moe Dagfinn , Østbye Eivind 
Published: July 2006

AbstractA 7-cm-thick flowstone sequence has been dated by extended Uranium series techniques to less than 1.25 myr, with a probable growth interval of ≥350,000–≤730,000 yr B.P. The time span is in accordance with paleomagnetic results revealing normal polarity for the whole sequence, i.e., a depositional age of <730,000 yr B.P. Oxygen isotope variations suggest deposition during three warm periods, interrupted by two isotopically cold hiatuses characterized by bulk resolution and detrital laminae. Calculations suggest that climatic transitions may have involved a shift of 1.1–2.4°C in mean annual temperatures. Contemporary flooding of the cave due to adjacent glacier expansion provides evidence for the widely held view that speleothem deposition is halted by glacier proximity. The flowstone matrix contained appreciable amounts of pollen (pine, birch) as well as larger amounts of charcoal dust. The pollen assemblage suggests a climate comparable with the present, implying that Norway has experienced at least three glacial/interglacial transitions during the growth interval of the speleothem. The warmer periods were characterized by a forest environment, with ample evidence of fire.
Peat Accumulation in Northern Wetlands
Authors: Ovenden Lynn 
Published: July 2006

AbstractMean long-term rates of peat accumulation are higher in boreal and temperate peat deposits than in subarctic regions of Canada, although peatlands are extensive in the subarctic. Climatic change probably accounts for the development of southern peatlands during the middle to late Holocene and for the late Holocene decline in growth of many subarctic peat deposits. In northwestern peat deposits, peat of wetSphagnumlawns and treed wetlands tended to accumulate more rapidly than peat ofSphagnumhummocks and sedge fens. Long-term net rates of carbon accumulation in Canadian peatlands typically range from 10 to 35 g C/m2/yr.
A 14,000-Year Pollen Record from Sithylemenkat Lake, North-Central Alaska
Authors: Anderson Patricia M. , Reanier Richard E. , Brubaker Linda B. 
Published: July 2006

AbstractPollen analysis of a 14,000-yr-old sediment core from Sithylemenkat Lake provides the first Holocene vegetational history for the Kanuti Flats of north-central Alaska. Basal samples contain a curious and unusual combination of tundra and boreal taxa. Pollen assemblages dating from 13,500 to 9000 yr B.P. are more typical of southern Brooks Range sites and indicate the presence ofBetulashrub tundra with increasedPopulusca. 10,000 to 9000 yr B.P.Picea glaucaappeared ca. 9000 yr B.P. andAlnusca. 8000 yr B.P.P. glaucapopulations declined between 7800 and 5000 yr B.P. with a subsequent reforestation byP. marianaandP. glauca. This pattern is seen at other sites in northeastern Alaska and suggests that the Holocene history of boreal forest is more complex than thought previously.
Atmospheric summer circulation and coastal upwelling in the Arabian Sea during the Holocene and the last glaciation
Authors: Sirocko Frank , Sarnthein Michael , Lange Heinz , Erlenkeuser Helmut 
Published: July 2006

AbstractAccumulation rates of biogenic and lithogenic components were studied in 39 turbidite-free, well-dated sediment cores from the northern Indian Ocean to define the proportions of fluvial and eolian input and to reconstruct Quaternary patterns of coastal upwelling. The majority of dust deposited in the western Arabian Sea during the Holocene (about 100 × 106t yr−1) is advected from Arabia by northwesterly winds, which overlie the low-level southwest monsoon. The glacial increase in dust flux to 160 × 106t yr−1 culminated in the northern Arabian Sea, most probably due to (i) entrainment of dust, rich in chlorite, dolomite, and lithogenic carbonate in the then-dry Persian Gulf, and (ii) a southward shift of the mean position of the southwest monsoon during glacial summer. This shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off Somalia and Oman. Both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27,000 yr, as well as the Asian continental summer heat low. However, the glacial seasonal time span of the southwest monsoon season was much reduced, most likely because of a delay in the seasonal onset of the southwest monsoon.
Absolute Dating of the Late-Glacial Period in Switzerland Using Annually Laminated Sediments
Authors: Lotter André F. 
Published: July 2006

AbstractResults of a high-resolution late-glacial AMS14C chronology from Rotsee, central Switzerland, have given evidence that the atmospheric radiocarbon concentration was not constant between 13,000 and 9500 yr B.P. This resulted in three marked phases of constant radiocarbon age: at 12,700, at 10,000, and at 9500 yr B.P. New results of a late-glacial varve chronology from Soppensee, central Switzerland, suggest that the younger two phases of constant14C age each had a duration of ca. 400 calendar years. The length of the late-glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones Bölling (ca. 800 calendar yr vs 100014C yr) and Younger Dryas (ca. 900 calendar yr vs 100014C yr) agree with the expected time span, whereas the estimated duration of the Alleröd chronozone (ca. 400 calendar yr vs 100014C yr) is substantially shorter than expected. Furthermore, a tentative comparison of varve ages and14C ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late-glacial period.
Geoarchaeological and Paleohydrological Evidence for a Clovis-Age Drought in North America and Its Bearing on Extinction
Authors: Haynes C. Vance 
Published: July 2006

AbstractAt the Murray Springs Clovis site in southeastern Arizona, stratigraphic and geomorphic evidence indicates that an abnormally low water table 10,900 yr B.P. was followed soon thereafter by a water-table rise accompanied by the deposition of an algal mat (the “black mat”) that buried mammoth tracks, Clovis artifacts, and a well. This water-table fluctuation correlates with pluvial lake fluctuations in the Great Basin during and immediately following Clovis occupation of that region. Many elements of Pleistocene megafauna in North America became extinct during the dry period. Oxygen isotope records show a marked decrease in δ18O correlated with the Younger Dryas cold-dry event of northern Europe which ended 10,750 yr B.P., essentially the same time as the water table began to rise in southeastern Arizona. Clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress. If so, both climate and human predation contributed to Pleistocene extinction in America.
Relative Dating of Moraines Based on Landform Degradation, Lee Vining Canyon, California
Authors: Bursik Marcus 
Published: July 2006

AbstractCross-sectional topographic profiles of lateral moraines formed during different glaciations were measured at Lee Vining Canyon, California, to determine whether the degree of moraine degradation could be quantified and used for relative dating. Logarithmic plots of the value of a slope parameter against cross-sectional area show distinct linear trends for moraines of different relative ages. The slopes of these trends suggest that the degradation processes are not among those that can be modeled with the linear diffusion equation.