bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional Significance of an Early Holocene Moraine in Enchantment Lakes Basin, North Cascade Range, Washington
Authors: Waitt Richard B. , Yount James C. , Davis P. Thompson 
Published: July 2006

AbstractThe upper Enchantment Lakes basin in the North Cascade Range of Washington displays two moraine belts, each recording an episode of glacier advance after the end of the last glaciation. The inner belt, the Brynhild, 0.1 to 0.5 km beyond existing glaciers, postdates Mount St. Helens Wn tephra (∼450 yr old), which lies only beyond the moraines. The morainal surface is only slightly weathered, is almost barren of lichens, and is devoid of soil, evidence suggesting that the Brynhild moraines are no more than a century old. The outer moraine, the Brisingamen, 0.3 to 0.7 km beyond existing glaciers, is weathered and is covered with large lichens. On and behind the Brisingamen moraine the Mazama ash (6900 yr old) is present beneath the Mount St. Helens Yn and Wn tephras. Despite more than 7 millennia of weathering, the rock surface behind the Brisingamen moraine is measurably less weathered than the surface beyond, which was last glaciated during the Rat Creek advance about 13,000 yr ago. The age of the Brisingamen moraine therefore is probably early Holocene. The Brisingamen moraine evidently correlates with moraines near Glacier Peak, near Mount Rainier, in northeastern and central Oregon, in the southern Canadian Rockies, and in the northern U.S. Rocky Mountains. These regional effects suggest that a climatic episode of cooling or increased snowfall affected the entire region some time during the early Holocene.
Late-Glacial Vegetation Associated with Caribou and Mastodon in Central Indiana
Authors: Whitehead Donald R. , Jackson Stephen T. , Sheehan Mark C. , Leyden Barbara W. 
Published: July 2006

AbstractThe Christensen Mastodon Site, located in central Indiana, contains a rich assemblage of vertebrates (including mastodon, caribou, and giant beaver), invertebrates, and plant macrofossilsin situin lake and bog sediments of late-glacial age. Studies of pollen and plant macrofossils suggest the existence of open, white spruce-dominated boreal forests from > 14,000 yr B.P. to ca. 13,000 yr B.P. The regional decline of spruce, local occurrence of black spruce, white spruce, and larch, immigration of many hardwood taxa (e.g., ash, oak, elm), and the initiation of bog development are recorded beginning about 13,000 yr B.P. Recent reconstructions of late-glacial and early postglacial vegetational changes provide a context for understanding the disappearance of mastodons. The dramatic and rapid restriction of boreal forests along the retreating ice margin from 11,000 to 9000 yr B.P. may have caused a substantial reduction of mastodon populations. A diminished population would be more susceptible to small-scale, stochastic events such as short-term extremes of weather, outbreaks of disease, or predation pressure from paleoindian hunters.
Differential Glacio-Isostatic Uplift of Crustal Blocks at Glen Roy, Scotland
Authors: Sissons J. B. , Cornish R. 
Published: July 2006

AbstractDetailed measurements of the altitudes of the shorelines of former ice-dammed lakes in Glen Roy and vicinity in the Scottish Highlands prove erroneous the conventional view that former shorelines in areas affected by glacio-isostatic uplift are uniformly tilted and/or gently warped. The measurements demonstrate differential uplift of blocks of the earth's crust. The surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4.6 m/km and are tilted in different directions. In three areas 0.7–2.0 km long, shorelines are distorted by crustal movements; all these areas have landslides attributed to earthquakes that accompanied the release of stress. In the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area, and a fault scarp was produced. Possibly these local distortions accompanied catastrophic lake drainage by jökulhlaup, analogous to crustal movements associated with man-made lakes. A relationship between crustal movement and the limit of a glacial advance is demonstrated. These findings have implications for other parts of the world affected by glacioisostatic uplift.
Postglacial Temperature Anomalies and Glacial Isostasy
Authors: Tinkler K. J. 
Published: July 2006

AbstractThe isostatic depression of an ice-free land surface, originally caused by glacial ice, ought to be converted into a change in mean annual temperature according to the usual value for the environmental lapse rate, 6.5°C/1000 m. Calculations are undertaken to show the temperature changes, relative to present values at a site, that can be expected from this effect during the retreat of a major continental ice sheet. It is concluded that when restrained rebound is taken into account temperatures relative to the present could vary from 0°C at the start of deglaciation to about +2.32°C at the final disappearance of the Laurentide Ice Sheet. The decay of the warmer-than-present temperatures towards their current values is controlled, in this model, by isostatic recovery of the land surface. Variance estimates are built into the model and suggest that the anomaly might be as small as 0.75°C or as large as 4.0°C depending on the choice of values for crucial components such as maximum ice thickness, the proportion of isostatic deformation, and the amount of restrained rebound achieved by the time a site become ice free.
Time Variations of Erosional Force and Grain Size in Pleistocene Lake Sediments
Authors: Kashiwaya Kenji , Yamamoto Atsuyuki , Fukuyama Kaoru 
Published: July 2006

AbstractTheoretical investigations on models of the developmental processes of erosional features show that the time variations in erosional force have more sensitive influence on the time fluctuation of eroded material, such as sediments in lakes, than that of the quantity representing erosional features, such as volume of mountains. Time sequences of grain-size distributions from the Pleistocene sediments in Lake Biwa, central Japan indicate dominant periodicities of about 40,000 and 20,000 yr, very close to those predicted from the Milankovitch theory. The time variations of the grain-size parameters which may be indicators of erosional forces are very similar to that of the caloric summer insolation in the Northern Hemisphere.
Paleoenvironmental Changes at the Northern Limit of the Subantarctic Nothofagus Forest, lat 37°S, Argentina
Authors: Markgraf Vera 
Published: July 2006

AbstractPaleoenvironmental changes dating back to before 10,000 yr B.P. at the northernmost occurrences of Nothofagus forests in Argentina at about latitude 37°S permit the reconstruction of past changes in the intensity of the winter rains, related to the southern westerlies that appear to determine the forest boundary. The paleoenvironmental interpretation is based on changes in the proportions of different Nothofagus species and changes in the ratio betwen forest and steppe taxa. The relatively most diverse and dense Nothofagus forest developed only during the last 4500 yr, prior to human impact during the last 300 yr. Before the middle Holocene, climatic conditions must have been different from the modern ones, with less overall precipitation judging from the overall lower amount of tree pollen and the reduction to primarily Nothfagus pumilio. An interval dated to older than 10,000 yr B.P. is characterized by co-occurrence of Prumnopitys andina, Nothofagus pumilio, and shrub-steppe taxa. Prumnopitys andina is known today only from scattered upper montane forest sites in Chile between 36° and 43°S lat and its ecological requirements are essentially unknown. The taxa combination, however, suggests that late-glacial climate must have been drier, and probably cooler than today. This implies that the winter rains and, consequently, the seasonal shift of the westerly circulation was reduced during the late Pleistocene and did not reach modern levels before 8500 yr B.P.
Importance of the Rossendale Site in Establishing a Deglacial Chronology Along the Southwestern Margin of the Laurentide Ice Sheet
Authors: Teller James T. 
Published: July 2006

AbstractThe timing of deglaciation in the Lake Agassiz basin is critical in establishing the routing of meltwater and precipitation runoff from a 2,000,000-km2region of central North America and in evaluating the influence this water had on rivers and oceans into which it drained. Dates of 12,400 ± 420 and 12,100 ± 160 yr B.P. for moss at the Rossendale site in Manitoba have long been a key for those advocating an “early” deglacial chronology in this region. However, new dates for wood from this site and paleoecological interpretations of ostracods, molluscs, and the dated moss all support a “young” deglacial scenario. Of particular significance is the fact that the dated moss,Scorpidium scorpioides, is a subaquatic type subject to contamination by old carbon dissolved from bedrock. In fact, most subaquatic moss may be unreliable for radiocarbon dating. For these reasons, the 12,400 and 12,100 yr B.P. dates are rejected. New dates of 9600 ± 70 and 9510 ± 90 yr B.P. for wood from the same organic-rich unit containing the dated moss, ostracods, and molluscs fit well with the “young” deglacial chronology of the southwestern Laurentide ice margin advocated by many. In short, the ice margin appears to have retreated into the southern Lake Agassiz basin after 12,000 yr B.P. and north of the Rossendale site by 11,000 yr B.P. About 10,000 yr B.P., following the Moorhead low-water phase, Lake Agassiz rose to the Campbell level. The dated organic matter at Rossendale was deposited in a lagoon behind the Campbell beach.
Glacial/Interglacial Size Variation in Fossil Spotted Hyenas (Crocuta crocuta) from Britain
Authors: Klein Richard G. , Scott Katharine 
Published: July 2006

AbstractThe lower carnassial lengths of spotted hyenas (Crocuta crocuta) in 12 late Pleistocene samples from Britain indicate that, on average, local hyenas of the last (Devensian) glaciation were significantly larger than their last-interglaciation (Ipswichian) counterparts. Together with the tendency for spotted hyena carnassial length to increase with latitude in present-day Africa, this suggests that spotted hyena body size is inversely related to temperature, as predicted by Bergmann's rule. The implication is that spotted hyena carnassial length can be used as an independent gauge of Pleistocene temperature variation, though the combined African and British data imply that the relationship between carnassial length and temperature is curvilinear, such that as temperature declines, equal amounts of further decline produce progressively smaller increases in average carnassial length.
Bagnold's Barchan: A 57-Yr Record of Dune Movement in the Eastern Sahara and Implications for Dune Origin and Paleoclimate Since Neolithic Times
Authors: Haynes C. Vance 
Published: July 2006

AbstractDiscovery in 1980 of Camp 18 of the 1930 Bagnold expedition in northwestern Sudan has resulted in an exceptionally long record of barchan movement from which an average rate of 7.5 m/yr has been calculated. Measurements of the rate of dune advance since 1980 have not varied significantly, indicating a state of quasiequilibrium exists. The dune field is moving over an undulating sand sheet exhibiting various stages of Holocene pedogenesis and containing Neolithic sites. The sand sheet overlies Pleistocene alluvium with stronger stages of pedogenesis. All of these deposits may be a significant source of dune sand. Wind-blown grass fragments trapped by advancing slipfaces mark former slipface positions and indicate late Holocene rainfall events, which can be radiocarbon dated. Parabolic forms (revealed by SPOT images) at the windward ends of the dune fields are transitional to barchans, suggesting sand accumulation in vegetation germinated during a Holocene wet period. In addition, sand streaks from sand-sheet undulations suggest that active eolian erosion of sand sheets contributes to the sand supply of dune fields. Pedogenesis during pluvial periods contributes to silt and clay fractions of bimodal sand sheet sediments. From wind streaks on LANDSAT images and an estimated average rate of dune advance, positions of dune fields during past hyperarid periods can be estimated.
Younger Dryas Climatic Reversal in Northeastern USA? AMS Ages for an Old Problem
Authors: Peteet D. M. , Vogel J. S. , Nelson D. E. , Southon J. R. , Nickmann R. J. , Heusser L. E. 
Published: July 2006

AbstractLate-glacial macrofossils from a 10-m core from Alpine Swamp, New Jersey, were radiocarbon dated using accelerator mass spectrometry (AMS). The arrival of the first trees to the area following deglaciation is indicated by maximum percentages of spruce pollen and a date of 12,290 ± 440 yr B.P. on a single spruce needle. Subsequent spread of deciduous hardwoods was followed by the expansion of boreal taxa, including spruce (Picea), fir (Abies), larch (Larix laricina), paper birch (Betula papyrifera), and alder (Alnus). Three AMS dates on paper birch seeds and a spruce needle during this boreal expansion indicate that it took place between 11,000 and 10,000 yr B.P. The timing of this vegetational shift and its correlation with late-glacial pollen stratigraphy from many sites in southern New England indicate that a climatic reversal correlative with the Younger Dryas characterized the North Atlantic seaboard of the United States.
Holocene Climatic Change and the Distribution of Peatlands in Western Interior Canada
Authors: Zoltai Stephen C. , Vitt Dale H. 
Published: July 2006

AbstractDates of basal fen peat at 52 locations across west-central Canada indicate that peat deposition began <6000 yr B.P. in a broad zone north of the present-day grassland. The isopleth of >6000 yr B.P. basal fen peat parallels the foothills of the Rocky Mountains, and extends eastward along 54°30′ north latitude. The absence of >6000 yr B.P. peat within this zone is attributed to a warmdry early to middle Holocene climate that caused severe seasonal droughts and prevented the establishment of peat-forming fen vegetation. Wetlands west (and probably north) of this line experienced lower water tables, but supported fen vegetation. As the climate became cooler and moister, stable water tables allowed the development of fens and rapid peat accumulation ensued, reaching the modern distribution of fens between 2000 and 3500 yr B.P. Projections of climatic parameters indicate that the mean annual growing degree days were 6 to 21% higher during the early and middle Holocene, and that precipitation was reduced through most of the area, resulting in much higher (by 17 to 29%) aridity than at present.
Late-Pleistocene Eolian Sand Sheets in Alaska
Authors: Lea Peter D. , Waythomas Christopher F. 
Published: July 2006

AbstractNonglaciated lowlands in central and southwestern Alaska contain extensive deposits of upper-Quaternary eolian sand, derived largely from major outwash rivers. Although surface dunes are common, deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata. We hypothesize that (1) many of the subhorizontally stratified deposits represent full-glacial eolian sand sheets, formed when sand supply was limited by seasonally variable combinations of ice cementation, snow cover, high groundwater tables, and vegetation, and (2) many surface dunes reflect late-glacial and postglacial reworking under conditions of increased short-term availability of loose sand. The morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum, rather than full-glacial paleowind vectors or the age of the bulk of the underlying deposits.
Climatic Fluctuations in Northern Patagonia during the Last 1000 Years as Inferred from Tree-Ring Records
Authors: Villalba Ricardo 
Published: July 2006

AbstractMillennium-old alerce trees (Fitzroya cupressoides (Mol.) Johnst.) have been used to develop a 1120-year reconstruction of the summer temperature departures for the Andes of northern Patagonia in Argentina. Four main climatic episodes can be distinguished in this proxy paleoclimatic record. The first, a cold and moist interval from A.D. 900 to 1070, was followed by a warm-dry period from A.D. 1080 to 1250 correlative with the Medieval warm epoch of Europe. Afterward, a long, cold-moist period followed from A.D. 1270 to 1670, peaking around A.D. 1340 and 1650. These cold maxima are contemporaneous with two principal Little Ice Age events registered in the Northern Hemisphere. Warmer conditions then resumed between A.D. 1720 and 1790. These episodes are supported by glaciological and palynological data in Patagonia. Following a cold period in the early 1800s, tree-ring indices have oscillated around the long-term mean, except for a warmer period from A.D. 1850 to 1890. Correlations between the Rio Alerce reconstruction and the regional weather stations indicate that the tree-ring variations are correlated with a homogeneous summer weather pattern covering Patagonia east of the Andes from 38° to 50°S.
Late Quaternary Glacial History of the South Orkney Plateau, Antarctica
Authors: Herron Margaret J. , Anderson John B. 
Published: July 2006

AbstractPiston cores from the South Orkney Plateau penetrated overcompacted diamictons in water depths of up to 250 m. Detailed textural and petrological analyses of these diamictons indicate that they are basal tills. Seismic records from the plateau show a widespread surface of glacial erosion and provide additional evidence of an ice cap grounded to a depth of 250 m. Piston cores from the slope of the plateau penetrated diatomaceous muds resting directly on poorly sorted muds with very little to no biogenic material. The ice-rafted debris in these glacial-marine sediments is composed almost exclusively of material derived from the South Orkney Islands. This implies deposition beneath an ice shelf as opposed to iceberg rafting. In contrast, diatomaceous muds contain relatively abundant exotic iceberg-rafted material and reflect a glacial-maritime setting similar to that of today. The sharp contact separating diatomaceous surface sediments from basal tills and sub-ice shelf deposits indicates that the ice cap and ice shelf retreated from the plateau rapidly. Radiocarbon dates for diatomaceous muds from a glacial trough on the plateau indicate that the ice cap and ice shelf retreated from the plateau prior to 6000 to 7000 years ago. The homogeneity of surficial diatomaceous sediments suggests that sea ice conditions over the plateau have not changed radically since that time.
Age and Paleoclimatic Significance of the Stansbury Shoreline of Lake Bonneville, Northeastern Great Basin
Authors: Oviatt Charles G. , Currey Donald R. , Miller David M. 
Published: July 2006

AbstractThe Stansbury shoreline, one of the conspicuous late Pleistocene shorelines of Lake Bonneville, consists of tufa-cemented gravel and barrier beaches within a vertical zone of about 45 m, the lower limit of which is 70 m above the modern average level of Great Salt Lake. Stratigraphic evidence at a number of localities, including new evidence from Crater Island on the west side of the Great Salt Lake Desert, shows that the Stansbury shoreline formed during the transgressive phase of late Pleistocene Lake bonneville (sometime between about 22,000 and 20,000 yr B.P.). Tufa-cemented gravel and barrier beaches were deposited in the Stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m. We refer to the fluctuations as the Stansbury oscillation. The Stansbury oscillation cannot have been caused by basin-hypsometric factors, such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin, or by changes in drainage basin size. Therefore, changes in climate must have caused the lake level to reverse its general rise, to drop about 45 m in altitude (reducing its surface area by about 18%, 5000 km2), and later to resume its rise. If the sizes of Great Basin lakes are controlled by the mean position of storm tracks and the jetstream, which as recently postulated may be controlled by the size of the continental ice sheets, the Stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the Laurentide ice sheet.
Paleoclimatic Reconstruction in Northern Oman Based on Carbonates from Hyperalkaline Groundwaters
Authors: Clark Ian D. , Fontes Jean-Charles 
Published: July 2006

AbstractA paleoclimatic reconstruction for the past 35,000 years for northern Oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs. High-pH groundwaters (pH up to 11.9) discharge from the mantle sequence of the Oman Ophiolite as the product of modern, low-temperature serpentinization. Under arid climatic conditions, hyperalkaline discharge occurs at the surface. Uptake of atmospheric CO2precipitates characteristic laminated travertines, accompanied by strong kinetic depletion of13C and18O. Pluvial climates supporting a shallow bicarbonate-groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite-replaced roots and stems. All such carbonates have modern initial14C contents, allowing radiocarbon dating and paleoclimatic reconstruction for the late Pleistocene and Holocene. Our reconstruction shows a dominantly wet late Pleistocene up to 19,000 yr B.P., when a phase of climatic deterioration began, leading to a period of hyperaridity which dominated from ca. 16,300 to 13,000 yr B.P. The early Holocene pluvial occurred from 12,500 to ca. 6500 yr B.P. and was followed by renewed climatic deterioration and the current phase of hyperaridity. Comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the A'Rub al Khali of central Saudi Arabia and the summer insolation-driven monsoon record of east Africa and the Arabian Sea is remarkably good.
Magnetic susceptibility evidence of monsoon variation on the Loess Plateau of central China during the last 130,000 years
Authors: An Zhisheng , Kukla George J. , Porter Stephen C. , Xiao Jule 
Published: July 2006

AbstractThe magnetic susceptibility of loess and paleosols in central China represents a proxy climate index closely related to past changes of precipitation and vegetation, and thus to summer monsoon intensity. Time series of magnetic susceptibility constructed for three loess-paleosol sequences in the southern part of the Chinese Loess Plateau document the history of summer monsoon variation during the last 130,000 yr. They correlate closely with the oxygen isotope record of stages 1 to 5 in deep-sea sediments. Soils were forming during intervals of strong summer monsoon, whereas loess units were deposited at times of reduced monsoon intensity. The Chinese loess-paleosol sequence can thus be viewed as a proxy record of Asian monsoon variability extending over the last 2.5 myr.
ESR ages of middle Pleistocene corals from the Ryukyu islands
Authors: Ikeda Sumiko , Kasuya Masao , Ikeya Motoji 
Published: July 2006

AbstractElectron spin resonance ages of 11 corals from the lower part of the Ryukyu Group, Japan can be classified into two groups (about 600,000 and 800,000 yr). The result indicates that the lower part of the Ryukyu Group is correlated to at least two of the oxygen isotope stages 15, 17, 19, 21, and 23. Lowermost part of the Ryukyu Group was probably deposited during a large transgression and may be correlated worldwide.