bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics and Possible Source of a 1479 A.D. Volcanic Ash Layer in a Greenland Ice Core
Authors: Fiacco R. Joseph , Palais Julie M. , Germani Mark S. , Zielinski Gregory A. , Mayewski Paul A. 
Published: October 2002

AbstractA microparticle concentration peak in a GISP2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479-1480 A.D. Mt. St. Helens Wn eruption. These glass shards are compositionally similar to the Wn tephra and constitute 83% of the total particle population. The shards are very coarse-grained (up to 40 μm diameter), suggesting rapid transport from their source to Greenland. A major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards. This difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol. Large-scale climatic perturbations following this eruption were evidently negligible. Glaciochemical seasonal indicators suggest a late-fall to early-winter 1479 A.D. eruption.
Optical Dating of Holocene Dune Sands in the Ferris Dune Field, Wyoming
Authors: Stokes Stephen , Gaylord David R. 
Published: October 2002

AbstractOptical dating of late Quaternary quartz dune sands from the Clear Creek portion of Ferris dune field, Wyoming, demonstrates the considerable potential of the technique as a chronostratigraphic tool. A sequence of radiocarbon-dated Holocene interdune strata permit optical dating of the intercalated dune sand to be tested; the concordance is good. The optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at Clear Creek peaked during two relatively short phases at ca. 8500 and 4000 yr B.P. The dates indicate that aeolian accumulation maxima (at least in the Clear Creek area) may not be synchronous with previously defined phases of marked aridity.
A Vegetation History of the Far North of New Zealand during the Late Otira (Last) Glaciation
Authors: Newnham Rewi , Ogden John , Mildenhall Dallas 
Published: October 2002

AbstractDuring the latter part of the last (Otira) glaciation the forest cover of New Zealand was much reduced. It has frequently been postulated, however, that diverse mixed forest communities survived in the far north of North Island. Pollen diagrams and radiocarbon dates from two last glacial and postglacial (Aranuian) sits on the Aupouri Peninsula in the far north of New Zealand are compared with other published palynological and plant macrofossil evidence from the region. Mixed kauri/podocarp/angiosperm forest was present at times during the late Otiran (and Aranuian) and no evidence was found for substantial loss of forest. However, radiocarbon samples from one site, at least, seem to have been contaminated with young carbon; this introduces uncertainty into the chronology established at that site. Possibly nondeposition or erosion has obscured part or all of the late Otiran record at all the sites studied so that very much reduced forest cover at that time cannot be ruled out.
Radiocarbon Ages from Two Submerged Strandline Features in the Western Gulf of Maine and a Sea-Level Curve for the Northeastern Massachusetts Coastal Region
Authors: Oldale Robert N. , Colman Steven M. , Jones Glen A. 
Published: October 2002

AbstractNew radiocarbon dates provide ages for two submerged strandline features on the Massachusetts inner shelf. These ages provide limited control on a relative sea-level (RSL) curve for the late Wisconsinan and Holocene. The curve indicates a late Wisconsinan high stand of RSL of +33 m about 14,000 yr ago and a very short-lived relative low stand of about -43 m at about 12,000 yr ago followed by a rise to present sea level. Rapid changes of RSL around 12,000 yr ago may be related to changes in global glacial meltwater discharge and eustatic sea-level change shown by dated corals off Barbados. Variations in the magnitude and timing of RSL change from south to north along the coast of the western Gulf of Maine are due to greater crustal depression and later deglaciation to the north.
Manganese Accumulation in Rock Varnish on a Desert Piedmont, Mojave Desert, California, and Application to Evaluating Varnish Development
Authors: Reneau Steven L. 
Published: October 2002

AbstractRock varnish coatings tend to become thicker, darker, and more continuous over time, leading to the use of changes in overall varnish color and the percentage of clast surfaces covered by varnish as relative-age indicators. Manganese is the most characteristic element of subaerial rock varnishes, and the progressive development of varnish coats can be quantified by measuring the amount of Mn accumulated on a given area of rock surface. Manganese oxides were dissolved off varnished clasts collected from alluvial surfaces on the Soda Mountains piedmont in the Mojave Desert, California, and the amount of Mn was measured using inductively coupled plasma emission spectroscopy. On the distal piedmont, maximum varnish development increases from a mid- to late-Holocene surface, typically containing up to 0.15 mg/cm2of accumulated Mn, to an early- to mid-Holocene surface with up to 0.21 mg/cm2. However, varnish is less developed on a nearby late Pleistocene surface, suggesting extensive abrasion of clasts on the Pleistocene desert pavements or disturbance of the clasts. Varnish is better developed on the proximal piedmont, typically containing up to 0.30 mg/cm2of Mn, although varnish from a Pleistocene surface is again no better developed than from a nearby early- to mid-Holocene surface. These data demonstrate that rock varnish can show significant spatial variation in degree of development on geomorphic surfaces of similar age, and imply that collecting varnish as old as a geomorphic surface may be difficult on surfaces as young as late Pleistocene.
Geochronological Potential of Isoleucine Epimerization in Calcite Speleothems
Authors: Lauritzen Stein-Erik , Erik Haugen John , Løvlie Reidar , Gilje-Nielsen Helge 
Published: October 2002

AbstractThe extent of isoleucine epimerization in a calcite speleothem was determined to evaluate the amino acid racemization method in abiotic calcite. A 5.5-cm-thick flowstone slab from Hamarnesgrotta, northern Norway, was analyzed for amino acid concentration, composition, and isoleucine epimerization at 26 levels through the sequence. U-series dates provide an independent chronologic control. Epimerization increases monotonically with stratigraphic depth and linearily with U-series age, independent of amino acid concentrations. The rate of epimerization is calibrated against the U-series dates, and extrapolation into lower strata beyond the U-series limit yields absolute age estimates that are consistent with paleomagnetic data from the same speleothem. The results suggest that, if adequately calibrated, amino acid dating is applicable to speleothem material reaching time spans beyond the range of conventional dating methods. Amino acids in the speleothem were probably derived from surface soils and are associated with brown humic stains in the calcite.
Evidence of Atmospheric Paleocirculation over the Gulf of Guinea since the Last Glacial Maximum
Authors: Lezine Anne-Marie , Tastet Jean-Pierre , Leroux Marcel 
Published: October 2002

AbstractHigh-resolution pollen and eolian input studies from core KS 84063 in the Gulf of Guinea record the response of the tropical atmospheric circulation to global paleoclimatic events during the last glacial/interglacial transition. Two depositional phases centered around 15,000 and 10,300 yr B.P. are characterized by maximum values of pollen concentration and of eolian activity index (EA1). Pollen spectra record the significant presence of Artemisia and Ephedra of Saharan origin and the scattered occurrence of Podocarpus from Guinean mountain forests; these demonstrate the intensity of the meridional atmospheric circulation over equatorial West Africa during dry periods. The early Holocene humid phase, ca. 8500 yr B.P., is marked by minima in pollen concentrations and EAI. Saharan taxa are absent and, in contrast, Podocarpus reached its highest relative values. This evidence has been interpreted as reflecting a weakening in the continentocean eolian transport and the importance of monsoonal fluxes. Downcore variations in Podocarpus percentages are used to identify the atmospheric circulation patterns over the low latitudes of West Africa during extreme (dry/humid) climatic conditions.
Isotopic Approach to Soil Carbonate Dynamics and Implications for Paleoclimatic Interpretations
Authors: Pendall Elise G. , Harden Jennifer W. , Trumbore Sue E. , Chadwick Oliver A. 
Published: October 2002

AbstractThe radiocarbon content and stable isotope composition of soil carbonate are best described by a dynamic system in which isotopic reequilibration occurs as a result of recurrent dissolution and reprecipitation. Depth of water penetration into the soil profile, as well as soil age, determines the degree of carbonate isotope reequilibration. We measured δ13C, δ18O and radiocarbon content of gravel rinds and fine (<2 mm) carbonate in soils of 3 .different ages (1000, 3800, and 6300 14 C yr B.P.) to assess the degree to which they record and preserve a climatic signal. In soils developing in deposits independently dated at 3800 and 6300 radiocarbon yr B.P., carbonate radiocarbon content above 40 cm depth suggests continual dissolution and reprecipitation, presumably due to frequent wetting events. Between 40 and 90 cm depth, fine carbonate is dissolved and precipitated as rinds that are not redissolved subsequently. Below 90 cm depth in these soils, radiocarbon content indicates that inherited, fine carbonate undergoes little dissolution and reprecipitation. In the 3800- and 6300-yr-old soils, δ13C in rind and fine carbonate follows a decreasing trend with depth, apparently in equilibrium with modern soil gas, as predicted by a diffusive model for soil CO2. δ18O also decreases with depth due to greater evaporative enrichment above 50 cm depth. In contrast, carbonate isotopes in a 1000-yr-old deposit do not reflect modern conditions even in surficial horizons; this soil has not undergone significant pedogenesis. There appears to be a lag of at least 1000 but less than 3800 yr before carbonate inherited with parent material is modified by ambient climatic conditions. Although small amounts of carbonate are inherited with the parent material, the rate of pedogenic carbonate accumulation indicates that Ca is derived primarily from eolian and rainfall sources. A model describing carbonate input and radiocarbon decay suggests that fine carbonate below 90 cm is mostly detrital (inherited) and that carbonate rinds have been forming pedogenically at a constant rate since alluvial fans were deposited.
Reversed-Polarity Glacial Sediments and Revised Glacial Chronology, West Branch Susquehanna River Valley, Central Pennsylvania
Authors: Gardner Thomas W. , Sasowsky Ira D. , Schmidt Victor A. 
Published: October 2002

AbstractA new exposure of glacial and glaciolacustrine sediments at Antes Fort allows for revision of the chronology of pre-Wisconsinan glaciation in central Pennsylvania. Lacustrine sediments from a proglacial lake in the West Branch Susquehanna River valley have reversed remanent polarity with a site mean paleomagnetic declination of 193.8° and inclination of -13.1°. The magnetization is probably a true detrital remanence from the time of deposition and is not significantly affected by postdepositional diagenesis. We propose that the Antes Fort till was deposited during either pre-Illinoian glaciation F or G of G. M. Richmond and D. S. Fullerton (1986, "Quaternary Science Reviews," Vol. 5, 183-196) between 770,000 and 970,000 yr ago. We suggest that it is equivalent to the Penny Hill till in the West Branch Susquehanna River valley and tentatively correlate it westward with the reversed polarity terrace deposits and Minford Silt in western Pennsylvania, West Virginia, and Ohio; the West Lebanon till in Indiana; and the A4 tills (or possible B tills) in Iowa and Nebraska.
Late-Glacial and Early Holocene Sea-Level Fluctuations in the Central Puget Lowland, Washington, Inferred from Lake Sediments
Authors: Anundsen Karl , Abella Sally , Leopold Estella , Stuiver Minze , Turner Sheila 
Published: October 2002

AbstractAnalyses of sediments, diatoms, and pollen in a 12.65-m-long sediment core taken from Lake Carpenter in the central Puget Lowland, Washington, provide detailed information regarding the history of deglaciation and late-glacial/early Holocene sea-level changes. The lake outlet, now 8.2 m above sea level, has been lowered 1-1.5 m by postglacial erosion. The lithology and pollen record suggest that no lengthy hiatuses in sedimentation have occurred. The basal sediments are glacialmarine and contain shell fragments and brackish/marine diatoms. Freshwater sediments above the basal section are interrupted only by a short section containing few fossils, most of which are brackish to marine indicators, and by the Mazama tephra at 9.5 m. The pollen record in the basal 4 m reveals a Pinus zone (ca. 13,850-11,000 yr B.P.) with a brief peak of Picea at ca. 13,700 yr B.P., and an Alnus/Pseudotsuga zone (ca. 11,000-6500 yr B.P.). The chronology is based on nine radiocarbon ages. A relative lowering of sea level below the 9.5-m threshold is recorded in the core at 12.41 m and dates 13,850 to 13,700 yr B.P. A marine episode occurred about 13,600 yr B.P., implying that relative sea-level temporarily rose above 9.5 m. No subsequent transgressions above the 9.5-m level have been recorded. Comparison of six radiocarbon dates ≥13,600 yr B.P. suggest that the marine reservoir correction of 760 yr currently used for this area may be too high for this time period.
Evidence of Active Dune Sand on the Great Plains in the 19th Century from Accounts of Early Explorers
Authors: Muhs Daniel R. , Holliday Vance T. 
Published: October 2002

AbstractEolian sand is extensive over the Great Plains of North America, but is at present mostly stabilized by vegetation. Accounts published by early explorers, however, indicate that at least parts of dune fields in Nebraska, Colorado, Kansas, New Mexico, and Texas were active in the 19th century. Based on an index of dune mobility and a regional tree-ring record, the probable causes for these periods of greater eolian activity are droughts, accompanied by higher temperatures, which greatly lowered the precipitation-to-evapotranspiration ratio and diminished the cover of stabilizing vegetation. In addition, observations by several explorers, and previous historical studies, indicate that rivers upwind of Great Plains dune fields had shallow, braided, sandy channels, as well as intermittent flow in the 19th century. Wide, braided, sandy rivers that were frequently dry would have increased sand supplies to active dune fields. We conclude that dune fields in the Great Plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high, with or without greenhouse warming.
Warming at 18,000 yr B.P. in the Tropical Andes
Authors: Helmens Karin F. , Kuhry Peter , Rutter Nathaniel W. , Van Der Borg Klaas , De Jong Arie F. M. 
Published: October 2002

AbstractPalynological, paleopedological, and glacial geomorphological evidence from the area of the high plain of Bogotá in the Colombian Eastern Cordillera indicates a significant climatic warming around 18,00014C yr B.P. Comparison of dated vegetation changes, pedogenic episodes, and glacier fluctuations provides the basis for defining the so-called “La Laguna Interstadial” that lasted from 19,500 to 17,000 yr B.P. During this interstadial period, mean annual temperatures in the tropical Andes were up to 4°C higher than during the preceding and following stadial periods, when full-glacial conditions prevailed and temperatures were up to 8°C colder than at present.
Paleosol Stable Isotope Evidence for Early Hominid Occupation of East Asian Temperate Environments
Authors: Wang Hong , Ambrose Stanley H. , Liu Chao-Li Jack , Follmer Leon R. 
Published: October 2002

AbstractHominids left Africa and occupied mainland Asia by 1.8 myr ago. About 1.15 myr agoHomo erectusand an associatedStegodon–Ailuropodafauna migrated from subtropical China across the Qinling Mountains into the temperate Loess Plateau. This migration may be an evolutionary milestone in human adaptability because it may represent the first occupation of a nontropical environment. Loess–paleosol stable isotope ratios from the last interglacial–glacial cycle provide comparative data for reconstructing the hominid paleoenvironments. The climate during Gongwangling hominid occupation about 1.15 myr ago was influenced by both Siberian–Mongolian winter and Indian summer monsoon systems characterized as a cold/cool, dry winter and warm/mild, semihumid summer and fall. The Gongwangling hominids preyed mainly on warm-climate-adapted animals such asStegodon–Ailuropodafauna, suggesting a warm season occupation. The stable isotope ratios also indicate that the Chenjiawo hominids occupied an environment similar to that of the Gongwangling about 650,000 yr ago. The associated fauna, with a mixture of forest and steppe, warm- and cold/cool-climate-adapted animal assemblage's, suggests a permanent occupation by this time. Thus, the reliable earliest and permanent occupation of temperate environments may have occurred 150,000 yr earlier in eastern Asia rather than in Europe.
Effects of Climate Change on Soils in Glacial Deposits, Wind River Basin, Wyoming
Authors: Hall Robert D. 
Published: October 2002

AbstractSoil chronofunctions are often quasilinear, but those relationships may be only gross, fortuitous generalizations that ignore changes in soils resulting from climatic and other cyclic external influences that govern soil formation or soil degradation. In the Rocky Mountains, soil development has been extensively used to estimate the age of sediments, but the number of soils is usually few, and large ranges in values for soil data may be dismissed as “normal variation.” In a detailed study of soils in the Wind River Range and Wind River Basin, characteristics of near-surface horizons do not follow age trends. However, the underlying carbonate-bearing horizons do have age-related characteristics. This “soil paradox” may be related to glacial–interglacial cycles in which (1) wind erodes near-surface horizons and then provides new parent material and (2) cryoturbation disrupts carbonate horizons, remobilizing carbonate and changing carbonate morphology but with only minimal loss of carbonate from the soil.
Wet Conditions during the Last Glaciation in the Chihuahuan Desert, Alta Babicora Basin, Mexico
Authors: Metcalfe Sarah , Say Alison , Black Stuart , McCulloch Robert , O'Hara Sarah 
Published: October 2002

AbstractA 467-cm core (B94/3) from the Alta Babicora basin in the Chihuahuan Desert, northern Mexico (29°N, 108°W), documents lake-level and climate changes over the past ca. 65,000 yr. Chronological control is provided by four accelerator mass spectrometry14C dates and five U-series dates on diatom silica. The core has been analyzed for magnetic susceptibility, loss-on-ignition, carbonate content, sediment chemistry and mineralogy, and pollen and diatom composition. The basin was occupied by a deep freshwater lake throughout the late Pleistocene which, based on shoreline evidence, was at least 19 m deeper than today. The lake shallowed after ca. 57,000 yr B.P. High variability typified the period between 54,600 and 38,000 yr B.P., probably with periodic desiccation and deflation. A deep-water lake was reestablished after 38,000 yr B.P. and persisted until ca. 29,000 yr B.P. Shallowing occurred through the last glacial maximum, although the lake was still deeper than at present. The Pleistocene–Holocene transition was marked by a distinctive change in the diatom flora. There is no diatom record for much of the Holocene, but other proxies indicate generally dry, stable catchment conditions. The Babicora record is more akin to those from the southwest United States than it is to Central America and northern South America. Wet conditions in the late Pleistocene are attributed to winter rainfall from midlatitudes in contrast to the modern, tropical, summer rainfall regime.
Current value of intraoperative sonography during surgery for hepatic neoplasms
Authors: Zacherl Johannes , Scheuba Christian , Imhof Martin , Zacherl Maximilian , Längle Friedrich , Pokieser Peter , Wrba Fritz , Wenzl Etienne , Mühlbacher Ferdinand , Jakesz Raimund , Steininger Rudolf 
Published: October 2002

AbstractNoninvasive liver imaging has developed rapidly resulting in increased accuracy for detecting primary and secondary hepatic tumors. Intraoperative ultrasonography (IOUS) was commonly considered to be the gold standard for liver staging, but the current value of IOUS is unknown in view of more sophisticated radiologic tools. The purpose of this prospective study was to evaluate the impact of IOUS on the treatment of 149 patients undergoing liver surgery for malignant disease (colorectal metastasis, 61 patients; hepatoma, 52 patients; other hepatic malignant tumors, 36 patients). The sensitivities of computed tomography (CT), helical CT, magnetic resonance imaging, and IOUS in patients with colorectal metastases were 69.2%, 82.5%, 84.9%, and 95.2% in a segment‐by‐segment analysis; in patients with hepatoma their sensitivities were 76.9%, 90.9%, 93.0%, and 99.3%; and in patients with other hepatic malignancies they were 66.7%, 89.6%, 93.3%, and 98.9%, respectively. Additional malignant lesions (AMLs) were first detected by inspection and palpation in 20 patients (13.4%). In another 18 patients (12.1%) IOUS revealed at least one AML. Overall, the findings obtained only by IOUS changed the surgical strategy in 34 cases (22.8%). It was concluded that IOUS, having undergone some refinement as well, still has immense diagnostic value in hepatectomy candidates. Frequently avoiding palliative liver resection and occasionally disproving unresectability as assessed by preoperative imaging, IOUS still has a significant impact on surgical decision making and should still be considered the gold standard.
Pyloric motility after pylorus‐preserving gastrectomy with or without the pyloric branch of the vagus nerve
Authors: Nakabayashi Toshihiro , Mochiki Erito , Garcia Moises , Haga Norihiro , Suzuki Tomoaki , Asao Takayuki , Kuwano Hiroyuki 
Published: October 2002

AbstractAn attempt was made to examine gastropyloric motility after pylorus‐preserving gastrectomy (PPG) and to determine the influence of the pyloric branch of the vagus nerve in the dog. Fifteen dogs were divided into three groups of five. PPG with preservation (PPPG) and resection of the pyloric branch of the vagus (RPPG) were performed, and controls were prepared. Interdigestive and digestive gastropyloroduodenal motility was recorded after a 2‐week recovery period using strain‐gauge force transducers (SG). Radiopaque markers (ROMs) were used to assess gastric emptying. No significant differences were found between PPPG and RPPG in terms of gastropyloroduodenal motility during either the interdigestive or the postprandial state. During phase III of the interdigestive state, pyloric relaxation correlated with contraction of the gastric body after both PPPG and RPPG. During the first month it was accompanied by tonic and phasic pyloric contractions after feeding and delayed gastric emptying in two groups. By the end of the first month these pyloric contractions had diminished, and the rate of gastric emptying was similar to that of the controls. We concluded that it is not necessary to preserve the pyloric branch of the vagus for gastropyloroduodenal motility after PPG. Gastric stasis during the early postoperative period is due to tonic and phasic contractions of the pylorus.