bluuebunny/crossref_metadata_2025 huggingface dataset:
Landform Development on Moraines of the Klutlan Glacier, Yukon Territory, Canada
Authors: Watson R. A.
Published: December 2004

The landform evolution of the Klutlan moraines is described and explained primarily with respect to processes that cause voids in which debris is deposited. Morainal deposits of different ages provide examples of landforms at different stages of development, so that continuous ideal evolutionary sequences can be inferred. Specific features are classified as those on material of the same depositional age that develop mostly in a vertical direction with numerous topographic reversals, and those cross-cutting materials of different depositional age that develop primarily in a horizontal direction. The evolution of slopes is often terminated by their destruction as the underlying ice melts, but former slopes on morainal debris are traceable to ice-ridge slopes on the original glacier surface. The general process of evolution is one of downwasting by surficial icemelt, in which a grand topographic reversal takes place as the original ice mass with a gently convex surface melts to leave a basin floored by a concave mantle of morainal debris. The primary glacial process of melting differs from the primary karst process of solution, but many minor glacial processes and major glacial forms are similar to minor karst processes and major karst forms.
Paleolimnology of Two Lakes in the Klutlan Glacier Region, Yukon Territory, Canada
Authors: Bradbury J. Platt , Whiteside M. C.
Published: December 2004

Lakes developed on progressively younger end moraines of the Klutlan Glacier were initially assumed to have originated shortly after moraine emplacement and to have persisted to the present. Limnological differences between lakes on old vs young moraines were thought to result from limnological maturation within the lakes and ponds themselves and in response to the development of soils and vegetation on moraine surfaces. This study represents a paleolimnological test of this hypothesis. If true, the first-formed sediments of lakes on old moraines should be comparable to sediments presently forming in lakes on young moraines. Geochemical and paleontological studies of surface sediment to a series of lakes on progressively older moraines provide baseline information for comparing successive levels of lake sediment cores from older moraines. Results indicate that the time of lake initiation seldom reflects moraine age. Even on the oldest moraine (Harris Creek), lake basins are presently forming. Their sediment character more closely relates to the rapidity of basin formation due to melting of buried ice than to age of the lake itself or of the moraine on which it is situated. Vegetation and soil development play an important but secondary role in determining the character of lake sediments; rapid subsidence can convert humic-water lakes surrounded by second-generation spruce forests into turbid-water lakes with unstable, slumping margins. A detailed paleolimnological study of two lakes, one on the unglaciated upland and another in an outwash channel penetrating the oldest moraine, revealed progressive limnologic changes through time, suggesting that their basins were stable for 1200 and 400 yr, respectively. The changes in diatom stratigraphy of these lakes appear to relate to natural limnological changes associated with lake maturation and accumulation of nutrients as well as to changes in the surrounding vegetation and soils.
Environmental Implications of a Beetle Assemblage from the Gervais Formation (Early Wisconsinan?), Minnesota
Authors: Ashworth Allan C.
Published: December 2004

The Gervais Formation of northwestern Minnesota is the oldest known Quaternary stratigraphic unit in the Red River Valley. Wood from the fossiliferous silt and peat member is > 46,900 yr old. The age of the unit is uncertain but may be early Wisconsinan. A well-preserved beetle assemblage consisting of extant species is described from the fossiliferous horizon. Presently, most of the species are widely distributed and occur in Minnesota. The remainder have restricted northern distributions. Included in this group is the weevilVitavitus thulius, known only from two localities in Northwest Territories. The sedimentary environment indicated by the beetles was a small lake, rich in aquatic and semi-aquatic vegetation. The margins were characterized by open areas and spruce woodland. Species with arctic-alpine distributions indicate a cold environment, but whether it was regional or local in extent could not be determined. If regional, a climate similar to that of the tundra-forest transition zone is postulated with mean July temperatures in the range 11° to 14°C. If the cold environment was restricted, however, the climate may have been similar to that of the Lake Superior region with a mean July temperature of 17°C.
Destructive Effects of Oxygen Starvation and Ash Falls on Benthic Life: A Pilot Study
Authors: Cita Maria Bianca , Podenzani Massimo
Published: December 2004

A quantitative study on faunal density and faunal diversity was carried out on benthic foraminifers from 15 samples of two eastern Mediterranean deep-sea cores. Samples were taken beneath, within, and above three distinctive levels well correlatable for over 1000 km: (a) Sapropel S-5, late Pleistocene in age, correlative with marine isotopic stage 5e and with the Tyrrhenian transgression, with an interpolated age of ∼ 125,000 yr: (b) the “Ischia” tephra Y-5, the most widespread ash layer of the eastern Mediterranean, correlative with the transition from isotopic stages 3 to 2 and having an interpolated age of ∼ 35,000 yr; and (c) Sapropel S-1, Holocene in age, correlative with the Flandrian transgression, radiometrically dated at ∼8000 yr B.P. The most severe effects on benthic life were induced by stagnation (a). Deglaciation corresponding to Termination II was so rapid that the benthic assemblages could not adapt themselves to the too-rapidly decreasing oxygen levels and were entirely destroyed. More than 1000 yr after the termination of stagnant conditions no recolonization had yet started. The lesser disturbance was induced in the benthic community by the ash fall (b). The faunal destruction was ephemeral in duration and the colonizing population did not differ from that predating the ash fall. A progressive faunal change, with increasing abundance of taxa tolerant to low oxygen levels, was recorded beneath Sapropel S-1 (c). The recolonizing assemblage differs from the previously existing one, and is more similar to those recorded from the floor of the Mediterranean.
Clinal Variation of Some Mammals During the Holocene in Missouri
Authors: Purdue James R.
Published: December 2004

Eastern cottontail (Sylvilagus floridanus), fox squirrel (Sciurus niger), and gray squirrel (Sciurus carolinensis) were examined for clinal variation during the Holocene. Modern samples of all three species displayed strong east-west patterns along the western edge of the eastern deciduous forest:S. floridanusandS. nigerdecrease andS. carolinensisincreases in size. Archeological samples ofS. carolinensisfrom Rodgers Shelter (23BE125), Benton County, Missouri, and Graham Cave (23MT2), Montgomery County, Missouri, indicated an increase in size from early to middle Holocene.Sylvilagus floridanusfrom Rodgers Shelter decreased in size from early to middle Holocene and then increased during the late Holocene to modern proportions. A literature survey reveals that clinal variation is a common phenomenon among modern homeotherms. In introduced species, clinal variation has developed after relatively few generations, indicating rapid adaptations to environmental conditions; often winter climatic variables are implicated. Morphological variation in the study species during the Holocene is interpreted as a response to changing climates. Studies of morphological clines may lead to another valuable data source for reconstructing past ecologies.
Holocene Climate of New England
Authors: Davis Margaret B. , Spear Ray W. , Shane Linda C. K.
Published: December 2004

Stratigraphic studies of pollen and macrofossils from six sites at different elevations in the White Mountains of New Hampshire demonstrate changes in the distributions of four coniferous tree species during the Holocene. Two species presently confined to low elevations extended farther up the mountain slopes during the early Holocene: white pine grew 350 m above its present limit beginning 9000 yr B.P., while hemlock grew 300–400 m above its present limit soon after the species immigrated to the region 7000 yr. B.P. Hemlock disappeared from the highest sites about 5000 yr B.P., but both species persisted at sites 50–350 m above their present limits until the Little Ice Age began a few centuries ago. The history of the two main high-elevation conifers is more difficult to interpret. Spruce and fir first occur near their present upper limits 9000 or 10,000 yr B.P. Fir persisted in abundance at elevations similar to those where it occurs today throughout the Holocene, while spruce became infrequent at all elevations from the beginning of the Holocene until 2000 yr B.P. These facts suggest a more complex series of changes than a mere upward shift of the modern environmental gradient. Nevertheless, we conclude that the minimum climatic change which would explain the upward extensions of hemlock and white pine is a rise in temperature, perhaps as much as 2°C. The interval of maximum warmth started 9000 yr B.P. and lasted at least until 5000 yr B.P., correlative with the Prairie Period in Minnesota.
Towards a Quaternary Time Scale
Authors: Berggren W. A. , Burckle L. H. , Cita M. B. , Cooke H. B. S. , Funnell B. M. , Gartner S. , Hays J. D. , Kennett J. P. , Opdyke N. D. , Pastouret L. , Shackleton N. J. , Takayanagi Y.
Published: December 2004

Nine first-appearance datums (FADs), twenty-three last-appearance datums (LADs), and three other micropaleontological datums are related to the magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction time scales to provide a preliminary basis for subdivision of the Quaternary in deep-sea sediments. The magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction scales have been correlated by determination on the same core materials, and absolute dates applied by 40K/40Ar or 14C dating of materials in known positions on one or another of these scales. FADS and LADs have been determined in cores for which either a magnetic-reversal, oxygen-isotope, or calcite-dissolution/coarse-fraction scale has also been available. Altogether 3 FADs and 5 LADs based on diatoms, 4 FADs and 5 LADs based on calcareous nannoplankton, 1 FAD and 8 LADs based on radiolarians, 1 FAD and 5 LADs based on planktonic foraminifers, 2 acme datums, and 1 ratio reversal datum have been determined, and absolute dates inferred by interpolation from known dates on the reference time scales. Some of the FADs and LADs apply or are synchronous only over limited areas of the oceans; others appear to be synchronous throughout the oceans. The base of the Quaternary is set at the top of the Olduvai event at 1.7 my. Four FADs, twelve LADs, two acme datums, and one ratio reversal datum occur above the base of the Quaternary at an average rate of about 1 per 100,000 yr. Five FADs and twelve LADs are recognized in the 0.8-my interval between the top of the Olduvai event and the Gauss/Matuyama Boundary at 2.5 my at an average incidence of about 1 per 50,000 yr.
Ice-Sheet Glaciation of the Puget Lowland, Washington, during the Vashon Stade (Late Pleistocene)
Authors: Thorson Robert M.
Published: December 2004

During the Vashon Stade of the Fraser Glaciation, about 15,000–13,000 yr B.P., a lobe of the Cordilleran Ice Sheet occupied the Puget lowland of western Washington. At its maximum extent about 14,000 yr ago, the ice sheet extended across the Puget lowland between the Cascade Range and Olympic Mountains and terminated about 80 km south of Seattle. Meltwater streams drained southwest to the Pacific Ocean and built broad outwash trains south of the ice margin. Reconstructed longitudinal profiles for the Puget lobe at its maximum extent are similar to the modern profile of Malaspina Glacier, Alaska, suggesting that the ice sheet may have been in a near-equilibrium state at the glacial maximum. Progressive northward retreat from the terminal zone was accompanied by the development of ice-marginal streams and proglacial lakes that drained southward during initial retreat, but northward during late Vashon time. Relatively rapid retreat of the Juan de Fuca lobe may have contributed to partial stagnation of the northwestern part of the Puget lobe. Final destruction of the Puget lobe occurred when the ice retreated north of Admiralty Inlet. The sea entered the Puget lowland at this time, allowing the deposition of glacial-marine sediments which now occur as high as 50 m altitude. These deposits, together with ice-marginal meltwater channels presumed to have formed above sea level during deglaciation, suggest that a significant amount of postglacial isostatic and(or) tectonic deformation has occurred in the Puget lowland since deglaciation.
Advance of the Late Wisconsin Cordilleran Ice Sheet in Southern British Columbia Since 22,000 Yr B.P.
Authors: Clague J. J. , Armstrong J. E. , Mathews W. H.
Published: December 2004

Radiocarbon dates from critical stratigraphic localities in southern British Columbia indicate that the growth history of the late Wisconsin Cordilleran Ice Sheet was different from that of most of the Laurentide Ice Sheet to the east. Much of southern British Columbia remained free of ice until after about 19,000 to 20,000 yr ago; only adjacent to the Coast Mountains is there a record of lowland glacier tongues in the interval 22,000 to 20,000 yr B.P. A major advance to the climax of late Wisconsin Cordilleran glacier ice in the northern States was not begun until after about 18,000 yr B.P. in the southwest of British Columbia and after about 17,500 yr B.P. in the southeast. The rate of glacier growth must have been very rapid in the two to three millennia prior to the climax, which has been dated in western Washington at shortly after 15,000 yr B.P.
Diatom Evidence on Wisconsin and Holocene Events in the Bering Sea
Authors: Sancetta Constance , Robinson Stephen W.
Published: December 2004

Previous work on surface (modern) sediments has defined diatom species which appear to be good indicators of various oceanographic/ecologic conditions in the North Pacific Ocean and marginal seas. Three long cores from the eastern and northern sides of the Aleutian Basin show changes in species assemblage which can be interpreted in terms of changes in the ocean environment during the last glaciation (Wisconsin) and the Holocene. The early and late Wisconsin maxima were times of prolonged annual sea-ice cover and a short cool period of phytoplankton productivity during the ice-free season. The middle Wisconsin interstade, at least in the southern Bering Sea, had greater seasonal contrast than today, with some winter sea-ice cover, an intensified temperature minimum, and high spring productivity. Variations in clastic and reworked fossil material imply varying degrees of transport to the basin by Alaskan rivers. The results of Jousé from the central Bering Sea generally correspond with those presented here, although there are problems with direct comparison.
Paleohydrologic Regimes in the Southwestern Great Basin, 0–3.2 my ago, Compared with Other Long Records of “Gobal” Climate
Authors: Smith George I.
Published: December 2004

Nine distinct paleohydrologic regimes in the southwestern Great Basin over the last 3.2 my are recorded by the lacustrine deposits in KM-3, a 930-m core from Searles Lake, California. These are characterized as being “wet,” “intermediate,” or “dry” (like today). Excepting the present incomplete regime, each lasted 0.12 to 0.76 my. Major regime changes 0.01, 0.13, 0.6, and 2.5 my ago appear to coincide with recognized changes in global ice-sheet histories as represented by 18O and other records from marine sediments, but comparable changes 0.3, 1.0, 1.3, and 2.0 my ago do not appear to coincide closely with comparable perturbations in ice-sheet histories. However, all regime boundaries (during the last 1.75 my) coincide closely in time with changes in sea-surface temperatures in the tropical Atlantic, and many coincide with other deep-sea and continental paleoclimatic boundaries.The average duration of these paleohydrologic regimes was about 0.4 my (standard deviation, 0.2 my or less, depending on assumptions), and it is suggested that the regime boundaries reflect times of change in global(?) sea-surface temperatures, possibly controlled in part by the Earth's 413,000-yr orbital eccentricity cycle. During the wettest and driest regimes in the Searles Lake area, lake levels were not sufficiently affected by the 23,000-, to 42,000-, or 100,000-yr climate cycles related to high-latitude ice-sheet fluctuations to produce changes in the lacustrine sediment character. During intermediate regimes, however, when lacustrine sedimentation in this area was more sensitive to climate, the sediments, in KM-3, record lake fluctuations with average frequencies near those of the ice sheets. This seems to indicate that the high-latitude ice-sheet fluctuations caused local climatic perturbations but did not dominate the hydrologic component of climate in this area. Other lacustrine deposits in the southwestern Great Basin of California and Nevada have ages comparable in part to those of the wet to intermediate regimes indicated by KM-3, and they may all be products of finite periods when lake expansion, alluvial fan growth, increased spring discharge, and fluvial deposition were promoted in this area by widespread wet climates. Glacier expansion in the Sierra Nevada may also have been primarily an expression of, and in phase with, these wet regimes.
High-Resolution Seismic Reflection Profiles for the Reconstruction of Postglacial Transgressive Shorelines: An example from Greece
Authors: van Andel Tjeerd H. , Lianos Nikolaos
Published: December 2004

In 1982 we carried out a shallow-penetration, high-resolution seismic profiling study on the shelf of the southern Argolid, Peloponnesos, Greece, to identify and map the shores of the late Pleistocene and Holocene, and to establish their coastal environments. Portable equipment and a local boat were used. The lowest glacial shore occurs at −115 to −118 m, within the range of global values. The subsequent rise across the distinct old land surface left behind many shore features (scaps, beaches and beach ridges, channels and lagoons) now buried under a few meters of post-transgressive deposits. These features cluster at a small number of depths below present sea level, suggesting that the rise of the sea, usually too fast to leave an imprint, was episodically interrupted by brief stillstands or even temporary reversals of climatic or tectonic origin. The clusters can be roughly dated with reference to a global sea-level-rise curve; after 6000 yr B.P. sparse archaeological data establish a local curve. The seismic profiling technique, convenient and not costly, holds promise for the identification of postglacial shores elsewhere prior to sampling for dating. It has wide application for environmental reconstructions of vanished coastal zones as a basis for prehistoric resource assessments. These applications are illustrated with examples from this study.
Holocene Sea-Level Changes Along the Strait of Magellan and Beagle Channel, Southernmost South America
Authors: Porter Stephen C. , Stuiver Minze , Heusser Calvin J.
Published: December 2004

Radiocarbon-dated marine sediments from five coastal sites along the Strait of Magellan and Beagle Channel in southernmost Chile permit construction of a curve of relative sea-level fluctuations during the Holocene. Morphologic and stratigraphic data point to coastal submergence during the early Holocene as the sea rose to a maximum level at least 3.5 m higher than present about 5000 yr ago. Progressive emergence then followed during the late Holocene. Data from widely separated localities define a smooth curve, the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads. Apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation. The sea-level curve resembles one derived by Clark and Bloom (1979, In “Proceedings of the 1978 International Symposium on Coastal Evolution in the Quaternary, Sao Paulo, Brasil,” pp. 41–60. Sao Paulo) using a spherical Earth model, both in amplitude and in the timing of the maximum submergence.
Holocene Climatic Change in the Northern Midwest: Pollen-Derived Estimates
Authors: Bartlein P. J. , Webb T. , Fleri E.
Published: December 2004

Mapping of Holocene pollen data in the midwestern United States has revealed several broadscale vegetational changes that can be interpreted in climatic terms. These changes include (1) the early Holocene northward movement of the spruce-dominated forest and its later southward movement after 3000 yr B.P. and (2) the eastward movement of the prairie/forest border into southwestern Wisconsin by 8000 yr B.P. and its subsequent westward retreat after 6000 yr B.P. When certain basic assumptions are met, multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation. To maximize the reliability of the regression equations, we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis. Reconstructions of precipitation during the Holocene indicated that from 9000 to 6000 yr B.P. precipitation decreased by 10 to 25% over much of the Midwest, while mean July temperature increased by 0.5° to 2.0°C. At 6000 yr B.P. precipitation was less than 80% of its modern values over parts of Wisconsin and Minnesota. After 6000 yr B.P. precipitation generally increased, while mean July temperature decreased in the north, and increased in the south. The time of the maximum temperature varies within the Midwest and is earlier in the north and later in the south.
On the Possible Utilization ofCamelopsby Early Man in North America
Authors: Haynes Gary , Stanford Dennis
Published: December 2004

Camelopswas a major faunal element in late Wisconsin biotic communities over much of North America. Interpretations of possible human association withCamelopsare often based on poorly evaluated evidence. Ideal standards for acceptable evidence are compared here to the actual evidence that has been advanced. Of 25 fossil assemblages examined, 2 might be examples only of geological contemporaneity of humans andCamelops;2 might indicate behavioral association of humans andCamelopsbones; and 2 might indicate actual human utilization ofCamelops(killing and/or butchering).Camelopsbones interpreted as artifacts are similar to modern specimens affected by noncultural processes.
Pollen Analysis of a Late Pliocene and Early Pleistocene Section from the Gubik Formation of Arctic Alaska
Authors: Nelson Robert E. , Carter L. David
Published: December 2004

A 14-m-thick section of marine and nonmarine sediments of the Gubik Formation of northern Alaska, exposed in bluffs near Ocean Point on the Colville River, has been studied by means of pollen analysis. Pollen from the marine sediments, of probable late Pliocene age, records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation. Pine and perhaps true fir were probably at or near their northern limit here, but hemlocks and hardwoods were absent. The suggested environment for the Arctic Slope during the time represented by the marine sediments is similar to that of present-day Anchorage. Pollen floras from the overlying fluvial strata, of early or middle Pleistocene age, record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day. These deposits were most likely contemporaneous with glacial conditions in the Brooks Range to the south. Pollen of woody taxa (spruce, alder, birch, heaths) is rare through most of the section, although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection. Inland climates during glacial episodes may have been similar to those of the present Arctic coast.
Palynological Evidence for Early Holocene Aridity in the Southern Sierra Nevada, California
Authors: Davis Owen K. , Scott Anderson R. , Fall Patricia L. , O'Rourke Mary K. , Thompson Robert S.
Published: December 2004

Sediments of Balsam Meadow have produced a 11,000-yr pollen record from the southern Sierra Nevada of California. The Balsam Meadow diagram is divided into three zones. (1) The Artemisia zone (11,000–7000 yr B.P.) is characterized by percentages of sagebrush (Artemisia) and other nonarboreal pollen higher than can be found in the modern local vegetation. Vegetation during this interval was probably similar to the modern vegetation on the east slope of the Sierra Nevada and the climate was drier than that of today. (2) Pinus pollen exceeded 80% from 7000 to 3000 yr B.P. in the Pinus zone. The climate was moister than during the Artemisia zone. (3) Fir (Abies, Cupressaceae, and oak (Quercus) percentages increased after 3000 yr B.P. in the Abies zone as the modern vegetation at the site developed and the present cool-moist climatic regime was established. Decreased fire frequency after 1200 yr B.P. is reflected in decreased abundance of macroscopic charcoal and increased concentration of Abies magnifica and Pinus murrayana needles.
Reconstructed Summer Degree Days in Central Alaska and Northwestern Canada since 1524
Authors: Jacoby Gordon C. , Cook Edward R. , Ulan Linda D.
Published: December 2004

Three time series based on precisely dated annual tree-ring widths have been used to reconstruct June plus July degree days for the central Alaska and northwestern Canada region. The time series are the longest recently developed chronologies for the area and represent 57 core samples from 27 trees. The degree-year-to-year variation and day reconstruction, extending back to A.D. 1524, exhibits much extended warming and cooling trends including a general warming trend from about 1840 to 1960. The reconstruction is in agreement with some subaretic glacial information and with data of percentage melting from arctic ice cores. This and similar reconstructions can provide quantitative information to compare with general circulation and energy budget models for longer time periods than are available in recorded meteorological data.
Late Quaternary Vegetation in the Southwestern Columbia Basin, Washington
Authors: Barnosky Cathy W.
Published: December 2004

A 33,000-yr pollen record from Carp Lake provides information on the vegetation history of the forest/steppe border in the southwestern Columbia Basin. The site is located in the Pinus ponderosa Zone but through much of late Quaternary time the area was probably treeless. Pollen assemblages in sediments dating from 33,000 to 23,500 yr B.P. suggest a period of temperate climate and steppe coinciding with the end of the Olympia Interglaciation. The Fraser Glaciation (ca. 25,000–10,000 yr B.P.) was a period of periglacial steppe or tundra vegetation and conditions too dry and cold to support forests at low altitudes. Aridity is also inferred from the low level of the lake between 21,000 and 8500 yr B.P., and especially after about 13,500 yr B.P. About 10,000 yr B.P. Chenopodiineae and other temperate taxa spread locally, providing palynological evidence for a shift from cold, dry to warm, dry conditions. Pine woodland developed at the site with the onset of humid conditions at 8500 yr B.P.; further cooling is suggested at 4000 yr B.P., when Pseudotsuga and Abies were established locally.
An Isotopic Study of Paleosol Carbonates from Olduvai Gorge
Authors: Cerling Thure E. , Hay Richard L.
Published: December 2004

The isotopic composition of paleosol carbonates from Olduvai Gorge can be used to give estimates of the paleoclimatic history of East Africa during the Plio-Pleistocene. Oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water, while carbon isotopes are indicative of major changes in the fraction of biomass using the Hatch-Slack (C4) photosynthetic pathway. Three major periods of climatic change in this terrestrial setting occurred at about 1.67, 1.3, and 0.6 myr. These involved major changes in flora as well as major changes in the isotopic composition of meteoric water. Overall, the climate has become warmer and more arid over the past 2.2 myr.
Spatial Patterns of Atmospheric Pollen Transport in a Montane Region,
Authors: Solomon Allen M. , Silkworth Alison B.
Published: December 2004

Annual pollen deposition (pollen cm−2yr−1) was sampled for 6 yr in the southern Sierra Nevada, the Owens Valley, and the Inyo Mountains of central California. Spatial pollen distributions were examined for anemophilous plants which are limited to growth sites (1) at high elevations on one or both mountain ranges, (2) on lower mountain slopes, and (3) on the Owens Valley floor, Pollen deposition values for high- and low-elevation plants changed by a factor of 5 to 10 between adjacent sample sites which straddle boundaries of the plant communities in which the source plants grow. Pollen deposition values were high and variable within communities in which the species grew. Pollen deposition beyond source populations was low and uniform despite great differences in distance of sites from pollen sources. The step function that seems to characterize pollen distribution patterns implies that pollen from distant populations may be of little value in interpreting vegetation stability and change reflected by fossil pollen stratigraphy. The physical isolation of pollen embedded in the local mountain-valley wind system from that in the prevailing westerlies may explain part of the spatial distribution of the pollen.
U-Series Analyses of the Lower Travertine at Ehringsdorf, DDR
Authors: Blackwell Bonnie , Schwarcz H. P.
Published: December 2004

U-series analyses have been made of travertine samples from the archaeological site at Ehringsdorf-Weimar. The lower Travertine, in which hominid remains were found, yields apparent ages from >350,000 to 200,000 yr. Correlation between isotope ratios yields an age of about 230,000 yr. One sample of the upper Travertine gives and age of 111,000 ± 47,000 yr. Both upper and lower travertines contain fauna and flora indicative of interglacial conditions. The lower Travertine was deposited during isotope stage 7, while the upper Travertine may have been formed during isotope stage 5. This contradicts most earlier biostratigraphic studies which assigned both lower and upper Travertines to stages of the Eem interglaciation (correlative with isotope stage 5). The fauna and flora of the lower Travertine are significantly different from those of the upper Travertine, however, and in some respects are transitional to those of the travertines of Bilzingsleben, which appear to be older yet.
Ross Ice Shelf Oxygen Isotopes and West Antarctic Climate History
Authors: Grootes Pieter M. , Stuiver Minze
Published: December 2004

The Ross Ice Shelf δ18O profile at station J-9 covers at least the last 30,000 yr. It identifies the depth in the core of ice from (i) the last glacial-interglacial transition (266 to 286 m) and (ii) the 1000-m surface elevation (about 140 m). Various processes contribute to the δ18O change observed in the core: (i) climatic warming, mainly caused by a decrease in winter sea ice extent around Antarctica of about 6° latitude early in the glacial-interglacial transition, (ii) decreasing ice sheet thickness later in the glacial-interglacial transition and during the Holocene, and (iii) decreases in elevation and effective distance from the open ocean as the source of the ice in the core shifts along the flow line toward J-9. Average δ18O values of the last 3000 yr imply a fairly stable climate. Yet shorter (102 to 103 yr) δ18O climatic oscillations up to 6‰ are seen in both the Holocene and the glacial portion of the record.
Oxygen Isotope Constraints on Surface Ocean Temperatures
Authors: Broecker Wallace S.
Published: December 2004

Published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time. The possible impacts of bioturbation and of the redistribution of 18O/16O ratios within the sea, putting aside the oxygen isotope results, are consistent with the CLIMAP project conclusion that tropical ocean temperatures remained within ±2°C of their present value.
The Holstein Interglaciation: Time-Stratigraphic Position and Correlation to Stable-Isotope Stratigraphy of Deep-Sea Sediments
Authors: Sarnthein Michael , Stremme Helmut E. , Mangini Augusto
Published: December 2004

Marine molluscan shells from para-type and other localities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic.
Late Quaternary Environmental Changes in the Upper Las Vegas Valley, Nevada
Authors: Quade Jay
Published: December 2004

Five stratigraphic units and five soils of late Pleistocene to Holocene age crop out in dissected badlands on Corn Creek Flat, 30 km northwest of Las Vegas, Nevada, and at Tule Springs, nearer to Las Vegas. The record is dominantly fluvial but contains evidence of several moister, marsh-forming periods: the oldest (Unit B) dates perhaps to the middle Wisconsin, and the more widespread Unit D falls between 30,000 and 15,000 yr B.P. Unit D therefore correlates with pluvial maximum lacustrine deposits elsewhere in the Great Basin. Standing water was not of sufficient depth or extent during either period to form lake strandlines. Between 14,000 and 7200 yr B.P. (Unit E), standing surface water gradually decreased, a trend also apparent in Great Basin pluvial lake chronologies during the same period. Groundwater carbonate cementation and burrowing by cicadas (Cicadae) accompany the moist-phase units. After 7200 yr B.P., increased wind action, decreased biotic activity, and at least 25 m of water-table lowering accompanied widespread erosion of older fine-grained deposits. Based on pack-rat midden and pollen evidence, this coincides with major vegetation changes in the valley, from sagebrush-dominated steppe to lower Mohave desertscrub.
Potential Role of Passenger Pigeons and Other Vertebrates in the Rapid Holocene Migrations of Nut Trees
Authors: Webb Sara L.
Published: December 2004

Rapid rates of species range extension during the Holocene represent seed dispersal distances of at least 6 to 8 km per generation for North American species ofFagus, Quercus, andCarya, taxa whose fruits are heavy nuts. Occasional seed dispersal by biotic seed predators is necessary for these dispersal distances. One likely agent for dispersal across long distances and habitat discontinuities was the extinct (since 1914 A.D.) passenger pigeon (Ectopistes migratorius). This bird's abundance, capacity for delayed digestion, and nomadic habits strongly suggest an occasional seed dispersal role, although a coevolutionary seed dispersal relationship cannot be inferred from available evidence. The capacity of some heavy seeds for dispersal distances greater than those of most light, wind-dispersed seeds has biogeographic and genetic implications.
Monsoon Fluctuations in Two 20,000-Yr B.P. Oxygen-Isotope/Pollen Records Off Southwest India
Authors: Van Campo Elise
Published: December 2004

Two marine pollen diagrams for sediments off the southwest coast of India provide a 20,000-yr history of the nearby continental vegetation, determined by the monsoon climate, within the framework of the isotopic stratigraphy. Two important phases of the evolution of the monsoon climate are a very arid period about 22,000–18,000 yr B.P. and a very humid period culminating at 11,000 yr B.P. The very arid period corresponds to the lowest pollen representation of mangrove vegetation, which is used here as an indirect indicator of monsoonal runoff. This aridity is due to a very weak southwest airflow, a great reduction of summer monsoonal rainfall, and reduced runoff of the western Ghats rivers. The extension of the monsoon over India after the last glacial maximum has been a gradual process following the northward progression of the Intertropical Convergence Zone. The very humid period, corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall, is a climatic response to the maximum summer insolation of the Northern Hemisphere at 11,000 yr B.P.
A Groundwater Hypothesis for the Origin of “Fire Areas” on the Northern Channel Islands, California
Authors: Cushing John , Wenner Adrian M. , Noble Elmer , Daily Marla
Published: December 2004

Pleistocene areas of red sediments and carbonized vegetation on the Northern Channel Islands, California, have in the past been interpreted as caused by fires of either natural or human origin. Some are associated with darkened mammoth and bird fossils, and these fossils have been considered as having been burned by early man. Reevaluation of these so-called “fire areas” indicates that the above phenomena are the result of low-temperature (≤100°C), nonheating processes occurring in groundwater. Evidence for this conclusion is derived from field observations on fossil carbonized vegetation, and the geology of the areas. Additional evidence derives from experiments on the red sediments and fossil wood, X-ray diffraction analyses, magnetic analyses, studies on the clay minerals smectite and illite, and the demonstration that fossil mammoth bone contains sufficient Fe and Mn to account for their discoloration. Much of the carbonization of vegetation probably occurred in water rather than in fire. Radiocarbon dates from the islands will probably need to be reevaluated. These data provide evidence contrary to the concept of the occurrence of significant fires, either natural or set by early man, on the Northern Channel Islands.
Use of Lacustrine Sedimentary Sequences as Indicators of Holocene Glacial History, Banff National Park, Alberta, Canada
Authors: Leonard Eric M.
Published: December 2004

Bottom sediments from three lakes in the Canadian Rocky Mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of Holocene glacial histories. Analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non-glacial sediment sources. Sedimentary histories of the three lakes are similar, suggesting that they record regional glacial/climatic forcing, rather than localized events, and thus that they may be useful in reconstructing Holocene glacial history. Lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500-7000 yr B.P., with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr B.P., possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr B.P. Sometime after 4000 yr B.P., sedimentation rates and glacial sediment output began to rise again, reaching approximately present levels by 2750-2650 yr B.P., and have not since returned to low mid-Holocene levels. In detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr B.P. Sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr B.P. and have remained very high since. If the lake sediments are interpreted as a proxy record of upvalley glacial activity, they allow the development of a glacial chronology which is at once generally consistent with, and more complete and easily datable than, the surficial glacial record.
A 9000-Year-old Ash Bed on the Faroe Islands
Authors: Mangerud Jan , Furnes Harald , Jóhansen Johannes
Published: December 2004

Radiocarbon datings of the Saksunarvatn ash bed on the Faroe Islands indicate an age of 9000–9100 yr B.P. The Saksunarvatn ash bed differs geochemically from both ash zone 1 in the North Atlantic and the Vedde Ash Bed of Norway and the Norwegian Sea. All mentioned ashes are assumed to originate from Iceland. The Vedde Ash has been dated at 10,600 ± 60 yr B.P. Consequently, the Saksunarvatn and Vedde ash beds provide an opportunity for precise dating of events around the Pleistocene/Holocene boundary in marine cores, especially from the region where the two plumes overlap.
A Reexamination of Late-Pleistocene Boreal Forest Reconstructions for the Southern High Plains
Authors: Holliday Vance T.
Published: December 2004

Previous paleoecological research on the Southern High Plains resulted in development of a late Quaternary chronology of “pollen-analytical episodes” and the proposal that boreal forest existed in the region in the late Pleistocene. These interpretations are now considered untenable because (1) a number of the radiocarbon ages are questionable, (2) there are serious problems of differential pollen preservation and reproducibility of the pollen data, (3) there is an absence of supporting geological or paleontological data, and (4) the soils of the area contain none of the distinctive pedological characteristics produced by a boreal forest. Available data suggest that the region was primarily an open grassland or grassland with some nonconiferous trees through most of the Quaternary.
Mid-Holocene Climate in Northern Minnesota
Authors: Forester Richard M. , Delorme L. Denis , Bradbury J. Platt
Published: December 2004

Study of Holocene ostracodes and diatoms from Elk Lake, in North-Central Minnesota, indicates that the local climate of the mid-Holocene can be subdivided into three intervals. Throughout interval 1 (ca. 7800 to 6700 yr B.P.), climate was colder and much drier than today. During intervals 2 and 3 (ca. 6700 to 4000 yr B.P.) average mean-annual air temperatures approached the modern mean (3.7°C), but warm summers persisted throughout interval 2, whereas during interval 3 warm summers fell into discrete episodes. Furthermore, average mean-annual precipitation was about 85 and 90% of modern during intervals 2 and 3, respectively. Transition times between the principal intervals were less than 50 yr. The expected effects of a retreating Laurentide Ice Sheet that initially maintained a winter-style circulation, followed by transitional climate states, and finally a near-modern circulation pattern may explain these local climatic events.
Late Quaternary Stratigraphic Charcoal Records from Madagascar
Authors: Burney David A.
Published: December 2004

The classic view regarding the cause of the extinction of at least 17 species of large mammals, birds, and reptiles in Madagascar during the late Holocene implicates human use of fire to modify the environment. However, analysis of the charcoal stratigraphy of three sediment cores from Madagascar shows that late Pleistocene and early- to mid-Holocene sediments deposited prior to human settlement often contain more charcoal than postsettlement and modern sediments. This observation, which is confirmed by independent measurements from direct assay and palynological counting techniques, suggests that widely held but previously untested beliefs concerning the importance of anthropogenic fires in late Holocene environmental changes and megafaunal extinctions of Madagascar may be based on an overly simplified version of actual prehistoric conditions. Moderate to low charcoal values characterized only the late Holocene millennia immediately prior to the presumed time of arrival of the first settlers. Human settlement is probably indicated in the stratigraphy by the sharp rise in charcoal content observed beginning ca. 1500 yr B.P. Fire appears to be a significant natural component of prehuman environments in Madagascar, but some factor, probably climate, has modulated the extent of natural burning.
Spores of the Dung Fungus Sporormiella: Increased Abundance in Historic Sediments and Before Pleistocene Megafaunal Extinction
Authors: Davis Owen K.
Published: December 2004

Spores of the dung fungus Sporormiella become abundant following the historic introduction of grazing herbivores at seven sites in the western United States. During the Holocene they are generally rare, but at six sites Sporormiella spores are abundant before the extinction of Pleistocene megaherbivores ca. 11,000 yr B.P. Sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung preserved in Bechan Cave, Southern Utah. Their abundance in late-glacial sediments may reflect the abundance of megaherbivores during Quaternary, thereby indicating the age of Pleistocene extinctions where other indicators are absent.
Time Scale of the Wisconsin/Holocene Transition: Oxygen Isotope Record in the Western Equatorial Pacific
Authors: Berger W. H. , Killingley J. S. , Vincent E.
Published: December 2004

An evaluation of both published and new oxygen isotope and radiocarbon data from the west equatorial Pacific (7 box cores, 2 piston cores, 2 gravity cores) indicates that there was no significant input of meltwater to the ocean before 14,000 14C yr B.P. This finding is in conflict with various early deglaciation scenarios suggested several years ago on the basis of Wisconsin/Holocene transition records from the Atlantic, but agrees with late-onset scenarios proposed more recently, both for Pacific and Atlantic deglaciation records.
Persistent Late Pleistocene-Holocene Seasonal Upwelling and Varves Off the Coast of California
Authors: Anderson Roger Y. , Hemphill-Haley Eileen , Gardner James V.
Published: December 2004

Seasonal production of siliceous phytoplankton and a seasonal flux of terrigenous clastic material produced varved sediments along the continental slope off California during the late Pleistocene to mid-Holocene. Light-colored sediment within laminations and in sediment-trap samples was deposited during summer upwelling and contains an abundance of the diatoms Skeletonema costatum and Chaetoceros spp. resting spores. Dark-colored sediment deposited in the fall and winter contains abundant Thalassiosira pacifica, and has more terrigenous material. Distribution of diatoms in varves shows that seasonal upwelling has persisted along the California coast and has remained strongly seasonal since the late Pleistocene.