bluuebunny/crossref_metadata_2025 huggingface dataset:
Postglacial Forest Patterns Associated with till and Outwash in Northcentral Upper Michigan
Authors: Brubaker Linda B.
Published: December 2004

Pollen analysis of lake sediments reveals that small areas of till and outwash in northcentral Upper Michigan have influenced plant distributions throughout postglacial time. Each substrate has different textural characteristics. Modern forest communities form a mosaic, with jack pine woodlands occupying the medium sands of the Yellow Dog Plains outwash and white pine-hardwood communities on both till and outwash soils in the Michigamme Highlands to the south.

The analysis of modern pollen samples from 21 lakes within the area indicates that pollen can be used to study the distribution of local vegetation in relation to substrate type. Fossil pollen from three of the lakes documents the character of ancient forest on Yellow Dog outwash, Michigamme outwash, and Michigamme till.

Unique boreal communities occupied each area immediately after deglaciation. Between 8000 and 7000 y.a., white pine and maples migrated into the study area and replaced jack pine in forests on the Highlands, but not on the Plains. Jack pine has continued to occupy the Plains since early postglacial time. White pine reached highest densities on Michigamme outwash, and deciduous trees increased primarily on till during the presumably dry climates which existed 8000-5000 yr BP. As the climate became more mesic, forests on the Highlands changed, so that by 3000 yr BP the communities on Michigamme outwash and till were indistinguishable on the basis of pollen. Present-day forest patterns of the area became established at that time.

Pollen influx rates, measured at each lake, generally support interpretations based on pollen percentages and were similar to values reported elsewhere. Variations in influx values are within the range expected for the method.
The Identification, Lateral Variation, and Chronology of two Buried Paleocatenas at Woodhall Spa and West Runton, England
Authors: Valentine K.W.G. , Dalrymple J.B.
Published: December 2004

Two buried paleocatenas were studied to determine some features and techniques by which buried soils could be recognized, and to define their pedological characteristics, their lateral variation, and their contemporary environment. At Woodhall Spa, Lincolnshire, a ferric podzol to sandy gley sequence was developed in sands under marine clay and fen peat. The peat was radiocarbon dated at about 4100 yr BP. The buried soil was evident from its obvious catenary character and the soil characteristics and contemporary environment were determined using sand mineralogy, micromorphology, and pollen analysis. At West Runton, Norfolk, an apparently similar ferric podzol sequence occurred in Beestonian sands and gravels under a layer of Cromerian organic muds. However, only the uppermost profile contained definite evidence of soil formation. Other lower profiles contained pseudosoil features produced by sedimentation or diagenetic subsurface iron mobilization. It is suggested that the occurrence of a paleocatena is the most important criterion for the identification of a buried soil. Sedimentation and diagenesis cannot reproduce this lateral variation.
Emplacement of the St. Narcisse Moraine as a Climatic Event in Eastern Canada
Authors: Lasalle Pierre , Elson J.A.
Published: December 2004

The length (more than 300 km) and size of the St. Narcisse morainic system suggest that it represents an important glacial event, probably climatically controlled and not related to a surge. Dates on marine material (shells) both from within and external to the moraine suggest that its time of emplacement was roughly 11,000 years ago, well after the beginning of the Champlain Sea Episode, but still possibly correlative with the Valders event of the Lake Michigan area.
Global Changes in Postglacial Sea Level: A Numerical Calculation
Authors: Clark James A. , Farrell William E. , Peltier W.Richard
Published: December 2004

The sea-level rise due to ice-sheet melting since the last glacial maximum was not uniform everywhere because of the deformation of the Earth's surface and its geoid by changing ice and water loads. A numerical model is employed to calculate global changes in relative sea level on a spherical viscoelastic Earth as northern hemisphere ice sheets melt and fill the ocean basins with meltwater. Predictions for the past 16,000 years explain a large proportion of the global variance in the sea-level record, particularly during the Holocene. Results indicate that the oceans can be divided into six zones, each of which is characterized by a specific form of the relative sea-level curve. In four of these zones emerged beaches are predicted, and these may form even at considerable distance from the ice sheets themselves. In the remaining zones submergence is dominant, and no emerged beaches are expected. The close agreement of these predictions with the data suggests that, contrary to the beliefs of many, no net change in ocean volume has occurred during the past 5000 years. Predictions for localities close to the ice sheets are the most in error, suggesting that slight modifications of the assumed melting history and/or the rheological model of the Earth's interior are necessary.
A Direct Comparison of 14C and 230Th Ages at Searles Lake, California
Authors: Peng T. -H. , Goddard J. G. , Broecker W. S.
Published: December 2004

Thorium-230 dating on saline of the Lower Salt unit in pluvial Searles Lake, California, shows that this unit was formed between 24,500 and 32,000 years ago. The initial apparent 14C age of the lake is estimated to be about 900 years. After correcting for nonradiogenic 230Th and for the initial 14C age, excellent agreement between 230Th and 14C ages is obtained. The reliability of 230Th dating on salt deposit opens a new way for continuation of absolute chronology below the Lower Salt in Searles Lake.
Alternative Kinetic Models for the Interpretation of Amino Acid Enantiomeric ratios in Pleistocene Mollusks: Examples from California, Washington, and Florida
Authors: Wehmiller John F. , Belknap Daniel F.
Published: December 2004

Alternative kinetic models for amino acid racemization in Pleistocene molluscan samples are compared by examination of results for samples from marine Pleistocene deposits in California, Washington, and Florida. Linear kinetic models previously have been applied to the Florida samples [ Mitterer, R.M. (1975). Earth and Planetary Science Letters 28 , 275–282.] because these kinetics were observed in laboratory pyrolysis experiments with the particular genus involved (Mercenaria). Nonlinear kinetic models, extrapolated from deep-sea foraminifera racemization kinetics, are applied to samples of Protothaca and Saxidomus from California and Washington and seem more consistent with their local chronologic and stratigraphic control. Average or effective diagenetic temperatures can be estimated by each of these models if reliably dated samples are available. Linear models applied to such samples from California and Florida suggest average diagenetic temperatures that are cooler (by as much as 10°C) than would be inferred from available paleoclimatic records. Nonlinear kinetic models yield estimates of average diagenetic temperatures that are more consistent with these records: full-glacial (i.e., approximately 18,000 yr BP) temperature reductions of between 2 and 6°C are inferred for coastal California and southern Florida. The nonlinear kinetic model is used to expand (by a factor of 2.5 to 3.0) the time scale proposed by Mitterer (1975) for five marine Pleistocene units of Florida.
Pollen Indicators of Land-Use Change in Southern Connecticut
Authors: Brugam Richard B.
Published: December 2004

Changes in fossil pollen assemblages from a 2-m core from Linsley Pond, North Branford, Connecticut, are compared with historically documented land use changes in the lake watershed. Dating with 210Pb and 14C reveals two sedimentation rate changes in the core which are associated with the arrival of European farmers; the building of cabins and suburban housing subdivisions on the lake shore. At European settlement in 1700 ad Ambrosia and Rumex pollen first appear, Gramineae-type pollen increases, and Tsuga decreases. Just before the beginning of agricultural disturbance Fagus pollen declines. The chestnut blight of 1913 causes a reduction of Castanea pollen and a subsequent vegetational succession through Betula to Quercus. The sedimentation rate determined by the chestnut blight horizon is consistent with the rate deduced from 210Pb analysis.
The Fossil Coleoptera of the Two Creeks forest Bed, Wisconsin
Authors: Morgan Alan V. , Morgan Anne
Published: December 2004

A 21-kg sample of plant detritus from the Two Creeks forest bed at the junction of Kewaunee and Manitowoc Counties, Wisconsin, has produced a small, but well-preserved fauna of Coleoptera, Hymenoptera, and Diptera. Among the Coleoptera the majority of Carabidae (ground beetles) indicate moderately moist to fairly dry, open ground conditions with a sparsely vegetated substrate. Another significant beetle group is represented by the Scolytidae (bark beetles) nearly all of which inhabit spruce. The restricted number of Coleoptera species (21) is believed to represent an in situ assemblage and is part of about 50 taxa. Most of the Coleoptera identified to the species level have a transcontinental distribution, with the exception of two carabids which are extreme western forms, and nearly all reside within the boreal forest. The beetles indicate that the mean July temperature at Two Creeks approximately 11,850 yr B.P. was 14° to 16°C.
Paleoclimatic Research: Status and Opportunities
Authors: Hecht Alan D. , Barry Roger , Fritts Harold , Imbrie John , Kutzbach John , Mitchell J.Murray , Savin Samuel M.
Published: December 2004

This report considers the scientific opportunities and problems for paleoclimatic research for three time intervals, 0-1000 yr, 0-30,000 yr, and 0-1 my. Each of these intervals is appropriate to understanding different parts of the climate problem. The most recent interval is one for which there exists the possibility of determining year-by-year changes in certain parts of the climatic system over a time span which overlaps the instrumental record. The interval 0 to 30,000 yr is one for which the response of many parts of the climate system during a major change in climate can be examined, and for which laC dating provides good chronological control. The interval 0 to 1.000,000 yr is one for which there is reasonably good chronological control. a well-developed global record of changes in the ocean, and the opportunity of investigating glacial-interglacial changes in global climate which appear to have a cyclic or quasi-cyclic component.
Variations in Climate Since 1602 as Reconstructed from Tree Rings
Authors: Fritts Harold C. , Lofgren G. Robert , Gordon Geoffrey A.
Published: December 2004

Spatial anomalies of tree-ring chronologies can provide information on high-frequency spatial anomalies in paleoclimate representing droughts, colder-than-normal intervals, and other synoptic-scale features. Examples are presented in which 65 tree-ring chronologies are calibrated with spatial anomalies in North American meteorological records of seasonal temperature and precipitation, and with sea-level pressure over the North American and North Pacific sectors. Multivariate transfer functions are obtained that scale and convert the past spatial variations in the tree-ring record into estimates of past variations in the meteorological record. Objective verifications of the reconstructions are obtained using independent meteorological observations for time periods other than those used in the calibration. Historical information or other proxy data from the 19th century are also used for verifying the decadal (or longer) and regional reconstructions and for identifying strengths and weaknesses of the various sources of information. The reconstructed winter and summer temperatures for the United States and southwestern Canada and winter precipitation for the Columbia Basin and California during the 17th through 19th centuries were found to differ from the 20th century means with large-scale variations evident. Extreme winters similar to 1976–77 are also identified and found to be more frequent in the past, especially in the 17th century. The climatic reconstructions in this time domain are dominated by high-frequency, synoptic-scale fluctuations that can be interpreted as cyclonic-scale changes in atmospheric circulation. Such reconstructions may be useful for testing various climatic models and estimates developed primarily from 20th-century meteorological data against the longer estimated record for the 17th through 19th centuries.
On Time Scales and Causes of Abrupt Paleoclimatic Events
Authors: Flohn Hermann
Published: December 2004

During the last 7 × 105years the occurrence of abrupt climatic variations, of an intensity probably reaching 5°C/50 yr and with a duration of the order of several centuries can be demonstrated; their frequency is of the order 10−4(sometimes even 10−3) per year. Most impressive examples are sudden coolings in earlier interglacials; in some periods the variability of past climates was obviously much greater than now. Due to the effective spatial coherence of the atmospheric and oceanic circulation their extension, not necessarily of similar intensity, is probably hemispheric or even global. They are modified by feedback mechanisms within the geophysical climatic system; orbital changes play a selective role leading either to suppression or to growth. Any physical interpretation of such abrupt paleoclimatic events remain as yet speculative. One of the most attractive models is the occurrence of clusters of major volcanic eruptions which is more frequent than expected in random series. This is similar to the clustering of severe earthquakes in recent years; both events are probably interrelated responses to the (apparently discontinuous) motions of tectonic plates.
The Present Flora and Vegetation of the Moraines of the Klutlan Glacier, Yukon Territory, Canada: A Study in Plant Succession
Authors: Birks H. J. B.
Published: December 2004

The flora and vegetation of six ice-cored moraines of the Klutlan Glacier were analyzed in 65 plots by European plant-sociological techniques. The age of each plot was estimated from annual growth rings of shrubs or trees in the plots. Nine major vegetation types are distinguished: Crepis nana, Dryas drummondii, Hedysarum mackenzii, Hedysarum-Salix, Salix-Shepherdia canadensis, Picea-Salix, Picea-Arctostaphylos, Picea-Ledum, and Picea-Rhytidium. These contain plants aged 2–6, 9–23, 10–20, 24–30, 32–58, 58–80, 96–178, 177–240, and >163- >339 yr, respectively. Six other vegetation types are described from windthrow areas, drainage channels, volcanic tephra slopes, lake margins, fens, and drained lakes. The major vegetation types reflect a vegetational succession related to moraine age and stability, with the Crepis nana type as the pioneer vegetation developing through the other vegetation types to the Picea-Rhytidium type on the oldest moraines. Changes in species diversity and soil development, particularly humus accumulation, parallel the vegetational succession. This succession differs from patterns of revegetation of deglaciated landscapes in Alaska and British Columbia today and in Minnesota in late-Wisconsin times because of differences in climate, plant migration, and local ecology.
Limnology of the Klutlan Moraines, Yukon Territory, Canada
Authors: Whiteside M. C. , Bradbury J. Platt , Tarapchak S. J.
Published: December 2004

Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceranDaphnia pulex. Surface-sediment samples contained a total of 16 species of chydoridCladocera. Of these,Alonella excisaandAlona barbulataare apparently the pioneer species in the youngest lakes.Chydorus sphaericusonly appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.
Instantaneous Glacierization, the Rate of Albedo Change, and Feedback Effects at the Beginning of an Ice Age
Authors: Koerner R. M.
Published: December 2004

A study of the average annual- and melt-season albedos for the northwest side of the Devon Island Ice Cap shows that there is no step in the average albedo either at the equilibrium or firn line. Similarly, during a period of increasing glacierization there is nowhere any dramatic increase in the average annual- or melt-season albedo with time as the equilibrium line gradually moves downslope. This means that the inception of ice caps and permanent snowfields does not make a significant change to the rate of increasing albedo and its associated feedback effects during the same period of glacierization. The extension of the annual period of snowcover generally is much more important to the feedback process (by increasing albedo) than the specific lowering of the equilibrium line. A decreased variability of summer climate, and hence the disappearance of “anomalously” warm summers, may be an integral part of the glacierizing process.
Holocene Desert Soil Formation under Sodium Salt Influence in a Playa-Margin Environment
Authors: Peterson Frederick F.
Published: December 2004

A visually prominent desert soil with a horizon of clay accumulation (Typic Natrargid) has formed under an arid climate in Panamint Valley, California, in sandy, very calcareous, saline fan alluvium in less than about 3500 yr, and probably less than 2000 yr. Such soils can be used as stratigraphic markers, but could be confused with other desert soils with clay-accumulation horizons (Haplargids) which occur much more commonly on desert alluvial fans, are mostly late Pleistocene or older, and do not form in parent materials that are still calcareous. This Natrargid formed in a playa-margin environment, where clay for translocation and sodium salts that engender rapid clay movement probably were provided by dust fall.
Biostratigraphic Correlation of Pleistocene Marine Deposits and Sea Levels, Atlantic Coastal Plain of the Southeastern United States
Authors: Cronin Thomas M.
Published: December 2004

Marine ostracodes from 50 localities were studied to determine the age and elevation of Pleistocene sea levels in the Atlantic coastal plain from Maryland to northern Florida. Using ostracode taxon and concurrent ranges, published planktic biostratigraphic, paleomagnetic, and radiometric data, ostracode assemblage zones representing early (1.8-1.0 my), middle (0.7-0.4 my), and late (0.3-0.01 my) Pleistocene deposition were recognized and used as a basis for correlation. Ostracode biofacies signifying lagoonal, oyster bank, estuarine, open sound, and inner sublittoral environments provided estimated ranges of paleodepths for each locality. From these data the following minimum and maximum Pleistocene sea-level estimates were determined for the southeastern coastal plain: late Pleistocene, 2–10 m from Maryland to northern Florida; middle Pleistocene, 6–15 m in northern South Carolina; early Pleistocene, 4–22 m in central North Carolina, 13–35 m in southern North Carolina, and 6–27 m in South Carolina. Climatically induced glacio-eustatic sea-level fluctuations adequately account for the late Pleistocene sea-level data, but other factors, possibly differential crustal uplift, may have complicated the early Pleistocene record.
New Evidence from Beneath the Western North Atlantic for the Depth of Glacial Erosion in Greenland and North America
Authors: Laine Edward P.
Published: December 2004

Interpretation of Deep Sea Drilling Project results and air-gun seismic profiles suggests that about 106 km3 of sediment have been eroded from eastern North America and southern Greenland and deposited in the adjacent North Atlantic since the beginning of continental glaciation. This volume is a minimum estimate which does not account for sediment beneath the continental shelf nor that portion carried south of the Blake-Bahama Outer Ridge by the Western Boundary Undercurrent. It represents erosion of about 100 m of solid rock and indicates that more than 90% of the sediment eroded from these areas was deposited as sands, silts, and clays in the adjacent western North Atlantic. Glaciation accounts for between 55 and 95 m of this average 100 m, and fluvial processes account for the remainder. The documented erosion in part substantiates W. A. White's (1972, Geological Society of America Bulletin83, 1037–1056) hypothesis of deep erosion and exhumation of shield regions, but is not in agreement with the entire volume of erosion implied by his model.
Holocene Sea-Level Changes in Palau, West Caroline Islands
Authors: Easton William H. , Ku Teh-Lung
Published: December 2004

14C ages supplemented by 230Th/234U determinations have been obtained for calcareous deposits on Koror, Babelthuap, Auluptagel, and Adorius Islands in the Palau Group, West Caroline Islands. Test borings for a bridge between Koror and Babelthuap reveal shoreface terraces consisting largely of bioclastic sand, but resembling fringing reefs. The base of the shoreface terraces dates to between 7000 and 8000 14C yr B.P. and the upper surfaces are slightly younger than 4000 yr B.P. Spacing of the subsurface isochrons indicates that the rate of sedimentation increased up-section on Koror terrace and decreased up-section on Babelthuap terrace. The average rate of deposition in the terraces was 0.5 cm/yr. Isochrons in the Babelthuap shoreface terrace are 7 m higher than those in the Koror terrace. If deposition was sufficient to keep the surfaces of the terraces at low tide level, then the Babelthuap side was essentially stable and the Koror side was uplifted between about 8000 and 6300 yr ago, and then subsided until 4000 yr ago; since then there has been about 2 m of uplift. “Top hat” microatolls on Koror terrace indicate that relative sea level has dropped about 30 cm in the past 75 yr. In the absence of good evidence for changes of level in water ponded in a moat, it is likely that the microatolls indicate uplift of the terrace. On the other hand, if tectonic activity was minimal, then differences in the two terraces are due to differences in sedimentation with the Koror side of the channel being substantially subtidal between about 7000 and 5000 yr B.P. Taking the composite eustatic sea-level curve of Hawaii and elsewhere as a reference standard, it is deduced that Auluptagel Island has risen 0.8 m in the last 2900 yr, and Adorius Island has risen approximately 8 m in the last 5000–6000 yr.
Estimates of Past Climate at Paleolake Chad, North Africa, Based on a Hydrological and Energy-Balance Model
Authors: Kutzbach John E.
Published: December 2004

Modeling the combined hydrological and energy balances of Paleolake Chad and its drainage basin yields an estimate of at least 650 mm/yr for annual precipitation during portions of the early Holocene (10,000 to 5000 yr B.P.); the current rainfall in Chad Basin is 350 mm/yr. Two versions of the model are developed. The first version is one in which precipitation and lake area are linearly related. This version requires specification first of the area, net radiation, and Bowen ratio of the lake and second of the paleovegetation, net radiation, and Bowen ratio of the surrounding basin. In the second version of the model the ralationship between precipitation and lake area is nonlinear because the runoff ratio and Bowen ratio of the basin are made functions of precipitation. As the lake increases in area in response to increased precipitation, this version of the model allows for further increases in runoff (from the basin into the lake) as the vegetation changes from steppe to savanna and swamp. This nonlinear process may provide a partial explanation for the expansive paleolakes of the early Holocene. The results derived from both models are in good agreement with previously derived estimates of precipitation for North Africa during the early Holocene.
The Origin and Distribution of Subbottom Sediments in Southern Lake Champlain
Authors: Freeman-Lynde R. P. , Hutchinson D. R. , Folger D. W. , Wiley B. H. , Hewett M. J.
Published: December 2004

Three units, correlatable with recent Lake Champlain, late-glacial marine Champlain Sea, and proglacial Lake Vermont sediments, have been identified from about 200 km of high-resolution seismic reflection profiles and eight piston cores collected in southern Lake Champlain. Lake Vermont deposits are nonfossiliferous and range from thin to absent nearshore and on bedrock highs to more than 126 m thick near Split Rock Point. Champlain Sea sediments contain marine foraminifers and ostracodes and are fairly uniform in thickness (20–30 m). Recent Lake Champlain sediments range in thickness from 0 to 25 m. Average sedimentation rates for Lake Vermont are considerably higher (4–8 cm/yr) than those for the Champlain Sea (0.8–1.2 cm/yr) and Lake Champlain (0.14–0.15 cm/yr). Bedrock, till, and deltaic and alluvial deposits were also identified on the acoustic records but were not sampled. An unconformity separating Champlain Sea deposits from Lake Champlain deposits is associated with numerous benches at water depths of 20–30 m. These benches, the alluvial deposits, and the onset of deltaic deposition are probably associated with a low water level stillstand at the close of the Champlain Sea episode.
The Los Chocoyos Ash, Guatemala: A Major Stratigraphic Marker in Middle America and in Three Ocean Basins
Authors: Drexler John W. , Rose W. I. , Sparks R. S. J. , Ledbetter M. T.
Published: December 2004

The Los Chocoyos Ash, having erupted from vents near the Lake Atitlán caldera, Guatemala, is perhaps the largest Quaternary silicic pyroclastic unit in Central America. It consists of an underlying H-tephra member and an overlying ash-flow member. One-hundred-and-five samples of ash from the Guatemalan Highlands and deep-sea cores in the equatorial Pacific and Gulf of Mexico were analyzed by neutron activation and/or electron microprobe. Glass shard chemistry, determined by microprobe, is useful for distinguishing several very widespread, distinct, deep-sea ash layers, but needs support from trace-element data when applied on land to distinguish between many individual eruptions from the same province. Data from this study support the correlation of the Worzel ‘D’ layer and the Los Chocoyos Ash proposed by Hahn et al. (1979) and Bowles et al. (1973). Chemical data from this study are used to correlate the Y-8 ash layer of the Gulf of Mexico with the Los Chocoyos Ash. The recognition of the Los Chocoyos Ash in the Gulf of Mexico and equatorial Pacific increases the known areal extent of the unit to more than 6 × 106 km2 and allows an age of 84,000 yr B.P. to be assigned to the formation on the basis of oxygen-isotope stratigraphy, biostratigraphy, and Pa-Th-isotope data. Trace-element data obtained from seven other ash layers in the Gulf of Mexico and the equatorial Pacific, when combined with new land-based data, should allow further correlation and dating of ash units in Central America.
Milankovitch Theory of Ice Ages: Hypothesis of Ice-Sheet Linkage Between Regional Insolation and Global Climate
Authors: Denton George H. , Hughes Terence J.
Published: December 2004

J. D. Hays, J. Imbrie, and N. J. Shackleton (1976, Science 194, 1121–1132) showed that the astronomical theory explained many features of late Quaternary ice-age climates, but they did not specify the physical mechanisms involved. Here it is proposed that interlocked variations of ice-sheet heat sinks in both polar hemispheres amplified and transmitted Milankovitch summer half-year insolation changes (a version of the astronomical theory) between 45° and 75°N into the globally synchronous climate changes recorded in geologic records. It is suggested that late Quaternary ice sheets had terrestrial components (grounded above sea level, melting margins, fluctuations controlled by climate) and marine components (grounded below sea level, drained largely by ice streams, limited melting margins, fluctuations controlled primarily by sea level and secondarily by climate, interior surface elevations coupled to downdraw through ice streams). Northern Hemisphere ice sheets were largely marine (with minor melting margins) in the Arctic and terrestrial (with major melting margins) in the midlatitudes. West Antarctic and peripheral East Antarctic ice was marine-based and lacked melting margins. Because of their geographic array, these terrestrial and marine components formed an ice-sheet system whose variations were coupled on a global scale. Milankovitch summer isolation changes near midlatitude Northern Hemisphere melting margins controlled most variations of this system, because advance or retreat of melting margins initiated concurrent eustatic sea-level change. Such sea-level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres. This initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams. Arctic summer insolation change was less important because northern melting margins were relatively minor. Its greatest influence was on surface ablation of ice streams that controlled interior downdraw. This affected eustatic sea level and activated global linkage of marine sectors. By analogy with present-day Antarctica, late Quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics. It is suggested that the effectiveness of these ice-sheet heat sinks varied with their areal extent and interior surface elevation. Thus, it is postulated that concurrent growth or decay of these interlocked ice-sheet heat sinks in both polar hemispheres served as the global amplifier of regional Milankovitch summer insolation.
The Late Wisconsinan Savanna Terrace in Tributaries to the Upper Mississippi River
Authors: Flock Mark A.
Published: December 2004

The Savanna Terrace, composed of alternating red and gray clayey sediments of late Wisconsinan age, can be found in five states along the upper Mississippi valley from Pepin County, Wisconsin, to Jackson County, Illinois. The terrace is the highest glaciofluvial-lacustrine deposit without a loess cover in the upper Mississippi valley. Chemical, physical, and mineralogical data show that two different sources provided sediment. The red clay is believed to have come from Lake Superior sources, while the gray clay is believed to have come from sources farther west. Large-scale flood events from glacial Lakes Agassiz, Grantsburg, and Superior were probably the main contributors of the sediments. The red clay in the terrace is similar in composition to red glaciolacustrine sediment found in eastern and northern Wisconsin. It also is mineralogically similar to the Hinckley Sandstone and the Fond du Lac Formation, which occur under and around Lake Superior. Radiocarbon dates obtained from the lower Illinois valley indicate that the terrace sediments were deposited sometime between about 13,100 and 9500 yr ago. Soils developed on the terrace are variable in their physical, chemical, and mineralogical properties, which reflect the composition of the clayey sediments.
New Tree-Ring Dates for Recent Eruptions of Mount St. Helens
Authors: Yamaguchi David K.
Published: December 2004

Distinctive patterns of growth rings in increment cores from old-growth Douglas-fir (Pseudotsuga menziesii) stands identify A.D. 1800 as a more precise date for the eruption of tephra layer T by Mount St. Helens, Washington. Layer T was previously inferred to date to about A.D. 1802. Growth patterns also establish A.D. 1480 as the date of eruption of the earlier layer Wn, previously estimated as dating to about A.D. 1500. The timing of radial tree growth places a small limitation on the seasonal resolution of these new tree-ring dates.
Periodic JöKulhlaups from Pleistocene Glacial Lake Missoula—New Evidence from Varved Sediment in Northern Idaho and Washington
Authors: Waitt Richard B.
Published: December 2004

Newly examined exposures in northern Idaho and Washington show that catastrophic floods from glacial Lake Missoula during late Wisconsin time were repeated, brief jökulhlaups separated by decades of quiet glaciolacustrine and subaerial conditions. Glacial Priest Lake, dammed in the Priest River valley by a tongue of the Purcell trench lobe of the Cordilleran ice sheet, generally accumulated varved mud; the varved mud is sharply interrupted by 14 sand beds deposited by upvalley-running currents. The sand beds are texturally and structurally similar to slackwater sediment in valleys in southern Washington that were backflooded by outbursts from glacial Lake Missoula. Beds of varved mud also accumulated in glacial Lake Spokane (or Columbia?) in Latah Creek valley and elsewhere in northeastern Washington; the mud beds were disrupted, in places violently, during emplacement of each of 16 or more thick flood-gravel beds. This history corroborates evidence from southern Washington that only one graded bed is deposited per flood, refuting a conventional idea that many beds accumulated per flood. The total number of such floodlaid beds in stratigraphic succession near Spokane is at least 28. The mud beds between most of the floodlaid beds in these valleys each consist of between 20 and 55 silt-to-clay varves. Lacustrine environments in northern Idaho and Washington therefore persisted for two to six decades between regularly recurring, colossal floods from glacial Lake Missoula.
Stratigraphic Evidence of Human Disturbance in an Estuary
Authors: Brush Grace S. , Davis Frank W.
Published: December 2004

Prior to European settlement, oligohaline and mesohaline sections of Chesapeake Bay draining Piedmont saprolite supported diverse and abundant diatom and macrophyte populations. Compositional changes in diatoms and macrophytes in oligohaline sections correspond with 17th- and 19th-century deforestation and increased siltation, while effects on downstream populations were less notable. After deforestation, previously sparse diatom populations in a mesohaline estuary draining sandy Coastal Plain soils became more abundant. Fertilization of cultivated land was accompanied by increased production of both attached and free-floating diatoms. After the discharge of sewage, diatom populations increased enormously in the affected areas, followed by a dramatic decrease. The decrease suggests silica limitation after intense phosphorus enrichment. The loss of macrophytes and increase in planktonic diatoms in oligohaline areas in recent years resemble the historical sequences observed in lakes undergoing eutrophication. However, in the estuary, similar declines have also occurred in macrophyte populations in mesohaline areas where eutrophication is much less severe, but where chlorine and herbicide toxicity during the past 20 yr is similar to upstream areas.
Interlaboratory Comparison of Amino Acid Enantiomeric Ratios in Fossil Pleistocene Mollusks
Authors: Wehmiller John F.
Published: December 2004

Enantiomeric (d/l) ratios of eight amino acids in three homogeneous powdered fossil Pleistocene mollusk samples have been compared. Eleven laboratories have contributed results to this effort. Three gas chromatographic methods and one ion-exchange chromatographic method were used. In general, the coefficients of variation (c.v.) are best for alanine, glutamic acid, and aspartic acid (3–8%). For leucine and phenylalanine, the c.v.'s are between 5 and 10%. For isoleucine, proline, and valine the c.v.'s range from 10 to 18%. Individual laboratories usually report analytical precision of between 2 and 5%, but it is clear that significant differences between laboratories' results are often encountered, and that these analytical differences could, in some cases, lead to very significant differences (25% or more) in age estimates based upon enantiomeric ratios. Multiple analyses of desalted hydrolyzates of these powder samples suggest that interlaboratory differences are often caused by instrumental and/or derivatization procedures rather than the wet-chemical sample preparative steps. It is proposed that the powder samples described here be used in all future publications of fossil amino acid enantiomeric ratio data.
Central Arctic Ocean Response to Pleistocene Earth-Orbital Variations
Authors: Boyd Robin F. , Clark David L. , Jones Glenn , Ruddiman W.F. , McIntyre A. , Pisias N.G.
Published: December 2004

Three central Arctic Ocean sediment cores were sampled for percentage carbonate, number of foraminifera, and texture. These three parameters were used in spectral analyses to test the idea that the ice-covered Arctic Ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice-free oceans. The record for two of the cores represents approximately 1 my, and the record for the third, approximately 400,000 yr. The 100,000-yr frequency is well represented in all of the cores. A 40,000-yr frequency may be present, as well. An unexpected 70,000-yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity. The strong 100,000-yr signal confirms that, in spite of ice feedback, the Arctic Ocean has responded to orbital forcing in much the same manner as have ice-free oceans.
Outburst Floods from Glacial Lake Missoula
Authors: Clarke G. K. C. , Mathews W. H. , Pack R. T.
Published: December 2004

The Pleistocene outburst floods from glacial Lake Missoula, known as the “Spokane Floods”, released as much as 2184 km3of water and produced the greatest known floods of the geologic past. A computer simulation model for these floods that is based on physical equations governing the enlargement by water flow of the tunnel penetrating the ice dam is described. The predicted maximum flood discharge lies in the range 2.74 × 106−13.7 × 106m3sec−1, lending independent glaciological support to paleohydrologic estimates of maximum discharge.
Mapping of Glacial Landforms from Seasat Radar Images
Authors: Ford J. P.
Published: December 2004

Glacial landforms in the drumlin drift belt of Ireland and the Alaska Range can be identified and mapped from Seasat synthetic-aperture radar (SAR) images. Drumlins cover 60% of the Ireland scene. The width/length ratio of individual drumlins can be measured on the SAR images, allowing regional differences in drumlin shape to be mapped. This cannot be done with corresponding Landsat multispectral scanner (MSS) images because of lower spatial resolution and because of shadowing effects that vary seasonally. The Alaska scene shows the extent and nature of morphological features such as medial and lateral moraines, stagnant ice, and fluted ground moraine in glaciated valleys. Perception of these features on corresponding Landsat MSS images is limited by seasonal differences in solar illumination. Because SAR is not affected by such differences or by cloud cover, it is particularly well suited for monitoring glacial movement. The disadvantage of distorted high-relief features on Seasat SAR images can be reduced in future SAR systems by modifying the radar illumination geometry.
Isotopic Evidence for Glacial Meltwater Recharge to the Cambrian-Ordovician Aquifer, North-Central United States
Authors: Siegel D. I. , Mandle R. J.
Published: December 2004

The chemistry of water in the Cambrian-Ordovician aquifer in six midwestern states has been studied as part of the Northern Midwest Regional Aquifer-System Analysis of the U.S. Geological Survey. Dissolved-solids concentrations generally increase perpendicular to the direction of regional groundwater flow, from less than 400 mg/liter in southeast Minnesota, southwest Wisconsin, and northeast Iowa to more than 10,000 mg/liter in northwest Missouri. Isotopic ratios of hydrogen and oxygen are significantly depleted from north to south, with an areal distribution approximately parallel to the distribution of dissolved solids. For example, δ18O in southern Iowa and northern Missouri is about 6 parts per thousand lighter than δ18O of modern recharge water in Minnesota and Wisconsin. Covariance between δ18O and δD of the groundwater, similar to that of modern precipitation, suggests that the differences in isotopic ratios between groundwater and modern recharge water reflect meteoric signatures of water during past recharge events rather than geochemical processes such as isotopic exchange with aquifer materials. The pronounced parallelism between the distribution of isotopes and dissolved solids over large areas probably reflects largescale recharge of Pleistocene glacial meltwater into the aquifer system, which probably had a paleoflow system with a gradient from northeast to southwest rather than from northwest to southeast.
Toward the Definition of Criteria for the Recognition of Artificial Bone Alterations
Authors: Morlan Richard E.
Published: December 2004

Cutting, fracturing, flaking, and polishing of bones and other osseous materials may in some instances be interpreted as evidence of former human activity. Such interpretations must avoid confusion with the wide variety of natural processes that alter bones. Reliable criteria are prerequisite to sound inferences based on bone, regardless of whether they have been redeposited or recovered from primary assemblages. Criteria must be defined by means of actualistic studies (neotaphonomy) and experiments that demonstrate causal relationships between patterns of alteration and the processes that produce them. The criteria can be empoyed in the interpretation of fossil bones (paleotaphonomy) on the basis of uniformitarian principles. At the present time, such relationships are relatively well understood in the case of cut marks on bones, and modest progress has been made in investigating fractured and flaked bones. Polished bones are little understood and difficult to interpret.
Observations on Elephant Mortality and Bones in Water Holes
Authors: Conybeare A. , Haynes Gary
Published: December 2004

An unusually severe drought in 1982 led to a temporary die-off of elephants at a natural water source in Hwange National Park, Zimbabwe. Compared to living populations, the age structure of the animals killed by drought is strongly biased toward 2-to 8-year-old animals. However, the fresh carcasses of these young elephants were commingled with weathered remains of adults that had died earlier, creating a mixed skeletal sample whose age structure was much closer to that of living populations. Observations of elephant bones that have accumulated due to natural mortality at water holes might provide analogs for paleoecological interpretations of fossil proboscidean assemblages.
A Comparison of Radiolarian and Foraminiferal Paleoecology in the Southern Indian Ocean: New Evidence for the Interhemispheric Timing of Climatic Change
Authors: Howard William R. , Prell Warren L.
Published: December 2004

The deglacial transition between oxygen-isotope Stages 6 and 5e (about 127,000 yr B.P.) is marked by both oxygen isotopic depletion and estimated sea-surface temperature (SST) increase in two subantarctic Indian Ocean cores. The data show synchroneity between warming of foraminifera-based SST estimates and depletion of δ18O, but an earlier warming trend on the basis of radiolarian SST estimates. These data have been previously interpreted to indicate that the high-latitude Southern Ocean warms prior to significant melting of glacial-age ice sheets. Comparison of core-top assemblages with surface and subsurface conditions in the Southern Indian Ocean reveals that (1) a three-part foraminiferal zonation reflects the surface hydrographic regime, with abrupt faunal transitions at two major fronts: the Subtropical Convergence (STC) and the Antarctic Polar Front (APF); and (2) a two-part radiolarian zonation coincides with a two-part subsurface hydrographic regime, with an abrupt faunal transition corresponding to the southern terminus of subtropical lower water (STLW) between the STC and the APF. It is suggested that shifts of these surface and subsurface regimes are recorded by these foraminiferal and radiolarian assemblages. In this interpretation, the observed lead of radiolarian SST with respect to δ18O indicates an early response to a southward shift of STLW, while the later foraminiferal SST warming indicates a southward shift of the STC. Thus, the origin of the Southern Hemisphere SST lead may be related to STLW, which emanates from the subtropical gyres, rather than the polar regions.
Response of a Marine Ice Sheet to Changes at the Grounding Line
Authors: Van der Veen C. J.
Published: December 2004

A numerical model was designed to study the stability of a marine ice sheet, and used to do some basic experiments. The ice-shelf/ice-sheet interaction enters through the flow law in which the longitudinal stress is also taken into account. Instead of applying the model to some (measured) profile and showing that this is unstable (as is common practice in other studies), an attempt is made to simulate a whole cycle of growth and retreat of a marine ice sheet, although none of the model sheets is particularly sensitive to changes in environmental conditions. The question as to what might happen to the West Antarctic Ice Sheet in the near future when a climatic warming can be expecied as a result of the CO2 effect, seems to be open for discussion again. From the results presented in this paper one can infer that a collapse, caused by increased melting on the ice shelves, is not very likely.
Sedimentation and Stratigraphy at Eyjabakkajökull—An Icelandic Surging Glacier
Authors: Sharp Martin
Published: December 2004

A model for sedimentation by surging glaciers is developed from analysis of the debris load, sedimentary processes, and proglacial stratigraphy observed at the Icelandic surging glacier, Eyjabakkajökull. Three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce: (a) sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures, failure, and glacitectonic deformation of the overridden sediments; (b) reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses. These induce intense folding and thrusting during which basal debris-rich ice is elevated into an englacial position in a narrow marginal zone. As the terminal area of the glacier stagnates between surges, debris from this ice is released supraglacially and deposited by meltout and sediment flows; (c) local variations in overburden pressure beneath stagnant, crevassed ice cause subglacial lodgement tills, which are sheared during surges, to flow into open crevasses and form “crevasse-fill” ridges.