bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geomorphology, Deformation, and Chronology of Marine Terraces along the Pacific Coast of Central Baja California, Mexico
Authors: Woods Alan J. 
Published: December 2004

AbstractThree emergent marine terraces are prominent between Playa El Marron and Arroyo El Salinito and comprise the most extensive Pleistocene planation surfaces in central Baja California, Mexico. The deposits of the lowest terrace, the Tomatal, are 120,000 ± 20,000 yr old (Sangamonian?) while the absolute ages of the two higher and older terraces, the Andrés and Aeropuerto, are unknown. The Tomatal terrace is particularly well developed and comprises degraded sea cliffs, paleodunes, and lagoonal sequences. Shingle paleobeach ridges also occur locally and reflect shore progradation and tombolo formation. The Tomatal shoreline is nearly horizontal at 7 ± 1 m above present mean sea level, whereas the older Aeropuerto terrace has been tilted so that it decreases in elevation toward the southeast. Nonetheless, coastal tilting is not nearly as great as at many other localities in California and Baja California. This is despite the fact that the entire Baja California peninsula has been assumed to be tectonically unstable during the Pleistocene, primarily because of the forces generated by plate motion.
Late-Glacial and Postglacial Sedimentation in Lake Superior Based on Seismic-Reflection Profiles
Authors: Johnson Thomas C. 
Published: December 2004

AbstractSeismic reflection profiles (3.5 kHz) were obtained along more than 3500 km of shiptrack in Lake Superior within the last 2 yr. The acoustic character of profiles is categorized as: (I) a single, strong reflector at the lake floor, (II) a thick, acoustically transparent layer overlying a strong reflector, and (III) relatively thick sediment with internal acoustic reflectors. These profiles, in conjunction with sediment cores from the area, reveal that varved glacial-lacustrine sediment settled out preferentially in a trough between Isle Royale and the north shore, and to a lesser extent in other topographic depressions; bottom currents generated by storm waves prevent clay accumulation on till or bedrock in the open lake wherever the bottom is shallower than 100 m; bottom currents prevent deposition or erode bottom sediment in certain deep-water (> 200 m) valleys; and lacustrine sediment is disturbed by creep or slumping off Grand Portage, Minnesota, and by other processes such as dewatering in many other areas. These factors complicate sedimentation in Lake Superior, and must be considered when investigating any aspect of the lake sediment.
An Altitudinal Cline in Tropical African Grass Floras and Its Paleoecological Significance
Authors: Livingstone D.A. , Clayton W. D. 
Published: December 2004

AbstractAt altitudes below 1300 m most species of grasses in tropical Africa are ones that use 4-carbon photosynthesis. Above 4000 m only species of the subfamily Pooideae using 3-carbon photosynthesis are found. At intermediate altitudes the percent of 3-carbon genera and species in the grass flora is a very regular function of altitude. The correlate of altitude that controls the distribution of grasses appears to be temperature. Fossil grass cuticles are identifiable to genus and should provide a useful paleothermometer. If no other errors were involved, the regular altitudinal distribution of genera in the flora of tropical East Africa would permit paleotemperature estimates with 95% confidence limits of ± 1.2°C.
Late-Glacial Vegetation and Climate at the Manis Mastodon site, Olympic Peninsula, Washington
Authors: Petersen Kenneth L. , Mehringer Peter J. , Gustafson Carl E. 
Published: December 2004

As the late Wisconsin Cordilleran Ice Sheet retreated, sediment accumulated in shallow depressions at the Manis Mastodon Archaeological site on the Olympic Peninsula, near Sequim, Washington. Pollen, plant macrofossils, and bones of mastodon, caribou, and bison occur within the lower 47 cm of these deposits. The fossil pollen and seed assemblages indicate persistence for 1000 yr (11,000–12,000 yr B.P.) of an herb-and-shrub-dominated landscape at a time when forest species appear elsewhere in Washington and in adjacent British Columbia.At present, Sequim is near the northern coastal limits of both Cactaceae andCeratophyllum. Mean annual precipitation is 42.7 cm and summer temperatures average 15°–16°C in July. The absence of coniferous trees and the presence of cactus andCeratophyllumin late-glacial sediments are explained by a regional climate that was drier and at least as warm as today. These conditions persisted in the rain shadow of the Olympic Mountains until at least 11,000 yr B.P.
Correlation of Late Quaternary Tephra Layers in a Long Pluvial Sequence near Summer Lake, Oregon
Authors: Davis Jonathan O. 
Published: December 2004

Near Summer Lake in southern Oregon, 54 tephra beds of late Quaternary age are exposed in pluvial lake sediments of Lake Chewaucan. Seven of the tephra beds near the top can be correlated with tephra deposits younger than 117,000 yr at Mount St. Helens, Washington, at Crater Lake, Oregon, and in northwestern Nevada in the deposits of pluvial Lake Lahontan. However, most of the section at Summer Lake lies below the correlated units, and contains 39 tephra beds older than 117,000 yr.Major-element chemistry of tephra glasses was determined by electron microprobe analysis; petrography supports the correlations made from chemical evidence. Compositions correlated range from 70 to 76% SiO2; the least silicic Summer Lake glass contained 57%.Extrapolation of depositional rate suggests that most of the sediments at Summer Lake are younger than about 335,000 yr, but older lake beds containing tephra layers occur at one place. The long lacustrine record suggests that Lake Chewaucan persisted through the last interpluvial stage, and that the lake may have dried up at the end of the Pleistocene due to diversion of the Chewaucan River by relict shore features.
An Analysis of the Chronology of Late Pleistocene Mammalian Extinctions in North America
Authors: Grayson Donald K. 
Published: December 2004

AbstractSome 35 genera of mammals became extinct in North America as the Pleistocene came to an end. Current attempts to explain those extinctions generally assume that all of the losses took place between 12,000 and 10,000 yr B.P., even though 13 of the 35 genera lack radiocarbon dates of reasonable validity that would place them in this 2000-yr period. Analyses of the structure of the radiocarbon chronology available for the extinct taxa suggest that some may lack terminal Wisconsin dates simply because they are so poorly represented in the paleontological record. These analyses also suggest, however, that the population numbers of many genera that became extinct toward the end of the Pleistocene may have significantly dwindled by 12,000 yr B.P., and that many of the genera that have yet to be dated to terminal Wisconsin times may not have survived beyond 12,000 yr B.P. If this is the case, current explanations of the extinctions are in need of extensive modification.
Suggested Terminology for Quaternary Dating Methods
Authors: Colman Steven M. , Pierce Kenneth L. , Birkeland Peter W. 
Published: December 2004

AbstractClassification of Quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods. We recommend the use of the terms numerical-age, calibrated-age, relative-age, and correlated-age to describe these levels. We also classify dating methods by type into sideral, isotopic, radiogenic, chemical and biological, geomorphic, and correlation methods. The use of “absolute” is inappropriate for most dating methods, and should be replaced by “numerical.” The use of “date” should be minimized in favor of “age” or “age estimate.” We recommend use of the abbreviations ka and Ma for most ages; calender dates can be used where appropriate and yr B.P. can be used for radiocarbon ages.
Postglacial Response of a Stream in Central Iowa to Changes in Climate and Drainage Basin Factors
Authors: Van Nest Julieann , Bettis E. Arthur 
Published: December 2004

AbstractPostglacial geomorphic development of the Buchanan Drainage, a small tributary to the South Skunk River, is reconstructed by documenting relationships among four allostratigraphic units and 17 radiocarbon dates. Formation and headward expansion of the valley was both episodic and time-transgressive. Response to downstream conditions in the South Skunk River largely controlled the early formation of the basin. Downcutting through Pleistocene deposits produced a gravelly lag deposit that was buried by alluvium in the downstream portion of the valley during the early Holocene (10,500–7700 yr B.P.). Lag deposits formed in a similar manner continued to develop in the upper portion of the drainageway into the late Holocene (3000-2000 yr B.P.). Episodes of aggradation during the middle Holocene (7700-6300 yr B.P.) and late Holocene (3000-2000 yr B.P.) were separated by a period of soil formation. Holocene geomorphic events in the drainageway coincide with some vegetational and climatic changes as documented in upland pollen sequences from central Iowa. Analysis of plant macrofossil assemblages recovered from alluvium indicates that during the middle Holocene forest contracted and prairie expanded into the uplands within the basin. Vegetational changes within the basin apparently had only minor influence on rates of hillslope erosion, and the widely accepted relationship between prairie (versus forest) vegetative cover and increased rates of hillslope erosion did not hold. Instead, greater amounts of erosion occurred under forested conditions when local water tables were higher and seepage erosion was more effective.
Climatic transfer function from quaternary molluscs in European loess deposits
Authors: Rousseau Denis-Didier 
Published: December 2004

AbstractCorrespondence and multiple regression analysis of terrestrial molluscs in the loess sections of Achenheim (Alsace, France) has permitted the reconstruction of climatic variations during the last three glacial-interglacial cycles back to 339,000 yr B.P. The sequence has been dated according to the SPECMAP chronology of Imbrie et al. (1984) and the fossil faunas have been calibrated in relation to recent assemblages sampled in defined ecological conditions in Sweden and France. Transfer functions that relate the abundances of different species to climate allow the reconstruction of temperature and precipitation. Estimates for the coldest (February) and warmest (August) months in present-day Alsace were obtained and variations in temperature between −13° and 2°C in winter and 10° and 17°C in summer were determined. These results are consistent with those yielded by transfer functions using other continental fossils. Estimates differ for past precipitation. Summer precipitation is always less than present (with values between 50 and 78 mm, while modern August values are 76 mm higher). Winter estimates are always higher than the present mean (between 76 and 33 mm, while the recent February value is 34 mm). Comparisons between cycles show that the climatic patterns described for one cycle cannot be strictly applied to the others. Comparisons have been made with the pollen stratigraphy of La Grande Pile, the nearest quantified sequence to Achenheim, and with some Atlantic cores in order to study the magnitude of deviations from modern mean values of the climatic parameters.
Stratigraphy of the Colorado Creek Mammoth Locality, Alaska
Authors: Thorson Robert M. , Guthrie R. Dale 
Published: December 2004

AbstractThe Colorado Creek mammoth locality in west-central Alaska contains the remains of two mammoths that were scavenged by carnivores. Sedimentologic interpretations of the reworked eolian deposits surrounding the bones, supplemented by 10 radiocarbon dates, indicate that the lower and upper mammoths died and were buried within separate, but superimposed, thaw gullies about 23,000 and 16,000 yr ago, respectively. From our results, we propose a polycyclic taphonomic model for thaw gullies governed largely by slope aspect, rather than regional climate, and in which mixing between faunal horizons is more likely than not. Variations in the rate of silt influx and the position of the permafrost table provide a paleoclimatic proxy record that can be correlated to other records in eastern Beringia.
Implications of Late Quaternary Mammalian Fauna from Lukenya Hill (South-Central Kenya) for Paleoenvironmental Change and Faunal Extinctions
Authors: Marean Curtis W. 
Published: December 2004

AbstractLate Quaternary paleoenvironmental data for East Africa are derived primarily from montane sources and thus we know little about the changing composition of East African savannas. Four archaeological sites at Lukenya Hill in the savanna of the Athi-Kapiti Plains of Kenya that date to the last 40,000 yr preserve a large mammalian fauna. The prehistoric hunters concentrated on migratory ungulates and virtually ignored the resident inselberg ungulates throughout the occupation. Faunas of the last glacial maximum are dominated by an extinct small alcelaphine antelope. Arid-adapted ungulates are present that are regionally absent historically, and Pelorovis is present as well. The small alcelaphine and arid-adapted ungulates are absent in the Holocene deposits. This suggests that there was an expansion of dry savannas during the last glacial maximum. The last glacial maximum aridity, combined with a lack of pastoral-set fires, would have resulted in a vegetative mosaic distinct from the present. Dry woody growth and dry and/or tall grass, all of which are poor forage for ungulates, would have been common where seasonally moist short grasslands are presently extant. These conditions favored the large-bodied, highly hypsodont species in Africa that became extinct with the onset of wet conditions during the early Holocene.
Ultra-Compact Dwarf Galaxies in Galaxy Clusters
Authors: Drinkwater Michael J. , Gregg Michael D. , Couch Warrick J. , Ferguson Henry C. , Hilker Michael , Jones J. Bryn , Karick Arna , Phillipps Steven 
Published: December 2004

AbstractWe review the evidence that the ultra-compact dwarf (UCD) galaxies we recently discovered in the Fornax Cluster form a new, previously unknown class of galaxies and we discuss possible scenarios for their formation. We then present recent results that UCDs are also present in the Virgo Cluster, and that there is a much larger than expected population of fainter UCDs in the Fornax Cluster. The size and properties of this population may lead us to revise our original ‘galaxy threshing’ hypothesis for the formation of UCDs.
Galactic Winds and the Missing Baryons
Authors: Veilleux Sylvain , Rupke David S. 
Published: December 2004

AbstractGalaxy-scale winds are poised to solve a number of ailments in modern cosmology. However, we know little about trends of wind properties with host galaxy properties. In an attempt to quantify the impact of galactic winds on their host galaxies and the environment, we are conducting a systematic survey of star-forming and active galaxies at z = 0–0.5. Preliminary results on the star-forming galaxies are presented.
“INTERNAL THECAE” OF EUNOTIA SOLEIROLII (BACILLARIOPHYCEAE): DEVELOPMENT, STRUCTURE AND FUNCTION AS RESTING SPORES1
Authors: Hans‐Adolf  , Stosch Von , Fecher Klaus 
Published: December 2004

ABSTRACTThe “double thecae” or “internal septa” of Eunotia soleirolii (Kütz.) Rabenh, are shown to represent the thecae of resting spores, as characterized by their physiology, as well as morphology. They differ from all resting spores of centric diatoms by the formation of both their valves as a result of unequal cell divisions; and, from the majority of centric spores by the presence of several girdle bands in both their thecae. Spore formation can be induced by high or low pH, high temperature (24 C), and iron, silica, phosphate or nitrate deficiencies, whereas low temperatures defer it. Spores do not germinate directly, but dormancy can be removed by dark treatments (–2 to 15 C) for a minimum of 4–5 wk. Longer dark treatments result in higher germination rates. At 15 C, a minimum of 2 mo is required and 4 mo is better. Heat treatments (27–42 C) are ineffective, but may shorten the dormancy‐breaking subsequent cold period. Instances of secondary dormancy, as well as relative dormancy, were observed. Germination usually occurs in the light between 2 and 21 C. An equal division of the spore is followed by unequal divisions of both new cells with only the two resulting large cells being viable. The experiences in the laboratory aided the discovery of stages of spore germination in nature.
SYNARTHROPHYTON, A NEW GENUS OF CORALLINACEAE (CRYPTONEMIALES, RHODOPHYTA) FROM THE SOUTHERN HEMISPHERE1
Authors: Townsend Roberta A. 
Published: December 2004

ABSTRACT Synarthrophyton gen. nov. is described based on southern Australian material of Melobesia patena Hooker fils & Harvey, which shows features intermediate between Mesophyllum Lemoine and Lithothamnium Philippi. It has the thin‐walled rounded epithallial cells and coaxial hypothallium characteristic of Mesophyllum and the type of procarp and male structures common to Lithothamnium. Synarthrophyton is unique within the subfamily Melobesioideae (J. E. Areschoug) Yendo because it displays secondary pit connections. Details of the vegetative and reproductive morphology of S. patena (Hooker fils. & Harvey) comb. nov. are given and its taxonomic position in the Corallinaceae Lamouroux discussed.
OSMOREGULATION IN THE MARINE DIATOM CYLINDROTHECA FUSIFORMIS1
Authors: Paul John S. 
Published: December 2004

ABSTRACTA mechanism for the regulation of internal osmolarity in the diatoms (Bacillariophyta) was investigated using the intertidal lestuarian pennate diatom, Cylindrotheca fu‐siformis Reimann & Lewin. The intracellular pools of the free sugar, mannose, and its respective polymer, poly‐mannose, were found to be in a dynamic equilibrium which rapidly responds to changes in external osmotic pressure. Increasing the salinity shifts the steady state in the direction of free mannose, while decreasing the salinity stimulates polymerization of the free mannose to its polysaccharide. The mechanism requires a response of certain key enzymes to osmotic pressure rather than to levels of any particular ion since increasing the external osmolarity with an organic solute (sorbitol) was as effective in eliciting a response as using inorganic ions.
SHORT‐TERM RESPONSES OF NUTRIENT‐DEFICIENT ALGAE TO NUTRIENT ADDITION1
Authors: Healey F. Patrick 
Published: December 2004

ABSTRACTChanges in net photosynthesis, dark respiration, ATP content, and some other aspects of composition were measured following phosphate or ammonium addition to cultures of the green alga Scenedesmus quadricauda (Turp.) Bréb. deficient in phosphorus or nitrogen. The deficient nutrient was rapidly taken up. Light‐saturated net photosynthesis was depressed below the pre‐addition rate during nutrient uptake and did not increase markedly above that rate until several hours after uptake was complete. Dark respiration, on the other hand, was markedly stimulated during uptake of the deficient nutrient and to a lesser extent after uptake was complete. Phosphate addition to P‐deficient cells caused a large increase in the ATP content within 2–4 h of addition, whereas ammonium addition to N‐deficient cells caused much less or no increase in ATP content. Short‐term enrichment experiments to detect nutrient limitations are evaluated in the light of these and similar results taken from the literature. The available evidence shows that photosynthetic responses cannot reliably be used in short‐term enrichments but changes in respiration or ATP content may be useful in certain circumstances.
PHOSPHATE‐LIMITED GROWTH KINETICS OFSELENASTRUM CAPRICORNUTUM(CHLOROPHYCEAE)1
Authors: Brown Edward J. , Button Don K. 
Published: December 2004

ABSTRACTMost theoretical studies of phytoplankton growth in aquatic environments assume that relative nutrient utilization abilities regulate species composition. The steady‐state phosphate‐limited growth kinetics ofSelenastrum capricornutumPrintz were examined using continuous cultures to characterize the green alga's ability to compete for orthophosphate (Pi) when Pi limits growth. The maximal specific growth rate forSelenastrumat 20 C was 1.20 day−1, and the concentration where half maximal growth rate occurs was 40 nM Pi. There was an apparent threshold of 10 nM Pi. Cell yields varied inversely with growth rate; thus ability to utilize Pi could not be characterized in terms of the Monod half‐saturation constant and maximal growth rate. Instead, we computed the Pi affinity from steady‐state flux vs. external Pi concentrations. This affinity was 2.8 l·mg dry wt−1· day−1forSelenastrum.Kinetic evidence from this study suggests thatSelenastrumwill not be growth competitive with some other common aquatic heterotrophs and autotrophs when Pi limits microbial growth in lakes.
SEXUAL REPRODUCTION IN THE TOXIC DINOFLAGELLATEGONYAULAX MONILATA1
Authors: Walker Linda M. , Steidinger Karen A. 
Published: December 2004

ABSTRACTThe sexual cycle ofGonyaulax monilataHowell was observed in stationary cultures and in nitrogen‐deficient medium. The armored, isogamous gametes fuse in a characteristic manner with cingula at oblique angles. Nuclear fusion lags slightly behind cytoplasmic fusion. The zygote enlarges for several days. The dark, double‐flagellated planozygote encysts within 1–3 wk. Early hypnozygotes are round to ovoid and contain lipid and one or two large golden‐yellow globules. As the hypnozygote matures, the globules become smaller and the cytoplasm darkens and pulls from the wall. All cysts examined contained only one nucleus. A very dark, uninucleate post‐hypnozygotic cell escapes through an archeopyle and within 24 h divides into daughter cells which divide in 24–48 h forming a small chain. The production of thick walled zygates in culture implies that such resting stages in marine sediments could serve as a source stock for blooms. This species causes toxic red tides and the existence of benthic “seed beds” consisting of hypnozygotes is now plausible.
EFFECT OF SILICATE LIMITATION ON VALVE MORPHOLOGY IN THALASSIOSIRA AND COSCINODISCUS (BACILLARIOPHYCEAE)1
Authors: Booth Beatrice , Harrison Paul J. 
Published: December 2004

ABSTRACT Coscinodiscus radiatus Ehrenb. and Thalassiosira eccentrica (Ehrenb.) Cleve were grown in a silicate‐limited chemostat at silicate concentrations below 1 μg‐atoms · l−1. The resulting abnormal valves of C. radiatus lacked a thickened ring around the foramina; their pore membranes were thinner and their loculi shallower than those in normal cells. Abnormal valves of T. eccentrica had a fasciculate areolae pattern; they lacked a silica covering over the foramina and some tangential areolae walls. Neither abnormal valve could be termed a new species.