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Articles 2881 - 2910 of 4541

Full-Text Articles in Earth Sciences

Intercontinental Migration Of Neogene Amphicyonids (Mammalia, Carnivora): Appearance Of The Eurasian Beardog Ysengrinia In North America, Robert M. Hunt Jr. Jan 2002

Intercontinental Migration Of Neogene Amphicyonids (Mammalia, Carnivora): Appearance Of The Eurasian Beardog Ysengrinia In North America, Robert M. Hunt Jr.

Department of Earth and Atmospheric Sciences: Faculty Publications

At the beginning of the Neogene a remarkable faunal turnover occurred within the North American carnivore community. The dominant larger Oligocene carnivores (creodonts, nimravid cats, the amphicyonid Daphoenus) became extinct during the late Oligocene and were replaced in the early Miocene by amphicyonine amphicyonids and hemicyonine ursids that entered North America from Eurasia. During a five million-year interval from ~23 to 18 Ma, large amphicyonines appear in late Arikareean and early Hemingfordian faunas of the North American midcontinent. Although most fossils are from western Nebraska and southeastern Wyoming, occurrences of amphicyonines at several sites in the eastern United States …

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Concordant Paleolatitudes For Neoproterozoic Ophiolitic Rocks Of The Trinity Complex, Klamath Mountains, California, Edward A. Mankinen, Nancy Lindsley-Griffin, John R. Griffin Jan 2002

Concordant Paleolatitudes For Neoproterozoic Ophiolitic Rocks Of The Trinity Complex, Klamath Mountains, California, Edward A. Mankinen, Nancy Lindsley-Griffin, John R. Griffin

Department of Earth and Atmospheric Sciences: Faculty Publications

New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel …

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Creep Critters From Nebraska's Past, Roger K. Pabian Jan 2002

Creep Critters From Nebraska's Past, Roger K. Pabian

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Groundwater-Level Changes In Nebraska-Spring 2000 To Spring 2001/Groundwater-Level Changes In Nebraska-Predevelopment To Spring 2001, Conservation Survey Division Jan 2002

Groundwater-Level Changes In Nebraska-Spring 2000 To Spring 2001/Groundwater-Level Changes In Nebraska-Predevelopment To Spring 2001, Conservation Survey Division

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Banner County Test Hole Logs, Frank A. Smith Jan 2002

Banner County Test Hole Logs, Frank A. Smith

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Arctic Ocean Snow Melt Onset Dates Derived From Passive Microwave, A New Data Set, Mark R. Anderson, Sheldon D. Drobot Jan 2002

Arctic Ocean Snow Melt Onset Dates Derived From Passive Microwave, A New Data Set, Mark R. Anderson, Sheldon D. Drobot

Department of Earth and Atmospheric Sciences: Faculty Publications

Snow melt onset is defined as the point in time when the appearance of liquid water in the snow pack changes the crystalline structure within the pack. Owing to the associated increase in surface albedo during melt, surface energy absorption increases rapidly after the onset of snow melt. Monitoring interannual variations in snow melt onset is therefore useful for accurately modeling surface conditions, and it is also valuable for validating climate models and detecting climate change. Since microwave emission changes rapidly when liquid water appears in the snow pack, passive microwave remote sensing techniques can monitor melt onset. Passive microwave …

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Seasonal Migration Of Columbia Spotted Frogs (Rana Luteiventris) Among Complementary Resources In A High Mountain Basin, David S. Pilliod, Charles R. Peterson, Peter I. Ritson Dec 2001

Seasonal Migration Of Columbia Spotted Frogs (Rana Luteiventris) Among Complementary Resources In A High Mountain Basin, David S. Pilliod, Charles R. Peterson, Peter I. Ritson

United States Geological Survey: Staff Publications

Information on how animals partition their activities and travel among complementary resources, such as breeding or overwintering habitats, is needed for species conservation. In a mountain basin at 2500 m elevation in central Idaho, we studied the habitat use and movement patterns of 736 marked and 87 radio-tagged Columbia spotted frogs (Rana luteiventris) from 1995 to 1998. The goals of this study were to (i) identify and characterize R. luteiventris breeding, summer foraging, and overwintering habitats, (ii) describe the movement patterns of juvenile, male, and female R. luteiventris among these resources, and (iii …

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Effects Of Binary Combinations Of Herbicides On Freshwater Algae, Jill K. Taylor Dec 2001

Effects Of Binary Combinations Of Herbicides On Freshwater Algae, Jill K. Taylor

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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An Improved Method For Determining Snowmelt Onset Dates Over Arctic Sea Ice Using Scanning Multichannel Microwave Radiometer And Special Sensor Microwave/Imager Data, Sheldon D. Drobot, Mark R. Anderson Oct 2001

An Improved Method For Determining Snowmelt Onset Dates Over Arctic Sea Ice Using Scanning Multichannel Microwave Radiometer And Special Sensor Microwave/Imager Data, Sheldon D. Drobot, Mark R. Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

Ablation of snow over sea ice is an important physical process affecting the Arctic surface energy balance. An improved understanding of the spatial and temporal variations in snowmelt onset could be utilized to improve climate simulations in the Arctic, as well as monitor the Arctic for signs of climate change. Utilizing an updated approach for monitoring snowmelt onset over Arctic sea ice, spatial variability in passive microwave derived snowmelt onset dates is examined from 1979 through 1998. The improved technique, termed the advanced horizontal range algorithm (AHRA), utilizes temporal variations in 18/19G Hz and 37 GHz passive microwave horizontal brightness …

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Orbitally Induced Oscillations In The East Antarctic Ice Sheet At The Oligocene/Miocene Boundary, Tim R. Naish, Ken J. Woolfe, Peter J. Barrett, Gary S. Wilson, Cliff Atkins, Steven M. Bohaty, Christian J. Bücker, Michele Claps, Fred J. Davey, Gavin B. Dunbar, Alistair G. Dunn, Christopher R. Fielding, Fabio Florindo, Michael J. Hannah, David M. Harwood, Stuart A. Henrys, Lawrence A. Krissek, Mark Lavelle, Jaap Van Der Meer, William C. Mcintosh, Frank Niessen, Sandra Passchier, Ross D. Powell, Andrew P. Roberts, Leonardo Sagnotti, Reed P. Scherer, C. Percy Strong, Franco Talarico, Kenneth L. Verosub, Giuliana Villa, David K. Watkins, Peter-N. Webb, Thomas Wonik Oct 2001

Orbitally Induced Oscillations In The East Antarctic Ice Sheet At The Oligocene/Miocene Boundary, Tim R. Naish, Ken J. Woolfe, Peter J. Barrett, Gary S. Wilson, Cliff Atkins, Steven M. Bohaty, Christian J. Bücker, Michele Claps, Fred J. Davey, Gavin B. Dunbar, Alistair G. Dunn, Christopher R. Fielding, Fabio Florindo, Michael J. Hannah, David M. Harwood, Stuart A. Henrys, Lawrence A. Krissek, Mark Lavelle, Jaap Van Der Meer, William C. Mcintosh, Frank Niessen, Sandra Passchier, Ross D. Powell, Andrew P. Roberts, Leonardo Sagnotti, Reed P. Scherer, C. Percy Strong, Franco Talarico, Kenneth L. Verosub, Giuliana Villa, David K. Watkins, Peter-N. Webb, Thomas Wonik

Department of Earth and Atmospheric Sciences: Faculty Publications

Between 34 and 15 million years (Myr) ago, when planetary temperatures were 3-4°C warmer than at present and atmospheric CO2 concentrations were twice as high as today, the Antarctic ice sheets may have been unstable. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets. Here we present sediment data from shallow marine cores in the western Ross …

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Island Arcs, Accretionary Terranes And Midcontinent Structure New Understandings Of The Geologic Architecture Of The U.S. Midcontinent, Marvin P. Carlson Oct 2001

Island Arcs, Accretionary Terranes And Midcontinent Structure New Understandings Of The Geologic Architecture Of The U.S. Midcontinent, Marvin P. Carlson

Conservation and Survey Division: Faculty and Staff Publications

A data base collected over the last 100 years, containing both surface and subsurface information, has allowed us to begin to understand the physical framework of Nebraska. We have learned that even in the stable Midcontinent region of North America, there has been an active geologic history. This framework has been deciphered by our programs of surface geologic mapping and by the study of rock samples from both water wells and those deeper test wells for oil and gas. Determining the major structural features across the state (figure 1) has allowed us to better understand both the occurrences of its …

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Experimental Diatom Dissolution And The Quantification Of Microfossil Preservation In Sediments, D. B. Ryves, S. Juggins, Sherilyn C. Fritz, R. W. Battarbee Aug 2001

Experimental Diatom Dissolution And The Quantification Of Microfossil Preservation In Sediments, D. B. Ryves, S. Juggins, Sherilyn C. Fritz, R. W. Battarbee

Department of Earth and Atmospheric Sciences: Faculty Publications

Four laboratory experiments on fresh, modern diatoms collected from lakes in the Northern Great Plains of North America were carried out to assess the effects of dissolution on diatom abundance and composition. Marked differences in mean dissolution susceptibility exist between species, despite sometimes significant intra- specific variation between heterovalves. Twenty-four taxa were ranked according to susceptibility to dissolution using an exponential decay model of valve abundance. This dissolution ranking was used to derive two weighted indices of sample preservation. A third index (F) was based on a simple binary classification of valve morphology into dissolved and pristine categories, …

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Movement Of Rainbow And Brown Trout In Relation To Water Quality And Food Availability In Lake Ogallala, Nebraska, Corey M. Huxoll Aug 2001

Movement Of Rainbow And Brown Trout In Relation To Water Quality And Food Availability In Lake Ogallala, Nebraska, Corey M. Huxoll

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Environmental Change And The Central Great Plains, Carbon Sequestration, Mark A. Mesarch Aug 2001

Environmental Change And The Central Great Plains, Carbon Sequestration, Mark A. Mesarch

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Historical Water-Quality Data For The High Plains Regional Ground-Water Study Area In Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, And Wyoming, 1930–98, David W. Litke Jul 2001

Historical Water-Quality Data For The High Plains Regional Ground-Water Study Area In Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, And Wyoming, 1930–98, David W. Litke

United States Geological Survey: Publications

The High Plains aquifer underlies 174,000 square miles in parts of eight States and includes eight primary hydrogeologic units, including the well-known Ogallala Formation. The High Plains aquifer is an important resource, providing water for 27 percent of the Nation’s irrigated agricul¬tural lands in an otherwise dry landscape. Since the 1980’s there has been concern over the sustainability of the aquifer due to water-level declines caused by substantial pumping. Water quality of the aquifer is a more recent concern. As part of the U.S. Geological Survey’s National Water-Quality Assessment Program, historical water-quality data have been gathered for the High Plains …

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Late Quaternary Climate And Hydrology Of Tropical South America Inferred From An Isotopic And Chemical Model Of Lake Titicaca, Bolivia And Peru, Scott L. Cross, Paul A. Baker, Geoffrey O. Seltzer, Sherilyn C. Fritz, Robert B. Dunbar Jul 2001

Late Quaternary Climate And Hydrology Of Tropical South America Inferred From An Isotopic And Chemical Model Of Lake Titicaca, Bolivia And Peru, Scott L. Cross, Paul A. Baker, Geoffrey O. Seltzer, Sherilyn C. Fritz, Robert B. Dunbar

Department of Earth and Atmospheric Sciences: Faculty Publications

A simple mass balance model provides insight into the hydrologic, isotopic, and chemical responses of Lake Titicaca to past climatic changes. Latest Pleistocene climate of the Altiplano is assumed to have been 20% wetter and 5°C colder than today, based on previous modeling. Our simulation of lacustrine change since 15,000 cal yr B.P. is forced by these modeled climate changes. The latest Pleistocene Lake Titicaca was deep, fresh, and overflowing. The latest Pleistocene riverine discharge from the lake was about 8 times greater than the modern average, sufficient to allow the expansion of the great paleolake Tauca on the central …

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Ecosystems And Immune Systems: Hierarchical Response Provides Resilience Against Invasions, Craig R. Allen Jun 2001

Ecosystems And Immune Systems: Hierarchical Response Provides Resilience Against Invasions, Craig R. Allen

United States Geological Survey: Staff Publications

Janssen (2001) provides the stimulus for thoughtful comparison and consideration of the ranges of responses exhibited by immune systems and ecological systems in the face of perturbations such as biological invasions. It may indeed be informative to consider the similarities of the responses to invasions exhibited by immune systems and ecological systems. Clearly, both types of systems share a general organizational structure with all other complex hierarchical systems. Their organization provides these systems with resilience. However, when describing the response of ecological-economic systems to invasions, Janssen emphasizes the human-economic response. I would like to expand on his comparison by focusing …

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Distributions Of Roosting Sandhill Cranes As Identified By Aerial Thermography, Tierny L. Parrish, Wayne A. Hubert, Stanley H. Anderson, Michael Pucherelli, Warren Mangus Jun 2001

Distributions Of Roosting Sandhill Cranes As Identified By Aerial Thermography, Tierny L. Parrish, Wayne A. Hubert, Stanley H. Anderson, Michael Pucherelli, Warren Mangus

United States Geological Survey: Staff Publications

We used aerial thermography to determine the location of sandhill crane (Grus canadensis) roosting sites during a single night over a 142-km reach of the Platte River, Nebraska. We assessed the influences of human disturbance features, screening of disturbance features by woody vegetation, distance to surrounding cropland of various types and channel width on distribution patterns of sandhill crane roosting sites with the aid of a geographic information system (GIS). We found that roosting sites were farther from bridges and paved roads than random points along the river channel; a visual woody screen mitigated the effect of bridges …

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Effects Of Woody Cover In The Landscaping On Riparian Avifauna And A Preliminary Nesting Assessment, Micah W. Perkins May 2001

Effects Of Woody Cover In The Landscaping On Riparian Avifauna And A Preliminary Nesting Assessment, Micah W. Perkins

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Movements And Habitat Use By Hatchery-Reared Pallid Sturgeon In The Lower Platte River, Nebraska, Vaughn A. Snook May 2001

Movements And Habitat Use By Hatchery-Reared Pallid Sturgeon In The Lower Platte River, Nebraska, Vaughn A. Snook

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Characteristics Of Nest Sites Of Northern Bobwhites In Western Oklahoma, Darrell E. Townsend Ii, Ronald E. Masters, Robert L. Lochmiller, David M. Leslie Jr., Stephen J. Demaso, Alan D. Peoples May 2001

Characteristics Of Nest Sites Of Northern Bobwhites In Western Oklahoma, Darrell E. Townsend Ii, Ronald E. Masters, Robert L. Lochmiller, David M. Leslie Jr., Stephen J. Demaso, Alan D. Peoples

United States Geological Survey: Staff Publications

Previous authors have described nesting habitat of the northern bobwhite (Colinus virginianus) throughout its range, but few have compared structural or compositional differences of vegetation between nest sites and random non-use sites, and successful and non-successful nests. From 1996-1998, we compared cover and structure of 85 plant species from 80 nest sites of northern bobwhite in western Oklahoma. Nest sites were consistently associated with greater structural complexity than what was available at random. Bobwhites selected nest sites with a greater coverage of grass (ca. 50%) and woody (ca. 20-30%) vegetation with a relatively low percentage of bare ground, …

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Environmental Change And The Central Great Plain, Water Resources, David Gosselin Apr 2001

Environmental Change And The Central Great Plain, Water Resources, David Gosselin

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Agricultural Management Practices And The Groundwater System Of Northern Holt County, Nebraska, With A Focus On The Holt County Groundwater Education Project, Susan Olafsen Lackey, Charles Shapiro, William Kranz Apr 2001

Agricultural Management Practices And The Groundwater System Of Northern Holt County, Nebraska, With A Focus On The Holt County Groundwater Education Project, Susan Olafsen Lackey, Charles Shapiro, William Kranz

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Environmental Change And The Central Great Plains, David Gosselin Apr 2001

Environmental Change And The Central Great Plains, David Gosselin

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Nebraska's Test-Hole Drilling Program And Records, Duane R. Mohlman, Charles A. Flowerday Mar 2001

Nebraska's Test-Hole Drilling Program And Records, Duane R. Mohlman, Charles A. Flowerday

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Geology Of Pioneers Park, Lancaster County, Nebraska, Roger K. Pabian Mar 2001

Geology Of Pioneers Park, Lancaster County, Nebraska, Roger K. Pabian

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Locating Nests Of Birds In Grasslands From A Mobile Tower Blind, Thomas F. Fondell, Steven T. Hoekman, I. J. Ball Feb 2001

Locating Nests Of Birds In Grasslands From A Mobile Tower Blind, Thomas F. Fondell, Steven T. Hoekman, I. J. Ball

United States Geological Survey: Staff Publications

Locating nests of grassland passerines can be difficult, labor intensive, and disruptive to birds and vegetation. We developed a mobile tower blind for observing adult bird behavior and used it to locate nests in a western Montana grassland. We compared nest-search efficiency of behavioral observations from the tower versus the ground. Nests of savannah sparrow (Passerculus samhvichensis) were found in a higher proportion of territories searched from the tower (13/16 = 82%) than from the ground (4113 = 3 1%). Average search time for each nest found was lower from the tower (44 min) than from the ground …

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Tropical Climate Changes At Millennial And Orbital Timescales On The Bolivian Altiplano, Paul A. Baker, Catherine A. Rigsby, Geoffrey O. Seltzer, Sherilyn C. Fritz, Tim K. Lowenstein, Niklas P. Bacher, Carlos Veliz Feb 2001

Tropical Climate Changes At Millennial And Orbital Timescales On The Bolivian Altiplano, Paul A. Baker, Catherine A. Rigsby, Geoffrey O. Seltzer, Sherilyn C. Fritz, Tim K. Lowenstein, Niklas P. Bacher, Carlos Veliz

Department of Earth and Atmospheric Sciences: Faculty Publications

Tropical South America is one of the three main centers of the global, zonal overturning circulation of the equatorial atmosphere (generally termed the “Walker” circulation). Although this area plays a key role in global climate cycles, little is known about South American climate history. Here we describe sediment cores and down-hole logging results of deep drilling in the Salar de Uyuni, on the Bolivian Altiplano, located in the tropical Andes. We demonstrate that during the past 50,000 years the Altiplano underwent important changes in effective moisture at both orbital (20,000-year) and millennial timescales. Long-duration wet periods, such as the Last …

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The History Of South American Tropical Precipitation For The Past 25,000 Years, Paul A. Baker, Geoffrey O. Seltzer, Sherilyn C. Fritz, Robert B. Dunbar, Matthew J. Grove, Pedro M. Tapia, Scott L. Cross, Harold D. Rowe, James P. Broda Jan 2001

The History Of South American Tropical Precipitation For The Past 25,000 Years, Paul A. Baker, Geoffrey O. Seltzer, Sherilyn C. Fritz, Robert B. Dunbar, Matthew J. Grove, Pedro M. Tapia, Scott L. Cross, Harold D. Rowe, James P. Broda

Department of Earth and Atmospheric Sciences: Faculty Publications

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. …

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Ecoregions Of Nebraska And Kansas, Robert F. Diffendal Jr. Jan 2001

Ecoregions Of Nebraska And Kansas, Robert F. Diffendal Jr.

Robert F. Diffendal, Jr., Publications

Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources; they are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components. Ecoregions are directly applicable to the immediate needs of state agencies, including the development of biological criteria and water quality standards, and the establishment of management goals for nonpoint-source pollution. They are also relevant to integrated ecosystem management, an ultimate goal of most federal and state resource management agencies. The approach used to compile this map is based on the premise …

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