Earth Sciences Commons^™

Provenance Of Sand In Periglacial Sand Wedges And Sheet Sand, Northeastern Nebraska, Usa, William J. Wayne

Department of Earth and Atmospheric Sciences: Faculty Publications

Sand-wedge polygons on upland surfaces beneath thin loess in northeastern Nebraska record the existence of permafrost around the margin of the Wisconsinan glacier at its maximum advance. Strong unidirectional wind not only kept the upland surfaces free of snow, allowing frost to penetrate deeply and thermal contraction cracks to develop, but also dessicated the surface material so that frost action and sublimation of pore ice could loosen surface material. The strong NW-SE winds deflated soils from upland surfaces, made ventifacts of the cobbles in the lag that remained and created fields of yardangs oriented NW-SE. Sand derived from the soils …

Arsenic In Nebraska's Groundwater And Public Water Supplies, David Gosselin, Lynne Klawer, Angela Noe

Department of Earth and Atmospheric Sciences: Faculty Publications

Because arsenic (As) in drinking water is considered a primary contributor to cancer in humans, the U.S. Environmental Protection Agency (EPA) recently lowered the maximum contaminant level (MCL) for arsenic from 50 micrograms per liter (μg/L) to 10 μg/L (1 μg/L ~ I part per billion: ppb). This MCL will become effective in 2006. On a national scale, EPA has estimated that of the 74,000 public water supply systems regulated by this MCL, approximately 4,000 systems will have to make changes to comply with it. Of the affected systems, 97 percent are small systems that serve fewer than 10,000 people …

Sedimentology And Geochemistry Of An Urban Coastal Lake System: Coombabah Lake Nature Reserve, Gold Coast, Queensland, Tracy D. Frank, Christopher R. Fielding

Department of Earth and Atmospheric Sciences: Faculty Publications

A study was initiated to address environmental concerns associated with changes in land use in the catchment area of Coombabah Lake, a brackish coastal lake system located in southeast Queensland. Sedimentological and geochemical data derived from a series of cores that penetrate the ca. 0–6000 year-old lacustrine sequence indicate that throughout much of its history, Coombabah Lake has remained a quiet, shallow, water body fed by fine-grained sediment dropped from suspension. Discrete and laterally continuous, shelly horizons form the basis for the stratigraphy developed for the lake sequence. A lithological transition in the upper 50 cm of the sediment column, …

Do Meteorologists Suppress Thunderstorms? Radar-Derived Statistics And The Behavior Of Moist Convection, Matthew D. Parker, Jason C. Knievel

Department of Earth and Atmospheric Sciences: Faculty Publications

Most meteorologists are acquainted with the notion of a weather hole—that is, a place that receives less exciting weather than does its surroundings. Exciting weather takes many forms, but when people use the term weather hole, they tend to mean a place that thunderstorms often barely miss, or near which approaching storms often dissipate. For this paper, that is the meaning we adopt.

In our experience, many meteorologists and lay weather enthusiasts genuinely believe that they live in weather holes, and this belief, almost without fail, seems to stem from countless hours spent gazing at displays of radar reflectivity. We …

Diatom Biostratigraphy Of The Cenozoic Glaciomarine Pagodroma Group, Northern Prince Charles Mountains, East Antarctica, Jason M. Whitehead, David M. Harwood, Barrie Mckelvey, Andrew Mcminn

Department of Earth and Atmospheric Sciences: Faculty Publications

In the northern Prince Charles Mountains glaciomarine sediments of the Pagodroma Group outcrop on Fisher Massif (Mt Johnston and Fisher Bench Formations) and at the Amery Oasis (Battye Glacier and Bardin Bluffs Formations), at locations 300 and 250 km south of the Amery Ice Shelf edge, respectively. Most of the Pagodroma Group consists of ice-proximal glaciomarine diamict, and a much subordinate (<2%) amount of more ice-distal mudstone. Microfossil biostratigraphy based upon in situ and glacially reworked diatoms constrains the ages of the four formations, and identifies at least six intervals of marine fjordal deposition. Sparse diatoms in Mt Johnston Formation diamicts indicate an Early Oligocene age. However, it is …

Hydrologic Variation During The Last 170,000 Years In The Southern Hemisphere Tropics Of South America, Sherilyn C. Fritz, Paul A. Baker, Tim K. Lowenstein, Geoffrey O. Seltzer, Catherine A. Rigsby, Gary S. Dwyer, Pedro M. Tapia, Kimberly K. Arnold, Teh-Lung Ku, Shangde Luo

Department of Earth and Atmospheric Sciences: Faculty Publications

Despite the hypothesized importance of the tropics in the global climate system, few tropical paleoclimatic records extend to periods earlier than the last glacial maximum (LGM), about 20,000 years before present. We present a well-dated 170,000-year time series of hydrologic variation from the southern hemisphere tropics of South America that extends from modern times through most of the penultimate glacial period. Alternating mud and salt units in a core from Salar de Uyuni, Bolivia reflect alternations between wet and dry periods. The most striking feature of the sequence is that the duration of paleolakes increased in the late Quaternary. This …

Where Are The Women Geoscientist Professors?, Mary Anne Holmes, Suzanne O'Connell

Department of Earth and Atmospheric Sciences: Faculty Publications

Nearly 50 geo- and social scientists recently gathered for a workshop on women in the geosciences. The two-fold purpose was to compile data on the status of women in the geosciences, and to arrive at a consensus on strategies to increase the proportion of women and their diversity in the field. The Workshop on Women in the Geosciences was held September 25-27, 2003, in Washington, D.C.

Late-Holocene Lake-Level Variation In West Greenland, Frank A. Aebly, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

Situated between the North Atlantic and the Greenland ice sheet, the thousands of lakes in the Kangerlussuaq area of West Greenland (67°N) present excellent targets for paleoclimate studies. Paleoshorelines surrounding multiple closed-basin lakes in this area record fluctuations in lake level since deglaciation. Shorelines along two of these lakes, Hundeso and Lake E, were surveyed and trenched to reconstruct the history of lake-level change. The stratigraphies of the trenches were described, and a chronology has been developed using radiocarbon dating of organic material. Preliminary results indicate a highly variable hydrologic regime throughout the late Holocene.

Hundeso had high-stand lake levels …

Academic Specialties In U.S. Are Shifting; Hiring Of Women Geoscientists Is Stagnating, Mary Anne Holmes, Suzanne O'Connell, Connie Frey, Lois K. Ongley

Department of Earth and Atmospheric Sciences: Faculty Publications

Women have been receiving a greater proportion of the bachelor’s and master’s degrees in the geosciences over the last 10 years, reaching near 40% in 2000 (latest data available), while receiving only 28% of the Ph.D.s that year. Women are now only 20% of assistant professors at Ph.D.-granting institutions, a proportion that has not changed in the last four years. As part of a larger study to find what key barriers continue to prevent larger numbers of women geoscientists from becoming academics, data have been compiled from the National Science Board [NSB, 2002], and the American Geological Instititute's (AGI) Directory …

Sedimentary Aggregates In The Peoria Loess Of Nebraska, Usa, Joseph A. Mason, Peter M. Jacobs, Richard S. B. Greene

Department of Earth and Atmospheric Sciences: Faculty Publications

Loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples. However, these data may not adequately represent the effective particle size distribution during loess transport, if the transported dust contained aggregates of fine-grained material. Thin sections of minimally altered C and BC horizons in the late Pleistocene Peoria Loess of Nebraska, USA, indicate the presence of aggregates with diameters of 30–1000 Am. The larger aggregates (>250 μm) are unlikely to have been transported, and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition. Aggregates …

Late Quaternary Lake-Level Changes Constrained By Radiocarbon And Stable Isotope Studies On Sediment Cores From Lake Titicaca, South America, Harold D. Rowe, Thomas P. Guilderson, Robert B. Dunbar, John R. Southon, Geoffrey O. Seltzer, David A. Mucciarone, Sherilyn C. Fritz, Paul A. Baker

Department of Earth and Atmospheric Sciences: Faculty Publications

We present and compare AMS-¹⁴C geochronologies for sediment cores recovered from Lake Titicaca, South America. Radiocarbon dates from three core sites constrain the timing of late Quaternary paleoenvironmental changes in the Central Andes and highlight the site-specific factors that limit the radiocarbon geochronometer. With the exception of mid-Holocene sediments, all cores are generally devoid of macrophyte fragments, thus bulk organic fractions are used to build core chronologies. Comparisons of radiocarbon results for chemically defined fractions (bulk decalcified, humate, humin) suggest that ages derived from all fractions are generally coherent in the post-13,500 yr BP time interval. In the …

The Status Of Women In The Geosciences, Mary Anne Holmes, Connie Frey, Suzanne O'Connell, Lois K. Ongley

Department of Earth and Atmospheric Sciences: Faculty Publications

Most geoscientists agree that gender equity is a worthy goal for our field, but there is disagreement as to how to measure gender equity and what it actually means. Will the geosciences achieve gender equity when the proportion of women on our faculty and in professional positions accurately reflects the proportion in our undergraduate classes? Or is gender equity 50 percent of all positions in all fields, including undergraduate enrollment? By any of these measures, we are not yet there. Women earned 40 percent of the undergraduate degrees in geoscience (geology, oceanography, atmospheric sciences, geophysics) in 2001, and 38 percent …

Three-Dimensional Model Of Modern Channel Bend Deposits, M. Bayani Cardenas, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

We present a three-dimensional model of heterogeneous modern channel bend deposits developed through purely structure-imitating interpolation (kriging) of hydraulic properties. This model, augmented with ground-penetrating radar data and directional variograms, agrees with detailed observations in similar modern environments and leads to a process-based interpretation of the presented hydraulic conductivity structure. Integration of all available information permitted delineation and characterization of the modern streambed as a distinct hydrostratigraphic unit without coring or outcrop studies. Our results imply that the modern streambed is commonly oversimplified in available analytical and numerical models of groundwater-surface water interactions where it is assumed to be homogeneous …

A Late Quaternary Diatom Record Of Tropical Climatic History From Lake Titicaca (Peru And Bolivia), Pedro M. Tapia, Sherilyn C. Fritz, Paul A. Baker, Geoffrey A. Seltzer, Robert B. Dunbar

Department of Earth and Atmospheric Sciences: Faculty Publications

A composite high-resolution diatom stratigraphy from three piston cores and one box-core in the deep sub-basin of Lake Titicaca reveals large moisture variations during the past 30 kyr in the Altiplano region. Diatom sequences indicate orbital and millennial-scale variability in water level and salinity. The pelagic freshwater diatom species Cyclotella andina and Cyclotella stelligera dominate Glacial-age sediments, suggesting that the lake was above its present outlet. Generally, wet conditions continued until 11,000 cal yr BP, as indicated by high percentages of freshwater planktonic diatoms. Large pulses of benthic diatom species between about 11,000 and 10,000 cal yr BP suggest brief …

A Vegetation And Fire History Of Lake Titicaca Since The Last Glacial Maximum, Gina M. Paduano, Mark B. Bush, Paul A. Baker, Sherilyn C. Fritz, Geoffrey O. Seltzer

Department of Earth and Atmospheric Sciences: Faculty Publications

Fine-resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding Lake Titicaca (3810 m, Peru/Bolivia) since ca. 27,500 cal yr BP (hereafter BP). Time control was based on 26 accelerator mass spectrometer (AMS) radiocarbon dates. Seventeen AMS dates and 155 pollen and charcoal samples between ca. 17,500 BP and ca. 3,100 BP allow a centennial-scale reconstruction of deglacial and early- to mid-Holocene events. Local and regional fire signals were based on the separation of two charcoal size fractions, ≥180 μm and 179–65 μm. Charcoal abundance correlated closely with the proportion of woody taxa present …

Field Study Of Hydraulic Conductivity In A Heterogeneous Aquifer: Comparison Of Single-Borehole Measurements Using Different Instruments, Vitaly A. Zlotnik, Brian R. Zurbuchen

Department of Earth and Atmospheric Sciences: Faculty Publications

This field study compares three techniques for estimating the vertical distribution of horizontal hydraulic conductivity K_r in a heterogeneous aquifer and evaluates possible support volume effects. The dipole flow test (DFT), multilevel slug test (MLST), and borehole flowmeter test (BFT) are based on different kinematic flow structures and the shape and the size of the support volumes. The experiment design employed an identical characteristic linear scale for all tests. Vertical profiles of K_r ranging up to 260 m/day from tested wells in an alluvial aquifer exhibit a strong correlation in spite of the differences between test hydraulics. Results …

Moon Lake 11,000 Year Diatom-Inferred Salinity Data, Kathleen R. Laird, Sherilyn C. Fritz, Eric C. Grimm, P. G. Mueller

Department of Earth and Atmospheric Sciences: Faculty Publications

Estimates of past lake-water salinity from fossil diatom assemblages were used to infer past climatic conditions at Moon Lake, a climatically sensitive site in the northern Great Plains. A good correspondence between diatom-inferred salinity and historical records of mean annual precipitation minus evapotranspiration (P-ET) strongly suggests that the sedimentary record from Moon Lake can be used to reconstruct past climatic conditions. Century-scale analysis of the Holocene diatom record indicates four major hydrological periods: an early Holocene transition from an open freshwater system to a closed saline system by 7300 BP, which corresponds with a transition from spruce forest to deciduous …

The Application Of A Diatom-Based Transfer Function To Evaluate Regional Water-Quality Trends In Minnesota Since 1970, J. M. Ramstack, Sherilyn C. Fritz, D. R. Engstrom, S. A. Heiskary

Department of Earth and Atmospheric Sciences: Faculty Publications

Significant population growth over the last three decades, as well as efforts to improve surface-water quality mandated by the Clean Water Act, potentially have had opposing influences on aquatic ecosystems in the U.S. Because historical data on water-quality trends are limited over this time period, we developed a diatom-based transfer function to reconstruct chloride, color, acid neutralizing capacity (ANC), total phosphorus (TP), and pH in 55 Minnesota lakes. The lakes span three different ecoregions, as well as the Twin Cities metropolitan area, and differ in their history of settlement and land use, and in surficial geology, climate, and vegetation. Lakes …

Late Albian Adaptive Radiation In The Calcareous Nannofossil Genus Eiffellithus, David K. Watkins, James A. Bergen

Department of Earth and Atmospheric Sciences: Faculty Publications

Well preserved nannofossil assemblages in upper Albian and lower Cenomanian hemipelagic sections from Ocean Drilling Program (ODP) Leg 171B preserve a record of the early history and adaptive radiation of the genus Eiffellithus. Seven distinct taxa are recognized and differentiated, with one previously named taxon (E. monechiae) emended and four new species described: E. praestigium, E. vonsalisiae, E. equibiramus, and E. parvus. Sample census data indicate that most species evolved, rose to dominance, and then rapidly declined to extinction, to be replaced by other members of the genus. Newly evolved species tended to remain at low …

Lake Sediments Record Large-Scale Shifts In Moisture Regimes Across The Northern Prairies Of North America During The Past Two Millennia, Kathleen R. Laird, Brian F. Cumming, Sybille Wunsam, James A. Rusak, Robert J. Oglesby, Sherilyn C. Fritz, Peter R. Leavitt

Department of Earth and Atmospheric Sciences: Faculty Publications

Six high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the northern prairies of North America, show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia. The predominant broad-scale pattern seen at all sites is a major shift in moisture regimes from wet to dry, or vice versa (depending on location), that occurred after a period of relative stability. These large-scale shifts at the different sites exhibit spatial coherence at regional scales. The three Canadian sites record this abrupt shift between anno Domini 500 …

Climate Effects On Corn Yield In Missour, Q. Steven Hu, Gregory Buyanovsky

Department of Earth and Atmospheric Sciences: Faculty Publications

Understanding climate effects on crop yield has been a continuous endeavor aiming at improving farming technology and management strategy, minimizing negative climate effects, and maximizing positive climate effects on yield. Many studies have examined climate effects on corn yield in different regions of the United States. However, most of those studies used yield and climate records that were shorter than 10 years and were for different years and localities. Although results of those studies showed various influences of climate on corn yield, they could be time specific and have been difficult to use for deriving a comprehensive understanding of climate …

Sulfate Oxygen-17 Anomaly In An Oligocene Ash Bed In Mid-North America: Was It The Dry Fogs?, Huiming Bao, Mark H. Thiemens, David B. Loope, Xun-Lai Yuan

Department of Earth and Atmospheric Sciences: Faculty Publications

The oxygen and sulfur isotope compositions of sulfate, particularly the oxygen-17 anomaly, provide clues to the origin of sulfate. We report a variable oxygen-17 anomaly for water- and acid-leached sulfate from an Oligocene volcanic ash bed in the northern High Plains, U.S.A. We find no sulfate O-17 anomaly, however, in freshly collected ashes from recent eruptions around the world. The Oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the High Plains, thus a long-term background atmospheric sulfate accumulation is less likely the origin. Combining sulfur isotope data, we suggest that the anomalous sulfate was associated with volcanic …

Pliocene Summer Sea Surface Temperature Reconstruction Using Silicoflagellates From Southern Ocean Odp Site 1165, Jason M. Whitehead, Steven M. Bohaty

Department of Earth and Atmospheric Sciences: Faculty Publications

In the modern marine environment the silicoflagellate genus Dictyocha is rare, or absent, south of the Antarctic polar front (APF); the genus Distephanus, in contrast, is dominant. In sediments recovered from ODP Site 1165, 1600 km south of the front, however, three intervals where Dictyocha is abundant are interpreted to represent Pliocene warm events. Comparison of our data with Ciesielski and Weaver’s [1974] modern core top silicoflagellate relationship with sea surface temperature (SST) indicates that at Site 1165 mean annual SST was approximately 5C at 3.7 Ma (event I), and approximately 4C at 4.3–4.4 Ma (event II) and 4.55–4.8 …

Estimation Of Hydraulic Conductivity From Borehole Flowmeter Tests Considering Head Losses, Vitaly A. Zlotnik, Brian R. Zurbuchen

Department of Earth and Atmospheric Sciences: Faculty Publications

Recent numerical studies have demonstrated that the conventional interpretation of the borehole flowmeter test (BFT) may lead to considerable errors in estimates of the horizontal hydraulic conductivity (K_r) due to neglect of head loss across the electromagnetic borehole flowmeter (EBF). Even in uniform aquifers, the conventional interpretation underestimates K_r at the base and overestimates K_r at the top of the aquifer. In this paper, we derive exact analytical solutions for hydraulic head and streamlines induced by the BFT in a confined homogeneous aquifer. The solutions explicitly consider head loss across the EBF. The derived analytical solutions …

Intercontinental Migration Of Large Mammalian Carnivores: Earliest Occurrence Of The Old World Beardog Amphicyon (Carnivora, Amphicyonidae) In North America, Robert M. Hunt Jr.

Department of Earth and Atmospheric Sciences: Faculty Publications

North American amphicyonid carnivorans are prominent members of the mid-Cenozoic terrestrial carnivore community during the late Eocene to late Miocene (Duchesnean to Clarendonian). Species range in size from <5 kg to >200 kg. Among the largest amphicyonids are Old and New World species of the genus Amphicyon: A. giganteus in Europe (18–~15? Ma) and Africa, A. ingens in North America (15.9–~14.2 Ma). Amphicyon first appears in the Oligocene of western Europe, surviving there until the late Miocene. Migration to Africa and North America takes place in the early Miocene. The genus occurs in the Arrisdrift fauna (Namibia) of southwest Africa, indicating migration south …

A Daily Soil Temperature Dataset And Soil Temperature Climatology Of The Contiguous United States, Q. Steven Hu, Yongjun Zheng

Department of Earth and Atmospheric Sciences: Faculty Publications

Although affected by atmospheric circulations, variations in soil temperature result primarily from the radiation and sensible and latent heat exchanges at the surface and heat transfer in the soils of different thermal properties. Thus, soil temperature and its variation at various depths are unique parameters that are useful in understanding both the surface energy processes and regional environmental and climatic conditions. Yet, despite the importance, long-term quality data of soil temperatures are not available for the United States. The goal of this study is to fill this data gap and to develop a soil temperature dataset from the historical data …

Long-Lived Pluvial Episodes During Deposition Of The Navajo Sandstone, David B. Loope, Clinton M. Rowe

Department of Earth and Atmospheric Sciences: Faculty Publications

The Navajo Sandstone of the American Southwest was deposited at approximately 190 Ma in a giant, subtropical dune field near the western margin of Pangea. From this unit, we report thick intervals of dune cross-strata that were churned by insects and trampled by reptiles. Although dunes continued to migrate freely, the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years. We interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of “greening” in the Sahara …

Where Are The Women Geoscience Professors?, Mary Anne Holmes, Suzanne O'Connel

Department of Earth and Atmospheric Sciences: Faculty Publications

Compiles an extensive set of data on the status of women in the geosciences, identifying successful strategies for increasing diversity as well as obstacles that hinder efforts. The lessons learned and best practices that arise from this report will help geoscientists continue to increase the gender diversity of their community. Some of these lessons also provide insight into ways to improve the racial and ethnic diversity of the geosciences.

Mylanodon Rosei, A New Metacheiromyid (Mammalia: Palaeanodonta) From The Late Tiffanian (Late Paleocene) Of Northwestern Wyoming, Ross Secord, Philip D. Gingerich, Jonathan I. Bloch

Department of Earth and Atmospheric Sciences: Faculty Publications

Mylanodon rosei is a new genus and species of late Paleocene metacheiromyid palaeanodont from a new late Tiffanian locality, Y2K Quarry, in the Clarks Fork Basin, Wyoming. The type is an adult dentary with P₄ and a molariform double-rooted M₁. This provides the first evidence that molariform teeth were retained in early Metacheiromyidae. A second specimen is a juvenile dentary with a partial P₃ and an unerupted P₄. This is the first juvenile dentition known for a Paleocene metacheiromyid. The new specimens enable determination of dental homologies. Reduction of teeth in early metacheiromyids took …

Lake-Catchment Interactions With Climate In The Low Arctic Of Southern West Greenland, N. John Anderson, Sherilyn C. Fritz, Christopher E. Gibson, Bent Hasholt, Melanie J. Leng

Department of Earth and Atmospheric Sciences: Faculty Publications

Arctic hydrology plays a central role in the earth’s heat balance and ocean circulation (Vörösmarty et al. 2001). Future changes associated with human influence on the climate system are also predicted to cause major changes in the energy and hydrologic mass balance of Arctic catchments. Climate change will likely affect permafrost and snowmelt, which dominate Arctic hydrology and control the chemistry of surface runoff (and hence streams and lakes) as water percolates through the active layer. However, the controls and dynamic impact of snowmelt are poorly understood, because this critical timeframe is often missed by sampling programs. In the Søndre …