Physical Sciences and Mathematics Commons^™

Patterns Of Early Lake Evolution In Boreal Landscapes: A Comparison Of Stratigraphic Inferences With A Modern Chronosequence In Glacier Bay, Alaska, Sherilyn C. Fritz, Daniel R. Engstrom, Stephen Juggins

Department of Earth and Atmospheric Sciences: Faculty Publications

The chronosequence approach, which infers temporal patterns of environmental change from a spatial array of modern sites, has been a major tool for studying successional processes. A model of early lake ontogeny in boreal landscapes, developed from a chronosequence of lakes in Alaska, suggests that long-term soil development and related hydrological change produce a loss of alkalinity and base cations, a decrease in pH, an increase in DOC and a transient increase followed by a decrease in lakewater nitrogen concentrations over time. We compare this model of lake ontogeny with patterns of change reconstructed from diatom assemblages in 10 sediment …

Low Marine Sulphate And Protracted Oxygenation Of The Proterozoic Biosphere, Linda C. Kah, Timothy W. Lyons, Tracy D. Frank

Department of Earth and Atmospheric Sciences: Faculty Publications

Progressive oxygenation of the Earth’s early biosphere is thought to have resulted in increased sulphide oxidation during continental weathering, leading to a corresponding increase in marine sulphate concentration. Accurate reconstruction of marine sulphate reservoir size is therefore important for interpreting the oxygenation history of early Earth environments. Few data, however, specifically constrain how sulphate concentrations may have changed during the Proterozoic era (2.5–0.54 Gyr ago). Prior to 2.2 Gyr ago, when oxygen began to accumulate in the Earth’s atmosphere, sulphate concentrations are inferred to have been <200 >μM, on the basis of limited isotopic variability preserved in sedimentary sulphides4 and experimental …

Correction To ‘‘A Concept Of Maximum Stream Depletion Rate For Leaky Aquifers In Alluvial Valleys" By Vitaly A. Zlotnik, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

In the paper ‘‘A concept of maximum stream depletion rate for leaky aquifers in alluvial valleys’’ by Vitaly A. Zlotnik (Water Resources Research, 40(6), W06507, doi:10.1029/2003WR002932, 2004), equations (24), (25), (A11), and (A12) were published with typographical errors. The correct equations are published below.

Three-Dimensional Modeling Of Lacustrine Diatom Habitat Areas: Improving Paleolimnological Interpretation Of Planktic : Benthic Ratios, Jeffery R. Stone, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

Three-dimensional modeling of lake morphometry enables the calculation of lake volume, planar surface area, and basin surface area, which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level. We have applied three-dimensional modeling to Foy Lake, Montana, and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake. The model allows us to produce semiquantitative depth reconstructions and greatly improves lake-level reconstruction of this morphometrically complex basin. The conceptual model also was modified to examine the …

Impact Of Heterogeneity, Bed Forms, And Stream Curvature On Subchannel Hyporheic Exchange, M. Bayani Cardenas, J. L. Wilson, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Advection through hyporheic zones (HZ) consisting of heterogeneous channel bend streambed deposits and their equivalent homogenous medium was investigated using finite difference groundwater flow and transport simulations and forward particle tracking. The top prescribed head boundary was varied in order to mimic various stream channel head distributions resulting from the presence of bed forms and channel curvature. Flux calculations show that heterogeneity causes significant additional HZ flux compared to an equivalent homogenous medium. However, the major cause of HZ flux is a spatially periodic (sinusoidal) head distribution along the boundary, representing the effect of bed forms. The additional influence of …

Systematics And Phylogeny Of Late Paleocene And Early Eocene Palaeoryctinae (Mammalia, Insectivora) From The Clarks Fork And Bighorn Basins, Wyoming, Jonathan I. Bloch, Ross Secord, Philip D. Gingerich

Department of Earth and Atmospheric Sciences: Faculty Publications

New specimens of Palaeoryctes punctatus from the middle Clarkforkian of the Clarks Fork Basin include a left dentary preserving the crowns of I₁-C₁, P₃, and M_1-2, with alveoli for P₂, P₄, and M₃. The lower dental formula, previously unknown for this species, is 3.1.3.3. A maxillary fragment preserves the crowns of a broken P⁴, complete M¹, and a broken M². Specimens previously referred to Palaeoryctes cf. P. punctatus and cf. Palaeoryctes sp. from the late Tiffanian are morphologically distinct and …

A Concept Of Maximum Stream Depletion Rate For Leaky Aquifers In Alluvial Valleys, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Existing analytical models for evaluating stream depletion by wells in alluvial aquifers are based on the assumption that stream depletion supplies 100% of groundwater withdrawals. Analysis of specific hydrostratigraphic conditions in leaky aquifers indicates that stream depletion may range from 0 to 100%. A new concept of maximum stream depletion rate (MSDR) is introduced and defined as a maximum fraction of the pumping rate contributed by the stream depletion. Several new analytical solutions indicate that the MSDR is determined by aquifer hydrostratigraphic conditions, geometry of recharge and discharge zones, and locations of pumping wells.

Twentieth Century Water Quality Trends In Minnesota Lakes Compared With Presettlement Variability, Joy M. Ramstack, Sherilyn C. Fritz, Daniel R. Engstrom

Department of Earth and Atmospheric Sciences: Faculty Publications

Abstract: A diatom-based transfer function was used to reconstruct water chemistry before European settlement in 55 Minnesota lakes. The lakes span three natural ecoregions, which differ in their history of land use, as well as in surficial geology, climate, and vegetation. Postsettlement trends were compared with water chemistry change reconstructed from two presettlement core sections (circa 1750 and 1800) as a measure of natural variability. Presettlement water quality changes were generally small and nondirectional in all three ecoregions. In contrast, half of the urban lakes showed a statistically significant increase in chloride, whereas 30% of urban and 30% of agricultural …

What Does It Take To Get Tenure?, Annabelle Foos, Mary Anne Holmes, Suzanne O'Connell

Department of Earth and Atmospheric Sciences: Faculty Publications

Data from the National Science Foundation and the American Geological Institute indicate that women geoscientists remain underrepresented at all levels in academia. In addition, the proportion of women geoscience faculty declines with increasing rank, from around 20 percent as assistant professors to 5 percent as full professors.

In 2001, we began a project to collect information that can help mentor women faculty early in their geoscience careers and improve their chances of obtaining tenure. We also wanted to provide institutions with information on retention, tenure and promotion procedures and criteria as they are practiced across the country.

Tropical Westerlies Over Pangaean Sand Seas, David B. Loope, Maureen B. Steiner, Clinton M. Rowe, Nicholas Lancaster

Department of Earth and Atmospheric Sciences: Faculty Publications

Cross-equatorial, westerly winds are key features of tropical circulation in monsoonal regions. Although prominent in numerical climate models of Pangaea (the supercontinent straddling earth’s equator, Late Paleozoic to Early Mesozoic), such flow has not been confirmed previously by migration directions of ancient dunes. Windblown sandstones that span 100 million years of earth history are widely exposed in south-western USA. If recent paleomagnetic data from the Colorado Plateau are used to correct Mesozoic paleogeographic maps, the Plateau is placed about 10° further south than previously assumed, and the prevailing north-westerly surface winds recorded by dune-deposited sandstones are explicable as cross-equatorial westerlies …

Geology And Paleontology Of The Upper John Day Beds, John Day River Valley, Oregon: Lithostratigraphic And Biochronologic Revision In The Haystack Valley And Kimberly Areas (Kimberly And Mt. Misery Quadrangles), Robert M. Hunt Jr., Ellen Stepleton

Department of Earth and Atmospheric Sciences: Faculty Publications

The John Day Formation of north-central Oregon preserves a succession of speciose, superposed Oligocene through early Miocene mammalian faunas that establish the sequence of mid-Cenozoic mammalian evolution within the Pacific Northwest. Upper John Day rock units initially described by Merriam (1900, 1901) in the Kimberly and Haystack Valley areas were later divided into lower (Kimberly) and upper (Haystack Valley) members by Fisher and Rensberger (1972). We focused our study on the lithostratigraphic succession within the Haystack Valley Member. Rocks previously included in the Haystack Valley Member can be subdivided into four unconformity-bounded, genetic lithostratigraphic units that range in age from …

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 …

Paleocene Cyclic Sedimentation In The Western North Atlantic, Odp Site 1051, Blake Nose, Mary Anne Holmes, David K. Watkins, Richard D. Norris

Department of Earth and Atmospheric Sciences: Faculty Publications

Upper Paleocene (zone CP8b) cyclic sediment from Ocean Drilling Program (ODP) Site 1051 on Blake Nose, western North Atlantic, alternates from white carbonate-rich to green carbonate-poor in response to precessional forcing. Compositional differences between the two bed types are minor: mineral and nannofossil composition of the beds vary subtly, but grain size of the terrigenous component and biogenic silica content remain constant. Iron content determined by sediment magnetic susceptibility and iron intensity determined by a core-scanning XRF correlates negatively with carbonate content and are higher in green beds. Kaolinite content of green beds is slightly higher as well. Green beds …

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 …

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 …

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 …

Why Has The Land Memory Changed?, Q. Steven Hu, Yongjun Zheng

Department of Earth and Atmospheric Sciences: Faculty Publications

The ‘‘land memory’’ refers to an interseasonal predictability of the summer monsoon rainfall in the south- western United States, describing a relationship of the summer monsoon rainfall anomaly with anomalies in the antecedent winter season snow and land surface conditions in the western United States. This relationship has varied, however, showing a peculiar on-and-off feature in the last century. It is important to understand this variation so that the relationship can be used to assist making predictions of the monsoon rainfall for that region. This note offers the evidence and shows that the change of the land memory may have …

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, …

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 …