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Trace-Element And Physical Response To Melt Percolation In Summit (Greenland) Snow, Gifford J. Wong, Robert L. Hawley, Eric R. Lutz, Erich C. Osterberg

Dartmouth Scholarship

Surface melt on a glacier can perturb the glaciochemical record beyond the natural variability. While the centre of the Greenland ice sheet is usually devoid of surface melt, many high- Arctic and alpine ice cores document frequent summertime melt events. Current hypotheses interpreting melt-affected ice-core chemistry rely on preferential elution of certain major ions. However, the precise nature of chemistry alteration is unknown because it is difficult to distinguish natural variability from melt effects in a perennially melt-affected site. We use eight trace-element snow chemistry records recovered from Summit, Greenland, to study spatial variability and melt effects on insoluble trace …

Anthropogenic Osmium In Rain And Snow Reveals Global-Scale Atmospheric Contamination, Cynthia Chen, Peter N. Sedwick, Mukul Sharma

Dartmouth Scholarship

Osmium is one of the rarer elements in seawater, with typical concentration of approximately 10 x 10(-15) g g(-1) (5.3 x 10(-14) mol kg(-1)). The osmium isotope composition ((187)Os/(188)Os ratio) of deep oceans is 1.05, reflecting a balance between inputs from continental crust (approximately 1.3) and mantle/cosmic dust (approximately 0.13). Here, we show that the (187)Os/(188)Os ratios measured in rain and snow collected around the world range from 0.16 to 0.48, much lower than expected (>1), but similar to the isotope composition of ores (approximately 0.2) that are processed to extract platinum and other metals to be used primarily …

Neurological And Behavioral Abnormalities, Ventricular Dilatation, Altered Cellular Functions, Inflammation, And Neuronal Injury In Brains Of Mice Due To Common, Persistent, Parasitic Infection, Gretchen Hermes, James W. Ajioka, Krystyna A. Kelly, Ernest Mui, Fiona Roberts, Kristen Kasza, Thomas Mayr, Michael J. Kirisits, Robert Wollman, David J.P Ferguson, Craig W. Roberts, Jong-Hee Hwang, Toria Trendler, Richard P. Kennan, Yasuhiro Suzuki, Catherine Reardon, William F. Hickey, Lieping Chen, Rima Mcleod

Dartmouth Scholarship

Background:

Worldwide, approximately two billion people are chronically infected with Toxoplasma gondii with largely unknown consequences.

Methods:

To better understand long-term effects and pathogenesis of this common, persistent brain infection, mice were infected at a time in human years equivalent to early to mid adulthood and studied 5–12 months later. Appearance, behavior, neurologic function and brain MRIs were studied. Additional analyses of pathogenesis included: correlation of brain weight and neurologic findings; histopathology focusing on brain regions; full genome microarrays; immunohistochemistry characterizing inflammatory cells; determination of presence of tachyzoites and bradyzoites; electron microscopy; and study of markers of inflammation in serum. …

Predators And Life Histories Shape Lestes Damselfly Assemblages Along A Freshwater Habitat Gradient, Robby Stoks, Mark A. Mcpeek

Dartmouth Scholarship

Survey data from New England showed that assemblages of Lestes damselflies are organized along the entire gradient of pond permanence and predator presence. One assemblage occupies vernal ponds lacking large dragonfly predators and fish; four are largely confined to temporary ponds that typically contain dragonfly predators; one dominates fishless permanent ponds and lakes where dragonflies are the top predators; and one dominates permanent ponds and lakes where fish are the top predators. We determined the role of life history and predation in maintaining this striking pattern by conducting a series of transplant experiments in the field and a laboratory experiment …

Predators And Life Histories Shape Lestes Damselfly Assemblages Along A Freshwater Habitat Gradient, Robby Stoks, Mark A. Mcpeek

Dartmouth Scholarship

Survey data from New England showed that assemblages of Lestes dam- selflies are organized along the entire gradient of pond permanence and predator presence. One assemblage occupies vernal ponds lacking large dragonfly predators and fish; four are largely confined to temporary ponds that typically contain dragonfly predators; one dom- inates fishless permanent ponds and lakes where dragonflies are the top predators; and one dominates permanent ponds and lakes where fish are the top predators. We determined the role of life history and predation in maintaining this striking pattern by conducting a series of transplant experiments in the field and a …