University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Late Cenozoic Antarctic paleoclimate reconstructed from volcanic ashes in the Dry Valleys region of southern Victoria Land

Abstract: We report the discovery of numerous in situ Miocene and Pliocene airfall volcanic ashes that occur within the hyperarid Dry Valleys region of the Transantarctic Mountains in southern Victoria Land, Antarctica. Ashes that occur above 1000 m elevation rest at the ground surface, covered only by a thin ventifact pavement 1 to 2 cm thick. The ash deposits are loose and unconsolidated and show no signs of chemical weathering. Laser-fusion 40 Ar/ 39 Ar analyses of volcanic crystals and glass shards indicate that the ashes range from 4.33 Ma to 15.15 Ma in age. The Arena Valley ash (4.33 ± 0.07 Ma) rests on the surface of a well-developed desert pavement and ultraxerous soil profile at 1410 m elevation. Lack of geomorphic evidence of liquid water on surficial sediments coeval and older than the Arena Valley ash, together with the pristine condition of volcanic crystals and lack of authigenic clay formation, indicates a cold desert at and since 4.33 Ma. The Beacon Valley ash (10.66 ± 0.29 Ma), the Koenig Valley ash (13.65 ± 0.06 Ma), and the Nibelungen Valley ash (15.15 ± 0.02 Ma) fill the upper half of relict sand-wedge troughs that form only in cold-desert conditions. The lack of authigenic clay-sized minerals in these ash deposits, along with preservation of sharp lateral contacts with surrounding sand-and-gravel deposits, suggests that frozen conditions (without rain or well-developed active layers during summer months) have persisted in Beacon, Koenig, and Nibelungen Valleys since ash deposition. Ash-avalanche deposits that rest on rectilinear slopes contain matrix ash dated to 7.42 ± 0.31 Ma in upper Arena Valley and 11.28 ± 0.05 Ma in lower Arena Valley. Little slope development has occurred since emplacement of these ash-avalanche deposits. Such slope stability is consistent with cold-desert conditions well below 0 °C. Taken together, these ash deposits point to persistent polar conditions similar to the present at elevations above 1000 m in the western Dry Valleys region during at least the last 15.0 m.y. This conclusion contradicts the view that, during part of the Pliocene epoch, East Antarctica was largely free of glacier ice and that scrub vegetation (Nothofagus, Southern Beech) survived along the Transantarctic Mountain front in the Dry Valleys region and to at least lat 86°S (Webb and Harwood, 1993). Instead, it supports marine and geomorphological evidence that calls for a stable Antarctic cryosphere, much the same as today, since middle Miocene time.

Input-Output Budgets of Inorganic Nitrogen for 24 Forest Watersheds in the Northeastern United States: A Review

Abstract: Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeastern United States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha −1 yr −1 (mean = 6.4 kg N ha −1 yr −1 ;m edian =7 .0 kg Nh a −1 yr −1 ). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg Nh a −1 yr −1 (mean = 2.0 kg N ha −1 yr −1 ;m edian =1 .7 kg Nh a −1 yr −1 ). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha −1 yr −1 (mean = 4.4 kg N ha −1 yr −1 ;m edian =4 .6 kg Nh a −1 yr −1 ). Outputs of DIN in streamwater were predominantly NO3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.

Stoichiometry and microstructure effects on tungsten oxide chemiresistive films

Abstract: Highly oriented tungsten trioxide thin films have been grown on (0 1 2) r-cut sapphire substrates using reactive rf magnetron sputtering of a tungsten metal target in various oxygen/argon mixtures Parameters for growth of stoichiometric tungsten trioxide (WO 3 ) films were determined by X-ray photoelectron spectroscopy (XPS) In situ four-point Van der Pauw conductivity measurements were performed on as-grown films and after post-deposition annealing to study changes in the oxygen vacancy population Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) indicate that stoichiometric WO 3 films deposited at 450°C are dominated by the tetragonal phase with (0 0 1) orientation along the growth direction, and films deposited at 650°C possess coexisting (0 0 2), (0 2 0), and (2 0 0) in-plane orientations of the monoclinic phase Tetragonal and monoclinic-phase WO 3 films exhibit a change in conductivity of 01 Ω −1 cm −1 to 20 ppm H 2 S at 250°C, but display different response kinetics