Test of the climatological dispersion model in the strait of canso area,Nova Scotia

Abstract

The Climatological Dispersion Mode1 is used to estimate mean annual and mean monthly concentrations of sulphur dioxide in the Strait of Canso area of Noua Scotia. It is found that the wind distribution at the southern end of the Strait is more likely to produce a reliable estimate of the concentration of pollutants from the taller stacks, whereas the surface wind distribution from a central location in the Strait can be used, because of low‐level channelling, to estimate concentrations of pollutants from the lower sources. Data on winds aloft over the Strait, are utilized in support of this thesis. The procedure does not apply well to the summer months; otherwise the resulting patterns of predicted concentrations of sulphur dioxide are generally consistent with observed values. More accurate and sensitive instruments are needed in future studies of long‐term average conditions.     

Toward an Immersive 3D Virtual BoK Exploratorium: A Proof of Concept

The UCGIS GIS&T Body of Knowledge document provided an opportunity for the GIS educational community to link course content and curricular sequencing to a catalog of subject matter. Focusing on learning objectives, a selection of relevant citations, and basic background for each topic, it has been used to a limited degree for both course topic selection and curriculum development. However, the static format of the document, lack of an index, and dated nature of the material limit its utility for education. Based on the success of our research team in developing a virtual platform for a new, more interactive, and collaborative environment to catalogue and interactively add to the body knowledge (Ahearn et al. 2013), this article describes efforts to develop a multi‐user virtual user environment that will add social presence to the experience. It describes the successes and failures of using Second Life as the initial platform for this work, illustrates the available interactions and limitations, and depicts ongoing efforts to move beyond Second Life for this development. Finally it discusses a possible methodology to leverage the power of virtual crowd sourcing within competitive gaming environments such as Unity to allow for the creation of on‐demand virtual 3‐D visualizations of GIS&T concepts in a digital Exploratorium.     

Provenance, age, and environment of mid-Wisconsinan slackwater lake sediment in the St. Louis Metro East area, USA

Valleys tributary to the Mississippi River contain fossiliferous slackwater lake sediment (Equality Formation) deposited in response to aggradation of the Mississippi River valley during the last glaciation. In the St. Louis Metro East area, the lower part of the Equality Formation is primarily laminated, fossiliferous silt and clay deposited from about 44,150 to 24,310 ¹⁴C yr B.P. The upper Equality Formation is primarily very fine sand to silt deposited from about 21,200 to 17,000 ¹⁴C yr B.P. Among the four cores that sample this succession in the St. Louis Metro East area, core MNK-3 (38.64EN, 90.01EW) was selected for detailed study. Three sources are distinguished by the following characteristics: (1) gray smectite-quartz-Se-rich, feldspar-poor material of the Des Moines, Wadena, and James lobes; (2) reddish brown kaolinite-Cu-Fe-rich sediment of the Superior and Rainy lobes; and (3) brown illite-dolomite-Sr-rich sediment of the Lake Michigan and Green Bay lobes. The earliest sediments (44,150 to 41,700 ¹⁴C yr B.P.) were derived from the central and western provenances and are chronocorrelative with the lower Roxana Silt. A hiatus occurred from about 41,700 to 29,030 ¹⁴C yr B.P. when much of the middle Roxana Silt (Meadow Member) was deposited on adjacent uplands. The youngest sediment includes evidence of heightened activity of the Superior Lobe at about 29,000 ¹⁴C yr B.P., the Lake Michigan and Green Bay lobes from about 25,000 to 24,000 ¹⁴C yr B.P., and the Wadena-Des Moines-James lobes at about 21,000 ¹⁴C yr B.P.     

Osmium isotope systematics of ureilites

The ¹⁸⁷Os/¹⁸⁸Os for 22 ureilite whole rock samples, including monomict, augite-bearing, and polymict lithologies, were examined in order to constrain the provenance and subsequent magmatic processing of the ureilite parent body (or bodies). The Re/Os ratios of most ureilites show evidence for a recent disturbance, probably related to Re mobility during weathering, and no meaningful chronological information can be extracted from the present data set. The ureilite ¹⁸⁷Os/¹⁸⁸Os ratios span a range from 0.11739 to 0.13018, with an average of 0.1258 ± 0.0023 (1σ), similar to typical carbonaceous chondrites, and distinct from ordinary or enstatite chondrites. The similar mean of ¹⁸⁷Os/¹⁸⁸Os measured for the ureilites and carbonaceous chondrites suggests that the ureilite parent body probably formed within the same region of the solar nebula as carbonaceous chondrites. From the narrow range of the ¹⁸⁷Os/¹⁸⁸Os distribution in ureilite meteorites it is further concluded that Re was not significantly fractionated from Os during planetary differentiation and was not lost along with the missing ureilitic melt component. The lack of large Re/Os fractionations requires that Re/Os partitioning was controlled by a metal phase, and thus metal had to be stable throughout the interval of magmatic processing on the ureilite parent body.     

Re-Os isotopic systematics and platinum group element composition of the Tagish Lake carbonaceous chondrite

The Tagish Lake meteorite is a primitive C2 chondrite that has undergone aqueous alteration shortly after formation of its parent body. Previous work indicates that if this type of material was part of a late veneer during terrestrial planetary accretion, it could provide a link between atmophile elements such as H, C, N and noble gases, and highly siderophile element replenishment in the bulk silicate portions of terrestrial planets following core formation. The systematic Re-Os isotope and highly siderophile element measurements performed here on five separate fractions indicate that while Tagish Lake has amongst the highest Ru/Ir (1.63 ± 0.08), Pd/Ir (1.19 ± 0.06) and ¹⁸⁷Os/¹⁸⁸Os (0.12564-0.12802) of all carbonaceous chondrites, these characteristics still fall short of those necessary to explain the observed siderophile element systematics of the primitive upper mantles of Earth and Mars. Hence, a direct link between atmophile and highly siderophile elements remains elusive, and other sources for replenishment are required, unless an as yet poorly constrained process fractionated Re/Os, Ru/Ir, and Pd/Ir following late accretion on both the Earth and Mars mantles.The unique elevated Ru/Ir combined with elevated ¹⁸⁷Os/¹⁸⁸Os of Tagish Lake may be attributed to Ru and Re mobility during aqueous alteration very early in its parent body history. The Os, Ir, Pt, and Pd abundances of Tagish Lake are similar to CI chondrites. The elevated Ru/Ir and the higher Re/Os and consequent ¹⁸⁷Os/¹⁸⁸Os in Tagish Lake, are balanced by a lower Ru/Ir and lower Re/Os and ¹⁸⁷Os/¹⁸⁸Os in CM-chondrites, relative to CI chondrites. A model that links Tagish Lake with CI and CM chondrites in the same parent body may explain the observed systematics. In this scenario, CM chondrite material comprises the exterior, grading downward to Tagish Lake material, which grades to CI material in the interior of the parent body. Aqueous alteration intensifies towards the interior with increasing temperature. Ruthenium and Re are mobilized from the CM layer into the Tagish Lake layer. This model may thus provide a potential direct parent body relationship between three separate groups of carbonaceous chondrites.     

U-Th zonation-dependent alpha-ejection in (U-Th)/He chronometry

Both theoretical and empirical evidence shows that intracrystalline U-Th heterogeneity in zircon can lead to biases in (U-Th)/He ages if not accurately accounted for in α-ejection corrections. We present a model for age correction for U-Th zoned crystals. We apply this to spherical and prismatic grains with bipyramidal terminations. The spherical calculation is simplistic but allows rapid calculation of the approximate effects of a wide variety of U-Th zoning patterns. The bipyramidal calculation is computationally intensive but permits an more complete estimate of the combined effects of crystal morphology and source zoning as relevant to zircon. Our principle findings are: (1) the assumption of U-Th homogeneity can result in errors of up to ∼30% (in rare cases, higher) for ejection-corrected ages for typical grain sizes and realistic zonation. (2) Tetragonal prisms with bipyramidal terminations, which are typical of most zircons, exhibit bulk retentivities that can differ by several percent from models considering crystals with pinacoidal terminations. When extreme cases, such as dipyramids, are considered, the bias can exceed 10% or more. (3) Morphologic effects can be accounted for to better than 1% precision by using new second-order polynomial parameters that describe retentivity as a function of surface-area-to-volume ratio calculated through more complete analysis of crystal dimensions including the height of pyramidal crystal sections. We illustrate application of our model using U-Th concentration profiles determined from single zircons by laser ablation ICP-MS from zoned Tardree Rhyolite zircons.     

Geo-ontology Tools: The Missing Link

Numerous authors have presented ontology building tools that have all been developed as part of academic projects and that are usually adaptations of more generic tools for geo-spatial applications. While we trust that these tools do their job for the special purpose they have been built, the GIScience user community is still a long way away from off-the-shelf ontology builders that can be used by GIS project managers. In this article, we present a comparative study of ontology building tools described in some twenty peer-reviewed GIScience journal articles. We analyze them from the perspective of two application domains, crime analysis and transportation/land use. For the latter, we developed a database schema, which is substantially different from the three main templates commonly used. The crime analysis application uses a rule base for an agent-based model that had no precursor. In both cases, the currently available set of tools cannot replace manual coding of ontologies for use with ESRI-based application software. Based on these experiences, we outline a requirements list of what the tools described in the first part of the article are missing to make them practical from an applications perspective. The result is an R&D agenda for this important aspect of GIScience.     

Evaluating crustal contamination in continental basalts: the isotopic composition of the Picture Gorge Basalt of the Columbia River Basalt Group

Crustal contamination of basalts located in the western United States has been generally under-emphasized, and much of their isotopic variation has been ascribed to multiple and heterogeneous mantle sources. Basalts of the Miocene Columbia River Basalt Group in the Pacific Northwest have passed through crust ranging from Precambrian to Tertiary in age. These flows are voluminous, homogenous, and underwent rapid effusion, all of which are disadvantages for crustal contamination while en route to the surface. The Picture Gorge Basalt of the Columbia River Basalt Group erupted through Paleozoic and Mesozoic oceanic accreted terranes in central Oregon, and earlier studies on these basalts provided no isotopic evidence for crustal contamination. New Sr, Nd, Pb, and O isotopic data presented here indicate that the isotopic variation of the Picture Gorge Basalt is very small, ⁸⁷Sr/⁸⁶Sr=0.70307–0.70371, _Nd=+7.7-+4.8, ¹⁸O=+5.6±6.1, and ²⁰⁶Pb/²⁰⁴Pb=18.80–18.91. Evaluation of the Picture Gorge compositional variation supports a model where two isotopic components contributed to Picture Gorge Basalt genesis. The first component (C1) is reflected by low ⁸⁷Sr/⁸⁶Sr, high _Nd, and nonradiogenic Pb isotopic compositions. Basalts with C1 isotopic compositions have large MgO, Ni, and Cr contents and mantle-like ¹⁸O=+5.6. C1 basalts have enrichments in Ba coupled with depletions in Nb and Ta. These characteristics are best explained by derivation from a depleted mantle source which has undergone a recent enrichment by fluids coming from a subducted slab. This C1 mantle component is prevalent throughout the Pacific Northwest. The second isotopic component has higher ⁸⁷Sr/ ⁸⁶Sr and ¹⁸O, lower _Nd, and more radiogenic Pb isotopic compositions than C1. There is a correlation in the Picture Gorge data of Sr, Nd, and Pb isotopes with differentiation indicators such as decreasing Mg#, and increasing K₂O/TiO₂, Ba, Ba/Zr, Rb/Sr, La/Sm, and La/Yb. Phase equilibrium and mineralogical constraints indicate that these compositional characteristics were inherited in the Picture Gorge magmas at crustal pressures, and thus the second isotopic component is most likely crustal in origin. Mixing and open-system calculations can produce the isotopic composition of the most evolved Picture Gorge flows from the most primitive compositions by 8 to 21% contamination of isotopic compositions similar to accreted terrane crust found in the Pacific Northwest. Therefore, in spite of the disadvantages for crustal contamination and their narrow range in isotopic compositions, the process controlling isotopic variation within the Picture Gorge Basalt is primarily crustal contamination. We suggest that comprehensive analyses for basaltic suites and careful consideration of these data must be made to test for crustal contamination, before variation resulting from mantle heterogeneity can be assessed.Deceased