The hierarchical tessellation model and its use in spatial analysis

The hierarchid tessellation model belongs to a class of spatial data models based on the recursive decomposition of space. The quadtree is one such tessellation and is characterized by square cells and a 1:4 decomposition ratio. To relax these constraints in the tessellation, a generalized hierarchical tessellation data model, called Adaptive Recursive Tessellations (ART), has been proposed. ART increases flexibility in the tessellation by the use of rectangular cells and variable decomposition ratios. In ART, users can specify cell sizes which are intuitively meaningful to their applications, or which can reflect the scales of data. ART is implemented in a data structure called Adaptive Recursive Run-Encoding (ARRE), which is a variant of two-dimensional run-encoding whose running path can vary with the different tessellation structures incorporated in an ART model. Given the recognition of the benefits of implementing statistical spatial analysis in GIS, the use of hierarchical tessellation models such as ART in spatial analysis is discussed. Three examples are introduced to show how ART can: (1) be applied to solve the quadrat size problem in quadrat analysis of point patterns; (2) act as the data model in the variable resolution block kriging technique for geostatistical data to reduce variation in kriging error; and (3) facilitate the evaluation of spatial autocorrelation for area data at multiple map resolutions via the construction of a connectivity matrix for calculating spatial autocorrelation indices based on ARRE.     

The dowsing rod: a most contentious instrument

'Since this matter remains in dispute and causes much dissention amongst miners, I consider it ought to be examined on its own merits.'– Georgius Agricola .     

Oxidized Nitrogen in the Remote Pacific: The Role of Electrical Discharges over the Oceans

Simulations of oxidized nitrogen performed withglobal transport tracer models systematicallyunderestimate the concentrations of total nitrate atremote marine locations in the Mid-Pacific. Higheremission rates in the models of nitrogen oxides( ) from continental sources or alarger influx from the stratosphere do not seem tobe able to account for the shortfall. We are led toconclude that there has to be a substantial sourcelocated in oceanic areas. We speculate that -emission from electrical discharges overthe oceans could be the source we are looking for.Airborne observations of atmospheric concentrationsof oxidized nitrogen and ozone in the remoteatmosphere and observations of nitrate wetdeposition in remote sites are used as additionalconstraints to check the plausibility of thishypothesis. We find that a larger emission of due to lightning activity over the oceansindeed results in a much improved simulation oftotal nitrate in the remote Pacific, particularly inthe Equatorial and Tropical South Pacific and thatsuch a scenario is generally consistent withavailable observations of nitrate wet deposition andatmospheric concentrations of oxidized nitrogen andozone. An alternative hypothesis is that there is ahitherto unknown in situ source of over thePacific Ocean.     

英国钙华苔藓植物区系特征及其主要钙华沉积类型

根据1998— 2000年作者采自英国39个钙华沉积区1245份的野外苔藓植物标本研究, 英国钙华苔藓植物区系具有下列特征:(1)区系种类由19科34属50种(含变种亚种)组成, 其中含英国钙华苔藓新记录26种;(2)区系生活型含高丛集型(10 %)、矮丛集型(32%)、交织型(44 %)、扇型(2 %)和平埔型(12 %)5 种类型;(3)区系地理成分含北温带分布(46 %)、温带欧洲分布(6 %)、欧洲-非洲分布(2 %)、欧洲-北美分布(10 %)、旧世界温带分布(4%)和世界广泛分布(34%)等6种成。根据钙华生长的环境特征, 英国苔藓植物钙华可划分为泉华、瀑华、溪流钙华和洞穴弱光带钙华4 种基本类型及12 种小类型。      

Collating Historic Weather Observations for the East Asian Region:Challenges,Solutions,and Reanalyses

正1.Introduction Historic instrumental weather observations,made on land or at sea from as early as the 17th century(e.g.,Camuffo et al.,2010),are integral to extending our understanding of the decadal and centennial variations of Earth’s climate and for comparison with paleo-proxy data.The potential of such data is shown to best effect when used in dynamical 4D global     

The Geology of the Great Dyke, Zimbabwe: Crystallization, Layering, and Cumulate Formation in the P1 Pyroxenite of Cyclic Unit 1 of the Darwendale Subchamber

The P1 layer of the Great Dyke is an 200 m thick pyroxenitesuccession in Cyclic Unit 1 and, as the topmost lithology ofthe Ultramafic Sequence, represents the transition from ultramaficto mafic rocks. Of critical importance to this part of the stratigraphyis the strong lateral environmental change from axis to marginas a result of the flared structure of the Great Dyke. Duringthe formation of the P1 layer the axial zone was underlain bya great thickness of hot ultramafic cumulates whereas the samelayer in the marginal zone progressively offiaps the lower ultramaficlayers and is in close proximity to the underlying wall/floorrocks. Heat loss through the floor was therefore much greaterin the marginal zone than in the axis. Major lateral variations are observed, with all lithologicalunits and layers thinning towards the margins of the subchambertogether with a progressive change in the form of the cumulates.Discordant relationships towards the margin between layer types(modal, cryptic, and form) are a feature of the P1 unit whichhas also been recognized in other parts of the Great Dyke (Prendergast,1991). Pyroxene compositions show significant variations withinan overall fractionation trend and decoupling occurs betweenmajor and minor element components of bronzite, suggesting strongcompositional heterogeneity of the magma. This type of crypticlayering has not previously been described and is informallycalled ‘cryptorhythmic’ layering. Pyroxene compositional variation is related to reaction andmodification by trapped intercumulus liquid, and few mineralspreserve liquidus compositions. A similar situation must existfor most layered intrusions. The strong dependence of pyroxenecompositions on incompatible element content in the whole-rockshows that the original liquidus compositions were modifiedby postcumu-lus overgrowth and reaction with the trapped intercumulusliquid. Well-constrained data arrays indicate that most cumulatesin the P1 layer behaved as a closed system with little or nomigration of intercumulus liquid. Liquidus compositions cantherefore be deduced and the residual porosity and degree ofpostcumulus formation were modelled using a computer program.Residual porosity is shown to be between 1 and 13% (by mass).Rocks in the marginal facies have a relatively large proportionof discrete postcumulus phases but instead of representing crystallizationof trapped liquid these are shown to be mainly heteradcumulusphases, i. e., interstitial minerals that have grown largelyby adcumulus processes in equilibrium with the main body ofmagma. The heteradcumulus component can be as high as 27%. Thesephases occur as oikocrysts which give rise to a well-developednodular pyroxenite (the ‘potato’ reef). The formationof the nodules caused local redistribution of primary sulphideliquid. The liquid layers which gave rise to cumulates in the marginalfacies are shown to be enriched in iron and incompatible elementscompared with the axial zone, indicating that the P1 pyroxenitelayer formed by crystallization of a magma which was eithercompositionally stratified or exhibited a strong lateral compositionalgradient.     

Paper II – Dirt,dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia,and their implications for sedimentary ancient DNA studies

Arnold, L. J., Roberts, R. G., MacPhee, R. D. E., Haile, J. S., Brock, F., Möller, P., Froese, D. G., Tikhonov, A. N., Chivas, A. R., Gilbert, M. T. P. & Willerslev, E. 2010: Paper II – Dirt, dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia, and their implications for sedimentary ancient DNA studies. Boreas, Vol. 40, pp. 417–445. 10.1111/j.1502‐3885.2010.00181.x. ISSN 0300‐9483 The sedimentary ancient DNA (sedaDNA) technique offers a potentially invaluable means of investigating species evolution and extinction dynamics in high‐latitude environments. An implicit assumption of the sedaDNA approach is that the extracted DNA is autochthonous with the host deposit and that it has not been physically transported from older source deposits or reworked within the sedimentary profile by postdepositional mixing. In this paper we investigate whether these fundamental conditions are upheld at seven perennially frozen wetland sites across the Taimyr Peninsula and coastal lowlands of north‐central Siberia. Optically stimulated luminescence (OSL) and radiocarbon (¹⁴C) dating are used to constrain the ages of both the inorganic and organic fractions of perennially frozen deposits from which sedaDNA of extinct and extant species have been recovered. OSL and ¹⁴C age/depth profiles, as well as single‐grain equivalent dose (D_e) distribution characteristics, are used to assess the stratigraphic integrity of these sedaDNA sequences by (i) identifying the presence of primary or reworked organic and inorganic material, and (ii) examining the types of depositional and postdepositional processes that have affected specific sedimentary facies. The results of this study demonstrate that even though DNA preservation and stratigraphic integrity are commonly superior in perennially frozen settings, this does not, in itself, guarantee the suitability of the sedaDNA approach. The combined OSL and ¹⁴C chronologies reveal that certain perennially frozen sites may be poorly suited for sedaDNA analysis, and that careful site selection is paramount to ensuring the accuracy of any sedaDNA study – particularly for ‘latest appearance date’ estimates of extinct taxa.     

Isotope signatures associated with early meteoric diagenesis

The environments in which carbonate diagenesis proceeds have been documented in previous studies of Holocene and late Pleistocene sediments and limestones on Barbados, West Indies. Variations in the carbon and oxygen isotopic composition of limestones, produced during early freshwater diagenesis, have been observed in this study to occur in specific patterns. Six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework: (1) the subaerial exposure surface is characterized by strongly ¹²C-enriched limestones. δ¹³C compositions of underlying limestones grow progressively heavier with increasing depth; (2) the subaerial exposure surface may also be marked by slight ¹⁸O-enrichment; (3) an abrupt shift in δ¹⁸O values may differentiate sediments above the exposure surface from those below; (4) sediments altered in the marine-meteoric mixing zone may be characterized by positive covariance between their δ¹⁸O and δ¹³C compositions; (5) the vadose-phreatic boundary may be marked by a sharp increase in δ¹³C values in the seaward portions of a fresh groundwater system; and (6) samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of δ¹⁸O and a wide range of δ¹³C compositions. Analysis of samples from five Palaeozoic and Mesozoic formations, which contained petrographic evidence of early freshwater diagenesis, showed that isotope patterns similar to those observed in Barbados limestones have been preserved in rocks as old as Mississippian. These isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks. They might be used to identify limestones diagenetically altered in meteoric environments, to identify mixing zone cements and dolomites, and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations.     

Measurements of Air Concentrations of SO2, NO2 and NH3 at Rural and Remote Sites in Asia

Sensitive diffusive samplers for concentration measurements in ambient airhave been used successfully in Sweden for several years. The samplers have theadvantage of being stable at room temperature before, as well as after,sampling, easy to handle, and cost-efficient. Furthermore, they do not requireelectricity or field calibration. In order to test their use in tropical andsubtropical environments and to obtain a preliminary set of data to validateatmospheric chemistry transport models in this part of the world, duplicatesamples were collected at 11 sites every second month during one year. Eightof the sites were background sites in Asia. It was not possible within theproject to compare the measured concentrations with other measurementtechniques. However, the reproducibility of the duplicates was satisfactoryover the whole measuring range (almost three orders of magnitude of theconcentration for SO₂) and reasonable agreement with modelcalculations was obtained at least for SO₂ andNH₃. Further testing of the measuring technique in tropicalareas is, however, warranted.