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121.
Alkane and PAH biomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments 总被引:2,自引:0,他引:2
Mark B. Yunker Robie W. Macdonald Lloyd R. Snowdon Brian R. Fowler 《Organic Geochemistry》2011,42(9):1109-1146
We present the first sedimentary biomarker study encompassing the entire Arctic Ocean. A large data set of organic markers for terrigenous, petroleum and combustion inputs [alkanes, hopanes and steranes, parent and alkyl polycyclic aromatic hydrocarbons (PAHs)] is examined for patterns in space and time using principal components analysis (PCA) and partial least squares (PLS). Biomarker patterns reveal the central Arctic Ocean basin sediments to be compositionally distinct from those of the Mackenzie River/Beaufort Sea and Barents Sea, but similar to those of the Laptev Sea. PAH distributions reflected in PAH ratios and PCA projections demonstrate that Arctic Ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion PAHs are not significant. We find only modest changes between the glacial and post-glacial sediments for atmospherically transported hydrocarbon biomarkers, while particle associated biomarkers were captured strongly at basin edges during the glacial period, and much more evenly transported across basins during the post-glacial period. The orders of magnitude decreases in particle associated petrogenic alkanes and PAHs in central basins during glacial times, coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations, reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the Pleistocene/Holocene central Arctic basins. The proximity of large coal deposits of various maturity levels along the Lena River, the overlap in PAH and biomarker composition of the Laptev Sea and surficial sediments from the central Arctic Ocean and the location of the Laptev Sea at the origin of the main Transpolar Drift all point to eroded coals from the Lena River/Laptev Sea as the likely source of petrogenic hydrocarbons to the central Arctic Ocean. The ubiquitous presence of allochthonous coal in Arctic Ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves. 相似文献
122.
Studies of entrainment across the top of the boundary layer rely to a great extent on identification of the boundary-layer
top, inversion properties, entrainment-zone depth, and the temporal changes in all of these. A variety of definitions and
techniques have been used to provide automated and objective estimates; however, direct comparisons between studies is made
difficult by the lack of consistency in techniques. Here we compare boundary-layer depth, entrainment-zone thickness, and
entrainment rate derived from several commonly used techniques applied to a common set of large-eddy simulations of the idealized,
dry, convective boundary layer. We focus in particular on those techniques applicable to lidar backscatter measurements of
boundary-layer structure. We find significant differences in all the quantities of interest, and further that the behaviour
as functions of common scaling parameters, such as convective Richardson number, also differ, sometimes dramatically. The
discretization of the possible values of some quantities imposed by the vertical grid is found to affect some of the results
even when changes to model resolution does not affect the entrainment rate or scaling behaviour. This is a particular problem
where entrainment parameters are derived from a single mean profile (e.g. the buoyancy-flux profile), but not where they are
derived from the statistical properties of large numbers of individual profiles (e.g. the probability distribution of the
local boundary-layer top at each model grid point). 相似文献
123.
The March 11, 2002 Masafi, United Arab Emirates earthquake: Insights into the seismotectonics of the northern Oman Mountains 总被引:2,自引:1,他引:1
Arthur Rodgers Abdel-Rahman Fowler Abdullah M.S. Al-Amri Abdullah Al-Enezi 《Tectonophysics》2006,415(1-4):57-64
A moderate (M 5) earthquake struck the northeastern United Arab Emirates (UAE) and northern Oman on March 11, 2002. The event was felt over a wide area of the northern Emirates and was accompanied by smaller (felt) events before and after the March 11 main shock. The event was large enough to be detected and located by global networks at teleseismic distances. We estimated focal mechanism and depth from broadband complete regional waveform modeling. We report a normal mechanism with a slight right-lateral strike-slip component consistent with the large-scale tectonics. The normal component suggests relaxation of obducted crust of the Semail ophiolite (specifically, the Khor Fakkan Block) while the right-lateral strike-slip component of the mechanism is consistent with shear across the Oman Line. Felt earthquakes are rare in the region, however no regional seismic network exists in the UAE to determine local seismicity. This event offers a unique opportunity to study the active tectonics of the region as well as inform future studies of seismic hazard in the UAE and northern Oman. 相似文献
124.
In this study we present rainfall results from equilibrium 1 ×– and 2 × CO2 experiments with the CSIRO 4-level general circulation model. The 1 × CO2 results are discussed in relation to observed climate. Discussion of the 2 × CO2 results focuses upon changes in convective and non-convective rainfall as simulated in the model, and the consequences these changes have for simulated daily rainfall intensity and the frequency of heavy rainfall events. In doing this analysis, we recognize the significant shortcomings of GCM simulations of precipitation processes. However, because of the potential significance of any changes in heavy rainfall events as a result of the enhanced greenhouse effect, we believe a first examination of relevant GCM rainfall results is warranted. Generally, the model results show a marked increase in rainfall originating from penetrative convection and, in the mid-latitudes, a decline in largescale (non-convective) rainfall. It is argued that these changes in rainfall type are a consequence of the increased moisture holding capacity of the warmer atmosphere simulated for 2 × CO2 conditions. Related to changes in rainfall type, rainfall intensity (rain per rain day) increases in the model for most regions of the globe. Increases extend even to regions where total rainfall decreases. Indeed, the greater intensity of daily rainfall is a much clearer response of the model to increased greenhouse gases than the changes in total rainfall. We also find a decrease in the number of rainy days in the middle latitudes of both the Northern and Southern Hemispheres. To further elucidate these results daily rainfall frequency distributions are examined globally and for four selected regions of interest. In all regions the frequency of high rainfall events increases, and the return period of such events decreases markedly. If realistic, the findings have potentially serious practical implications in terms of an increased frequency and severity of floods in most regions. However, we discuss various important sources of uncertainty in the results presented, and indicate the need for rainfall intensity results to be examined in enhanced greenhouse experiments with other GCMs. 相似文献
125.
Some 2088 lightning-caused forest fires that occurred between 1960 and 1971 in northern Idaho are described and analyzed relative to the properties of pattern, central tendency, and spatial variability. Pattern analysis reveals that randomness characterizes both the distribution of total fires and of annual mean areal centers. A model is proposed relating the latitudinal and longitudinal behavior of mean areal centers to shifts in storm tracks and resultant adjustments in fuel-moisture conditions. Rank correlation analysis reveals that northwest shifts in mean areal centers are associated with higher fuel-moisture conditions whereas southeast movements in mean areal centers are related to reduced fuel-moisture conditions. No significant differences were revealed in the variability of the annual standard distances of fire distribution, nor was there any association between temperature and azimuthal adjustments in mean areal centers. 相似文献
126.
Elevation, timber type, size and density of stand, position on slope, and slope aspect were assessed as to their effects upon the location of 2088 lightning-caused forest fires in a 1.4 million-hectare tract of northern Idaho. χ2 analysis revealed that relative fire frequency was greatest between 1050 and 1650 m on the upper 1/3 of those slopes which lie perpendicular to dominant storm tracks and which are covered with Hemlock, Alpine Fir and Spruce. 相似文献
127.
Phillip M. Fowler 《自然地理学》2013,34(1):88-95
Surficial spatial variation in air photo linears is evaluated as a mineral search methodology having potential in differentiating between ore-bearing and non-ore-bearing areas. Linear density, bearing, length, and pattern were compared in equal sized plots of mineralized and adjacent non-mineralized ground in each of 10 study areas. Variance and discriminant analysis indicate that the variables of density and pattern are useful in the prediction and classification of areas as either mineralized or non-mineralized. 相似文献
128.
Although future climate change will significantly affect New Zealand's climate, how regional climates will be changed remains highly uncertain. As a consequence, pre‐screening sensitivity analysis is recommended for climate‐sensitive activities. A ‘bottom‐up’ approach intended to serve this purpose in the context of non‐irrigated pasture is developed and demonstrated in the Hawke's Bay context. This is achieved using a simple daily water balance model to simulate near‐surface hydrological processes and empirical relationships between transpiration and pasture dry matter production. The Hawke's Bay case study indicates that the methodology has merit and is worthwhile pursuing nationally (with refinements). 相似文献
129.
Christopher S. Fowler 《Urban geography》2016,37(1):1-25
Neighborhoods and neighborhood change are often at least implicitly understood in relation to processes taking place at scales both smaller than and larger than the neighborhood itself. Until recently our capacity to represent these multiscalar processes with quantitative measures has been limited. Recent work on “segregation profiles” by Reardon and collaborators expands our capacity to explore the relationship between population measures and scale. With the methodological tools now available, we need a conceptual shift in how we view population measures in order to bring our theories and measures of neighborhoods into alignment. I argue that segregation can be beneficially viewed as multiscalar; not a value calculable at some “correct” scale, but a continuous function with respect to scale. This shift requires new ways of thinking about and analyzing segregation with respect to scale that engage with the complexity of the multiscalar measure. Using block-level data for eight neighborhoods in Seattle, Washington, I explore the implications of a multiscalar segregation measure for understanding neighborhoods and neighborhood change from 1990 to 2010. 相似文献
130.
A. C. Fowler 《地球物理与天体物理流体动力学》2013,107(2):99-140
Abstract We reconsider the problem of formulation of a model for polythermal glaciers, focussing attention in particular on the temperate zone where ice and water can coexist at the melting temperature. The energy equation for the ice-water mixture in this zone introduces a moisture flux, and a constitutive law for this flux is required. By analogy with the flow through a porous medium, we use Darcy's law (i.e. the second momentum equation of a two-phase flow model with “porous” geometry), and then require a mechanical constitutive relation relating the water pressure p w to the average ice pressure p i . Experience in two phase flows suggests that p w =p i may be problematical, and experience in soil mechanics suggests it is inaccurate. A constitutive relation is therefore presented based on work of Nye (1976), and its effect on the well-posedness of the model is examined. Considerations of the sort presented here have clear relevance in the formulation of similar problems in other geophysical situations, notably mantle convection. 相似文献