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101.
Yvonne-Marie Hermanns Antonio Martinez Cortizas Helge Arz Rüdiger Stein Harald Biester 《Journal of Paleolimnology》2013,49(4):563-573
There is ongoing debate about the relative influence of aquatic production, flux, and sedimentation of aquatic and terrestrial organic matter on mercury accumulation in lake sediments. In this study, lake sediments spanning the past 4,250 years, were collected from remote, organic-rich Lake Hambre, Patagonia (53° S) and investigated for changes in the accumulation of pre-anthropogenic mercury and organic matter of aquatic and terrestrial origin. Natural mercury accumulation varied by up to a factor of four, comparable to the recent anthropogenic forcing of the mercury cycle (factor 3–5). Hydrogen and Oxygen indices (HI and OI, Rock–Eval©) and nitrogen/carbon ratios of the organic matter, combined with multi-element sediment data, reveal intense changes in aquatic productivity as well as influx of terrestrial organic matter into the lake. Evaluation of the multi-element dataset using Principal Component Analysis shows clear covariation of mercury with other soil-derived elements such as copper and yttrium. This covariance reflects a common transport mechanism, i.e. leaching of trace-element-bearing organic matter complexes from catchment soils. Correlation between changes in aquatic productivity and mercury concentrations occurs in some sections of the record, but we do not suggest they are linked by a direct causal relationship. Mass balance approaches suggest that mercury scavenging and accumulation in this organic-rich lake is controlled by the supply of mercury from catchment soils rather than the amount of organic material produced within the water column. A common controlling mechanism, i.e. changing climate, however, is thought to independently drive variations in both the flux of terrestrial organic matter mercury complexes and aquatic productivity. 相似文献
102.
George Xian Collin Homer Brett Bunde Patrick Danielson Jon Dewitz Joyce Fry 《国际地球制图》2013,28(6):479-497
We estimated urbanization rates (2001–2006) in the Gulf of Mexico region using the National Land Cover Database (NLCD) 2001 and 2006 impervious surface products. An improved method was used to update the NLCD impervious surface product in 2006 and associated land cover transition between 2001 and 2006. Our estimation reveals that impervious surface increased 416 km2 with a growth rate of 5.8% between 2001 and 2006. Approximately 1110.1 km2 of non-urban lands were converted into urban land, resulting in a 3.2% increase in the region. Hay/pasture, woody wetland, and evergreen forest represented the three most common land cover classes that transitioned to urban. Among these land cover transitions, more than 50% of the urbanization occurred within 50 km of the coast. Our analysis shows that the close-to-coast land cover transition trend, especially within 10 km off the coast, potentially imposes substantial long-term impacts on regional landscape and ecological conditions. 相似文献
103.
Understanding the interactions of climate, physical erosion, chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems. Interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change. The primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern Arizona. The research was conducted along the steep environmental gradient encompassed by the Santa Catalina Mountains Critical Zone Observatory (SCM-CZO). The gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature (>10 °C) and precipitation (>50 cm a?1), with concomitant shift in vegetation communities from desert scrub to mixed conifer forest. Regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate-landscape position interactions control regolith development. Regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi-quantitative X-ray diffraction (XRD) analyses of bulk soils and specific particle size classes. Depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation, but varied inconsistently for convergent positions. The relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient. Quartz/Plagioclase (Q/P) ratios were used as a general proxy for bulk regolith chemical denudation. Q/P was generally higher in divergent landscape positions compared to the adjacent convergent hollows. Convergent landscape positions appear to be collecting solute-rich soil–waters from divergent positions thereby inhibiting chemical denudation. Clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites. The increased depth to paralithic contact, chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity. Landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface. The combined data from this research demonstrates a strong interactive control of climate, landscape position and erosion on the development of soil and regolith. 相似文献
104.
We present a synoptic overview of the Miocene-present development of the northern Alpine foreland basin (Molasse Basin), with
special attention to the pattern of surface erosion and sediment discharge in the Alps. Erosion of the Molasse Basin started
at the same time that the rivers originating in the Central Alps were deflected toward the Bresse Graben, which formed part
of the European Cenozoic rift system. This change in the drainage direction decreased the distance to the marine base level
by approximately 1,000 km, which in turn decreased the average topographic elevation in the Molasse Basin by at least 200 m.
Isostatic adjustment to erosional unloading required ca. 1,000 m of erosion to account for this inferred topographic lowering.
A further inference is that the resulting increase in the sediment discharge at the Miocene–Pliocene boundary reflects the
recycling of Molasse units. We consider that erosion of the Molasse Basin occurred in response to a shift in the drainage
direction rather than because of a change in paleoclimate. Climate left an imprint on the Alpine landscape, but presumably
not before the beginning of glaciation at the Pliocene–Pleistocene boundary. Similar to the northern Alpine foreland, we do
not see a strong climatic fingerprint on the pattern or rates of exhumation of the External Massifs. In particular, the initiation
and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the
convergence of Adria and Europe, irrespective of erosion rates. However, the recycling of the Molasse deposits since 5 Ma
and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the Molasse Basin
in order to restore a critical wedge. In conclusion, we see the need for a more careful consideration of both tectonic and
climatic forcing on the development of the Alps and the adjacent Molasse Basin. 相似文献
105.
106.
A generalized transformation approach for simulating steady-state variably-saturated subsurface flow
A numerical method is proposed to accurately and efficiently compute a direct steady-state solution of the nonlinear Richards equation. In the proposed method, the Kirchhoff integral transformation and a complementary transformation are applied to the governing equation in order to separate the nonlinear hyperbolic characteristic from the linear parabolic part. The separation allows the transformed governing equation to be applied to partially- to fully-saturated systems with arbitrary constitutive relations between primary (pressure head) and secondary variables (relative permeability). The transformed governing equation is then discretized with control volume finite difference/finite element approximations, followed by inverse transformation. The approach is compared to analytical and other numerical approaches for variably-saturated flow in 1-D and 3-D domains. The results clearly demonstrate that the approach is not only more computationally efficient but also more accurate than traditional numerical solutions. The approach is also applied to an example flow problem involving a regional-scale variably-saturated heterogeneous system, where the vadose zone is up to 1 km thick. The performance, stability, and effectiveness of the transform approach is exemplified for this complex heterogeneous example, which is typical of many problems encountered in the field. It is shown that computational performance can be enhanced by several orders of magnitude with the described integral transformation approach. 相似文献
107.
Jon Loveday 《Monthly notices of the Royal Astronomical Society》2000,312(3):557-566
We present a measurement of the K -band luminosity function (LF) of field galaxies obtained from near-infrared imaging of a sample of 345 galaxies selected from the Stromlo-APM Redshift Survey. The LF is reasonably well fitted over the 10-mag range −26 M K −16 by a Schechter function with parameters α =−1.16±0.19, M *=−23.58±0.42 and φ *=0.012±0.008 Mpc−3 , assuming a Hubble constant of H 0 =100 km s−1 Mpc−1 . We have also estimated the LF for two subsets of galaxies subdivided by the equivalent width of the H α emission line at EW(H α )=10 Å. There is no significant difference in LF shape between the two samples, although there is a hint (∼1 σ significance) that emission-line galaxies (ELGs) have M * roughly 1 mag fainter than non-ELGs. Contrary to the optical LF, there is no difference in faint-end slope α between the two samples. 相似文献
108.
Benjamin Felzer Starley Thompson David Pollard Jon Bergengren 《Journal of Paleolimnology》2000,24(1):15-28
The Paleoclimates from Arctic Lakes and Estuaries (PALE) project has chosen to conduct high resolution data-model comparisons for the Arctic region at 21 and 10 (calendar) ka BP. The model simulations for 21, 10, and 0 ka BP were conducted with the GENESIS 2.0 GCM. The 10 ka BP simulation was coupled to the EVE vegetation model. The primary boundary conditions differing from present at 21 ka BP were the northern hemisphere ice sheets and lower CO2, and at 10 ka BP were the orbital insolation and smaller northern hemisphere ice sheets. The purpose of this article is to discuss the hydrological consequences of these simulations.At the Last Glacial Maximum (21 ka BP) the large ice sheets over North America and Eurasia and the lower CO2 levels produced a colder climate than present, with less precipitation throughout the Arctic, except where circulation was altered by the ice sheets. At 10 ka BP greater summer insolation resulted in a warmer and wetter Beringia, but conditions remained cold and dry in the north Atlantic sector, in the vicinity of the remnant ice sheets. Less winter insolation at 10 ka BP resulted in colder and drier conditions throughout the Arctic. Precipitation - evaporation generally correlated with precipitation except where changes in the surface type (ice sheets, vegetation at 10 ka BP, or sea level at 21 ka BP) caused large changes in the evaporation rate. The primary hydrological differences (from present) at 21 and 10 ka BP correlated with the temperature differences, which were a direct result of the large-scale boundary condition changes. 相似文献
109.
Heather Katherine Handley Colin G. Macpherson Jon P. Davidson 《Contributions to Mineralogy and Petrology》2010,159(6):885-908
The Gede Volcanic Complex (GVC) of the Sunda island arc (West Java, Indonesia) consists of multiple volcanic centres and eruptive
groups with complex magmatic histories. We present new petrological, mineralogical, whole-rock major and trace element and
Sr–O isotopic data to provide constraints on the relative importance of fractional crystallisation and magma mixing in petrogenesis,
as well as on the role and nature of the arc crust. Banded juvenile scoria from Young and Old Gede provide unequivocal evidence
for the (late-stage) interaction of distinct magmas at Gede volcano. However, the relatively small-degree compositional zoning
observed in plagioclase phenocrysts of all eruptive groups (up to ~20 mol% An) may be attributed to physical changes in magma
properties (e.g. P, T, and PH2O) rather than changes in melt composition. Major element and trace element variations within each eruptive series are inconsistent
with magmatic evolution through simple mixing processes. Instead, mixing of variably fractionated magma batches is suggested
to account for the significant scatter in some element variation diagrams. No correlation is observed between textural complexity
and/or mineral disequilibrium and whole-rock geochemistry. REE data and geochemical modelling indicate that fractional crystallisation
involving amphibole in the mid- to lower crust, and fractionation of plagioclase, clinopyroxene, Fe–Ti oxide ± olivine ± orthopyroxene
provide strong control on the geochemical evolution of GVC rocks. Two-pyroxene geothermobarometry provides pre-eruption crystallisation
temperatures of 891–1,046°C and pressures of 3.4–6.5 kbar, equivalent to ~13–24 km depth beneath the volcanoes (mid- to lower
crust). Low, mantle-like clinopyroxene δ18O values of GVC lavas and poor correlation of Sr isotope ratios with indices of differentiation precludes significant assimilation
of isotopically distinct crust during magmatic differentiation. Therefore, we suggest that the geochemical character of the
moderately thick West Javan arc crust is relatively immature compared to typical continental crust. Trace element ratios and
strontium isotopes show that the magmatic source composition of the older geographical units, Gegerbentang and Older Quaternary,
is distinct from the other GVC groups. 相似文献
110.
Finn Løvholt Sylfest Glimsdal Carl B. Harbitz Natalia Zamora Farrokh Nadim Pascal Peduzzi Hy Dao Helge Smebye 《Earth》2012,110(1-4):58-73
In the aftermath of the 2004 Indian Ocean tsunami, a large increase in the activity of tsunami hazard and risk mapping is observed. Most of these are site-specific studies with detailed modelling of the run-up locally. However, fewer studies exist on the regional and global scale. Therefore, tsunamis have been omitted in previous global studies comparing different natural hazards. Here, we present a first global tsunami hazard and population exposure study. A key topic is the development of a simple and robust method for obtaining reasonable estimates of the maximum water level during tsunami inundation. This method is mainly based on plane wave linear hydrostatic transect simulations, and validation against results from a standard run-up model is given. The global hazard study is scenario based, focusing on tsunamis caused by megathrust earthquakes only, as the largest events will often contribute more to the risk than the smaller events. Tsunamis caused by non-seismic sources are omitted. Hazard maps are implemented by conducting a number of tsunami scenario simulations supplemented with findings from literature. The maps are further used to quantify the number of people exposed to tsunamis using the Landscan population data set. Because of the large geographical extents, quantifying the tsunami hazard assessment is focusing on overall trends. 相似文献