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31.
Abigail L. Langston Gregory E. Tucker Robert S. Anderson Suzanne P. Anderson 《Applied Geochemistry》2011
Understanding the relationship between subsurface flow paths on hillslopes and chemical weathering of bedrock is fundamental to understanding the timing and mechanisms that weather bedrock to saprolite. The link between chemical weathering of bedrock and contact time with reactive water along flow paths motivates this study. Water drives the chemical alteration of rock into saprolite, yet connected porosity generally declines with depth into the weathered profile. Saprolite formation, therefore, reflects coupled weathering and permeability development over time. This study uses numerical modeling and soil-moisture monitoring to explore the hydrology of the unsaturated zone and the influence of fracture density, hillslope gradient, and permeability contrasts within the saprolite development horizon on saprolite development. 相似文献
32.
A.?K.?BarkerEmail author P.?M.?Holm V.?R.?Troll 《Contributions to Mineralogy and Petrology》2014,168(3):1052
The Cape Verde hotspot, like many other Ocean Island Basalt provinces, demonstrates isotopic heterogeneity on a 100–200 km scale. The heterogeneity is represented by the appearance of an EM1-like component at several of the southern islands and with a HIMU-like component present throughout the archipelago. Where the EM1-like component is absent, a local DMM-like component replaces the EM1-like component. Various source lithologies, including peridotite, pyroxenite and eclogite have been suggested to contribute to generation of these heterogeneities; however, attempts to quantify such contributions have been limited. We apply the minor elements in olivine approach (Sobolev et al. in Nature 434:590–597, 2005; Science, doi: 10.1126/science.1138113, 2007), to determine and quantify the contributions of peridotite, pyroxenite and eclogite melts to the mantle heterogeneity observed at Cape Verde. Cores of olivine phenocrysts of the Cape Verde volcanics have low Mn/FeO and low Ni*FeO/MgO that deviate from the negative trend of the global array. The global array is defined by mixing between peridotite and pyroxenite, whereas the Cape Verde volcanics indicate contribution of an additional eclogite source. Eclogite melts escape reaction with peridotite either by efficient extraction in an area of poor mantle flow or by reaction of eclogite melts with peridotite, whereby an abundance of eclogite can seal off the melt from further reaction. Temporal trends of decreasing Mn/FeO indicate that the supply of eclogite melts is increasing. Modelling suggests the local DMM-like end-member is formed from a relatively peridotite-rich melt, while the EM1-like end-member has a closer affinity to a mixed peridotite–pyroxenite–eclogite melt. Notably the HIMU-like component ranges from pyroxenite–peridotite-rich melt to one with up to 77 % eclogite melt as a function of time, implying that sealing of melt pathways is becoming more effective. 相似文献
33.
Dorothy Z. Oehler Franois Robert Malcolm R. Walter Kenichiro Sugitani Abigail Allwood Anders Meibom Smail Mostefaoui Madeleine Selo Aurlien Thomen Everett K. Gibson 《Precambrian Research》2009,173(1-4):70
NanoSIMS is a relatively new technology that is being applied to ancient carbonaceous structures to gain insight into their biogenicity and syngeneity. NanoSIMS studies of well preserved organic microfossils from the Neoproterozoic (0.8 Ga) Bitter Springs Formation have established elemental distributions in undisputedly biogenic structures. Results demonstrate that sub-micron scale maps of metabolically important elements (carbon [C], nitrogen [measured as CN ion], and sulfur [S]) can be correlated with kerogenous structures identified by optical microscopy. Spatial distributions of C, CN, and S in individual microfossils are nearly identical, and variations in concentrations of these elements parallel one another. In elemental maps, C, CN, and S appear as globules, aligned to form remnant walls or sheaths of fossiliferous structures. The aligned character and parallel variation of C and CN are the strongest indicators of biogenicity.Nitrogen/carbon atomic ratios (N/C) of spheroids, filaments, and remnants of a microbial mat suggest that N/C may reflect original biochemical differences, within samples of the same age and degree of alteration. Silicon (Si) and oxygen (O) maps illustrate that silica is intimately interspersed with organic carbon of the microfossils. This relationship is likely to reflect the process of silica permineralization of biological remains and thus may be an indicator of syngeneity of the fossilized material with the mineral matrix.The NanoSIMS characterization of Bitter Springs microfossils can be used as a baseline for interpreting less well preserved carbonaceous structures that might occur in older or even extraterrestrial materials. An example of such an application is provided by comparison of Bitter Springs results with NanoSIMS of Archaean carbonaceous structures from Western Australia, including a spheroid in the 3 Ga Farrel Quartzite and material in a secondary vein in the 3.43 Ga Strelley Pool Chert. Results reinforce a biogenic, syngenetic interpretation for the Archaean spheroid.NanoSIMS has several advantages in the study of ancient organic materials: the technique allows characterization of extremely small structures that are present in low concentrations; organic matter does not have to be isolated by acid treatment but can be analyzed in polished thin section; preparation is simple; samples are minimally altered during analysis; results provide sub-micron scale spatial distribution coupled with concentration information for at least five elements; the biologically important elements of carbon and nitrogen can be assessed; and the ability to study organic remains in situ permits petrographic assessment of spatial relationships between organic matter and mineral constituents. These advantages could be of significant benefit for interpretation of poorly preserved and fragmentary carbonaceous remains that might occur in some of Earth's oldest samples as well as in meteorites or extraterrestrial material brought to Earth in future planetary missions. 相似文献
34.
Abigail K. Barker Paul M. Holm David W. Peate Joel A. Baker 《Contributions to Mineralogy and Petrology》2010,160(1):133-154
High-precision Pb isotope data and Sr–Nd–Hf isotope data are presented together with major and trace element data for samples spanning the 4.6 Ma history of volcanism at Santiago, in the southern Cape Verde islands. Pb isotope data confirm the positive Δ8/4 signature of the southern islands indicating that the north–south compositional heterogeneity in the Cape Verde archipelago has persisted for at least 4.6 Ma. The Santiago volcanics show distinct compositional differences between the old, intermediate and young volcanics, and suggest greater involvement of an enriched mantle (EM1)-like source over time. Isotopic variations in the Santiago volcanics indicate convergence towards a homogeneous EM1-like end-member and distinct temporal variations in the FOZO-like end-member. Santiago and Santo Antão (a northern island, Holm et al. 2006), show a simultaneous decrease in 208Pb/204Pb of the high 206Pb/204Pb FOZO-like source with time. Such systematic archipelago-wide variations in the FOZO-like component suggest that this component is more likely to be present as a coherent package of recycled ocean crust rather than as multiple small heterogeneities dispersed in the upwelling mantle. The temporal variations in 208Pb/204Pb reflect minor lateral variations in Th/U of this recycled ocean crust package entering the melting zone beneath the islands. The location of the EM1-like component is more equivocal. A shallow lithospheric location is possible, but this would require a coincidence between spatial compositional variations in the lithosphere (EM1 is spatially restricted to the southern islands) and flow lines in the upwelling mantle revealed by seismic anisotropy. Therefore, we favour a deeper asthenospheric mantle source for the EM1-like source. 相似文献
35.
Land fragmentation due to rapid urbanization in the Phoenix Metropolitan Area: Analyzing the spatiotemporal patterns and drivers 总被引：4，自引：0，他引：4
Milan K. Shrestha Abigail M. YorkChristopher G. Boone Sainan Zhang 《Applied geography (Sevenoaks, England)》2012,32(2):522-531
Rapid urbanization of the Phoenix Metropolitan Area exemplifies the dominant US Southwest urban growth pattern of the past six decades. Using a combination of multitemporal land cover data, gradient analysis, and landscape metrics, we quantify and characterize spatiotemporal patterns of land fragmentation observed in Phoenix. We analyze historical, qualitative data to identify five major socio-ecological drivers critical to understanding the urbanization processes and fragmentation patterns: population dynamics, water provisioning, technology and transportation, institutional factors, and topography. A second objective is to assess the applicability and accuracy of National Land cover Database (NLCD)-—a widely used land cover dataset—-to detect and measure urban growth and land fragmentation patterns in the relatively treeless desert biome of the US Southwest. In contrast to studies in the temperate eastern USA where NLCD has proved inaccurate for detection of exurban development, our study demonstrates that NLCD is a reliable data source for measuring land use in the southwest, even in low-density environments. By combining qualitative analyses of social-ecological drivers with fragmentation analyses, we move toward an improved understanding of urbanization and insights on the human modification framework used widely in land change science. 相似文献
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37.
Quantifying the reefscape transformation of a coastal Caribbean coral reef during a phase shift and the associated coastal landscape change 
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下载免费PDF全文 Abigail Martínez‐ Rendis Gilberto Acosta González José Luis Hernández‐Stefanoni Jesús Ernesto Arias González 《Marine Ecology》2016,37(3):697-710
Caribbean coral reefs are under strong natural and human pressures and many have undergone phase shifts as a result of local and global change. However few studies have quantified the extent of these phase shifts and the potential impacts that they have on coral reef communities. A temporal comparative analysis of several coral reefscape and landscape metrics was conducted for data from Mahahual, Quintana Roo, Mexico, between the years 2000 and 2006, when a phase shift occurred. Landscape metrics were calculated from coral reef and coastal cover maps obtained by multispectral satellite image classification using IKONOS satellite imagery. These metrics showed that the coastal landscape and reefscape of Mahahual lost 85 ha of vegetation cover and 43 ha of coral cover over 6 years, respectively. Coastal landscape transformation was induced by the construction of a cruise ship pier and multiple associated tourist developments along the coast, such as hotels and restaurants, meanwhile alteration of the reefscape may be associated with potential stressors such as coastal development, bleaching events and hurricanes. 相似文献
38.
Nutrient budgets for European seas: a measure of the effectiveness of nutrient reduction policies 总被引：3，自引：0，他引：3
Artioli Y Friedrich J Gilbert AJ McQuatters-Gollop A Mee LD Vermaat JE Wulff F Humborg C Palmeri L Pollehne F 《Marine pollution bulletin》2008,56(9):1609-1617
Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic. 相似文献
39.
Population increases, land-use changes and marketing opportunities are important factors affecting crop-livestock integration
particularly with respect to their effect on soil fertility and feed supply for ruminant livestock. As the human population
density rises, crop farmers and grazers are finding it profitable to establish contracts for paddocking, and they are reaching
agreement on equitable ways to make use of crop residues and take care of livestocks. As the processes of intensification
proceed, mixed crop-livestock systems are evolving as the viable and dominant farming system, allowing smallholder farmers
to capitalize on the complementarity between crops and livestock. Strategies directed to raise the productivity of specific
crop-livestock systems need to consider the stage of development of the target area in relation to intensification and the
nature of crop-livestock interactions. Information related to crop and livestock systems in West Africa is currently available
from various sources e.g., household surveys, aerial surveys, rural appraisal, experimental etc., and held by different agencies.
The approach used in this study shows how such data (biophysical and socioeconomic) can be integrated within a GIS environment
and synthesized to identify the evolution of systems across environments and also to identify constraints and potential of
the systems. Potential for integrated crop-livestock systems remains untapped and/or knowledge of its existence is unknown
for large parts of Nigeria. Using data from 36 case studies and georeferenced data on cropping intensities and livestock population
for the entire country, it was possible to predict emerging crop-livestock systems using GIS. Indeed, depending on availability
of data, it is now possible to extend a similar approach in other African countries. The potential contribution of this technology
is largely unknown in West and Central Africa, where few operational programs use them. Major technological innovations and
appropriate government policies have potential to shift the balance in regional developments, if targeted carefully at areas
where the right conditions exist. Further research could then target specific areas thus ensuring efficient allocation of
resources while policy makers can achieve development goals by directing policies and resources to domains that have the greatest
potential.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
40.
The wreck of the Rainbow Warrior, a 40-m ship sunk on 12 December 1987 in Matauri Bay (34° 59′ S, 173° 56′ E), Cavalli Islands, northeastern New Zealand, offers an opportunity to investigate the impact of artificial substrate on temperate carbonate sedimentation. Surface sediment samples showed no significant textural or compositional difference between sediments near the wreck and those far from it. The large and diverse carbonate-producing community resident on the wreck (dominated by bryozoans, corals and sponges) has not had a measurable influence on adjacent bottom sediments (dominated by bivalves and barnacles), even after 21 years. It is likely that carbonate production on the Rainbow Warrior is insufficient to leave any sedimentary record over the potential lifetime of the wreck on the seafloor, which informs our understanding of the long-term impacts of shipwrecks (and other artificial substrata) on the local benthic environment in shallow temperate ecosystems. 相似文献