Ocean and coastal issues and policy responses in the Caribbean     

Nelson Andrade Colmenares  J. Jairo Escobar 《Ocean & Coastal Management》2002,45(11-12)

The Paper presents the regional perspective on the conditions and efforts for the integrated coastal management (ICM) that exist in the Wider Caribbean Region (WCR).The Caribbean Action Plan was adopted in 1981 with an initial workplan of activities of evaluation and control of marine pollution, evaluation of impacts on the coastal area, fishing studies, watershed management, evaluation of natural hazard effects, energy accounting systems studies, urbanisation of the coastal area, building capacity and training. The Convention for the Protection and Development of the Marine Environment of the WCR is the only regional legal framework for the protection and sustainable development of marine resources.The Paper describes some region-wide ICM-related programme initiated or supported by the CEP as well as actions at the national level. Other ICM-related general activities and training programmes of CEP are also presented.Trends in national policies in ICM and current developments and issues are also highlighted and recommendations made.  相似文献   

Morphology and downslope sediment displacement in a deep-sea valley,the Valencia Valley (Northwestern Mediterranean)     

Suzanne O'Connell  Belen Alonso  Kim A. Kastens  Andrés Maldonado  Alberto Malinverno  C. Hans Nelson  Alberto Palanques  William B. F. Ryan 《Geo-Marine Letters》1985,5(3):149-156

The Valencia Valley is a Quaternary, 200 km long deep-sea valley in the Valencia Trough, Western Mediterranean Sea. A swathmapping survey approximately mid-way along the valley length, where the floor has an average gradient of 1:250 (0.2°), shows valley walls that rise 200 to 350 m above the valley floor, with slopes of 2 to 18°. Sediment forming the walls is undergoing retrogressive, upslope-directed slumping with increasing bedding disruption along steeper walls. The valley exhibits a winding course with steep outer and gentler inner walls around bends, and bedforms on the valley floor. Lateral migration around bends is less than 5 km and the valley is deeply entrenched into Quaternary-bedded sediments.  相似文献   

Ionospheric and magnetospheric “plasmapauses”     

Joseph M. Grebowsky  I.H. Hoffman  Nelson C. Maynard 《Planetary and Space Science》1978,26(7):651-660

During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of ～5.2 R_e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2.0–5.4. The locations of the Explorer 45 plasmapause crossings (determined by the saturation of the d.c. electric field double probe) during this month were compared to the latitudinal decreases of the H⁺ density observed on ISIS 2 (by the magnetic ion mass spectrometer) near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Hence, the abruptly decreasing H⁺ density on the low latitude side of the ionospheric trough is not a near earth signature of the equatorial plasmapause. Vertical flows of the H⁺ ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 km s^?1 near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H⁺ trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause. The existence of upward accelerated H⁺ flows to possibly supersonic speeds during the refilling of magnetic flux tubes in the outer plasmasphere could produce an equatorial plasmapause whose field lines map into the ionosphere at latitudes which are poleward of the H⁺ density decrease.  相似文献   

Spectral reflectivities of the Galilean satellites and Titan, 0.32 to 0.86 micrometers     

Robert M. Nelson  Bruce W. Hapke 《Icarus》1978,36(3):304-329

A spectrophotometric observational study of the Galilean satellites and Titan was carried out at 0.004-μm (40-Å) resolution over the spectral range 0.32 to 0.86 μm. A standard lunar area was used as a primary spectroscopic standard to establish the relative reflection spectra of the objects by ratioing the sky-corrected satellite spectra to the standard area on the Moon. J1 (Io) is found to have a spectral edge at 0.33 μm that has not been previously reported. The increase in reflectivity from 0.4 to 0.5 μm and the band at 0.56 μm are confirmed. A weak band at 0.56 μm is probable on J2 (Europa) and possible on J3 (Ganymede). J4 (Callisto) shows no spectral features that have not been previously reported. On Titan, no temporal variations in the methane bands greater than 2% were found, indicating that the effective path length in the Titan atmosphere did not change over the 3-month period of this study. A new absorption band of methane at 0.68 μm was found on Titan. We propose an extension of the evaporite model of Fanale et al. (1974, 1977) and the sulfur mixing models of Wamsteker et al. (1974) in which the primary constituent of the surface of J1 is elemental sulfur sublimated onto the surface by photodissociation of hydrogen sulfide outgassing from the interior. The sulfur is continually renewed by sublimation, sputtering, and redeposition. At low temperatures irradiation produces stable S₂, S₃, S₄, S₆, and long chain polymers. Some of these allotropes have an edge at 0.33 μm, a rising reflectance between 0.4 and 0.5 μm a band at 0.56 μm. All of these features are found in the spectrum of J1. We conclude that the lunar ratioing technique used in this study is well suited for determining the relative reflection spectra of solar system objects.  相似文献   

FARMWORKER HOUSING AND SPACES OF BELONGING IN WOODBURN,OREGON*     

Lise Nelson 《Geographical review》2007,97(4):520-541

ABSTRACT. This article traces the history of efforts to build subsidized farmworker housing in Woodburn, Oregon, during the early 1990s. Although the northern Willamette Valley has been dependent on Mexican and Mexican American farmworkers since the 1940s, until the 1980s most of those workers had been migratory and lived in labor camps. Political economic transformations shifted these dynamics, causing an increasing number of farmworkers to settle permanently in towns such as Woodburn. Rising housing costs, in combination with skyrocketing demand for low‐income housing, led to a housing crisis in the late 1980s. The Farmworker Housing Development Corporation, established in 1991, successfully built two housing projects in Woodburn despite fierce resistance from city leaders and many longtime residents. These housing projects not only provided safe and affordable housing for farmworkers but also claimed a space of belonging for a group profoundly marginalized in terms of economics, race, and legal status in Oregon and throughout the United States.  相似文献   

Variable post-Paleozoic deformation detected by seismic reflection profiling across the northwestern “prong” of New Madrid seismic zone     

J. H. McBride  A. J. M. Pugin  W. J. Nelson  T. H. Larson  S. L. Sargent  J. A. Devera  F. B. Denny  E. W. Woolery 《Tectonophysics》2003,368(1-4):171

High-resolution shallow seismic reflection profiles across the northwesternmost part of the New Madrid seismic zone (NMSZ) and northwestern margin of the Reelfoot rift, near the confluence of the Ohio and Mississippi Rivers in the northern Mississippi embayment, reveal intense structural deformation that apparently took place during the late Paleozoic and/or Mesozoic up to near the end of the Cretaceous Period. The seismic profiles were sited on both sides of the northeast-trending Olmsted fault, defined by varying elevations of the top of Mississippian (locally base of Cretaceous) bedrock. The trend of this fault is close to and parallel with an unusually straight segment of the Ohio River and is approximately on trend with the westernmost of two groups of northeast-aligned epicenters (“prongs”) in the NMSZ. Initially suspected on the basis of pre-existing borehole data, the deformation along the fault has been confirmed by four seismic reflection profiles, combined with some new information from drilling. The new data reveal (1) many high-angle normal and reverse faults expressed as narrow grabens and anticlines (suggesting both extensional and compressional regimes) that involved the largest displacements during the late Cretaceous (McNairy); (2) a different style of deformation involving probably more horizontal displacements (i.e., thrusting) that occurred at the end of this phase near the end of McNairy deposition, with some fault offsets of Paleocene and younger units; (3) zones of steeply dipping faults that bound chaotic blocks similar to that observed previously from the nearby Commerce geophysical lineament (CGL); and (4) complex internal deformation stratigraphically restricted to the McNairy, suggestive of major sediment liquefaction or landsliding. Our results thus confirm the prevalence of complex Cretaceous deformations continuing up into Tertiary strata near the northern terminus of the NMSZ.  相似文献   

Sedimentation rates, basin analysis and regional correlations of three Neoarchaean and Palaeoproterozoic sub-basins of the Kaapvaal craton as inferred from precise U–Pb zircon ages from volcaniclastic sediments     

Wladyslaw Altermann  David R. Nelson 《Sedimentary Geology》1998,120(1-4):225-256

Calculation of sedimentation rates of Neoarchaean and Palaeoproterozoic siliciclastic and chemical sediments covering the Kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents. Zircons from tuff beds in carbonate facies of the Campbellrand Subgroup in the Ghaap Plateau region of the Griqualand West basin, Transvaal Supergroup, South Africa were dated using the Perth Consortium Sensitive High Resolution Ion Microprobe II (SHRIMP II). Dates of Ma and Ma for the middle and the upper part of the Nauga Formation indicate that the decompacted sedimentation rate for the peritidal flat to subtidal below-wave-base Stratifera and clastic carbonate facies, southwest of the Ghaap Plateau at Prieska, was of up to 10 m/Ma, when not corrected for times of erosion and non-deposition. Dates of Ma for the upper Gamohaan Formation and for the upper Monteville Formation, indicate that some 2000 m of carbonate and subordinate shale sedimentation occurred during 16 Ma to 62 Ma on the Ghaap Plateau. For these predominantly peritidal stromatolitic carbonates, decompacted sedimentation rates were of 40 m/Ma to over 150 m/Ma (Bubnoff units). The mixed siliciclastic and carbonate shelf facies of the Schmidtsdrif Subgroup and Monteville Formation accumulated with decompacted sedimentation rates of around 20 B. For the Kuruman Banded Iron Formation a decompacted sedimentation rate of up to 60 B can be calculated. Thus, for the entire examined deep shelf to tidal facies range, Archaean and Phanerozoic chemical and clastic sedimentation rates are comparable. Four major transgressive phases over the Kaapvaal craton, followed by shallowing-upward sedimentation, can be recognized in the Prieska and Ghaap Plateau sub-basins, in Griqualand West, and partly also in the Transvaal basin, and are attributed to second-order cycles of crustal evolution. First-order cycles of duration longer than 50 Ma can also be identified. The calculated sedimentation rates reflect the rate of subsidence of a rift-related basin and can be ascribed to tectonic and thermal subsidence. Comparison of the calculated sedimentation rates to published data from other Archaean and Proterozoic basins allows discussion of general Precambrian basin development. Siliciclastic and carbonate sedimentation rates of Archaean and Palaeoproterozoic basins equivalent to those of younger systems suggest that similar mechanical, chemical and biological processes were active in the Precambrian as found for the Phanerozoic. Particularly for stromatolitic carbonates, matching modern and Neoarchaean sedimentation rates are interpreted as a strong hint of a similar evolutionary stage of stromatolite-building microbiota. The new data also allow for improved regional correlations across the Griqualand West basin and with the Malmani Subgroup carbonates in the Transvaal basin. The Nauga Formation carbonates in the southwest of the Griqualand West basin are significantly older than the Gamohaan Formation in the Ghaap Plateau region of this basin, but are in part, correlatives of the Oaktree Formation in the Transvaal and of parts of the Monteville Formation on the Ghaap Plateau.  相似文献   

A Study of Spectra, Structure and Correlation Functions and Their Implications for the Stationarity of Surface-Layer Turbulence     

Nelson L. Dias  Marcelo Chamecki  Akemi Kan  Cristhiane M. P. Okawa 《Boundary-Layer Meteorology》2004,110(2):165-189

  相似文献   

Partial molar volumes of oxide components in silicate liquids     

S. A. Nelson  I. S. E. Carmichael 《Contributions to Mineralogy and Petrology》1979,71(2):117-124

Densities of 21 silicate liquids have been determined from 1,000 ° to 1,600 ° C. The compositions studied contain from two to eight oxide components and have the following ranges in composition (mole %): SiO₂, 35–79%; TiO₂, 4–36%; Al₂O₃, 5–25%; FeO, 11–41%; MgO, 7–28%; CaO, 7–35%; Na₂O, 5–50%; and K₂O, 4–20%. The compositions thus cover the upper range observed in magmas for each oxide. Precision for each determination of liquid density is always better than ±1%.Volumes/gfw (gram formula weight) calculated from the density measurements and the chemical compositions of the analyzed liquids have been combined with data on 96 silicate liquids reported in the literature. From this data set we derive, by using multiple linear regression, partial molar volumes of the components SiO₂, TiO₂, A1₂O₃, FeO, MgO, CaO, Na₂O, and K₂O at five temperatures. The standard deviation of the multiple regression is 1.8% of the molar volumes, which is considered about equal to the total errors due to compositional and instrumental uncertainties.These derived partial molar volumes have been used to calculate volumes/gfw of natural silicate liquids which are found to agree within 1% of the measured values. No compositional dependence of the partial molar volumes can be detected within the error considered to be typical of the measurements. This is further supported by the close agreement between the calculated volumes of CaMgSi₂O₆ and Fe₂SiO₂ liquids derived from the initial slopes of their fusion curves and their heats of fusion, and the volumes obtained by summing the respective partial molar volumes. The experimental data indicate that silicate liquids mix ideally with respect to volume, over the temperature and composition range of this data set.  相似文献   

Observations on the settlement patterns of Janua (Dexiospira) brasiliensis (Polychaeta: Serpulidae)     

Walter G. Nelson 《Estuaries and Coasts》1979,2(4):213-217

The polychaete Janua (Dexiospira) brasiliensis (Grube) is shown to exhibit gregarious settling patterns on both natural (Zostera marina) and artificial (aquarium glass) substrates. J. (D.) brasiliensis tends to be found more often on older (=longer) Zostera blades and on the upper (=older) portions of the blades on which it is found, probably as a result of requiring a diatom mat before being able to settle on the Zostera surface. On both Zostera and the aquarium glass, J. (D.) brasiliensis forms small clumps (2 cm) with the animals within the clumps distributed at random.  相似文献