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1.
Oil-weathering processes in ice-free subarctic and Arctic waters include spreading, evaporation, dissolution, dispersion of whole-oil droplets into the water column, photochemical oxidation, water-in-oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms, sinking, and sedimentation. While many of these processes also are important factors in ice-covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil-weathering mechanisms. Flow-through seawater wave-tank experiments in a cold room at −35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time-series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first-year columnar ice through spring breakup. 相似文献
2.
This study explores the origin and geochemical evolution ofapatite, monazite, and xenotime along two metamorphic traverses.The first, from the Kigluaik Mountains, Seward Peninsula, Alaska,consists of a localized (85 cm) orthopyroxeneclinopyroxene-bearingdehydration zone. The second consists of orthopyroxene ±clinopyroxene-bearing granulite facies metabasite layers interlayeredwith metapelites over a 34 km traverse, along the ValStrona, IvreaVerbano Zone, Northern Italy (IVZ). In bothdehydration zones small Th- and U-poor inclusions of monaziteand/or xenotime occur in the apatite. These inclusions are metasomaticallyinduced and nucleated within the apatite via the coupled substitutionsNa+ + (Y + REE)3+ = 2 Ca2+ and Si4+ + (Y + REE)3+ = P5+ + Ca2+.These are not present in apatite from the original amphibolitefacies gneiss. Apatite, in both dehydration zones, also showsa relative increase in both F and Cl compared with apatite fromthe amphibolite facies zone. Granulite facies metabasites inthe IVZ also contain isolated monazite grains, which range fromuniform to complexly zoned in Th the (1330·1 mol% ThSiO4). These are the product of breakdown and subsequentmobilization of the lanthanides and actinides from monazite-(Ce)in the metapelite layers into the metabasite layers at the startof granulite facies metamorphism. KEY WORDS: apatite; monazite; xenotime; KClNaCl brines; metasomatism; phosphate minerals; charnockiteenderbite; granulite facies metamorphism 相似文献
3.
The Seven Rivers Formation exposed in Slaughter Canyon, Guadalupe Mountains, New Mexico, reveals complex relations between long- and short-term relative changes in sea-level, shelf configuration and sedimentation, which interacted to create a distinct toplap geometry. At least five sandstones diverge basinward from a prominent boundary unit marking the surface of toplap at the top of the Seven Rivers Formation and create a series of prograding, shingled clinoforms. The boundary unit is a horizontal, well-sorted, quartz arenite underlain across the shelf by peritidal carbonate or by other merging sandstones. Preserved palaeotopography is indicated by facies changes downdip and the presence of horizontal geopetal indicators in inclined beds. Near the boundary unit (updip), merging sandstones contain rare sedimentary structures including evaporite moulds and irregular fenestrae and are bounded above and below by peritidal carbonate with microbial laminae, fenestral fabrics and mudcracks. Laterally (downdip), the sandstone-bounding peritidal carbonate facies pass into subtidal carbonate facies (ooid-peloid-fusulinid-dasyclad-mollusc pack- and grainstone) and interbedded sandstones contain sedimentary structures such as ripple marks and trough to planar cross-stratification, as well as ooids, fusulinids and other carbonate grains. Toplap is interpreted to have developed by sediment bypass across a subaerially exposed shelf while sedimentation continued in still-submerged areas downdip from the shelf crest, and hence represents depositional toplap. Physical tracing of subaerial exposure surfaces suggests that the shoreline migrated up and down palaeoslope several times. The vertical component of five short-term shoreline migrations decreased during formation of the toplap geometry. Sea-level rose to approximately the same position following each fall to create the toplap geometry. This depositional toplap is the stratigraphic result of high-‘frequency’ relative changes of sea-level that combined to produce the larger-scale geometry. We suggest that changing amplitudes of relative sea-level may play a significant role in the stratigraphic evolution of platforms and that separating ‘short-term’and ‘long-term’relative sea-level may be ambiguous in such instances. 相似文献
4.
A STATISTICAL FRAMEWORK FOR TREE‐RING RECONSTRUCTION OF HIGH‐MAGNITUDE MASS MOVEMENTS: CASE STUDY OF SNOW AVALANCHES IN EASTERN CANADA 下载免费PDF全文
DANIEL GERMAIN 《Geografiska Annaler: Series A, Physical Geography》2016,98(4):303-311
This paper investigates the application of the peaks‐over‐threshold method in combination with fitting of the generalized Pareto distribution for estimating the frequency of high‐magnitude geomorphic events, on the basis of tree‐ring data. In particular, attention is focused on extreme value distribution of tree‐ring responses and in the minimum threshold or index number required to assure the past occurrence of high‐magnitude events. The objective is to set a threshold, adapted to the sample distribution, which will make the distinction between high‐magnitude years and remaining years, where the response of sampled trees is too weak to be attributed to a high‐magnitude geomorphic event. The statistical framework proposed is based on the statistics of extremes. Through the use of simple, strong and effective mathematics, this model should strengthen the position of dendrogeomorphology in the evaluation and management of natural hazards. 相似文献
5.
6.
Holocene changes on a peatland in northwestern Ontario interpreted from testate amoebae (Protozoa) analysis 总被引:3,自引:0,他引:3
BARRY G. WARNER DANIEL J. CHARMAN 《Boreas: An International Journal of Quaternary Research》1994,23(3):270-279
Radiocarbon-dating and analyses of fossil testate amoebae (Protozoa) have established changes in soil moisture conditions on the developing surface of a Sphagnum -dominated peatland near Emo in northwestern Ontario.
The distribution and composition of modern testate amoebae communities were studied from peatlands in the region of Ontario and Minnesota as a guide to interpreting fossil assemblages. Although the core spans all of the Holocene, fossil testate amoebae were recovered only from the part post-dating 6500 BP. Earliest testate amoebae assemblages associated with bryophytic and cyperaceous-rich fen peat are dominated by species in the genera Cyclopyxis and Centropyxis . By 5000 BP, Amphitrema Jraaum, Assulina muscorum, Heleopera sphugni and Hyalosphenia subjaoa become important species as Sphagnum-rich peat accumulated at the site. Present-day microtopographic differentiation probably developed during historic time when the site became progressively drier, as indicated by a change of Nebela griseola, N. militaris and Trigonopyxis arcula . Although it is possible to derive quantitative estimates of changing soil moisture conditions from testate amoebae, care should be taken in interpreting results, particularly from non-Sphagnum-rich peats, until more is learned about the distribution and ecology of modern faunas. 相似文献
The distribution and composition of modern testate amoebae communities were studied from peatlands in the region of Ontario and Minnesota as a guide to interpreting fossil assemblages. Although the core spans all of the Holocene, fossil testate amoebae were recovered only from the part post-dating 6500 BP. Earliest testate amoebae assemblages associated with bryophytic and cyperaceous-rich fen peat are dominated by species in the genera Cyclopyxis and Centropyxis . By 5000 BP, Amphitrema Jraaum, Assulina muscorum, Heleopera sphugni and Hyalosphenia subjaoa become important species as Sphagnum-rich peat accumulated at the site. Present-day microtopographic differentiation probably developed during historic time when the site became progressively drier, as indicated by a change of Nebela griseola, N. militaris and Trigonopyxis arcula . Although it is possible to derive quantitative estimates of changing soil moisture conditions from testate amoebae, care should be taken in interpreting results, particularly from non-Sphagnum-rich peats, until more is learned about the distribution and ecology of modern faunas. 相似文献
7.
Sven HARTMANN Institute for Hydrosciences German Armed Forces University Munich Neubiberg Germany. 《国际泥沙研究》2001,16(2)
1 BASIC PROBLEMFlood protecton, sPreaing of settlements and occuPatin Of river valleys were maor reasons to damand lindt rivers throughout Europe in the ndd 19th century. Engineers of those days often knew very wellabout the effects of their plannings: shortening the river length would accelerat the now and thusencourage the erosion into the river's sedAnents. Two vital advanages could be obtalned from that kindof constrUction, landuse of the fOrmer flood plains on the one and increasin… 相似文献
8.
Thomas ELSNERand Sven HARTMANN Institute for Hydrosciences German Armed Forces University Munich Neubiberg Germany. Institute for Hydrosciences German Armed Forces University Munich Neubiberg Germany. 《国际泥沙研究》2001,16(2)
1 THE LOWhR unR INNThe Inn river has its source in the alPine region of the GraubUnden canton of Switzerand. ThecatChment area of about 260(X} kIn2 includes mountains of the central Alpes up to 40(X) m. The river runs5l7 km thrOugh the countries of SwitZerand, Austria and Germany on itS way into the Danube mver. Thedischarge of the river at its mouth in the city of Passau is mainly infiuenced by the snow melt in themountainous catchment area and vches between apProx. 200 m3ls durin… 相似文献
9.
10.
La teneur en fluor, déterminée au moyen d'une électrode spécifique d'ions dans quelques standards géochimiques, est présentée. 相似文献