On the performance of the new NWP nowcasting system at the Danish Meteorological Institute during a heavy rain period     

Bjarke Tobias Olsen  Ulrik Smith Korsholm  Claus Petersen  Niels Woetmann Nielsen  Bent Hansen Sass  Henrik Vedel 《Meteorology and Atmospheric Physics》2015,127(5):519-535

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Modelling the effect of climate change on the wave climate of the world’s oceans     

Erik Vanem  Bent Natvig  Arne Bang Huseby 《Ocean Science Journal》2012,47(2):123-145

This paper analyses the trends and the future projections of significant wave height in several ocean areas at different parts of the world. It uses a stochastic Bayesian hierarchical space-time model, with a regression component with atmospheric levels of CO₂ as covariates in order to estimate the expected long-term trends and make future projections towards the year 2100. The model was initially developed for an area in the North Atlantic ocean, and has been found to perform reasonably well there, and it is now investigated how the model performs for other ocean areas. 11 new ocean areas have been analysed with the model, and this paper presents the results pertaining to the estimated long-term trends and future projections of monthly maximum significant wave height for each of the 12 ocean areas.  相似文献   

The integrated impacts of human activities and rising sea level on the saltwater intrusion in the east coast of the Yucatan Peninsula,Mexico     

Deng  Yujun  Young  Caitlin  Fu  Xinyu  Song  Jie  Peng  Zhong-Ren 《Natural Hazards》2017,85(2):1063-1088

Natural Hazards - Saltwater intrusion is a major hazard to coastal communities as it causes degradation of fresh water resources. The impact of rising sea level on the saltwater intrusion into...  相似文献   

Development of Deltas in Some Danish Watercourses     

Bent Hasholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):10-16

Hasholt. Bent: Development of Deltas in Some Danish Watercourses. Geografisk Tidsskrift 84: 10–16. Copenhagen, January 1984.

Recurrent sedimentation has been observed in three watercourses in western Jutland where the slope of the water surface diminishes due to human intervention. The river bottom was surveyed by a scuba diver, the bedforms were described, and the grain-size distributions analysed. It is concluded that the sedimentation is due to the development of deltas.  相似文献   

Recent marginal changes of the Mittivakkat Glacier,Southeast Greenland and the discovery of remains of reindeer (Rangifer tarandus), polar bear (Ursus maritimus) and peaty material     

N. Tvis Knudsen  P. Nørnberg  Jacob C. Yde  Bent Hasholt  Jan Heinemeier 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):137-142

Geografisk Tidsskrift, Danish Journal of Geography 108(1):137–142, 2008

During field observations in August 2005 antler remains of a reindeer were found at a recently deglaciated site at about 500 m asl., and bones from a polar bear were found at about 300 m asl. along the margin of Mittivakkat Glacier, Southeast Greenland. Radio carbon dating determined the age of the samples to 720 ¹⁴C years and 350 ¹⁴C years, respectively. In August 2006 old surface vegetation covering peaty material became exposed due to ice recession close to the site where the antler was found. The radio carbon age of small roots from the material was determined to 1530 ¹⁴C years, and is in agreement with dating of woody remains of Salix glauca found close by, at the top of a nearby nunatak in 1999. The antler indicates that reindeer lived in the area when the glacier began to advance from a position where it was close to or smaller than today. The vegetation surface and peaty material indicate that the climate was warmer before the onset of the Little Ice Age in Southeast Greenland than today.  相似文献   

Limited denitrification in glacial deposit aquifers having thick unsaturated zones (Long Island, USA)     

Caitlin Young  Kevin D. Kroeger  Gilbert Hanson 《Hydrogeology Journal》2013,21(8):1773-1786

The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N₂/Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N₂, attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3–41.1 μmol L^?1) and high dissolved oxygen concentrations (58–100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area.  相似文献   

Geology and genesis of the Toongi rare metal (Zr,Hf, Nb,Ta, Y and REE) deposit,NSW, Australia,and implications for rare metal mineralization in peralkaline igneous rocks     

Carl?SpandlerEmail author  Caitlin?Morris 《Contributions to Mineralogy and Petrology》2016,171(12):104

The Toongi Deposit, located in central NSW, Australia, hosts significant resources of Zr, Hf, Nb, Ta, Y and REE within a small (ca. 0.3 km²), rapidly cooled trachyte laccolith. Toongi is part of regional Late Triassic to Jurassic alkaline magmatic field, but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body. The primary ore minerals are evenly dispersed throughout the rock and include lueshite/natroniobite and complex Na–Fe–Zr–Nb–Y–REE silicate minerals dominated by a eudialyte group mineral (EGM). The EGM occurs in a unique textural setting in the rock, commonly forming spheroidal or irregular-shaped globules, herein called “snowballs”, within the rock matrix. The snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball. Secondary ore minerals include REE carbonates, Y milarite, catapleiite and gaidonnayite that fill fractures and vesicles in the rock. Based on bulk-rock geochemical and Nd isotope data, and thermodynamic modelling of magma fractionation, the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle-derived magma that ponded at mid-crustal levels (ca. 0.3 GPa) and underwent extensive fractionation under low-oxygen fugacity conditions. The high Na₂O, peralkaline nature of the Toongi Deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid-crust and subsequently at shallow levels (ca. 0.1 GPa). This extended fractionation under low fO₂ and relatively low H₂O-activity conditions limited volatile release and allowed build-up of rare metal contents to ore grades. We speculate that the ore minerals may have originally formed from rare metal-rich sodic-silicate melt that formed immiscible globules (subsequently crystallized to EGM) in the magma shortly before emplacement and rapid cooling. Subsequent hydrothermal alteration caused relatively limited and localized remobilization of some ore metals into fractures and vesicles in the rock.  相似文献   

Ground-based measurements of the methane distribution on Titan     

Paulo F. Penteado  Caitlin A. Griffith 《Icarus》2010,206(1):345-7996

Using spectra taken with NIRSPEC (Near Infrared Spectrometer) and adaptive optics on the Keck II telescope, we resolved the latitudinal variation of the 3ν₂ band of CH₃D at 1.56 μm. As CH₃D is less abundant than CH₄ by a factor of 50±10×10^-5, these CH₃D lines do not saturate in Titan’s atmosphere, and are well characterized by laboratory measurements. Thus they do not suffer from the large uncertainties of the CH₄ lines that are weak enough to be unsaturated in Titan. Our measurements of the methane abundance are confined to the latitude range of 32°S-18°N and longitudes sampled by a 0.04″ slit centered at ∼195°W. The methane abundance below 10 km is constant to within 20% in the tropical atmosphere sampled by our observations, consistent with the low surface insolation and lack of surface methane [Griffith, C.A., McKay, C.P., Ferri, F., 2008. Astrophys. J. 687, L41-L44].  相似文献   

Acidic compounds in biodegraded petroleum     

Tanja Barth  Sylvi Hiland  Per Fotland  Kjell Magne Askvik  Bent Skaare Pedersen  Anna Elisabet Borgund 《Organic Geochemistry》2004,35(11-12):1513

Twelve oil samples have been characterised by titration, FT-IR and chromatographic analysis to determine the differences between the organic acid composition of biodegraded and non-biodegraded oils. The biodegraded oils have higher total acid and total base contents, both by titration and extraction. The molecular weight ranges of the extracted acids are lowest in the biodegraded oils, and the equivalent weight calculations indicate a dominance of multi-functional molecules. Gel permeation chromatography gives a molecular weight range with most of the molecules between 300 and 500 g/mol. FT-IR shows that the extracted acids from biodegraded oils are more carboxylic and aliphatic while the non-degraded oils are more phenolic. Molecular analysis of the derivatised extracts give UCM envelopes for biodegraded oils, and no molecular identification. The results indicate that the acidic constituents in biodegraded oils are a product of the biodegradation, as the composition is very different from the non-biodegraded oils.  相似文献   

O-Sr isotopic variations in Miocene granitoids from the Aegean: evidence for an origin by combined assimilation and fractional crystallization     

Rainer Altherr  Friedhelm Henjes-Kunst  Alan Matthews  Hans Friedrichsen  Bent Tauber Hansen 《Contributions to Mineralogy and Petrology》1988,100(4):528-541

Sr, O, and D/H isotopic compositions have been analyzed in Miocene metaluminous to slightly peraluminous (I-type) granitoids of the central Aegean. Individual plutonic complexes display significant variations in their ¹⁸O and initial⁸⁷Sr/⁸⁶Sr compositions.D and ¹⁸O compositions of minerals and whole-rocks are mostly in the magmatic range. Some samples from Naxos and Mykonos/Delos show low D and ¹⁸O values characteristic of meteoric-water-hydrothermal interaction, but as a whole the changes in ¹⁸O and Sr isotopic compositions as a result of hydrothermal alteration were slight, even in instances where marked alteration is petrographically observable. Consequently, the bulk-rock variations of ¹⁸O from 8.1 to 12.0 and of⁸⁷Sr/⁸⁶Sr from 0.70438 to 0.71450 may be regarded as primary and indicative of the conditions of their evolution. Heterogeneous isotopic compositions observed in the individual plutons of Serifos, Ikaria, Samos and Kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses, with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization. The granitoids of Serifos, Ikaria and Kos display weak correlations between the initial⁸⁷Sr/⁸⁶Sr and ¹⁸O and 1/Sr. The granitoid province shows a positive correlation between⁸⁷Sr/⁸⁶Sr and ¹⁸O and a non-linear relationship between⁸⁷Sr/⁸⁶Sr and 1/Sr, whereby 1/Sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases. It is argued that assimilation of older continental material by mantle-derived arc magmas with combined fractionation (AFC) is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock-types trend from granodiorites in the (south)west, near the inferred Oligocene-Miocene suture, to granites in the center and monzonites in the (north)east of the province.  相似文献