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Potentiometric titrations of deep Black Sea water give reasonably precise values of sulphide in the concentration range 30–300 μmol l−1 and a strong indication of thiols in the concentration range 10–30 μmol l−1. Organic analysis of Black Sea water should therefore include the search for compounds containing SH groups. A simple stoichiometric model indicates that sulphur-containing proteins might be the main source of thiols after hydrolysis and deamination. The alkalinity and total sulphide are simply related by At = 3287 ± 30 + (3.84 ± 0.10) [H2 S]t μmol kg−1. The slope of 3.84 instead of the stoichiometric slope of 2.31 indicates a lack of reduced sulphate in the form of hydrogen sulphide. 相似文献
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Simulating Icelandic vegetation cover during the Holocene Implications for long-term land degradation 总被引：2，自引：0，他引：2
Rannveig Ólafsdóttir Peter Schlyter & Hörður V. Haraldsson 《Geografiska Annaler: Series A, Physical Geography》2001,83(4):203-215
We have simulated the spatial relationship between temperature change and long-term potential vegetation cover dynamics. The results show that the potential vegetation and birch forest range is highly sensitive to the temperature conditions. Around 3000 BP the simulated potential vegetation cover began to decrease and at the time of the Viking settlement, in AD 874 (1076 BP ), vegetation and forest cover was already in decline. The climate driven decline continued to an unprecedented low potential for vegetation for the Holocene that lasted c. 600 years, i.e. between AD c . 1300 and 1900. These interpretations are further supported by geomorphological and pollen data. 相似文献
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Leo Kristjansson Agust Gudmundsson Hreinn Haraldsson 《International Journal of Earth Sciences》1995,84(4):813-830
We have carried out stratigraphic mapping in the Upper Miocene basalt lava pile around the fjords Mjoifjördur and Seydisfjördur, eastern Iceland. The mapping is based on conventional methods including the use of interbasaltic clastic horizons and petrographically distinct lava groups. These units are also used to provide correlations with the Nordfjördur area south of Mjoifjördur. We present a 3-km composite stratigraphic column for the area between Mjoifjördur and Seydisfjördur. The geology of this area shows some differences from the classical model of Walker for the structure of eastern Iceland partly due to the fact that most of Mjoifjördur is not in the vicinity of central volcanoes. Detailed laboratory measurements of remanent magnetization were carried out on oriented core samples from 363 lavas in 10 selected profiles. The local paleomagnetic polarity stratigraphy supports correlations made on the basis of other criteria. Over 20 geomagnetic reversals are recorded in the eastern Iceland lava pile in a period approximately 13-10 Ma ago. The geomagnetic field during this period averages to a central axial dipole field, and its overall statistical properties resemble those obtained in earlier surveys in Iceland. 相似文献
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David W. Dyrssen Per O. J. Hall Conny Haraldsson Melissa Chierici Jens M. Skei H. Göte östlund 《Aquatic Geochemistry》1996,2(2):111-129
Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.502 + H2S S(colloidal) + H2O. The elemental sulfur, being stabilized with HS–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10–6 m2 s–1 which lies in the range of values given by Fröyland. Finally, the 14C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren. 相似文献
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Magni Hreinn Jónsson Bjarni Bessason Einar Haflidason 《Soil Dynamics and Earthquake Engineering》2010
The South Iceland Lowland is an active seismic zone. In May 2008 a magnitude 6.3 (Mw) earthquake struck the area. The 370-m-long base-isolated Oseyrar Bridge situated close to the epicentre was hit by strong ground motion. Concrete stoppers at the top of all piers were badly smashed and all four wing walls of the abutments were severely damaged. The study showed that it is possible with numerical models to back-calculate the observed damage based on recorded ground motion in the area. The recorded loads were larger than prescribed by Eurocode 8 for the site even though the magnitude and location of the earthquake was as expected. The main reason was a near-fault pulse which is not covered in the code. The pulse dominated the bridge response and is therefore important to consider. Finally, an improved design is presented that could have prevented the damage. 相似文献
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Conny Haraldsson Leif G. Anderson Martin Hassellöv Stefan Hulth Kristina Olsson 《Deep Sea Research Part I: Oceanographic Research Papers》1997,44(12):2031-2044
A system for rapid, high precision potentiometric determination of alkalinity in sea water and sediment pore water is presented. Two titration units were used: a 40 ml unit for seawater and a small volume unit for sediment pore water. Titration time was normally less than 10 minutes per sample, including sample exchange. With a 40 ml sample volume, the relative standard deviation of the alkalinity obtained in the laboratory was 0.05% and at sea 0.1 %. The small-volume system (0.5–1.5 ml) gave a precision of 0.07%. Five titration points, in two groups after the second equivalence point, were used to evaluate the equivalence volume. Results from equilibrium calculations and computer simulated alkalinity titrations show that it was possible to use a non-modified Gran function [(V0 +v)*10(E/Z)] and still achieve good accuracy and precision. 相似文献
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Iceland is facing severe land degradation in many parts of the country. This study aims to increase the understanding of the complex interactions and interconnectivity between the critical factors that help maintain the land degradation processes in sub-arctic environments. A holistic approach in the form of a causal loop diagram (CLD) is applied for diagnosing the influencing factors. To further study the relationship between vegetation cover and its degradation, a dynamic model that uses a long-term temperature data as the main indicator function is constructed to simulate potential vegetation cover during the Holocene. The results depict an oscillating vegetation cover. Gradual degradation in potential vegetation cover begins ca. 3000 BP and accelerates greatly after ca. 2500 BP. From the time of the Norse settlement in the latter halve of the 9th century to present time, the simulated vegetation cover retreats ca. 25% in relation to climatic cooling. 相似文献
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Flow field-flow fractionation (FlFFF) coupled to an inductively coupled plasma mass spectrometer (ICPMS) has been used to determine the chemical composition of colloids from a freshwater sample as a function of size. Organic carbon and iron are the most abundant colloidal components, and are considered as the major carrier phases for other chemical elements present. The size distribution of organic carbon colloids shows a single peak with an estimated hydrodynamic diameter between 1 and 1.5 nm, while the iron colloids show a more complex distribution centred at larger colloid sizes with estimated hydrodynamic diameters up to 5 nm. The association of 32 trace elements with these two carrier colloids has been quantified by deconvolution analysis, and the resulting distributions are shown to be chemically consistent. The observed distributions are also shown to be broadly consistent with predictions from speciation modelling for the subset of 8 elements for which appropriate stability constants are available. 相似文献
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