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21.
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B. Hansen S.
sterhus H. Htún R. Kristiansen K. M. H. Larsen 《Progress in Oceanography》2003,59(4):443-474
The flow of Atlantic water between Iceland and the Faroe Islands is one of three current branches flowing from the Atlantic Ocean into the Nordic Seas across the Greenland–Scotland Ridge. By the heat that it carries along, it keeps the subarctic regions abnormally warm and by its import of salt, it helps maintain a high salinity and hence density in the surface waters as a precondition for thermohaline ventilation. From 1997 to 2001, a number of ADCPs have been moored on a section going north from the Faroes, crossing the inflow. Combining these measurements with decade-long CTD observations from research vessel cruises along this section, we compute the fluxes of water (volume), heat, and salt. For the period June 1997–June 2001, we found the average volume flux of Atlantic water to be 3.5±0.5 Sv (1 Sv=106 m3·s−1). When compared to recent estimates of the other branches, this implies that the Iceland–Faroe inflow is the strongest branch in terms of volume flux, transporting 47% of the total Atlantic inflow to the Arctic Mediterranean (Nordic Seas and Arctic Ocean with shelf areas). If all of the Atlantic inflow were assumed to be cooled to 0 °C, before returning to the Atlantic, the Iceland–Faroe inflow carries a heat flux of 124±15 TW (1 TW=1012 W), which is about the same as the heat carried by the inflow through the Faroe–Shetland Channel. The Iceland–Faroe Atlantic water volume flux was found to have a negligible seasonal variation and to be remarkably stable with no reversals, even on daily time scales. Out of a total of 1348 daily flux estimates, not one was directed westwards towards the Atlantic. 相似文献
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Kai Kristiansen George W. Greene Jacob N. Israelachvili 《Geochimica et cosmochimica acta》2011,75(22):6882-6892
“Pressure solution”, frequently found in clay-rich sandstone, is characterized by enhanced quartz dissolution at inter-grain contacts. The origin of pressure solution and many other related dissolution processes remains elusive. Using an Electrochemical Surface Forces Apparatus we visualized and measured the dissolution of silica glass surfaces close to an electrode surface. The dissolution rates correlate quantitatively with the electrode potential via the Butler-Volmer equation for corrosion. Our experimental results demonstrate that at low temperature, apparent pressure solution and many other mineral dissolution phenomena can be driven by electrochemical processes rather than a pressure-driven process. This finding highlights the role of electrochemical surface potentials in dissolution phenomena at dissimilar material interfaces, and provides new perspectives on pressure solution in particular and a new theoretical basis for predictive control of dissolution phenomena in general. 相似文献
25.
The content and distribution of nitrate in groundwater and surface water in the Karup Basin area have been investigated and analyzed. In addition to existing analyses, chemical profiles of the groundwater of the upper part of the water table sand aquifer were measured at a number of sites. The profiles indicate, in general, an upper oxidation zone with nitrate and a lower reduction zone free of nitrate. However, below plantation areas, the nitrate content in the oxidation zone is significantly low as well. The eight profiles are graphed separately, and all results are finally plotted on a single map by a graphic method that takes into consideration both the concentration and the level of the sampled water. The great variation in the nitrate content of the water from one water-supply well to another can easily be explained by plotting the values on maps using this graphing procedure, in conjunction with an examination of the nitrate zonation found in the profiles. The influence of agricultural activities is significantly related to the concentration of nitrate in surface water and groundwater under such water table conditions and circumstances as are found in the Karup Basin. 相似文献
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J. Bradford Hubeny Ellen Kristiansen Andrew Danikas Jun Zhu Francine M. G. McCarthy Mark G. Cantwell Barbara Warren Douglas Allen 《Estuaries and Coasts》2018,41(2):404-420
Salem, MA, located north of Boston, has a rich, well-documented history dating back to settlement in 1626 ce, but the associated anthropogenic impacts on Salem Sound are poorly constrained. This project utilized dated sediment cores from the sound to assess the proxy record of anthropogenic alterations to the system and compared the proxy records to the known history. Proxies included bulk stable isotopes of organic matter, magnetic susceptibility, and trace metal concentrations. Our data reveal clear changes in organic matter composition and concentration associated with land use changes and twentieth century sewage disposal practices. Further, metal data correspond with local industrial activity, particularly the historic tanning industry in Peabody, MA. Although conservation practices of past decades have improved the state of Salem Sound, the stratigraphic record demonstrates that the environment is still affected by anthropogenic influences, and has not attained conditions consistent with pre-anthropogenic baseline. The approach and results of this study are applicable to coastal embayments that are being assessed for remediation, especially those with scant historic or monitoring data. 相似文献
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Geir Terje Eigestad Helge K. Dahle Bjarte Hellevang Fridtjof Riis Wenche Tjelta Johansen Erlend Øian 《Computational Geosciences》2009,13(4):435-450
The Johansen formation is a candidate site for large-scale CO2 storage offshore of the south-western coast of Norway. An overview of the geology for the Johansen formation and neighboring
geological formations is given, together with a discussion of issues for geological and geophysical modelling and integrated
fluid flow modelling. We further describe corresponding simulation models. Major issues to consider are capacity estimation
and processes that could potentially cause CO2 to leak out of the Johansen formation and into the formations above. Currently, these issues can only be investigated through
numerical simulation. We consider the effect of different boundary conditions, sensitivity with respect to vertical grid refinement
and permeability/transmisibility data, and the effect of residual gas saturations, since these strongly affect the CO2-plume distribution. The geological study of the Johansen formation is performed based on available seismic and well data.
Fluid simulations are performed using a commercial simulator capable of modelling CO2 flow and transport by simple manipulation of input files and data. We provide details for the data and the model, with a
particular focus on geology and geometry for the Johansen formation. The data set is made available for download online. 相似文献
30.
E. Omdal M. V. Madland T. G. Kristiansen N. B. Nagel R. I. Korsnes A. Hiorth 《Rock Mechanics and Rock Engineering》2010,43(5):557-580
A laboratory test program, which simulated reservoir conditions of pressure and temperature, was conducted on outcrop and
reservoir chalk samples of various porosities. All the samples experienced a stress path following uniaxial strain condition
K
0 that led to compaction failure, i.e. pore collapse. The experiments were loaded by depletion of pore pressure conducted under
load controlled conditions. This depletion phase was followed by a creep period, where time-dependent deformation was monitored.
The intention of creating such reservoir condition in these laboratory experiments was to gain knowledge of the nature of
chalk compaction. Chalk is an important reservoir rock for the oil and gas industry with unique storage capability with porosities
up toward 50%. However, this rock is also very weak which has resulted in significant reservoir compaction and in turn severe
seabed subsidence and casing failure. Mapping of the mechanical behavior of chalk in terms of deformation is thus decisive
for a proper understanding of these reservoirs. The results of this study show that chalk is indeed a rate-dependent material
under laboratory loading conditions as time effects were revealed as the loading rate was varied. However, the results raise
uncertainty about the importance of rate dependency for chalk under completely drained conditions. Further, such high-porosity
chalk suffers for substantial plastic strains and obvious strain hardening. Indeed, a relation between deformation/porosity
and hardening is proposed by the introduction of real-time modulus values. Time-dependent deformation, also called creep was
influenced by the depletion phase, as consolidation or transient creep influenced the deformation response for as much as
175 h after a change in load. This indicates that transient creep is dependent on the stress history. However, observations
suggest the existence of a universal mechanism for steady state creep, governed by neither the initial porosity nor the stress
history or chalk type, which thus seems to be an independent strain contributor. Finally, time dependence is found on the
K
0 development for chalk tested at typically laboratory rates, which has been discussed as a reflection of the nature of the
grain re-arrangement during failure and plastic deformation. Ultimately, such time dependence of the K
0 may contribute to the understanding of stress path data deduced from field data. 相似文献