On shear-wave triplication in transversely isotropic media

The exact solution to the problem of qSV triplication in homogenous transversely isotropic media has been long known, but the result is algebraically complex and is seldom applied in practice. We present an appropriate approximation (not assuming weak qSV-anisotropy) that simplifies the conditions for the onset of off-axis triplication as anisotropy is increased, identifying the anisotropy parameter σ as the controlling parameter. It follows that commonly reported surface-seismic P-wave move-out measurements imply that many formations in the earth's sedimentary crust support off-axis qSV triplications. For typical Vp/Vs velocity ratios and a horizontally stratified earth, however, off-axis qSV triplications appear to only occur for shear-wave incidence angles too far from the vertical to be sampled by surface-seismic converted-wave survey geometries.     

Societal need for improved understanding of climate change, anthropogenic impacts, and geo-hazard warning drive development of ocean observatories in European Seas

Society’s needs for a network of in situ ocean observing systems cross many areas of earth and marine science. Here we review the science themes that benefit from data supplied from ocean observatories. Understanding from existing studies is fragmented to the extent that it lacks the coherent long-term monitoring needed to address questions at the scales essential to understand climate change and improve geo-hazard early warning. Data sets from the deep sea are particularly rare with long-term data available from only a few locations worldwide. These science areas have impacts on societal health and well-being and our awareness of ocean function in a shifting climate.Substantial efforts are underway to realise a network of open-ocean observatories around European Seas that will operate over multiple decades. Some systems are already collecting high-resolution data from surface, water column, seafloor, and sub-seafloor sensors linked to shore by satellite or cable connection in real or near-real time, along with samples and other data collected in a delayed mode. We expect that such observatories will contribute to answering major ocean science questions including: How can monitoring of factors such as seismic activity, pore fluid chemistry and pressure, and gas hydrate stability improve seismic, slope failure, and tsunami warning? What aspects of physical oceanography, biogeochemical cycling, and ecosystems will be most sensitive to climatic and anthropogenic change? What are natural versus anthropogenic changes? Most fundamentally, how are marine processes that occur at differing scales related?The development of ocean observatories provides a substantial opportunity for ocean science to evolve in Europe. Here we also describe some basic attributes of network design. Observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in European Seas adding needed certainty to estimates of future oceanic conditions. Observatory data can be analysed along with other data such as those from satellites, drifting floats, autonomous underwater vehicles, model analysis, and the known distribution and abundances of marine fauna in order to address some of the questions posed above. Standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit. The connection of ocean observatory effort into larger frameworks including the Global Earth Observation System of Systems (GEOSS) and the Global Monitoring of Environment and Security (GMES) is integral to its success. It is in a greater integrated framework that the full potential of the component systems will be realised.     

RING CURRENT DYNAMICS DURING THE 13–18 JULY 2000 STORM PERIOD

We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of two small to moderate geomagnetic storms followed by a great storm with indices Dst=−300 nT and Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath region behind the third shock was characterized by B _z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive B _z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum B _z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model with initial and boundary conditions inferred from measurements from the hot plasma instruments on the Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H⁺, O⁺, and He⁺ ring current ion distributions. We found that the O⁺ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave excitation at frequencies below O⁺ gyrofrequency. We found that the wave gain of O⁺ band waves is greater and is located at larger L shells than that of the He⁺ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were observed by the imaging proton sensor (IPS) on Polar at the locations of maximum predicted wave gain, in good agreement with model simulations.     

六元体系Li–Na–K–Mg–Cl–SO4–H2O多温相平衡预测

采用基于扩展UNIQUAC模型的AQSOL027软件针对水盐体系Li–Na–K–Mg–Cl–SO₄–H₂O的六个五元子体系进行相平衡理论计算,首次报道了多个五元子体系在多个温度条件下的相图,将计算相图与已有实验相图以及基于其它热力学模型的计算相图进行了比较。结果表明：AQSOL027在相图计算中具有较好的准确性和可靠性。AQSOL027是一款基于Excel、用于计算复杂多温水-盐体系Li–Na–K–Mg–Ca–H–Cl–(HSO₄/SO₄)–(CO₂/HCO₃/CO₃)–(H₃BO₃/B₄O₇/BO₂)–OH–H₂O的计算机软件,集成了扩展UNIQUAC模型和相平衡算法,该软件可结合SysCAD和Aspen过程模拟器,实现盐田工艺过程的计算机辅助设计。     

Survey of waste water disposal practices at Antarctic research stations

To inform the future practices to be employed for handling waste water and grey water at the Swedish Antarctic station, Wasa, in Dronning Maud Land, the Swedish Polar Research Secretariat took the initiative to survey the practices of the 28 nations with stations in Antarctica. A questionnaire was sent out to all members of the Antarctic Environment Officers Network during the autumn of 2005. Questions were asked about the handling of waste water and grey water, the type of sewage treatment, and installation and operational costs. The response to the questionnaire was very good (79%), and the results showed that 37% of the permanent stations and 69% of the summer stations lack any form of treatment facility. When waste water and grey water containing microorganisms are released, these microorganisms can remain viable in low-temperature Antarctic conditions for prolonged periods. Microorganisms may also have the potential to infect and cause disease, or become part of the gut flora of local bird and mammal populations, and fish and marine invertebrates. The results from 71 stations show that much can still be done by the 28 nations operating the 82 research stations in Antarctica. The technology exists for effective waste water treatment in the challenging Antarctic conditions. The use of efficient technology at all permanent Antarctic research stations would greatly reduce the human impact on the pristine Antarctic environment. In order to protect the Antarctic environment from infectious agents introduced by humans, consideration should also be given to preventing the release of untreated waste water and grey water from the smaller summer stations.     

First 10 min intervals of Pi2 onset at geosynchronous altitudes during the expansion of energetic ion regions in the nighttime sector

We examined the temporal variations of the geomagnetic field and energetic ions at geosynchronous altitudes associated with substorms during the nighttime using a superposed epoch analysis timed by Pi2 onset. We focused on the first 10 min intervals of Pi2 onset and on subsequent intervals to study the substorm expansion. We conclude that the first 10 min interval of Pi2 onset is a transitional state of the substorm dominated by MHD processes associated with earthward flow and its bifurcation. Intervals of field line variations following the first 10 min were well organized by dipolarization (substorm current wedge) due to the reduced cross-tail current. We also show that energetic ion regions localized in the local time sector from 2000 to 0000 LT in the first 10 min intervals of Pi2 onset expanded to the post-midnight sector, reaching 0400 LT within 20 min after Pi2 onset. We conclude that the expansion of the energetic plasma regions can be attributed to the inflation of the inner magnetosphere during dipolarization.     

Deposition rates, mixing intensity and organic content in two contrasting submarine canyons

The hydrographically different conditions characterising the Western Iberian Margin (NE Atlantic) and the Gulf of Lions (Mediterranean) may play an important role in determining the biogeochemical characteristics of the sediments. To investigate this, we compared the Nazaré and Cap de Creus canyons, and their respective adjacent open slopes in terms of the organic carbon (C_org) contents, chlorophyll-a (chl-a) concentrations, C:N and chl-a:phaeopigment ratios, and also in terms of modelled mixing intensities, chl-a and ²¹⁰Pb deposition and background concentrations in sediments. Chlorophyll-a and ²¹⁰Pb profiles were fitted simultaneously with a reactive transport model to estimate mixing intensity, deposition and background concentrations. Further, to account for the possibility that the decay of chl-a may be lower in the deep sea than in shallow areas, we estimated the model parameters with two models. In one approach (model 1), the temperature dependent decay rate of chl-a as given by Sun et al. [Sun, M.Y., Lee, C., Aller, R.C. (1993) Laboratory Studies of Oxic and Anoxic Degradation of chlorophyll-a in Long-Island sound sediments. Geochimica et Cosmochimica Acta, 57, 147-157] for estuaries was used. In the other approach (model 2), an extra parameter was estimated to derive the chlorophyll-a degradation rate. An F-test, taking into account the different number of parameters in the models, was used to single out the model that significantly fitted the data best. In most cases, the model parameters were best-explained with model 1, indicating the empirical relationship by Sun et al. (1993) is a valid means to estimate the chlorophyll-a degradation rate in deep sea sediments. To assess the robustness with which the model parameters were estimated we provide a first application of Bayesian analysis in the modelling of tracers in sediments. Bayesian analysis allows calculating the mean and standard deviation for each model parameter and correlations among parameters. The model parameters for stations for which ²¹⁰Pb and chlorophyll-a profiles were available were robustly fitted as evidenced by an average coefficient of variation of 0.22. C_org contents, chl-a concentrations, chl-a:phaeo ratios, mixing intensities, depositions and background concentrations of chl-a and ²¹⁰Pb indicated that the Cap de Creus canyon and adjacent slope were less active in terms of organic matter accumulation and burial than the Nazaré canyon and respective open slope.     

Salt diapir velocity assessment from temperature and thermal indicator anomalies: application to Lulu-1, Danish North Sea

A method is exhibited for assessing the time of onset of diapirism and salt flow-speed. Using vitrinite reflectance measurements from wells drilled on top of a salt structure it is possible to determine the excess maturity caused by the focusing of heat due to the higher thermal conductivity of salt. The method is based on calculation of the thermal anomaly surrounding a rising salt diapir. For a given salt speed, predicted vitrinite reflectance values are calculated and compared with the observed values at given depths. The process is repeated with various speeds of the rising salt until consistency of predicted and observed values is obtained, thus constraining an assessment of the velocity of the salt. The method can easily be tailored to thermal indicators other than vitrinite reflectance, thereby enhancing the resolution of the thermal history, and constraining both the onset of salt rise as well as the speed. The well, Lulu-1, from the Danish North Sea, is used to illustrate the procedure.     

A simple method for estimating excess pressure over horsts from seismic sections

Observations in the North Sea Basin max indicate significant overpressure in sediments over horst blocks but not over grabens at the same submudline depth. The purpose is to show that over a horst, of top width W, with grabens on either side of top widths G₁ and G₂, respectively, the equivalent mud density. _r can be estimated approximately from the simple equation.