Collisional processes in the eastern Mediterranean

In the eastern Mediterranean the collision of the Erastosthenes and the Anaximander Seamounts with the Cyprus arc results in a unique tectonic setting due to the small size of the eastern Mediterranean basin. As a result of the collision, some of the motion between the African plate and the Eurasian plate is taking place by thrust faulting along the north African passive margin. It seems that the stress at the plate boundary along the Cyprus arc may be transmitted southward to cause the reactivation of a pre-existing fault zone along the passive margin of eastern north Africa.

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Zusammenfassung Im östlichen Mittelmeerbecken hat die Kollision des Erastosthenes und des Anaximander Seamounts mit dem Cypern-Bogen eine spezielle tektonische Situation geschaffen, die durch den engen Raum dieses Beckens bestimmt wird. Als Ergebnis dieser Kollision erscheinen Überschiebungen der Afrikanischen Platte auf Eurasische Platte entlang des passiven nordafrikanischen Randes. Es erscheint möglich, daß das Streßfeld an der Plattengrenze entlang des Zypernbogens südwärts wirkt und dadurch die alte Störungszone entlang des passiven Kontinentrandes von Nordafrika reaktiert wird.

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Résumé En Méditerrannée orientale, la collision des guyots Eratosthène et Anaximandre avec l'arc de Chypre a engendré une situation tectonique particulière, due à la faible dimension du bassin est-méditerrannéen. Cette collision a eu pour conséquence la production de charriages de la plaque africaine sur la plaque eurasiatique le long de la marge passive nord-africaine. Il semble que les contraintes règnant au bord de la plaque le long de l'arc de Chypre se soient transmises vers le Sud pour y provoquer la réactivation d'une zône failleuse préexistante le long de la marge passive du NE de l'Afrique.

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Modelling groundwater contamination above a nuclear waste repository at Gorleben, Germany

The candidate repository for high-level nuclear waste in the Gorleben salt dome, Germany, is expected to host 8,550 tonnes of uranium in burnt fuel. It has been proposed that 5,440 waste containers be deposited at a depth of about 800?m. There is 260?C280?m of siliciclastic cover sediments above the proposed repository. The potential groundwater contamination in the siliciclastic aquifer is simulated with the TOUGHREACT and TOUGH2-MP codes for a three-dimensional model with 290,435 elements. Two deterministic cases are simulated. The single-phase case considers the transport of radionuclides in the liquid phase only. The two-phase case accounts for hydrogen gas generated by the corrosion of waste containers and release of gaseous C-14. The gas release via a backfilled shaft is assumed to be steady (non-explosive). The simulation period is 2,000,000 years for the single-phase case and 7,000 years for the two-phase case. Only the radioactive dose in the two-phase case is higher than the regulatory limit (0.1?mSv/a).     

Using periodic hydrologic and geochemical sampling with limited continuous monitoring to characterize remote karst aquifers in the Kaweah River Basin,California, USA

Hydrogeologic field work in remote settings is often challenging: assessing spring behaviour and aquifer characteristics can be expensive in both time commitment and resources needed to assess these systems. In this study, we document the hydrology and geochemistry of 47 perennial karst springs in the Kaweah River, a mountain river basin in the Sierra Nevada, California. After preliminary hydrogeochemical characterization and grouping, selected springs were continuously monitored to further assess aquifer characteristics in each group. Later, in areas without previous dye‐tracing work, traces were conducted to establish connections between large sinking streams and springs. The springs have a wide range of inter‐spring and intra‐spring variability in discharge and geochemistry. We assessed this variability by performing statistical comparisons with spring chemistry and principal components analysis of all measured variables. Results show that springs can be divided into two distinct groups: high elevation springs of the Mineral King Valley and lower elevation springs throughout the rest of the basin. Continuous discharge, temperature and specific conductivity data from four springs (two from each group) were then used to characterize the hydrograph recession behaviour of springs in each group. Both groups showed statistically similar baseflow recession slopes, suggesting that both groups contain baseflow storage compartments with similar hydrogeologic properties. The biggest difference between each group is the variability in amount of water remaining in the aquifer during baseflow conditions. High elevation springs have lower baseflow discharges, relative to peak flow, than lower elevation springs, despite the fact that more precipitation falls at higher elevation. This is likely caused by differences in the amount of soil and epikarst storage, which are related to recent geomorphic events: high elevation aquifers were glaciated as recent as 41 thousand years ago (kya), while there is no evidence that low elevation aquifers were glaciated. As a result, lower elevations have developed thicker soils, weathered bedrock and epikarst. Copyright © 2016 John Wiley & Sons, Ltd.     

Feedback and sensitivity in an electrical circuit: an analog for climate models

Earth’s climate sensitivity is often interpreted in terms of feedbacks that can alter the sensitivity from that of a no-feedback Stefan-Boltzmann radiator, with the feedback concept and algebra introduced by analogy to the use of this concept in the electronics literature. This analogy is quite valuable in interpreting the sensitivity of the climate system, but usage of this algebra and terminology in the climate literature is often inconsistent, with resultant potential for confusion and loss of physical insight. Here a simple and readily understood electrical resistance circuit is examined in terms of feedback theory to introduce and define the terminology that is used to quantify feedbacks. This formalism is applied to the feedbacks in an energy-balance model of Earth’s climate and used to interpret the magnitude of feedback in the climate system that corresponds to present estimates of Earth’s climate sensitivity.     

Modeling of Hα Eruptive Events Observed at the Solar Limb

We present spectra and slit-jaw images of limb and on-disk eruptive events observed with a high temporal resolution by the Ond?ejov Observatory optical spectrograph. Analysis of the time series of full width at half-maximum (FWHM) in Hα, Hβ, and radio and soft X-ray (SXR) fluxes indicates two phenomenologically distinct types of observations which differ significantly in the timing of FWHM and SXR/radio fluxes. We investigated one such unusual case of a limb eruptive event in more detail. Synthesis of all observed data supports the interpretation of the Hα broadening in the sense of regular macroscopic plasma motions, contrary to the traditional view (emission from warm dense plasma). The timing and observed characteristics indicate that we may have actually observed the initiation of a prominence eruption. We test this scenario via modeling of the initial phase of the flux rope eruption in a magnetohydrodynamic (MHD) simulation, calculating subsequently – under some simplifying assumptions – the modeled Hα emission and spectrum. The modeled and observed data correspond well. Nevertheless, the following question arises: To what extent is the resulting emission sensitive to the underlying model of plasma dynamics? To address this issue, we have computed a grid of kinematic models with various arbitrary plasma flow patterns and then calculated their resulting emission. Finally, we suggest a diagnostics based on the model and demonstrate that it can be used to estimate the Alfvén velocity and plasma beta in the prominence, which are otherwise hard to obtain.     

The X-ray jet and lobes of PKS 1354+195 (=4C 19.44)

We present a Chandra image of the quasar, jet, and lobes of PKS 1354+195 (=4C 19.44). The radio jet is 18 arcsec long, and appears to be very straight. The length gives many independent spatial resolution elements in the Chandra image while the straightness implies that the geometrical factors are constant along the jet although their values are uncertain. We also have 4 frequency radio images with half to one arcsecond angular resolution, and use HST and Spitzer data to study the broad band spectral energy distributions. The X-ray and radio spectra are both consistent with a spectrum f _ν ∝ ν ^−0.7 for the integrated jet. Using that spectral index, the model of inverse Compton scattering of electrons on the cosmic microwave background (IC/CMB) gives magnetic field strengths and Doppler factors that are relatively constant along the jet. Extended X-ray emission is evident in the direction of the otherwise unseen counter-jet. X-ray emission continues past the radio jet to the South, and is detected within both the southern and northern radio lobes.     

Evaluation of the budget for silicic acid in Cascadia Basin deep water

Between 2 and 3 km depth, North Pacific deep waters contain a plume of water with high silicic acid concentrations. The plume extends outward from Cascadia Basin (the Washington Margin), where waters can contain in excess of 200 μM off the coast of Oregon and Washington. To identify the source of the high Si concentrations in Cascadia Basin, we measured silicic acid and germanium concentrations in deep waters, and their fluxes from sediments using incubated cores. The mean flux of silicic acid into bottom waters is 0.81±0.05 mmol/m²-day, and the Ge/Si ratio of this flux is 0.7±0.1 μmol/mol. A box model, incorporating these results with hydrographic data, indicates that (1) no more than 5% of the silicic acid added to Basin deep waters can have a hydrothermal source (either hot or warm seeps), and (2) the total input of silicic acid to Basin deep waters is 0.06±0.02 Tmol/y. This input is nearly all from remineralized biogenic debris and should contribute about 0.5% of the 14 Tmol/y that are estimated to be necessary to maintain the North Pacific plume.