The formation of iron hydroxide coatings in an Emscher Marl: inverse reactive transport modeling of reactive surface area

The possible effects of iron oxide coatings on the reactive surface area of calcite in column experiments have been studied and then modeled numerically. A column with six compartments separated by teflon filters was packed with Emscher Marl (essentially calcite). The marl was initially mixed with corundum as an internal standard. Hydrochloric acid with pH 3 was percolated through the column for a given period, after which the mineralogical changes were quantified by X-ray diffraction ex-situ. Then, the column compartments were re-filled and again percolated with HCl. This procedure was repeated five times. The losses and gains of calcite in the column compartments provided the data basis for modeling the entire experiment with the reactive transport code TOUGHREACT using a kinetic rate law. The experimental results showed that during the first period, loss of calcite in the first compartment is about 50 % less than that determined from the theoretical analysis. This showed the entrance of acid into the higher compartments through preferential flow paths (wormholes) which was observed at the boundary between sample and cell wall. This pattern could also be verified by the relatively high Peclet and low Damköhler numbers, showing a strongly advection-dominant system. Apart from calcite dissolution, structural Fe²⁺ released from calcite oxidized and formed iron hydroxide (FeOOH) coatings along preferential fluid pathways. Despite specific assumptions such as using pure calcite in the model, a comparison between modeling results and lab observations is instructive. The simulated calcite change patterns in the most compartments are consistent with the experiments. Some discrepancies are noted in the last compartment, which may bring the attention to a need for model improvements.     

Der postkaledonische paläozoische Vulkanismus in Ostgrönland

Ohne Zusammenfassung     

Operator splitting methods for degenerate convection–diffusion equations II: numerical examples with emphasis on reservoir simulation and sedimentation

We present an accurate numerical method for a large class of scalar, strongly degenerate convection–diffusion equations. Important subclasses are hyperbolic conservation laws, porous medium type equations, two-phase reservoir flow equations, and strongly degenerate equations coming from the recent theory of sedimentation–consolidation processes. The method is based on splitting the convective and the diffusive terms. The nonlinear, convective part is solved using front tracking and dimensional splitting, while the nonlinear diffusion part is solved by an implicit–explicit finite difference scheme. In addition, one version of the implemented operator splitting method has a mechanism built in for detecting and correcting unphysical entropy loss, which may occur when the time step is large. This mechanism helps us gain a large time step ability for practical computations. A detailed convergence analysis of the operator splitting method was given in Part I. Here we present numerical experiments with the method for examples modelling secondary oil recovery and sedimentation–consolidation processes. We demonstrate that the splitting method resolves sharp gradients accurately, may use large time steps, has first order convergence, exhibits small grid orientation effects, has small mass balance errors, and is rather efficient.     

Ordovician magnetostratigraphy: Llanvirn-Caradoc limestones of the Baltic platform

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Palaeomagnetic sampling has been performed covering 43 stratigraphic levels within the Baltoscandian Ordovician carbonates. After removing a ubiquitous Permo-Carboniferous (287 ± 14 Ma) remagnetization between 200 and 500 C, a Llanvirn-Caradoc reversal stratigraphy is delineated by components with maximum unblocking temperatures up to 550-580 C. Three reversed (SE, down) and three normal (NW. up) antipodal polarity intervals have been recognized. A primary/early diagenetic remanence age is therefore inferred for the stratigraphically linked polarity chrons. Primary magnetizations are resident in detrital/biogenic or early diagenetically formed single- and pseudo-single domain magnetite phases and subordinate early diagenetic pigmentary haematite.
The recognition of a primary remanence within these well-dated Ordovician carbonates has the following important tectonic and magnetostratigraphic consequences.
(1) Accurate time-calibration of the Baltic APW path implies that rapid counterclockwise rotation took place in late Tremadoc and Llandeilo times. The Arenig-Llanvirn epochs are characterized by a 'still stand'. Baltica occupied intermediate to high Southerly latitudes during the early Ordovician (Tremadoc-Llanvirn). Systematic northward drift is recognized in post-Llanvirn times.
(2) A time-calibrated Ordovician reversal stratigraphy is proposed. Presently available data suggest the geomagnetic field was predominantly reversely polarized during Tremadoc and Arenig times. Two normal polarity zones of short duration are identified within mid-Llanvirn and mid-Llandeilo strata. Discontinuities within the succession may mask other short-period events. Late Llandeilo to mid-Caradoc times were then characterized by a normal polarity field.     

Green corona emission,calcium plage activity and solar sector magnetism

The relationship between coronal green line emission and solar sector magnetism has been studied statistically for the years 1965–1969. This period includes the rising portion and the maximum phase of solar cycle no. 20. In the years around solar maximum the results suggest the existence of longitudinal magnetic arcades at the solar sector boundaries. The arcades extend from at least 50°N to 50°S and are flanked by north-south oriented coronal holes about 90° apart. In the rising portion of the cycle the general picture consists of a high green line intensity structure to the west of the boundary and a region of low intensity several days wide to the east of it.Analyses of the calcium plage distribution in the years 1962–1969 show that, on the average, there is a tendency for the plage activity to peak near the sector boundaries. It is further concluded that the activity distribution suggested by Wilcox (1971a, b) is not typical of the behaviour of solar activity relative to the sector boundaries.     

Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from the Western Mediterranean Sea

The life habits and microhabitat selection of speleophilic gobiid fishes were investigated on the Balearic Island of Ibiza (western Mediterranean Sea). Corcyrogobius liechtensteini (Kolombatović, 1891) was the most frequent species within submarine crevices, cavities and caves. Didogobius splechtnai Ahnelt & Patzner, 1995 co-occurred with C. liechtensteini in several cases but showed a clear spatial separation based on a different microhabitat preference. The microhabitat selection of both species was confirmed by habitat-choice experiments in anaquarium. Corcyrogobius liechtensteini was frequent in depths between 5 m and 25 m and attained abundances of 14.2 individuals · m⁻². This species inhabited the ceilings and upper parts of the walls within the caves. D. splechtnai was mainly found between 7 m and 11 m and showed abundances of approximately 2 indivi-duals · m⁻². This species occupied the fine sediment bottoms in the innermost parts of crevices and caves. The growth and the maximum age of both species were determined by length-frequency distributions. The overall sex ratio from catches of three different years are given for C. liechtensteini .     

A multi-model comparison of Atlantic multidecadal variability

A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models.     

Simulating the effects of the 1991 Mount Pinatubo volcanic eruption using the ARPEGE atmosphere general circulation model

The climate changes that occured following the volcanic eruption of Mount Pinatubo in the Phillippines on 15 June 1991 have been simulated using the ARPEGE atmosphere general circulation model （AGCM）. The model was forced by a reconstructed spatial-time distribution of stratospheric aerosols intended for use in long climate simulations. Four statistical ensembles of the AGCM simulations with and without volcanic aerosols over a period of 5 years following the eruption have been made, and the calculated fields have been compared to available observations. The model is able to reproduce some of the observed features after the eruption, such as the winter warming pattern that was observed over the Northern Hemisphere （NH） during the following winters. This pattern was caused by an enhanced Equator-to-pole temperature gradient in the stratosphere that developed due to aerosol heating of the tropics. This in turn led to a strengthening of the polar vortex, which tends to modulate the planetary wave field in such a way that an anomalously positive Arctic Oscillation pattern is produced in the troposphere and at the surface, favouring warm conditions over the NH. During the summer, the model produced a more uniform cooling over the NH.