Metamorphic reactions between fluid inclusions and mineral hosts. I. Progress of the reaction calcite+quartz=wollastonite+CO2 in natural wollastonite-hosted fluid inclusions

 At the Bufa del Diente contact-metamorphic aureole, brine infiltration through metachert layers embedded in limestones produced thick wollastonite rims, according to Cc+Qz=Wo+CO₂. Fluid inclusions trapped in recrystallized quartz hosts include: (1) high salinity four phase inclusions [Th(V-L)=460–573° C; Td(salts)=350–400° C; (Na+K)_Cleq=64–73 wt%; X _{CO 2}≤0.02]; (2) low density vapour-rich CO₂-bearing inclusions [Th(L-V)≈500±100° C; X _{CO 2}=0.22–0.44; X _NaCl≤0.01], corresponding to densities of 0.27± 0.05 gcm⁻³. Petrographical observations, phase compositions and densities show that the two fluids were simultaneously trapped in the solvus of the H₂O-CO₂-salts system at 500–600° C and 700±200 bars. The low density fluid was generated during brine infiltration at the solvus via the wollastonite producing reaction. Identical fluid types were also trapped as inclusion populations in wollastonite hosts 3 cm adjacent to quartz crystals. At room temperature, both fluid types additionally contain one quartz and one calcite crystal, generated by the back-reaction Wo+CO₂=Cc+Qz of the host with the CO₂-proportion of the fluid during retrogression. All of the CO₂ was removed from the fluid. On heating in the microstage, the reaction progress of the prograde reaction was estimated via volume loss of the calcites. In vapour-rich fluids, 50% progress is reached at 490–530° C; 80% at 520–560° C; and 100% at 540–590° C, the latter representing the trapping temperatures of the original fluid at the two fluid solvus. The progress is volume controlled. With knowledge of compositions and densities from unmodified inclusions in quartz and using the equation of state of Duan et al. (1995) for H₂O-CO₂-NaCl, along with f _{CO 2}-values extracted from it, the reaction progress curve was recalculated in the P-T-X-space. The calculated progress curve passes through the two fluid solvus up to 380° C/210 bars, continues in the one fluid field and meets the solvus again at trapping conditions. The P-T slope is steep, most of the reaction occurs above 450° C and there is high correspondence between calculated and measured reaction progress. We emphasize that with the exception of quartz, back-reactions between inclusion fluids and mineral hosts is a common process. For almost any prograde metamorphic mineral that was formed by a devolatilization reaction and that trapped the equilibrium fluid or any peak metamorphic fluid as an inclusion, a fluid-host back-reaction exists which must occur somewhere along the retrograde path. Such retrograde reactions may cause drastic changes in density and composition of the fluid. In most cases, however, evidence of the evolving mineral assemblages is not given for they might form submicroscopical layers at the inclusion walls. Received: 15 March 1995 / Accepted: 1 June 1995     

On the ice age glaciation of the Tibetan highlands and its transformation into a 3-D model

We present an interdisciplinary study on data and modeling intercomparison, concerning the possible existence of a Tibetan ice sheet and its climatological implications during the ice age. In the ice sheet model the fields of ice flow and temperature are calculated, and a highly parameterized formulation of the yearly snow balance is used, defining the forcing at the surface of the ice sheet. The data set used, supplies the height of the equilibrium line of the glaciers (=ELA) and documents the maximum extension of the glaciated areas. With prescribed snow accumulation above the ELA and melting below, the model is integrated for 10 000 model years and the model glaciation is then compared with the data.The main results are: Provided the height of the glacial equilibrium line has been reconstructed correctly, a Tibetan ice sheet can be bult up within 10 000 model years, using moderate rates of precipitation (maximum snow fall: 100 mm/year). Comparison of data and model glaciation suggests an increase of precipitation from the NW to the E of Tibet and from the S to the NE, which reflects the presently observed pattern of the monsoon circulation.     

Erprobung des Dreissena-Monitors,eines neuen Biotestsystems mit der Zebramuschel (Dreissena polymorpha), in der Rhein-Gütemeßstation Karlsruhe Evaluation of the Dreissena-monitor at the River Rhine — a New Biological Monitoring System Based on the Zebra Mussel Dreissena polymorpha

Object of the present study is a new biomonitor using Dreissena polymorpha PALLAS as testorganism. The status of the shell gape and the valve movements are parameters to indicate toxic discharges. With the aid of some toxicity tests using trichloroethylene, chloroform, ethylparathion, and copper(II)sulfate, the detection efficiency of the “Dreissena-monitor” was described and compared with those of biomonitors in literature. The use of the monitors in the control of sewage, drinking water, and natural waters is discussed. The critical concentrations at which an alarm was set by the “Dreissena-monitor” were 0.03 to 0.1 mg/L with copper(II)sulfate, 7.5 to 8.2 mg/L with trichloroethylene, 33 mg/L with chloroform, and 0.8 to 0.9 mg/L ethyl parathion. Thereby, the alarm was always set within 5 to 35 minutes. Possible fields of application are especially the control of sewage effluents and their immediate environments.     

The probability of proof in geomorphology —an example of the application of information theory to a new kind of glacigenetic morphological type,the ice-marginal ramp (Bortensander)

The scientific acceptance of presentations of proof is largely dependent upon the parts of mathematical logic upon which they are based. This explains the trend of introducing quantitative methods into tho disciplines which — due to the historical dimensions of their subjects — have so far followed a qualitative analysis of character coincidences i.e. a typogenetic form of reasoning. But the application of reductionistic quantification such as was followed in the GMK 25 project foundered because of the polymorphic structure of the phenomena. It was this that made geomorphological proof so difficult, since an inductive basis for general lawful relations can only be provided by regionally detailed observations of complexes with developments of their own. The application of information theory however e.g. in relation to the glacigenetic Type ‘Bortensander’ or ice-marginal ramps (IMR) now allows the determination of the probability of the coincidental occurrence of characteristics and a measure of the probability of the causal nexus upon which this is based. By transposing the basis of induction on to an abstract plane a high degree of proof of typogenetic arguments in geomorphology may be provided. The quantification here does not count the elements of the proof directly but is related to the occurrence of those indicators which form the empirically based qualitative units of the inductive key. The author gratefully acknowledges the translation of this paper rendered by Cyril A. Halstead, Glasgow     

Evaluation of an urban land surface scheme over a tropical suburban neighborhood

A two-step statistical downscaling method has been reviewed and adapted to simulate twenty-first-century climate projections for the Gulf of Fonseca (Central America, Pacific Coast) using Coupled Model Intercomparison Project (CMIP5) climate models. The downscaling methodology is adjusted after looking for good predictor fields for this area (where the geostrophic approximation fails and the real wind fields are the most applicable). The method’s performance for daily precipitation and maximum and minimum temperature is analysed and revealed suitable results for all variables. For instance, the method is able to simulate the characteristic cycle of the wet season for this area, which includes a mid-summer drought between two peaks. Future projections show a gradual temperature increase throughout the twenty-first century and a change in the features of the wet season (the first peak and mid-summer rainfall being reduced relative to the second peak, earlier onset of the wet season and a broader second peak).     

Catchments as reactors: a comprehensive approach for water fluxes and solute turnover

Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples.     

Palaeoenvironment in northern Norway between 22.2 and 14.5 cal. ka BP

The stratigraphy of lake Endletvatn on northern Andøya, northern Norway, has been revisited to improve the understanding of the palaeoenvironment in the region during the Last Glacial Maximum (LGM). Four high‐quality cores were analysed with respect to various lithological parameters and macrofossil content, supplemented by 47 AMS radiocarbon dates. The sediments indicate a low‐energy environment with a mean sedimentation rate of 0.5 mm a^?1. We infer perennially frozen ground in the surroundings during the LGM. Climate proxies indicate a high arctic climate (i.e. July mean temperatures between 0 and 3°C) throughout most of the LGM. The warmest periods are marked by a rise in seed, moss and animal fossils, and often also by higher organic production in the lake. These periods took place from 21.4 to 20.1, from 18.8 to 18.1, around 17 and from 16.4 cal. ka BP onwards. The shifts between the different climatic regimes occurred rapidly – probably during one or two decades. The present data do not support recently published conclusions stating that Picea, Pinus and Betula pubescens grew on Andøya during parts of the LGM. The highest relative sea level after the final deglaciation on northern Andøya is bracketed between 36 and 38 m a.s.l. It occurred between 21.0 and 20.3 cal. ka BP, peaking around 20.7 cal. ka BP. The final deglaciation of the northern tip of Andøya occurred 22.2 cal. ka BP. Then the western margin of the Andfjorden ice stream receded to the Kjølhaugen Moraine and shortly thereafter to the Endleten Moraine. Our research confirms that northern Andøya is a key location for understanding the natural environment in northwestern Europe during the LGM.     

An improved sampling rule for mapping geopotential functions of a planet from a near polar orbit

One of the limiting factors in the determination of gravity field solutions is the spatial sampling. Especially during phases, when the satellite repeats its own track after a short time, the spatial resolution will be limited. The Nyquist rule-of-thumb for mapping geopotential functions of a planet, also referred to as the Colombo–Nyquist rule-of-thumb, provides a limit for the maximum achievable degree of a spherical harmonic development for repeat orbits. We show in this paper that this rule is too conservative, and solutions with better spatial resolutions are possible. A new rule is introduced which limits the maximum achievable order (not degree!) to be smaller than the number of revolutions if the difference between the number of revolutions and the number of nodal days is of odd parity and to be smaller than half the number of revolutions if the difference is of even parity. The dependence on the parity is reflected in the eigenvalue spectrum of the normal matrix and becomes especially important in the presence of noise. The rule is based on applying the Nyquist sampling theorem separately in North–South and East–West direction. This is only possible for satellites in highly inclined orbits like champ and grace. Tables for these two satellite missions are also provided which indicate the passed and (in case of grace) expected repeat cycles and possible degradations in the quality of the gravity field solutions.