Sublimation pressure and sublimation enthalpy of H2O ice Ih between 0 and 273.16 K

The sublimation of water in the region of extremely low pressures and temperatures meets increasing interest for the exploration of icy cosmic bodies. At temperatures below 130 K, the shape of the sublimation curve of H₂O is not known; neither experimental data nor theoretical treatments exist for this region. Based upon theoretical upper and lower bounds for the heat capacity of water vapor in this range, a narrow region in the pressure-temperature diagram is identified which must necessarily enclose the sublimation curve down to virtually any lower pressures and temperatures. Within this region, an approximate sublimation curve is computed from the 2006 Gibbs potential of ice Ih, using available heat capacity data points of water vapor between 10 and 130 K. The theoretical zero-point limiting law of the sublimation pressure is derived. Valid between 20 and 273.16 K, correlation equations for the sublimation enthalpy and the sublimation pressure are fitted to the computed data. All quantities are expressed in the 1990 temperature scale ITS-90. Under cosmic conditions, our results suggest that the sublimation of ice is unlikely below 50 K and impossible below 23 K.     

Alternative Validation of a LC-MS/MS-Multi-Method for Pesticides in Drinking Water

The development of instrumental analytics such as the LC-MS/MS has made it possible to quickly determine many component concentrations in a single chromatogram. However, the validation of such multi-methods needs new strategies for robustness and optimization. Statistical execution of analytical tests is one tool that can be utilized to meet this requirement. A Central Composite Design (CCD) was utilized for the validation of an LC-MS/MS multi-method for 84 analytes. The experimental design includes six design variables and two non-design variables (response variables). Concentration, ionization temperature, dwell time, gradient, flow (of eluent), and spraying/curtain gas (continuous design variables) were varied on five different levels; the whole design encompassed 91 runs. To investigate the robustness of a LC-MS/MS method both peak sensitivity and chromatographic separation had to be verified. Therefore, two non-design variables were necessary. The distribution of the peaks over analysis time was applied to describe the quality of the chromatographic separation. The sensitivity was described with the signal to noise ratio (S/N). The evaluation of the measured data was accomplished with the Analysis of Variance (ANOVA) and the Response Surface Methodology (RSM). Three main effects (concentration, ionization temperature, dwell time) and no significant interaction effect were found for the response variable “S/N”. The variables of concentration, ionization temperature, and dwell time had no significant effects for the response variable “S/N”. The ANOVA of the response variable chromatographic separation abandoned no significant effects as well. Therefore, robustness of the method can be guaranteed for all non significant design variables.     

Fidelity and time resolution of the magnetostratigraphic record in Siwalik sediments: high-resolution study of a complete polarity transition and evidence for cryptochrons in a Miocene fluviatile section

The Surai Khola section in southwest Nepal, a 5000 m continuously exposed record of fluvial sedimentation since Middle Miocene, was revisited for high-resolution magnetostratigraphy in sequences with expected cryptochrons and reversals of the geomagnetic field. Polarity intervals with durations of a few tens of thousands of years are recorded as zones of stable palaeomagnetic directions. Polarity transitions are recorded as zones with complex demagnetization behaviour of specimens in the sedimentary column. Almost antiparallel palaeoremanence directions, residing in different haematite phases in the same specimens, could generally not be separated properly by thermal demagnetization. Differing demagnetization paths for neighbouring specimens during a reversal suggest that measured transitional directions are not true geomagnetic field directions, but rather are generated by the superposition of variable amounts of at least two almost antiparallel components of magnetization. Accompanying studies of recent river sand deposits demonstrate that these sediments acquire a true depositional remanent magnetization (DRM) with considerable inclination errors and scattered directions for individual specimens.     

The exceptional Oder flood in summer 1997 — distribution patterns of the oder discharge in the Pomeranian Bight

The exceptional Oder flood in summer 1997 was a unique event in order to investigate the impacts on and the consequences for the ecosystem of the Baltic Sea of about 6.5 km³ additional water loaded with nutrients and contaminants and discharged within only 5 weeks. About 15 institutions participated in this investigation in both the Szczecin Lagoon and the Pomeranian Bight. The Baltic Sea Research Institute Warnemünde studied the water and nutrient inflow, the spreading of the Oder discharge, and the impact of the discharge on the ecosystem. The main topic of the presented investigations is a detailed study of the spatial and temporal spreading of the extreme river discharge in the Pomeranian Bight and the southern Baltic Sea by satellite data, ship observations and continuous buoy measurements as well as numerical modelling. The meteorological conditions were characterized by mainly easterly winds which guided the outflowing riverine water along the German coast into the Arkona Sea. The spatial and temporal development of the distribution patterns of the Oder discharge was monitored by about 80 Sea Surface Temperature (SST) images of NOAA satellites. Shipborne measurements showed that the vertical extent of the Oder plume ranged between 5 and 7 metres. The concentrations of inorganic nutrients, except higher silicate, were comparable to typical winter/early spring values (seasonal maximum) in this region. The high dilution effect of the flood water reduced the concentration of contaminants and thus, prevented a direct negative impact of trace metals and chlorinated organic compounds on the marine environment. Coupled physical-biochemical modelling in combination with SST-images demonstrated the temporal development and satellite data in the visible spectral range delivered the maximum extent of discharged river water into the southern Arkona Sea where a further western transport was limited by the upwelling region off Hiddensee. Thus, all detected effects of the Oder flood were confined to the Pomeranian Bight and the southern Arkona Sea, without long-term consequences for the ecosystem.     

Plate kinematics and the gravity field

Both the system of plate motions and the global gravity field or the geoid are now so precisely known that it seems worthwhile to look for quantitative relationships. Some aspects, such as the general occurrence of positive gravity and geoid anomalies in regions of plate convergence, have long been known. Our aim is to describe the gravitational field in terms of plate-kinematic parameters and we present a preliminary step in this direction: for four plates (Pacific, Nazca, Indian, American) we have computed the correlation of the Gem 8 geoid heights (with reference to an ellipsoid of 1/298.255 ellipticity) with distance from the poles of motion and distance from the axes in an “absolute” frame. The geoid tends first to drop from the ridge axes to at least 10° distance and then to rise toward the convergence zones. This trend is strongest for the Indian plate in collision with Eurasia, is smaller, but very clear for the oceanic Pacific and Nazca plates, and is not developed for the American plate which does not subduct. We did not find a consistent relationship for the geoid with distance from the pivots. A possible interpretation of the results is the return flow of the large-scale mantle circulation.     

Chemical reactions of sea water with rocks and freshwater: Experimental and field observations on brackish waters in Israel

Four major processes are observed to take place in the coastal aquifer of Israel, detectable even in the short times of water contact with the carbonate-containing host rocks. Three are chemical reactions, Ca²⁺-Mg²⁺ exchange, Na⁺-Ca²⁺ or Na⁺-Mg²⁺ base exchange, SO^2?₄ reduction and the fourth is dilution by freshwater. These reactions and their effects on the chemical composition of the waters were demonstrated experimentally. The range of chemical changes observed in the laboratory experiments overlap the range of the studied natural waters. This indicates that simulation of geologically long-term rock-water interaction could be achieved in laboratory experiments even at low temperatures.     

Atmospheric noble gases in volcanic glasses from the southern Lau Basin: origin from the subducting slab?

Noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the Valu Fa Ridge (VFR) in the southern Lau Basin. The samples are the least differentiated ones from this area, and they display enrichments in fluid-mobile elements similar to the nearby island arc. ³He/⁴He ratios are slightly below average MORB (6.8–7.8 times atmospheric), whereas Ne, Ar, Kr, and Xe have isotopic compositions very similar to air. Together with previously published data from the Valu Fa Ridge and other spreading segments in the Lau Basin, our data show a systematic latitudinal variation of increasing Ne, Ar, Kr, and Xe abundances from north to south as well as Ne and Ar isotopic compositions changing from MORB-like to atmosphere-like in the same direction. Moreover, isotopic compositions and noble gas abundances of the lavas correlate strongly with Ba/Nb ratios and H₂O concentrations. Based on these observations and mass balance arguments, we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust. Our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar He and Ne. In addition to the fact that ratios of He to heavy noble gases are small in aged ocean crust, He has possibly fractionated from the other noble gases due to its higher diffusivity, and thus He transport from the subducting slab into the mantle wedge is probably insignificant. We propose that the ³He/⁴He ratios lower than MORB observed in the VFR lavas result from radiogenic ingrowth of He in a highly depleted, and hence degassed, mantle wedge after the enrichment of U and Th released from the downgoing slab.