On reducing ambiguity in the interpretation of transient electromagnetic sounding data1

An attempt to resolve non-uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow-up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non-uniqueness in the determination of the depth to fresh/saline groundwater interface to be resolved.     

Ein Cluster-Verfahren zur richtungsstatistischen Analyse tektonischer Daten

Zusammenfassung Es wird ein Cluster-Verfahren vorgestellt, mit dem in einer Menge von Richtungsdaten die Einzelwerte mit Hilfe eines vorgegebenen variablen Trennmaßes zu verschiedenen Gruppen zusammengefaßt werden. Richtungsstatistische Parameter werden für jede Gruppe berechnet. Außerdem wird ein Signifikanztest für die Trennung der Gruppen voneinander durchgeführt.

---

A cluster algorithm for orientation data is presented. It separates groupes of neighboring data by the use of a variable measure of separation. Statistical orientation parameters are calculated for each group and a significance test for the separation of the groups is carried out.

---

Résumé Un algorithme pour l'analyse des groupes de vecteurs est présenté. Il sépare des groupes de données voisines en utilisant une mesure variable de séparation. Des paramètres statistiques d'orientation sont calculés pour chacun d'eux, et un test de signification pour séparation des groupes est effectué.

---

«» , , , . . .

     

Impacts of experimental dredged material disposal on a shallow, sublittoral macrofauna community in Mecklenburg Bay (western Baltic Sea)

An experimental disposal of dredged material was performed in June 2001 at two adjacent sites in Mecklenburg Bay (western Baltic Sea) to investigate the impacts on a sublittoral fauna community (macrozoobenthos). Temporal changes in community parameters were analysed: Total abundance and multidimensional scaling (MDS) ordination results showed that dredged material disposal causes significant changes in benthic assemblages in comparison to the original situation before the disposal activities. The bivalves Arctica islandica and Macoma balthica were almost not affected by the disposal. Abundances of the polychaete N. hombergii as well as the epibenthic cumacean D. rathkei decreased by a factor of 1.4-3.9 whereas most other invertebrates suffered even more. Two years after the experimental disposal a high level of benthic recovery was found, but also a change in dominance structure. These changes are rather due to inter-annual variability in regional benthic recruitment processes in the Mecklenburg Bay than due to the disposal.     

The distribution of short-lived radioisotopes in the early solar system and the chronology of asteroid accretion, differentiation, and secondary mineralization

We evaluate initial (²⁶Al/²⁷Al)_I, (⁵³Mn/⁵⁵Mn)_I, and (¹⁸²Hf/¹⁸⁰Hf)_I ratios, together with ²⁰⁷Pb/²⁰⁶Pb ages for igneous differentiated meteorites and chondrules from ordinary chondrites for consistency with radioactive decay of the parent nuclides within a common, closed isotopic system, i.e., the early solar nebula. The relative initial isotopic abundances of ²⁶Al, ⁵³Mn, and ¹⁸²Hf in differentiated meteorites and chondrules are consistent with decay from common solar system initial values, here denoted by I(Al)_SS, I(Mn)_SS, and I(Hf)_SS, respectively. I(Mn)_SS and I(Hf)_SS = 9.1 ± 1.7 × 10⁻⁶ and 1.07 ± 0.08 × 10⁻⁴, respectively, correspond to “canonical” I(Al)_SS = 5.1 × 10⁻⁵. I(Hf)_SS so determined is consistent with I(Hf)_SS = 9.72 ± 0.44 × 10⁻⁵ directly determined from an internal Hf-W isochron for CAI minerals. I(Mn)_SS is within error of the lowest value directly measured for CAIs. We suggest that erratically higher values measured for CAIs in carbonaceous chondrites may reflect proton irradiation of unaccreted CAIs by the early Sun after other asteroids destined for melting by ²⁶Al decay had already accreted. The ⁵³Mn incorporated within such asteroids would have been shielded from further “local” spallogenic contributions from within the solar system. The relative initial isotopic abundances of the short-lived nuclides are less consistent with the ²⁰⁷Pb/²⁰⁶Pb ages of the corresponding materials than with one another. The best consistency of short- and long-lived chronometers is obtained for (¹⁸²Hf/¹⁸⁰Hf)_I and the ²⁰⁷Pb/²⁰⁶Pb ages of angrites. (¹⁸²Hf/¹⁸⁰Hf)_I decreases with decreasing ²⁰⁷Pb/²⁰⁶Pb ages at the rate expected from the 8.90 ± 0.09 Ma half-life of ¹⁸²Hf. The model solar system age thus determined is T_SS,Hf-W = 4568.3 ± 0.7 Ma. (²⁶Al/²⁷Al)_I and (⁵³Mn/⁵⁵Mn)_I are less consistent with ²⁰⁷Pb/²⁰⁶Pb ages of the corresponding meteorites, but yield T_SS,Mn-Cr = 4568.2 ± 0.5 Ma relative to I(Al)_SS = 5.1 × 10⁻⁵ and a ²⁰⁷Pb/²⁰⁶Pb age of 4558.55 ± 0.15 Ma for the LEW86010 angrite. The Mn-Cr method with I(Mn)_SS = 9.1 ± 1.7 × 10⁻⁶ is useful for dating accretion (if identified with chondrule formation), primary igneous events, and secondary mineralization on asteroid parent bodies. All of these events appear to have occurred approximately contemporaneously on different asteroid parent bodies. For I(Mn)_SS = 9.1 ± 1.7 × 10⁻⁶, parent body differentiation is found to extend at least to ∼5 Ma post-T_SS, i.e., until differentiation of the angrite parent body ∼4563.5 Ma ago, or ∼4564.5 Ma ago using the directly measured ²⁰⁷Pb/²⁰⁶Pb ages of the D’Orbigny-clan angrites. The ∼1 Ma difference is characteristic of a remaining inconsistency for the D’Orbigny-clan between the Al-Mg and Mn-Cr chronometers on one hand, and the ²⁰⁷Pb/²⁰⁶Pb chronometer on the other. Differentiation of the IIIAB iron meteorite and ureilite parent bodies probably occurred slightly later than for the angrite parent body, and at nearly the same time as one another as shown by the Mn-Cr ages of IIIAB irons and ureilites, respectively. The latest recorded episodes of secondary mineralization are for carbonates on the CI carbonaceous chondrite parent body and fayalites on the CV carbonaceous chondrite parent body, both extending to ∼10 Ma post-T_SS.     

Modelling ecohydrological feedbacks in forest and grassland plots under a prolonged drought anomaly in Central Europe 2018–2020

Recent studies have highlighted the importance of understanding ecohydrological drought feedbacks to secure water resources under a changing climate and increasing anthropogenic impacts. In this study, we monitored and modelled feedbacks in the soil–plant-atmosphere continuum to the European drought summer 2018 and the following 2 years. The physically based, isotope-aided model EcH₂O-iso was applied to generic vegetation plots (forest and grassland) in the lowland, groundwater-dominated research catchment Demnitzer Millcreek (NE Germany; 66 km²). We included, inter alia, soil water isotope data in the model calibration and quantified changing “blue” (groundwater recharge) and “green” (evapotranspiration) water fluxes and ages under each land use as the drought progressed. Novel plant xylem isotope data were excluded from calibration but were compared with simulated root uptake signatures in model validation. Results indicated inter-site differences in the dynamics of soil water storage and fluxes with contrasting water age both during the drought and the subsequent 2 years. Forest vegetation consistently showed a greater moisture stress, more rapid recovery and higher variability in root water uptake depths from a generally younger soil water storage. In contrast, the grassland site, which had more water-retentive soils, showed higher and older soil water storage and groundwater recharge fluxes. The damped storage and flux dynamics under grassland led to a slower return to younger water ages at depth. Such evidence-based and quantitative differences in ecohydrological feedbacks to drought stress in contrasting soil-vegetation units provide important insights into Critical Zone water cycling. This can help inform future progress in the monitoring, modelling and development of climate mitigation strategies in drought-sensitive lowlands.     

On the gravitational seiches of lake constance and their generation

Although the surface seiches of Lake Constance have been observed as early as 1549 and received serious scientific attention since 1893 in the classical work of Forel, they have only recently been investigated by modern hydrodynamical methods. It is the goal of this report to critically compare theoretical predictions of the periods and form of seiches with recent and historical observations as well as to examine the mechanisms of generation of these surface oscillations by means of applying measured atmospheric forcing in Lake Constance to a theoretical model. In the first part of this work, we review the findings of a large number of previous investigations, while the second part consists of a verification analysis of the model predictions of seiches. In the final part, we present a theory, predictions and observations of the excitation of seiches by arbitrary wind and barometric pressure gradient forcing.     

Das Spektrum der internen Bewegungsvorgänge der westlichen Ostsee im Periodenbereich von 0,3 bis 60 Minuten

Zusammenfassung Für ein Beobachtungsbeispiel (Stromgeschwindigkeit, Dichte) aus der Kieler Bucht wird eine Deutung ausgeprägter Maxima der zugehörigen Spektren zwischen 0,3 und 60 Minuten durch interne Wellen gegeben. Mit einer beobachteten Periode von zwei Minuten durchgeführte Rechnungen ergeben eine starke Abhängigkeit der Wellenlänge von der mittleren Strömung . Im Falle erhält man bei 23,5 m Wassertiefe eine Wellenlänge von etwa 70 m, im Falle von etwa 85 m. Die berechneten Schwingungen stellen uneigentliche interne Wellen dar (W. Krauß [1966]). Die Interpretation durch eine Grenzflächenwelle führt auf eine Wellenlänge von 86 m, die nur geringfügig von denen der internen Wellen 1. Ordnung in stetig sich ändernder Strömung abweicht.In einer theoretischen Untersuchung werden kleinräumige Anfangsstörungen (z. B. momentane Druckänderungen an der Meeresoberfläche) als mögliche Ursache für die Entstehung kurzperiodischer interner Wellen erkannt. Es zeigt sich, daß kurzzeitig wirksame Anfangsbeschleunigungen in ihrem Einwirkungsbereich stehende, allmählich abklingende interne Wellen erzeugen, während in der Umgebung gleichzeitig fortschreitende Wellen entstehen, deren Amplituden mit wachsender Entfernung vom Erregungsgebiet abnehmen. Die Perioden der Schwingungen haben größere Werte als die zu einer exponentiellen Schichtung gehörige Väisäläperiode und verändern sich in Abhängigkeit von der Größe des Anregungsgebietes wie die zellularer Stabilitätsschwingungen.

---

The powerspectrum of internal motions in the western baltic between the periods 0.3 and 60 minutes. Part 1: Interpretation of the wavelike component of the internal unrest in the sea

Summary The powerspectra of the internal unrest in the sea show marked peaks in the range of periods between 0.3 and 60 minutes. An interpretation of these phenomena is given in terms of internal waves for a specific example obtained from short periodic current and density variations in the Kieler Bucht. The numerical calculations for an observed period of two minutes show an important influence of the vertical distribution of the current on the wavelength. In the case of the wavelength amounts to about 70 m, where as in the case of the length is about 85 m, assuming a depth of the sea of 23.5 m. The computed oscillations represent improper internal waves (W. Krauß [1966]). Interpretation by internal boundary waves yields a wavelength of 86 m, which is slightly different only from those of the first mode of internal waves in the case of continuously varying .By a theoretical investigation it is shown that short periodic internal waves may be caused by local initial perturbations (for instance by sudden variations of pressure at the surface). The solution of the problem describes slowly decreasing standing internal waves, which are generated within the area upon which short-dated initial accelerations have acted. At the same time a train of progressive waves is developed in the environment travelling away from the centre of the excitation. The amplitudes of these waves diminish with increasing distance from the origin. The periods of the computed oscillations yield higher values than the Väisäläperiod belonging to an exponential stratification. The variability in these periods is caused by variations in depth, by variations in stability, and by changes in the horizontal dimensions of the area of initial perturbation. This dependence is similar to that of cellular oscillations of stability.

---

Spectre des oscillations internes de la mer Baltique Ouest pour des périodes comprises entre 0,3 et 60 minutes. 1ère Partie: Interprétation des éléments ondulatoires de mouvement

Résumé Pour un cas d'observation (vitesse de courant, densité) en baie de Kiel, des maximums bien marqués des spectres correspondants entre 0,3 et 60 minutes s'expliquent par des ondes internes. Des calculs effectués avec une période de deux minutes montrent que la longueur d'onde dépend beaucoup du courant moyen, . Pour , par 23,5 m de profondeur, on obtient une longueur d'onde environ 70 m; pour , une longueur d'environ 85 m. Les oscillations calculées représentent des ondes internes qui ne sont pas des ondes propres. L'interprétation par une onde de surface limite conduit à une longueur d'onde de 86 m très peu différente de celles des ondes internes du premier ordre dans un courant constamment variable.Une étude théorique montre que des perturbations initiales peu étendues (par exemple variations momentanées de la pression à la surface de la mer) peuvent être à l'origine d'ondes internes à courte période. Il apparaît que des accélérations initiales, agissant brièvement, font naître dans leur zone d'action des ondes internes stationnaires qui s'amortissent peu à peu, tandis qu'en même temps aux alentours se produisent des ondes progressives dont l'amplitude décroît à mesure qu'elles s'éloignent de la région où elles ont pris naissance. Les périodes des oscillations ont des valeurs plus grandes que celle de la période de Väisälä rapportée à une stratification exponentielle, et elles varient suivant la grandeur de la zone où elles ont pris naissance comme les oscillations de stabilité cellulaire.

     

Isotope-aided modelling of ecohydrologic fluxes and water ages under mixed land use in Central Europe: The 2018 drought and its recovery

Understanding the interactions of vegetation and soil water under varying hydrological conditions is crucial to aid quantitative assessment of land-use sustainability for maintaining water supply for humans and plants. Isolating and estimating the volume and ages of water stored within different compartments of the critical zone, and the associated fluxes of evaporation, transpiration, and groundwater recharge, facilitates quantification of these soil–plant-water interactions and the response of ecohydrological fluxes to wet and dry periods. We used the tracer-aided ecohydrological model EcH₂O-iso to examine the response of water ages of soil water storage, groundwater recharge, evaporation, and root-uptake at a mixed land use site, in northeastern Germany during the drought of 2018 and in the following winter months. The approach applied uses a dynamic vegetation routine which constrains water use by ecological mechanisms. Two sites with regionally typical land-use types were investigated: a forested site with sandy soils and a deep rooting zone and a grassland site, with loamier soils and shallower rooting zone. This results in much younger water ages (<1 year) through the soil profile in the forest compared to the grass, coupled with younger groundwater recharge. The higher water use in the forest resulted in a more pronounced annual cycle of water ages compared to the more consistent water age in the loamier soil of the grasslands. The deeper rooting zone of the forested site also resulted in older root-uptake water usage relative to soil evaporation, while the grassland site root-uptake was similar to that of soil evaporation. Besides more dynamic water ages in the forest, replenishment of younger soil waters to soil storage was within 6 months following the drought (cf. >8 months in the grassland). The temporal evaluation of the responsiveness of soil and vegetation interactions in hydrologic extremes such as 2018 is essential to understand changes in hydrological processes and the resilience of the landscape to the longer and more severe summer droughts predicted under future climate change.