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Lisker F.,University of Bremen | Laufer A.L.,Federal Institute for Geosciences and Natural Resources
Geology | Year: 2013

The Transantarctic Mountains (TAM) are the largest non-compressional mountain belt in the world. Their origin is traditionally related to crustal thickening during the Jurassic Ferrar magmatic event that was followed by episodic uplift in the Early and Late Cretaceous and since the Paleocene. This concept of a long-lived morphological high constitutes a base of virtually all Gondwana reconstructions and global climate models. Here we demonstrate that crossover age relationships between thermochronological (apatite fission track) data and stratigraphic information contradict this established interpretation. Instead these data, together with a wealth of independent thermal indicators and geological evidence require the existence of a vast intra-Gondwana basin between at least Late Triassic and Late Cretaceous times, including during the Ferrar magmatic event. Referred to here as the Mesozoic Victoria Basin (MVB), this basin formed during crustal extension across the paleo-Pacific margin of Antarctica and Australia. Uplift of the TAM with associated basin inversion commenced only with the development of the West Antarctic Rift System in Paleogene times. The recognition of the long-lived MVB has primary consequences for the general understanding of the landscape of Gondwana and the breakup between Antarctica and Australia, West Antarctic rifting and uplift of the TAM, and global long-term climate evolution and faunal radiation. © 2013 Geological Society of America. Source

Gunnink J.L.,TNO | Siemon B.,Federal Institute for Geosciences and Natural Resources
Near Surface Geophysics | Year: 2015

Airborne electromagnetic (AEM) measurements provide information regarding the electrical properties of the subsurface for large spatial coverage in a limited time. In mapping and modelling for geological and geohydrological purposes, electrical properties (e.g. resistivity) need to be converted to relevant parameters, like lithology. Helicopter-borne frequency-domain EM measurements from an area in the Netherlands were combined with borehole data to create a 3D model of two contrasting lithologies (sand and clay) that served as proxy for assessing the vulnerability of the aquifer to surface contamination. By comparing the lithology found in boreholes with the resistivity derived from AEM at that location, a probabilistic relationship between these two variables was determined. This relationship was used to convert the AEM resistivity models into a 3D model of clay probability. Using geostatistical Monte Carlo simulations, the boreholes (hard data) and the probability of clay from the AEM resistivity models (soft data) were combined. AEM improved the 3D model substantially, compared to using only borehole data. An independent validation dataset verified the improvement of the 3D model using AEM data. Areas with a high probability of clay occurrence could be distinguished and a clay thickness map with uncertainty (standard deviation) was calculated. Using a simple groundwater model, the capability of the clay to protect the underlying aquifer from contamination was quantified. This resulted in the delineation of distinct areas that are well protected due to the large travel time for infiltrating water from the surface to the aquifer. © 2015 European Association of Geoscientists & Engineers. Source

Spott O.,Helmholtz Center for Environmental Research | Russow R.,Helmholtz Center for Environmental Research | Stange C.F.,Federal Institute for Geosciences and Natural Resources
Soil Biology and Biochemistry | Year: 2011

At the end of the 19th century an experimental study had already reported N gas production during microbial nitrate reduction, which significantly exceeded the amount of nitrate N supplied to the microorganism. The observed excess gas production was suggested to be caused by a reaction of nitrous acid (produced during microbial nitrate reduction) with amino acids contained in the nutrient solution. Since the 1980's a number of 15N tracer experiments revealed that this biotic excess gas production was based on the formation of hybrid N2O and/or hybrid N2. It was shown that the N-N linkage forms due to a microbially mediated N-nitrosation reaction by which one N atom of nitrite or nitric oxide combines via a nitrosyl intermediate with one N atom of another N species (e.g., amino compound). Because of its cooccurrence with conventional denitrification this process was later on termed "codenitrification" Although the phenomenon of N2O and N2 formation by codenitrification was recognised over a century ago its impact on global N cycling is still unclear today. Nonetheless, the present literature review reveals codenitrification as a potentially important process of biospheric N cycling since (i) most codenitrifying species are already known as typical denitrifiers (e.g., Pseudomonas sp., Fusarium sp. etc.) and (ii) codenitrification was already reported to occur within the three domains archaea, bacteria, and eukarya (kingdom fungi). Furthermore, the present literature suggests that codenitrification acts not only as an additional source of N gas formation due to a mobilisation of organic N by N-nitrosation, but also acts as an N immobilising process due to a bonding of inorganic N (e.g., from NO3 - or NO2 -) onto organic compounds due to e.g., N- or even C-nitrosation reactions. From this it can be concluded that N gas formation by codenitrification represents a sub-phenomenon of a variety of possible biotic nitrosation reactions. Moreover, the review reveals that biotic nitrosation also occurs among nitrifying species, even under aerobic conditions. Furthermore, recent studies support the assumption that even anaerobic ammonium oxidation (anammox) appears to be based on biotically mediated N-nitrosation. Therefore, we propose to introduce the term BioNitrosation, which includes all biotically mediated nitrosation reactions resulting either in N gas release or in N immobilisation, independently from the acting microbial species or the environmental conditions. © 2011 Elsevier Ltd. Source

Torizin J.,Federal Institute for Geosciences and Natural Resources
Stochastic Environmental Research and Risk Assessment | Year: 2016

In applications of the weight of evidence (WofE) method, the informational redundancy in similar evidential patterns causes a significant increase in the posterior probability. Consequently, to estimate the posterior probability, combinations that pass the established conditional independence (CI) tests are considered rather than the combination of the ‘best’ information layers. This study introduces two methodological approaches to extend the WofE using a correction factor that eliminates the informational redundancy that is contained in different evidential layers. The proposed approaches allow the use of associated data in the same model without having to address issues with the constraints of the CI. The basic WofE approach that is used to estimate the weights is not changed, and only the interactions of the parameter layers and the transformation of the weights into probability values are considered. The method is applied to a real dataset that is used in a landslide susceptibility analysis on Lombok Island, Indonesia. © 2015, Springer-Verlag Berlin Heidelberg. Source

Costabel S.,Federal Institute for Geosciences and Natural Resources | Muller-Petke M.,Leibniz Institute for Applied Geophysics
Near Surface Geophysics | Year: 2014

In this paper three different despiking methods for surface-NMR data are investigated and compared. Two of these are applied in the time domain: a threshold is determined that identifies and marks a spiky event. Afterward, the marked time sequence is substituted with zeros or with the mean value of the signal amplitude of the measurement repetitions for the same passage on the time axis. The third despiking approach takes advantage of the wavelet-like nature of spiky events. It isolates and eliminates spiky signals in the wavelet domain, i.e., after transforming a single record with the help of the discrete wavelet transform. The latter is able to reconstruct the original signal content in the (spike-caused) distorted time sequence to some extent. If the spiky noise in surface-NMR measurements consists mainly of single spiky events, the three despiking methods show very similar results and are able to remove spiky noise from data very effectively, as we can show with two real data examples. However, a synthetic study shows that, if a series of spikes within a relatively short period of time occurs, the wavelet-based despiking approach shows significant shortcomings. Because the NMR signal content cannot be restored completely in a single record, the fitting of the signal after stacking leads to underestimation of the initial amplitude up to approximately 10%. Nevertheless, we can show that, in principle, the processing of surface-NMR data in the wavelet domain works and can lead to the same results as straight-forward applications. Moreover, waveletbased strategies have some interesting properties and thus have some potential for further development regarding surface-NMR processing, which is discussed in detail. © 2014 European Association of Geoscientists & Engineers. Source

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