Sidescan backscatter variations of cold seeps on the Hikurangi Margin (New Zealand): indications for different stages in seep development

Cold seeps on the Hikurangi Margin off New Zealand exhibit various seabed morphologies producing different intensity patterns in sidescan backscatter images. Acoustic backscatter characteristics of 25 investigated seep sites fall into four distinct types characterised by variations in backscatter intensity, distribution and inferred structural heights. The types reflect different carbonate morphologies including up to 20-m-high structures (type 1), low-relief crusts (type 2), scattered blocks (type 3) and carbonate-free sites (type 4). Each seep corresponds to a single type; intermediates were not observed. This correlates well with published data on seep fauna at each site, with the four types representing three different faunal habitats of successive stages of seep development. Backscatter signatures in sidescan sonar images of cold seeps may therefore serve as a convenient proxy for variations in faunal habitats.     

Improving Bayesian analysis for LISA Pathfinder using an efficient Markov Chain Monte Carlo method

We present a parameter estimation procedure based on a Bayesian framework by applying a Markov Chain Monte Carlo algorithm to the calibration of the dynamical parameters of the LISA Pathfinder satellite. The method is based on the Metropolis-Hastings algorithm and a two-stage annealing treatment in order to ensure an effective exploration of the parameter space at the beginning of the chain. We compare two versions of the algorithm with an application to a LISA Pathfinder data analysis problem. The two algorithms share the same heating strategy but with one moving in coordinate directions using proposals from a multivariate Gaussian distribution, while the other uses the natural logarithm of some parameters and proposes jumps in the eigen-space of the Fisher Information matrix. The algorithm proposing jumps in the eigen-space of the Fisher Information matrix demonstrates a higher acceptance rate and a slightly better convergence towards the equilibrium parameter distributions in the application to LISA Pathfinder data. For this experiment, we return parameter values that are all within ～1σ of the injected values. When we analyse the accuracy of our parameter estimation in terms of the effect they have on the force-per-unit of mass noise, we find that the induced errors are three orders of magnitude less than the expected experimental uncertainty in the power spectral density.     

Thermo-optical parameter acquisition and characterization of geologic properties: a 400-m deep BHE in a karstic alpine marble aquifer

To dimension a geothermal array, it is necessary to explore the geophysical and geologic qualities of the subsoil. At the following example the project engineering of a prospective geothermal array is shown from the investigation up to the execution planning. For the geothermic investigation a 400 m (1312 ft.) deep drilling was established and equipped with 50 mm (1.97 in.) duplex BHE. With the mounting of the BHE a fiberglass hybrid cable was inserted as a loop parallel to the shanks of the BHE. By means of optical frequency domain reflectometry (OFDR) an enhanced geothermal response test has been executed. Due the high local resolution of the resulting profile of conductivities the geological profile can be differentiated in areas with mainly conductive and areas of convective influenced heat transfer. By knowledge of these both parts and its parameters the incident of groundwater flow on the BHE can be calculated (Peclet number analysis/ Darcy velocity). With the help of the ascertained geophysical and hydraulic rock parameters solid rock, cleavages and karst cavity could be identified. Also the undisturbed ground temperature, the effective thermal conductivity and areas with different geothermal gradients and the groundwater velocity in cleaved and caveated rocks could be determined.     

Mechanism on how the spring Arctic sea ice impacts the East Asian summer monsoon

Observational analysis and purposely designed coupled atmosphere–ocean (AOGCM) and atmosphere-only (AGCM) model simulations are used together to investigate a new mechanism describing how spring Arctic sea ice impacts the East Asian summer monsoon (EASM). Consistent with previous studies, analysis of observational data from 1979 to 2009 show that spring Arctic sea ice is significantly linked to the EASM on inter-annual timescales. Results of a multivariate Empirical Orthogonal Function analysis reveal that sea surface temperature (SST) changes in the North Pacific play a mediating role for the inter-seasonal connection between spring Arctic sea ice and the EASM. Large-scale atmospheric circulation and precipitation changes are consistent with the SST changes. The mechanism found in the observational data is confirmed by the numerical experiments and can be described as follows: spring Arctic sea ice anomalies cause atmospheric circulation anomalies, which, in turn, cause SST anomalies in the North Pacific. The SST anomalies can persist into summer and then impact the summer monsoon circulation and precipitation over East Asia. The mediating role of SST changes is highlighted by the result that only the AOGCM, but not the AGCM, reproduces the observed sea ice-EASM linkage.     

Is μCT irradiation nondestructive? A noble gas study on matrix samples from the CV3 chondrite Allende

Micro-computed tomography (μCT) is a fast and powerful technology for studying textural, physical, and chemical properties of solid objects in three dimensions. While regularly used for sample documentation and curation, it is often assumed that μCT techniques are essentially nondestructive or at least very little destructive. However, there are very few studies proving or rejecting the assumption of nondestructiveness. Here we study whether X-ray tomographic imaging affects the noble gas budget of matrix samples from the CV3 carbonaceous chondrite Allende. We irradiated powdered and homogenized matrix samples in the Bruker SkyScan 1272 μCT instrument at three different X-ray tube acceleration voltages of 30, 70, and 100 keV. By comparing the noble gas concentrations and especially the elemental and isotopic ratios of the irradiated samples with data for two non-irradiated aliquots, we found no significant differences. Our study therefore demonstrates that X-ray tomographic imaging has no measurable effect on the noble gas budget and can therefore safely be used for sample characterization prior to noble gas studies.