Time-dependent convection at high latitudes

A fully time-dependent ionospheric convection model, in which electric potentials are derived by an analytic solution of Laplaces equation, is described. This model has been developed to replace the empirically derived average convection patterns currently used routinely in the Sheffield/SEL/UCL coupled thermosphere/ionosphere/plasmasphere model (CTIP) for modelling disturbed periods. Illustrative studies of such periods indicate that, for the electric field pulsation periods imposed, long-term averages of parameters such as Joule heating and plasma density have significantly different values in a time-dependent model compared to those derived under the same mean conditions in a steady-state model. These differences are indicative of the highly non-linear nature of the processes involved.     

Glacial advances constrained by Be exposure dating of bedrock landslides, Kyrgyz Tien Shan

Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first ¹⁰Be exposure ages for three prominent (> 10⁷ m³) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three ¹⁰Be ages reveal that one landslide in the Alamyedin River occurred at 11–15 ka, which is consistent with two ¹⁴C ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a ¹⁰Be age of 63–67 ka. The Ukok River landslide deposit(s) yielded variable ¹⁰Be ages, which may result from multiple landslides, and inheritance of ¹⁰Be. Two ¹⁰Be ages of 8.2 and 5.9 ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4 ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and ¹⁰Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4–0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential.     

Spectroscopy of candidate metal-deficient galaxies with the 6-m telescope

We present the first results of our program of search for the most metal-deficient blue compact galaxies (BCGs) carried out with the 6-m Special Astrophysical Observatory telescope. The results of spectrophotometry are presented and discussed for ten galaxies from the Case and Hamburg/SAO surveys. The selection of candidates, observations, and data reduction are described in detail. For all the galaxies studied, we measured the intensity of the [O III] λ4363 Å emission line, which allows us to properly determine the temperatures of H II regions and to deduce elemental abundances. We measured the intensities of all the detected emission lines in H II regions of the galaxies under study and determined the abundances of oxygen and neon in them and in some of these galaxies, of other elements (N, S, He, Ar, and Fe). The oxygen abundance log (O/H)+12 in six galaxies was derived with an error ≤0.1 dex. Six of the ten galaxies studied turned out to be metal-poor with an oxygen abundance ≤1/10 of its solar value [i.e., 12+log(O/H)≤7.92]. HS 0837+4717 with 12+log(O/H) ≤7.7 is one of the most metal-poor galaxies in this sample and one of the candidates for young galaxies. Low-contrast, broad emission components of the nebular [O III]λ4959 and 5007 Å lines were detected in its spectrum, suggesting high velocities of gas motions in this galaxy.     

ROSAT HRI observations of P Cyg and surrounding area

We present a detailed analysis of deep ROSAT HRI observations of the luminous blue variable P Cyg and its surrounding radio nebula. The HRI image provides a point source at the position of P Cyg. However, we show that this emission can be attributed to the ultraviolet leak of the ROSAT HRI. The X‐ray flux upper limit derived from the HRI data of this star is discussed in the context of X‐ray emission from hot stars. Furthermore, we present a search for diffuse X‐ray emission possibly associated with the radio nebula surrounding P Cyg. We compare our results to model predictions and X‐ray fluxes observed for shells around other hot stars. Additionally, we detect 10 X‐ray sources in the field of view. All but one of these X‐ray emitters have stellar counter parts in the Palomar Sky Survey. We suggest that they are active late‐type stars possibly belonging to Cyg OB1.     

Chemical composition of Russian Arctic precipitation in 2007-2015

The results of observations of the chemical composition of precipitation in the Russian Arctic in 2007-2015 are summarized including the data from NP-35 drifting ice station obtained in 2007-2008 in the framework of the joint program of Arctic and Antarctic Research Institute and Voeikov Main Geophysical Observatory. The qualitative and quantitative difference in the chemical composition of precipitation in the Atlantic, Siberian, and Pacific sectors of the Russian Arctic is revealed. It is found that the concentration of microelements (heavy metals) in precipitation at NP-35 ice station did not exceed 12% of total ions at the lowest mineralization. The comparative analysis is presented of the concentration of sulfate ions in precipitation in Norilsk and at NP-35 ice stations.     

Diffusion of Ar in muscovite

Hydrothermal treatment of closely sized muscovite aggregates in a piston-cylinder apparatus induced ⁴⁰Ar^∗ loss that is revealed in ⁴⁰Ar/³⁹Ar step heating spectra. Age spectra and Arrhenius data, however, differ from that expected from a single diffusion length scale. A numerical model of episodic loss assuming the presence of multiple diffusion domains yields excellent fits between synthetic and actual degassing spectra. We used this model to isolate ⁴⁰Ar^∗ loss from the grains that remained intact during hydrothermal treatment at 10 kbar permitting calculation of diffusion coefficients in the temperature range 730-600 °C. Diffusion data generated in this manner yield an activation energy (E) of 63 ± 7 kcal/mol and frequency factor (D_o) of 2.3  cm²/s. Experiments at 20 kbar yield diffusivities lower by about an order of magnitude and correspond to an activation volume of ∼14 cm³/mol. Together, these parameters predict substantially greater retentivity of Ar in muscovite than previously assumed and correspond to a closure temperature (T_c) of 425 °C for a 100 μm radius grain cooling at 10 °C/Ma at 10 kbar (T_c = 405 °C at 5 kbar. Age and log (r/r_o) spectra for the run products show strong correlations indicating that muscovites can retain Ar diffusion boundaries and mechanisms that define their natural retentivity during vacuum step heating. This may permit the application of high resolution, continuous ⁴⁰Ar/³⁹Ar thermochronology to low grade, regionally metamorphosed terranes.     

Extending the Capture Map Concept to Estimate Discrete and Risk-Based Streamflow Depletion Potential

A popular and contemporary use of numerical groundwater models is to estimate the discrete relation between groundwater extraction and surface-water/groundwater exchange. Previously, the concept of a “capture map” has been put forward as a means to effectively summarize this relation for decision-making consumption. While capture maps have enjoyed success in the environmental simulation industry, they are deterministic, ignoring uncertainty in the underlying model. Furthermore, capture maps are not typically calculated in a manner that facilitates analysis of varying combinations of extraction locations and/or reaches. That is, they are typically constructed with focus on a single reach or group of reaches. The former of these limitations is important for conveying risk to decision makers and stakeholders, while the latter is important for decision-making support related to surface-water management, where future foci may include reaches that were not the focus of the original capture analysis. Herein, we use the concept of a response matrix to generalize the theory of the capture-map approach to estimate spatially discrete streamflow depletion potential. We also use first-order, second-moment uncertainty estimation techniques with the concept of “risk shifting” to place capture maps and streamflow depletion potential in a stochastic, risk-based framework. Our approach is demonstrated for an integrated groundwater/surface-water model of the lower San Antonio River, Texas, USA.     

Origin of uranium and rare earth minerals in bone detritus from rare metal deposits

In order to ascertain the forms in which uranium is present in ores of the Melovoe rare metal sedimentary deposit of uranium and rare earth minerals (South Mangyshlak), we investigated a series of typical ore samples that were collected earlier; both the uranium content and the total content of rare earth metals in them lay within 0.1–0.3%. The study was carried out by analytical electron microscopy using transmission electron microscopy and scanning electron microscopy, electron microdiffraction, and microprobing. It was ascertained that both uranium and rare earth elements are present in ore mostly associated with biogenic phosphate in the form of natural minerals, such as uraninite, ningyoite, coffinite, autenite, and churchite. Iron hydroxides and graphitized organic matter are present in some samples. It is assumed that the co-occurrence of uranium and rare earth elements, which is nontypical for the sedimentary process, resulted from secondary epigenetic processes and alternation of reducing and oxidizing environmental conditions.     

Microearthquakes along the back-arc spreading system in the eastern Bismarck Sea

OBS’s were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges.     

Measurement of stress effects (scope for growth) and contaminant levels in mussels (Mytilus edulis) collected from the Irish Sea

The objective of this research was to quantify the impact of pollution along the coastlines of the Irish Sea. Pollution assessment was based on the combined measurement of scope for growth (SFG), and chemical contaminants in the tissues of mussels (Mytilus edulis) collected from 38 coastal sites around the Irish Sea during June-July in 1996 and 1997. On the UK mainland coast, the SFG showed a general trend with a significant decline in water quality in the Liverpool and Morecambe Bay region. High water quality was recorded along the west coast of Wales, as well as southwest England and northwest Scotland (clean reference sites outside the Irish Sea). Along the coast of Ireland there was a similar trend with reduced SFG within the Irish Sea region. SFG was generally low north of Duncannon and then improved north of Belfast. The poor water quality on both sides of the Irish Sea is consistent with the prevailing hydrodynamics and the spatial distribution of contaminants associated with urban/ industrial development. The decline in SFG of mussels on both sides of the Irish Sea was associated with a general increase in contaminant levels in the mussels. Certain contaminants, including PAHs, TBT, sigmaDDT, Dieldrin, gamma-HCH, PCBs, and a few of the metals (Cd, Se, Ag, Pb), showed elevated concentrations. Many of these contaminants were particularly elevated in the coastal margins of Liverpool Bay, Morecambe Bay and Dublin Bay. A quantitative toxicological interpretation (QTI) of the combined tissue residue chemistry and SFG measurements indicated that at the majority of coastal sites, c. 50 to > 80% of the observed decline in SFG was due to PAHs as a result of fossil fuel combustion and oil spills. TBT levels were highest at major ports and harbours, but these concentrations only made a minor contribution to the overall reduction in SFG. At no sites were individual metals accumulated to concentrations that could cause a significant effect on SFG. The study identified many sites where the observed reduction in SFG was far greater than predicted from the limited number of chemical contaminants analysed, thus indicating the presence of additional 'unknown toxicants'. Sewage (containing domestic, agricultural and industrial components) appears to be an important contributor to reduced SFG and linear alkylbenzenes (LABs) and As may provide suitable 'sewage markers'. There was a highly significant positive correlation between SFG and As (P < 0.001). This relationship may be due to reduced As uptake by algal food material and mussels at sites with elevated P04 concentrations (e.g. at sites with sewage inputs). Phosphate is a known competitive inhibitor of As accumulation, at least in algae. The results highlight that further research is required on 'sewage markers' in mussels. The SFG approach therefore provides a rapid, cost-effective and quantitative measure of pollution impact, as well as a means of identifying the causes through a QTI of tissue contaminants levels. It also serves to identify the presence of unidentified toxicants and areas that require further study.