Rare earth element geochemistry in cold-seep pore waters of Hydrate Ridge, northeast Pacific Ocean

The concentrations of rare earth elements (REEs), sulphate, hydrogen sulphide, total alkalinity, calcium, magnesium and phosphate were measured in shallow (<12 cm below seafloor) pore waters from cold-seep sediments on the northern and southern summits of Hydrate Ridge, offshore Oregon. Downward-decreasing sulphate and coevally increasing sulphide concentrations reveal sulphate reduction as dominant early diagenetic process from ~2 cm depth downwards. A strong increase of total dissolved REE (∑REE) concentrations is evident immediately below the sediment–water interface, which can be related to early diagenetic release of REEs into pore water resulting from the re-mineralization of particulate organic matter. The highest pore water ∑REE concentrations were measured close to the sediment–water interface at ~2 cm depth. Distinct shale-normalized REE patterns point to particulate organic matter and iron oxides as main REE sources in the upper ~2-cm depth interval. In general, the pore waters have shale-normalized patterns reflecting heavy REE (HREE) enrichment, which suggests preferential complexation of HREEs with carbonate ions. Below ~2 cm depth, a downward decrease in ∑REE correlates with a decrease in pore water calcium concentrations. At this depth, the anaerobic oxidation of methane (AOM) coupled to sulphate reduction increases carbonate alkalinity through the production of bicarbonate, which results in the precipitation of carbonate minerals. It seems therefore likely that the REEs and calcium are consumed during vast AOM-induced precipitation of carbonate in shallow Hydrate Ridge sediments. The analysis of pore waters from Hydrate Ridge shed new light on early diagenetic processes at cold seeps, corroborating the great potential of REEs to identify geochemical processes and to constrain environmental conditions.     

Modern and late Quaternary clay mineral distribution in the area of the SE Mediterranean Sea

The present-day clay mineral distribution in the southeastern Levantine Sea and its borderlands reveals a complex pattern of different sources and distribution paths. Smectite dominates the suspended load of the Nile River and of rivers in the Near East. Illite sources are dust-bearing winds from the Sahara and southwestern Europe. Kaolinite is prevalent in rivers of the Sinai, in Egyptian wadis, and in Saharan dust. A high-resolution sediment core from the southeastern Levantine Sea spanning the last 27 ka shows that all these sources contributed during the late Quaternary and that the Nile River played a very important role in the supply of clay. Nile influence was reduced during the glacial period but was higher during the African Humid Period. In contrast to the sharp beginning and end of the African Humid Period recorded in West African records (15 and 5.5 ka), our data show a more transitional pattern and slightly lower Nile River discharge rates not starting until 4 ka. The similarity of the smectite concentrations with fluctuations in sea-surface temperatures of the tropical western Indian Ocean indicates a close relationship between the Indian Ocean climate system and the discharge of the Nile River.     

Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control

The presence of a complex bedform arrangement on the sea floor of the continental shelf in the western Amundsen Sea Embayment, West Antarctica, indicates a multi-temporal record of flow related to the activity of one or more ice streams in the past. Mapping and division of the bedforms into distinct landform assemblages reveals their time-transgressive history, which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo-ice velocity, as suggested previously. A main control on the bedform imprint is the geology of the shelf, which is divided broadly between rough bedrock on the inner shelf, and smooth, dipping sedimentary strata on the middle to outer shelf. Inner shelf bedform variability is well preserved, revealing information about local, complex basal ice conditions, meltwater flow, and ice dynamics over time. These details, which are not apparent at the scale of regional morphological studies, indicate that past ice streams flowed across the entire shelf at times, and often had onset zones that lay within the interior of the Antarctic Ice Sheet today. In contrast, highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow, and may be a truer representation of fast palaeo-ice flow in these locations. A revised model for ice streams on the shelf captures complicated multi-temporal bedform patterns associated with an Antarctic palaeo-ice stream for the first time, and confirms a strong substrate control on a major ice stream system that drained the West Antarctic Ice Sheet during the Late Quaternary.     

Biological reduction of chlorinated solvents: Batch-scale geochemical modeling

Simulation of biodegradation of chlorinated solvents in dense non-aqueous phase liquid (DNAPL) source zones requires a model that accounts for the complexity of processes involved and that is consistent with available laboratory studies. This paper describes such a comprehensive modeling framework that includes microbially mediated degradation processes, microbial population growth and decay, geochemical reactions, as well as interphase mass transfer processes such as DNAPL dissolution, gas formation and mineral precipitation/dissolution. All these processes can be in equilibrium or kinetically controlled. A batch modeling example was presented where the degradation of trichloroethene (TCE) and its byproducts and concomitant reactions (e.g., electron donor fermentation, sulfate reduction, pH buffering by calcite dissolution) were simulated. Local and global sensitivity analysis techniques were applied to delineate the dominant model parameters and processes. Sensitivity analysis indicated that accurate values for parameters related to dichloroethene (DCE) and vinyl chloride (VC) degradation (i.e., DCE and VC maximum utilization rates, yield due to DCE utilization, decay rate for DCE/VC dechlorinators) are important for prediction of the overall dechlorination time. These parameters influence the maximum growth rate of the DCE and VC dechlorinating microorganisms and, thus, the time required for a small initial population to reach a sufficient concentration to significantly affect the overall rate of dechlorination. Self-inhibition of chlorinated ethenes at high concentrations and natural buffering provided by the sediment were also shown to significantly influence the dechlorination time. Furthermore, the analysis indicated that the rates of the competing, nonchlorinated electron-accepting processes relative to the dechlorination kinetics also affect the overall dechlorination time. Results demonstrated that the model developed is a flexible research tool that is able to provide valuable insight into the fundamental processes and their complex interactions during bioremediation of chlorinated ethenes in DNAPL source zones.     

Backtracking of Noble Gas Measurements Taken in the Aftermath of the Announced October 2006 Event in North Korea by Means of PTS Methods in Nuclear Source Estimation and Reconstruction

The announced October 2006 nuclear test explosion in the Democratic People’s Republic of Korea (DPRK) has been the first real test regarding the technical capabilities of the verification system built up by the Vienna-based Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect and locate a nuclear test event. This paper enhances the resolution of the DPRK events’ xenon source reconstruction published by Saey et al. (2007, “A long distance measurement of radioxenon in Yellowknife, Canada, in late October 2006”, GRL, Vol. 34, L20802) that was based solely on radio-xenon measurements taken at the remote radionuclide station in Yellowknife, Canada by involving additional measurements taken by a mobile noble gas system deployed quite close to the event location in the Republic of Korea (ROK). Moreover the horizontal resolution of the forward and backward atmospheric transport modelling methods applied for the source scenario reconstruction has been enhanced appropriately to reflect the considerably shorter source-receptor distances examined in comparison to the previously published source reconstruction. It is shown that the ¹³³Xe measurements in Yellowknife could register ¹³³Xe traces from the nuclear explosion during the first 3 days after the event, while the mobile measurements were rather sensitive to releases during days 2–4 after the explosion. According to the analysis, the most likely source scenario would consist of an initial (possibly up to 21 h delayed) venting of 1 × 10^?15 Bq ¹³³Xe during the first 24 h, followed by a two orders of magnitude weaker seepage during the following 3 days. Both measurements corroborate the scenario of a rather rapid venting and soil diffusion of the ¹³³Xe yielded during the explosion. While the Swedish mobile measurements were crucial to enhancement of the reconstruction of the source scenario, given the installation status of the IMS xenon network at the time of the event, a sensitivity analysis revealed that the fully developed network would have been able to detect ¹³³Xe traces from the Korean explosion at a number of stations and allowed for an even better constraint on the release function. The station Ussuriysk, Russia, being in operation in 2006, would have registered ¹³³Xe within 1 day and with a three orders of magnitudes stronger signal compared to the detection at Yellowknife.     

Computation and Analysis of the Global Distribution of the Radioxenon Isotope 133Xe based on Emissions from Nuclear Power Plants and Radioisotope Production Facilities and its Relevance for the Verification of the Nuclear-Test-Ban Treaty

Monitoring of radioactive noble gases, in particular xenon isotopes, is a crucial element of the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The capability of the noble gas network, which is currently under construction, to detect signals from a nuclear explosion critically depends on the background created by other sources. Therefore, the global distribution of these isotopes based on emissions and transport patterns needs to be understood. A significant xenon background exists in the reactor regions of North America, Europe and Asia. An emission inventory of the four relevant xenon isotopes has recently been created, which specifies source terms for each power plant. As the major emitters of xenon isotopes worldwide, a few medical radioisotope production facilities have been recently identified, in particular the facilities in Chalk River (Canada), Fleurus (Belgium), Pelindaba (South Africa) and Petten (Netherlands). Emissions from these sites are expected to exceed those of the other sources by orders of magnitude. In this study, emphasis is put on ¹³³Xe, which is the most prevalent xenon isotope. First, based on the emissions known, the resulting ¹³³Xe concentration levels at all noble gas stations of the final CTBT verification network were calculated and found to be consistent with observations. Second, it turned out that emissions from the radioisotope facilities can explain a number of observed peaks, meaning that atmospheric transport modelling is an important tool for the categorization of measurements. Third, it became evident that Nuclear Power Plant emissions are more difficult to treat in the models, since their temporal variation is high and not generally reported. Fourth, there are indications that the assumed annual emissions may be underestimated by factors of two to ten, while the general emission patterns seem to be well understood. Finally, it became evident that ¹³³Xe sources mainly influence the sensitivity of the monitoring system in the mid-latitudes, where the network coverage is particularly good.     

Seabirds in the North Sea Demobilized and Killed by Polyisobutylene (C4H8)n (PIB)

This paper reports on a mass stranding of seabirds in the North Sea in December 1998. Hundreds of birds were washed ashore alive in Zeeland (SW Netherlands), covered in a whitish, sticky substance, and were transported to a rehabilitation centre. About 10 days later, more (dead) casualties washed ashore further to the north on Texel and along the mainland coast, again covered in a glue-like substance. Common guillemots Uria aalge, northern fulmars Fulmarus glacialis and common scoters Melanitta nigra were the most numerous birds affected in this incident. Both strandings were temporarily (10 days) and geographically separated (ca. 120 km apart), but were apparently caused by a single source of pollution. The meteorology at the time was consistent with the course of a single incident. At least 1100 seabirds were affected by this substance, soon identified as polyisobutylene (C₄H₈)_n. PIB is known as a non-toxic, non-aggressive substance. Volunteers cleaning the birds in the rehabilitation centre reported serious discomfort and dizziness and the soft parts of the PIB-affected birds found dead (bill, eye, throat, feet, webs) appeared to dissolve in a few days time. Both effects cannot be attributed to PIB, and are therefore unexplained. Although the dumping of PIB in the marine environment is not explicitly prohibited under MARPOL, the effects on wildlife observed are enough to plead for counter-measures.     

The nature of the luminous X-ray emission of NGC 6240

We briefly review and extend our discussion of the ROSAT detectionof the extraordinarily luminous (>10⁴² erg/s) partly extended(>30 kpc diameter) X-ray emission from the ultraluminous infrared galaxy NGC 6240.The `standard'-model of starburst outflow is contrasted with alternatives and a comparison with the X-ray properties of ellipticals is performed.     

Dynamics of the boxy elliptical galaxy NGC 1600

We use three-integral models to infer the distribution function (DF) of the boxy E3–E4 galaxy NGC 1600 from surface brightness and line-profile data on the minor and major axes. We assume axisymmetry and that the mass-to-light ratio is constant in the central ∼1 R _e. Stars in the resulting gravitational potential move mainly on regular orbits. We use an approximate third integral K from perturbation theory and write the DF as a sum of basis functions in the three integrals E , L _z and K . We then fit the projected moments of these basis functions to the kinematic observables and deprojected density, using a non-parametric algorithm. The deduced dynamical structure is radially anisotropic, with σ _θ σ _r ≈ σ _φ σ _r ≈0.7 on the major axis. Both on the minor axis and near the centre the velocity distribution is more isotropic; thus the model is flattened by equatorial radial orbits. The kinematic data are fitted without the need for a central black hole; the central mass determined previously from ground-based data therefore overestimates the actual black-hole mass. The mass-to-light ratio of the stars is M L _V =6  h ₅₀. The anisotropy structure of NGC 1600 with a radially anisotropic main body and more nearly isotropic centre is similar to that found recently in NGC 1399, 2434, 3379 and 6703, suggesting that this pattern may be common amongst massive elliptical galaxies. We discuss a possible merger origin of NGC 1600 in the light of these results.