Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600 000 years

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by ⁴⁰Ar/³⁹Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO₃‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO₃‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.     

Excavation of the Aica-Mules pilot tunnel for the Brenner base tunnel: information gained on water inflows in tunnels in granitic massifs

The construction of the Aica-Mules tunnel, completed in 2010, provides a relevant case history for improving the knowledge of hydrogeological issues related to the excavation of deep tunnels in granitic massifs. The Aica-Mules tunnel is a 10 km-long structure, forming part of the high-speed railway connection between Austria and Italy across the Alpine chain, located at an average depth of 500–1,000 m below the surface. Prior to and during the construction, intense hydrogeological monitoring was set up, allowing the collection of abundant data concerning: (1) the evolution of water inflows into the tunnel; (2) the chemistry and temperature of drained groundwater; and (3) the influence of tunnel drainage on springs. Based on detailed analysis of geological/hydrogeological data, this article provides an insight into the permeability distribution in granitic rocks affected by relevant brittle tectonic deformation, and the consequences of water inflow during excavation. The available time series from the principal water discharges in the tunnel have been used in order to test the reliability of some of the most commonly applied analytical methods for the forecast of water inflows into tunnels.     

Comparative study of geophysical and soil–gas investigations at the Hartoušov (Czech Republic) natural CO2 degassing site

Our study at this natural analog site contributes to the evaluation of methods within a hierarchical monitoring concept suited for the control of CO₂ degassing. It supports the development of an effective monitoring concept for geological CO₂ storage sites—carbon capture and storage as one of the pillars of the European climate change efforts. This study presents results of comprehensive investigations along a 500-m long profile within the Hartou?ov (Czech Republic) natural CO₂ degassing site and gives structural information about the subsurface and interaction processes in relation to parameters measured. Measurements of CO₂ concentrations and investigation of the subsurface using electrical resistivity tomography and self-potential methods provide information about subsurface properties. For their successful application it is necessary to take seasonal variations (e.g., soil moisture, temperature, meteorological conditions) into consideration due to their influence on these parameters. Locations of high CO₂ concentration in shallow depths are related to positive self-potential anomalies, low soil moistures and high resistivity distributions, as well as high δ13C values and increased radon concentrations. CO₂ ascends from deep geological sources via preferential pathways and accumulates in coarser sediments. Repetition of measurements (which includes the effects of seasonal variations) revealed similar trends and allows us to identify a clear, prominent zone of anomalous values. Coarser unconsolidated sedimentary layers are beneficial for the accumulation of CO₂ gas. The distribution of such shallow geological structures needs to be considered as a significant environmental risk potential whenever sudden degassing of large gas volumes occurs.     

Public perception of climate engineering and carbon capture and storage in Germany: survey evidence

Climate engineering (CE) and carbon capture and storage are controversial options for addressing climate change. This study compares public perception in Germany of three specific measures: solar radiation management (SRM) via stratospheric sulphate injection, large-scale afforestation, and carbon capture and storage sub-seabed (CCS-S). In a survey experiment we find that afforestation is most readily accepted as a measure for addressing climate change, followed by CCS-S and lastly SRM, which is widely rejected. Providing additional information decreases acceptance for all measures, but their ranking remains unchanged. The acceptance of all three measures is especially influenced by the perceived seriousness of climate change and by trust in institutions. Also, respondents dislike the measures more if they perceive them as a way of shirking responsibility for emissions or as an unconscionable manipulation of nature. Women react more negatively to information than men, whereas the level of education or the degree of intuitive vs reflective decision making does not influence the reaction to information.

POLICY RELEVANCE

Current projections suggest that the use of climate engineering (CE) technologies or carbon capture and storage (CCS) is necessary if global warming is to be kept well below 2°C. Our article focuses on the perspective of the general public and thus supplements the dialogue between policymakers, interest groups, and scientists on how to address climate change. We show that in Germany public acceptance of potentially effective measures such as SRM or CCS-S is low and decreases even more when additional information is provided. This implies that lack of public acceptance may turn out to be a bottleneck for future implementation. Ongoing research and development in connection with CCS-S and SRM requires continuous communication with, and involvement of, the public in order to obtain feedback and assess the public’s reservations about the measures. The low level of acceptance also implies that emission reduction should remain a priority in climate policy.     

Heterogeneous and Homogeneous Chemistry of Reactive Halogen Compounds in the Lower Troposphere

This issue of the Journal of Atmospheric Chemistry contains a series of contributions describing recent developments in our understanding of the heterogeneous and homogeneous chemistry of reactive halogen compounds in the lower Troposphere. Twelve papers describe recent results in this very active area of research, were reported at the Annual Assembly of the European Geophysical Society 1998 in Nice, France, 20-24 April 1998. Considerable progress is documented on the elucidation of the various processes involved in the sources, transformation pathways and chemical consequences of the Reactive Halogen Species (RHS) in the troposphere.     

Hydrothermal precipitates associated with bimodal volcanism in the Central Bransfield Strait,Antarctica

Polymetallic sulfide-sulfate mineralization enriched in Pb-Ag-As-Sb-Hg occurs in the Bransfield Strait, a late Tertiary-Quaternary marginal basin close to the Antarctic Peninsula. The mineralization is associated with bimodal volcanism and pelagic and volcaniclastic sediment in rifted continental crust. Hydrothermal precipitates have been recovered from two shallow (1,050–1,000 m water depth) submarine volcanoes (Hook Ridge and Three Sisters) in the Central Bransfield Strait. Mineralization at Hook Ridge consists of polymetallic sulfides, massive barite, and pyrite and marcasite crusts in semilithified pelagic and volcaniclastic sediment. Native sulfur commonly infills void space and cements the volcaniclastic sediment. The polymetallic sulfides are dominated by sphalerite with minor galena, enargite, tetrahedrite-tennantite, pyrite, chalcopyrite, and traces of orpiment cemented by barite and opal-A. The presence of enargite at Hook Ridge, the abundance of native sulfur, and the low Fe content of sphalerite indicate a high sulfur activity of the hydrothermal fluids responsible for mineralization. The sulfur isotopic composition of Hook Ridge precipitates documents the complexity of the sulfur sources in this hydrothermal system with variable influence of biological activity and possibly magmatic contributions. Homogenization temperatures and salinities of fluid inclusions in barite and opal-A suggest that boiling may have affected the hydrothermal fluids during their ascent. The discovery of massive barite-silica precipitates at another shallow marine volcano (Three Sisters volcano) attests to the potential for hydrothermal mineralization at other volcanic edifices in the area. The characteristics of the mineralization in the Bransfield Strait with rifting of continental crust, the presence of bimodal volcanism, including highly evolved felsic volcanic rocks, the association with sediments, and the Pb-Ag-As-Sb-Hg enrichment are similar to the setting of massive sulfide deposits in the Okinawa Trough, and distinct from those of sediment-dominated hydrothermal systems such as Escanaba Trough, Middle Valley, and Guaymas Basin. The geological setting of the Bransfield Strait is also broadly similar to that of some of the largest volcanogenic massive sulfide deposits in the ancient record, such as the Iberian Pyrite Belt.Editorial handling: B. Lehmann     

Chemical fractionation of transition elements in Pacific pelagic sediments

Partitioning of transition elements in Pacific pelagic sediments (35 samples) was performed by sequential chemical leaching with barium chloride/triethanolamine (easily extractable fraction), acidic cation exchange resin (carbonate phases), and hydroxylamine hydrochloride and dilute hydrochloric acid solutions (hydrous oxides). Residual metal percentages are highest in red-brown clays and siliceous ooze, intermediate in calcareous materials and low in micronodules (2 samples, > 125 μm): residual metal contents seem to be controlled predominantly by the rate of admixture of volcanoclastic materials. At higher bulk metal concentrations, the non-residual fractions of Mn, Cu, Ni and Zn generally increase both in red-brown pelagic clays and in siliceous ooze. Mn, Ni, and Co concentrations are mainly associated with the easily reducible fraction (0.1 M NH₂OH·HCl), whereas Fe, Cu, and Zn exhibit higher percentages in the hydrochloric acid soluble fractions (0.3 M HCl); Zn and Cu are associated to some extent with the carbonate phase, copper with the easily extractable fraction.     

Characteristics of developing scour-holes at a sand-embedded cylinder

Characteristics of developing scour-holes at a sand-embedded 0.2 m diameter circular cylinder are presented. Non-intrusive, high-resolution topographic measurements of developing scour-holes were made with an experimental installation using a laser distance sensor （LDS） and precision step-motors. A clear-water experiment was conducted with bed shear stress equal to 95% of the critical bed shear stress for the initiation of sediment motion at the undisturbed plane sand bed with a d50 of 0.26 mm. During the running experiment of 21 hours duration, measurements were taken by the LDS in different azimuthal half-planes with θ= 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180° in order to study the spatio-temporal variation of geometric properties in developing scour-holes. After 21 hours, the equilibrium condition was approached, with a scour rate less than d50 per hour. Measurement of maximum scour depth in different azimuthal half-planes at different points in time during the experiment show that scour started at the cylinder side and surrounded the cylinder after about 20% of experiment time. Slopes of developing scour-holes presented three regions with different inclinations, which were attributed to vortex action. Both maximum scour depth and maximum scour radius at different azimuthal half-planes are well correlated with the maximum scour depth at plane with θ = 0°. When providing maximum scour depth at the cylinder front, the presented correlations are useful for simple calculation of scour-hole topography. This work provides an experimental database for advanced numerical simulation for loose sediment hydraulics.