Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia

Palynological results from Julietta Lake currently provide the most direct evidence to support the existence of a glacial refugium for Pinus pumila in mountains of southwestern Beringia. Both percentages and accumulation rates indicate the evergreen shrub survived until at least ∼ 19,000 ¹⁴C yr BP in the Upper Kolyma region. Percentage data suggest numbers dwindled into the late glaciation, whereas pollen accumulation rates point towards a more rapid demise shortly after ∼ 19,000 ¹⁴C yr BP. Pinus pumila did not re-establish in any great numbers until ∼ 8100 ¹⁴C yr BP, despite the local presence ∼ 9800 ¹⁴C yr BP of Larixdahurica, which shares similar summer temperature requirements. The postglacial thermal maximum (in Beringia ∼ 11,000-9000 ¹⁴C yr BP) provided Pinus pumila shrubs with equally harsh albeit different conditions for survival than those present during the LGM. Regional records indicate that in this time of maximum warmth Pinus pumila likely sheltered in a second, lower-elevation refugium. Paleoclimatic models and modern ecology suggest that shifts in the nature of seasonal transitions and not only seasonal extremes have played important roles in the history of Pinus pumila over the last ∼ 21,000 ¹⁴C yr BP.     

Nonlinear geodynamics of the Baikal rift system: An evolution scenario with triple equilibrium bifurcation

This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 M_LH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.     

Oxygen isotope fractionation factors involving cassiterite (SnO2): I. calculation of reduced partition function ratios from heat capacity and X-ray resonant studies

Oxygen isotope equilibrium fractionation constants (β¹⁸O-factors) of cassiterite were evaluated on the basis of heat capacity and X-ray resonant (Mössbauer spectroscopy and X-ray inelastic scattering) data.The low-temperature heat capacity of cassiterite was measured in the range from 13 to 340 K using an adiabatic calorimeter. Results of measurements of two samples agree very closely but deviate more than 5% from previous heat capacity data used for calculation of thermodynamic functions. The temperature dependence of heat capacity was treated using the modern version of the Thirring expansion, and the appropriate temperature dependence of the vibrational kinetic energy was found.Measurements of temperature-dependent Mössbauer parameters of cassiterite were conducted in the range from 300 to 900 K. The attempt to describe Mössbauer fraction and the second order Doppler (SOD) shift on the basis of the Debye model failed. The first term of the Thirring expansion of the Mössbauer SOD shift agrees with that calculated from the Sn sublattice vibration density of states (VDOS) obtained via synchrotron X-ray scattering. Based on this agreement we calculated the kinetic energy of the cassiterite Sn sublattice from VDOS.From the kinetic energy of the total cassiterite crystalline lattice and its Sn sublattice, β¹⁸O-factors of cassiterite were computed in the temperature range 300-1500 K by the method of Polyakov and Mineev (2000). Appropriate polynomials, which are valid at temperatures above 400 K, are the following:

     

Noril’sk–Talnakh Cu–Ni–PGE deposits: a revised tectonic model

The Norilsk mining district is located at the northwest margin of the Tunguska basin, in the centre of the 3,000×4,000 km Siberian continental flood basalt (CFB) province. This CFB province was formed at the Permo-Triassic boundary from a superplume that ascended into the geometric centre of the Laurasian continent, which was surrounded by subducting slabs of oceanic crust. We suggest that these slabs could have reached the core–mantle boundary, and they may have controlled the geometric focus of the superplume. The resulting voluminous magma intruded and erupted in continental rifts and related extensive flood basalt events over a 2–4 Ma period. Cu–Ni–PGE sulfide mineralization is found in olivine-bearing differentiated mafic intrusions beneath the flood basalts at the northwestern margin of the Siberian craton and also in the Taimyr Peninsula, some 300 km east of a triple junction of continental rifts, now buried beneath the Mesozoic–Cenozoic sedimentary basin of western Siberia. The Norilsk-I and Talnakh-Oktyabrsky deposits occur in the Norilsk–Kharaelakh trough of the Tunguska CFB basin. The Cu–Ni–PGE-bearing mineralized intrusions are 2–3 km-wide and 20 km-long differentiated chonoliths. Previous studies suggested that parts of the magma remained in intermediate-level crustal chambers where sulfide saturation and accumulation took place before emplacement. The 5–7-km-thick Neoproterozoic to Palaeozoic country rocks, containing sedimentary Cu mineralization and evaporites, may have contributed additional metal and sulfur to this magma. Classic tectonomagmatic models for these deposits proposed that subvertical crustal faults, such as the northeast-trending Norilsk–Kharaelakh fault, were major trough-parallel conduits providing access for magmas to the final chambers. However, geological maps of the Norilsk region show that the Norilsk–Kharaelakh fault offsets the mineralization, which was deformed into folds and offset by related reverse faults, indicating compressional deformation after mineralization in the Late Triassic to Early Jurassic. In addition, most of the intrusions are sills, not dykes as should be expected if the vertical faults were major conduits. A revised tectonic model for the Norilsk region takes into account the fold structure and sill morphology of the dominant intrusions, indicating a lateral rather than vertical emplacement direction for the magma into final chambers. Taking into account the fold structure of the country rocks, the present distribution of the differentiated intrusions hosting the Norilsk-I and Talnakh–Oktyabrsky deposits may represent the remnants of a single, >60 km long, deformed and eroded palm-shaped cluster of mineralized intrusions, which are perceived as separate intrusions at the present erosional level. The original direction of sill emplacement may have been controlled by a northeast-trending paleo-rise, which we suggest is present at the southeastern border of the Norilsk–Kharaelakh trough based on analysis of the unconformity at the base of the CFB. The mineralized intrusions extend along this rise, which we interpret as a structure that formed above the extensionally tilted block in the metamorphic basement. Geophysical data indicate the presence of an intermediate magma chamber that could be linked with the Talnakh intrusion. In turn, this T-shaped flat chamber may link with the Yenisei–Khatanga rift along the northwest-trending Pyasina transform fault, which may have served as the principal magma conduit to the intermediate chamber. It then produced the differentiated mineralized intrusions that melted through the evaporites with in situ precipitation of massive, disseminated, and copper sulfide ore. The Norilsk–Kharaelakh crustal fault may not relate to mineralization and possibly formed in response to late Mesozoic spreading in the Arctic Ocean.Editorial handling: P. Lightfoot     

Can the uncertainty of full carbon accounting of forest ecosystems be made acceptable to policymakers?

In accordance with the concept that only full accounting of major greenhouse gases corresponds to the goals of the United Nations Framework Convention on Climate Change and its Kyoto Protocol, this paper considers uncertainties of regional (national) terrestrial biota Full Carbon Accounting (FCA), both those already achieved and those expected. We analyze uncertainties of major components of the FCA of forest ecosystems of a large boreal region in Siberia (~300 × 10⁶ ha). Some estimates for forests of other regions and Russia as a whole are used for comparison. The systems integration of available information sources and different types of models within the landscape-ecosystem approach are shown to have enabled an estimation of the major carbon fluxes (Net Primary Production, NPP, and heterotrophic respiration, HR) for the region for a single year at the level of 7–12% (confidential interval, CI, 0.9), Net Ecosystem Production (NEP) of 35–40%, and Net Biome Production (NBP) of 60–80%. The most uncertain aspect is the assessment of change in the soil carbon pool, which limits practical application of a pool-based approach. Regionalization of global process-based models, introduction of climatic data in empirical models, use of an appropriate time period for accounting and reporting, harmonization and multiple constraints of estimates obtained by different independent methods decrease the above uncertainties of NEP and NBP by about half. The results of this study support the idea that FCA of forest ecosystems is relevant in the post-Kyoto international negotiation process.     

Medium-range forecasts of large ice cover discontinuities for hydrometeorological support of navigation in the Arctic basin

A brief characteristic of the Arctic ice cover discontinuities (ICD) is given. Their practical importance for vessels operating in this region as well as necessity of forecasting such indicators as the prevailing disposition of discontinuities and location of zones of their formation and closure are noted. The forecasting technique is based on the method of complex analogs. A summary of forecasts produced for the Arctic navigation areas since 1991 is provided. It is shown, that recent upgrading of the original methodology allowed to produce forecasts in on-line mode, to present digital maps of the forecast data, and to transfer them directly to the vessel’s automated workplace. A number of practical examples are presented for illustrating the navigation efficiency if forecast and actual ICD data are used. The results of forecast verification are given.     

The Obolon impact structure,Ukraine, and its ejecta deposits

Abstract— The Obolon impact structure, 18 km in diameter, is situated at the northeastern slope of the Ukrainian Shield near its margin with the Dnieper‐Donets Depression. The crater was formed in crystalline rocks of the Precambrian basement that are overlain by marine Carboniferous and continental Lower Triassic deposits. The post‐impact sediments comprise marine Middle Jurassic (Bajocian and Bathonian) and younger Mesozoic and Cenozoic deposits. Today the impact structure is buried beneath an about 300‐meter‐thick sedimentary rock sequence. Most information on the Obolon structure is derived from two boreholes in the western part of the crater. The lowest part of the section in the deepest borehole is composed by allogenic breccia of crystalline basement rocks overlain by clast‐rich impact melt rocks and suevites. Abundant shock metamorphic effects are planar deformation features (PDFs) in quartz and feldspars, kink bands in biotite, etc. Coesite and impact diamonds were found in clast‐rich impact melt rocks. Crater‐fill deposits are a series of sandstones and breccias with blocks of sedimentary rocks that are covered by a layer of crystalline rock breccia. Crystalline rock breccias, conglomeratic breccias, and sandstones with crystalline rock debris have been found in some boreholes around the Obolon impact structure to a distance of about 50 km from its center. Those deposits are always underlain by Lower Triassic continental red clay and overlain by Middle Jurassic marine clay. The K‐Ar age of impact melt glasses is 169 Ma, which corresponds to the Middle Jurassic (Bajocian) age. The composition of crater‐fill rocks within the crater and sediments outside the Obolon structure testify to its formation under submarine conditions.     

Fluid regime and diamond formation in the reduced mantle: Experimental constraints

The composition and potential diamond productivity of C–O–H fluids that could exist in the reduced regions of the Earth’s upper mantle and in the mantles of Uranus and Neptune were studied in experiments at 6.3 GPa and 1400–1600 °C and durations of 15–48 h. Hydrogen fugacity in the fluid phase was controlled by the Mo–MoO₂ or Fe–FeO buffers, using a specially modified double-capsule method. The oxygen fugacity in the samples was controlled by adding different amounts of water, stearic acid, anthracene, and docosane to a graphite charge. At high P–T conditions, the degree of decomposition of the heavy hydrocarbons added to the charge was 99.9%. The composition of the fluids coexisting with graphite/diamond in the buffered experiments varied from H₂O  H₂ > CH₄ (at fO₂ somewhat lower than the “water maximum”) to H₂ > CH₄ > (C₂H₄ + C₂H₆)>C₃H₈ (in C–H system). In the C–H system the maximum concentrations of major species in the synthesized fluid were: H₂ = 79 mol.% and CH₄ = 21 mol.%. The composition of the H₂-rich fluids, which were synthesized at 6.3 GPa and 1400–1600 °C for the first time, differs considerably from that of the ultra-reduced CH₄-rich fluids stable at 2.0–3.5 GPa and 1000–1300 °C. Thermodynamic calculations of the reduced C–O–H fluids at the P–T conditions of the experiments revealed CH₄-rich compositions (CH₄  H₂ > (C₂H₄ + C₂H₆)>C₃H₈), which however drastically differed from the synthesized compositions. The rates of diamond nucleation and growth in the experiments depended on the fluid composition. Diamond crystallization had a maximum intensity in the pure aqueous fluids, while in the H₂-rich fluids no diamond formation was observed. Only metastable graphite precipitated from the ultra-reduced fluids. The type of the initial hydrocarbon used for the fluid generation did not affect this process.     

Robotic optical telescopes global network MASTER II. Equipment, structure, algorithms

Presented paper describes the basic principles and features of the implementation of a robotic network of optical telescopes MASTER, designed to study the prompt (simultaneous with gamma radiation) optical emission of gamma-ray bursts and to perform the sky survey to detect unknown objects and transient phenomena. With joint efforts of Sternberg astronomical institute, High altitude astronomical station of the Pulkovo observatory, Ural state university, Irkutsk state university, Blagoveshchensk pedagogical university, the robotic telescopes MASTER?II near Kislovodsk, Yekaterinburg, Irkutsk and Blagoveshchensk were installed and tested. The network spread over the longitudes is greater than 6?h. A further expansion of the network is considered.