Large-scale solar magnetic field: Latitudinal dependence

Large-scale solar magnetic fields in the latitude range 50° S–50° N are analyzed in detail for a long time interval (1915–1990). We are primarily concerned with the two types of large-scale fields forming the two-and four-sector patterns on the Sun. The rotation parameters of these structures are obtained for all latitudes considered. The contribution of the two-sector structure grows and that of the four-sector structure decreases toward high latitudes. The magnetic field is activated simultaneously over a wide latitude range. Since both magnetic-field systems exhibit quasi-rigid rotation, their current systems must either be concentrated in a narrow latitude range or be situated beneath the convection zone, where rotation is only weakly differential. A period of about three years is manifest in the difference between the rotation periods for the two types of magnetic field. Physically, this may imply that these oscillations are external with respect to any level, and there is some phase delay due to their propagation from one level to another. We can conclude with a fair degree of certainty that as the activity level rises, the rotation speed decreases, and vice versa.     

New data on the lithology of coastal facies of the Turtas formation (Upper Oligocene,Southwestern Siberia)

Peculiarities of the material composition and microstructure of coastal facies of Turtas Lake–Sea were studied in its marginal southwestern part for the first time. Interpretation of the lithological data showed that the deposits considered were formed under the conditions of a slightly saline basin and nearby full-flow river network. Based on the lithological, geochemical, and micropaleontological studies of clay–siliceous rocks of the Lower Turtas Formation (the boundary zone between the Tyumen and Sverdlovsk regions), additional support for the freshwater lake regime of the Late Oligocene Turtas basin is given.     

Modified Technique for Calculating the Parameters of Climatic Variability of Upwelling by Thermal Index

Izvestiya, Atmospheric and Oceanic Physics - A modified technique for calculating the amplitude-phase characteristics of the seasonal cycle and long-term trends in the intensity of upwelling is...     

Stable boron isotope fractionation between dissolved B(OH)3 and B(OH)4

The stable boron isotope ratio (¹¹B/¹⁰B) in marine carbonates is used as a paleo-pH recorder and is one of the most promising paleo-carbonate chemistry proxies. Understanding the thermodynamic basis of the proxy is of fundamental importance, including knowledge on the equilibrium fractionation factor between dissolved boric acid, B(OH)₃, and borate ion, B(OH)₄⁻ (, hereafter α_(B3-B4)). However, this factor has hitherto not been determined experimentally and a theoretically calculated value (Kakihana and Kotaka, 1977, hereafter KK77) has therefore been widely used. I examine the calculations underlying this value. Using the same spectroscopic data and methods as KK77, I calculate the same α_(B3−B4) = 1.0193 at 300 K. Unfortunately, it turns out that in general the result is sensitive to the experimentally determined vibrational frequencies and the theoretical methods used to calculate the molecular forces. Using analytical techniques and ab initio molecular orbital theory, the outcome for α_(B3-B4) varies between ∼1.020 and ∼1.050 at 300 K. However, several arguments suggest that α_(B3-B4) ? 1.030. Measured isotopic shifts in various ¹⁰B-, ²D-, and ¹⁸O-labeled isotopomers do not provide a constraint on stable boron isotope fractionation. I conclude that in order to anchor the fundamentals of the boron pH proxy, experimental work is required. The critics of the boron pH proxy should note, however, that uncertainties in α_(B3-B4) do not bias pH reconstructions provided that organism-specific calibrations are used.     

Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits

This study couples in situ ¹⁶O, ¹⁷O and ¹⁸O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ¹⁸O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ¹⁸O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ¹⁸O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz.     

Trace elements in organic- and iron-rich surficial fluids of the boreal zone: Assessing colloidal forms via dialysis and ultrafiltration

On-site size fractionation of about 40 major and trace elements (TE) was performed on waters from boreal small rivers and their estuaries in the Karelia region of North-West Russia around the “Vetreny Belt” mountain range and in Paanajärvi National Park (Northern Karelia). Samples were filtered in the field using a progressively decreasing pore size (5 μm, 2.5 (3) μm, 0.22 (0.45) μm, 100 kDa, 10 and 1 kDa) by means of frontal filtration and ultrafiltration (UF) techniques and employing in-situ dialysis with 10 and 1 kDa membranes followed by ICP-MS analysis. For most samples, dialysis yields a systematically higher (factor of 2-3) proportion of colloidal forms compared to UF. Nevertheless, dialysis is able to provide a fast and artefact-free in-situ separation of colloidal and dissolved components.Similar to previous studies in European subarctic zones, poor correlation of iron concentration with that of organic carbon (OC) in (ultra)filtrates and dialysates reflect the presence of two pools of colloids composed of organic-rich and Fe-rich particles. All major anions and silica are present as dissolved species (or solutes) passing through the 1-kDa membrane. Size-separation ultrafiltration experiments show the existence of larger or smaller pools of colloidal particles different for each of the considered elements.The effect of rock lithology (acidic versus basic) on the colloidal speciation of TE is seen solely in the increase of Fe and some accompanying TE concentrations in catchment areas dominated by basic rocks compared to granitic catchments. Neither the ultrafiltration pattern nor the relative proportions of colloidal versus truly dissolved TE are affected by the lithology of the underlying rocks: within ±10% uncertainty, the two colloidal (10 kDa-0.22 μm and 1-10 kDa) and the truly dissolved (<1 kDa) pools show no difference in percentage of TE distribution between two types of bedrock lithology. The same conclusion is held for organic- and Fe-rich waters. In contrast, landscape context analysis demonstrated slight dominance, for most TE affected by UF, of large-size colloids (10 kDa-0.22 μm) in rivers and streams and small-size colloids and truly dissolved fractions in swamp stagnant surface waters. This supports the existence of two pathways of colloids formation: during the plant litter degradation in wetland zones and at the redox front in river riparian zone.     

Frictional Properties and Microstructure of Calcite-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities

We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO₃) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18–150 °C and sliding velocities of 0.1–10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength (μ = 0.6) than dry gouges (μ = 0.7–0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80–100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure calcite gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5–20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not necessarily indicative of seismic slip rates.