Survey of Geomagnetic Observations Made in the Northern Sector of Russia and New Methods for Analysing Them

An overview of the geomagnetic observations made in the northern part of Russia is presented from a historical perspective. Several stations were deployed on the territory of the former Soviet Union during the International Geophysical Year, 1957–1958, with the active participation and guidance of the Interagency Geophysical Committee which is inherited by the Geophysical Center of the Russian Academy of Sciences (GC RAS). In the 1990s, the majority of these stations, especially those in the remoter regions, were closed. Nowadays, the geomagnetic network, including the observatories of the INTERMAGNET program, has been restored. Examples of high-latitude geomagnetic variations in the Russian longitudinal sector are shown, and maps and trends of the secular variation over the territory of Russia presented. Particular attention is paid to the automated processing of data and to the analysis methods used. To process the growing amount of high-resolution geomagnetic data, sophisticated mathematical methods based on the fuzzy logic approach and new discrete mathematical analysis algorithms have been developed. The formal methods and algorithms for recognizing both artificial and natural disturbances in the magnetograms are described.     

Constraining groundwater modeling with magnetic resonance soundings

Magnetic resonance sounding (MRS) is a noninvasive geophysical method that allows estimating the free water content and transmissivity of aquifers. In this article, the ability of MRS to improve the reliability of a numerical groundwater model is assessed. Thirty-five sites were investigated by MRS over a ～5000 km(2) domain of the sedimentary Continental Terminal aquifer in SW Niger. Time domain electromagnetic soundings were jointly carried out to estimate the aquifer thickness. A groundwater model was previously built for this section of the aquifer and forced by the outputs from a distributed surface hydrology model, to simulate the observed long-term (1992 to 2003) rise in the water table. Uncertainty analysis had shown that independent estimates of the free water content and transmissivity values of the aquifer would facilitate cross-evaluation of the surface-water and groundwater models. MRS results indicate ranges for permeability (K = 1 × 10(-5) to 3 × 10(-4) m/s) and for free water content (w = 5% to 23% m(3) /m(3) ) narrowed by two orders of magnitude (K) and by ～50% (w), respectively, compared to the ranges of permeability and specific yield values previously considered. These shorter parameter ranges result in a reduction in the model's equifinality (whereby multiple combinations of model's parameters are able to represent the same observed piezometric levels), allowing a better constrained estimate to be derived for net aquifer recharge (～22 mm/year).     

Application of the data on the lithospheric magnetic anomalies in the problem of recognizing the earthquake prone areas

For the first time, an attempt is made to apply the data on the lithospheric magnetic anomalies of the Earth for determining the areas prone to strong earthquakes by means of the pattern recognition algorithms. The Caucasian region with the threshold magnitude of the strong earthquakes M₀ = 6 is considered. It is established that the data on the lithospheric magnetic anomalies are informative from the standpoint of recognizing the strong earthquake prone areas. Application of these data is promising for solving the similar problems for different seismically active regions.     

Satellite-based terrestrial production efficiency modeling

Production efficiency models (PEMs) are based on the theory of light use efficiency (LUE) which states that a relatively constant relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however in the application of the PEM methodology to global net primary productivity (NPP) monitoring. The objectives of this review are as follows: 1) to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS) identified in the literature; 2) to review each model to determine potential improvements to the general PEM methodology; 3) to review the related literature on satellite-based gross primary productivity (GPP) and NPP modeling for additional possibilities for improvement; and 4) based on this review, propose items for coordinated research.     

Identification of sinkhole development mechanism based on a combined geophysical study in Nahal Hever South area (Dead Sea coast of Israel)

Seismic refraction, magnetic resonance sounding (MRS), and the transient electromagnetic (TEM) method were applied to investigate the geological and hydrogeological conditions in the Nahal Hever South sinkhole development area at the Dead Sea (DS) coast of Israel. Microgravity and MRS results reliably reveal large karst cavity in the central part of investigated area. The map of the seismic velocity shows that sinkholes in Nahal Hever can be divided into two major groups: sinkholes close to the salt edge and sinkholes over compact salt formations between a few tens to a hundred meters from the major cavern. The present study shows that the formation of sinkholes of the first group is caused by soil collapsing into the cavern. In the area occupied by sinkholes of the second group, karst was not detected either by MRS or by seismic diffraction methods. TEM results reveal shallow clay layer saturated with DS brine underlain sinkholes of this group. It allows suggestion that the water drainage and intensive water circulation during rain events wash out fine rock particles from the unsaturated zone into the pre-existing cavern, initiating the formation of sinkholes of the second group. Karst development takes place at a very low bulk resistivity (<1 Ω m) of the DS aquifer, attesting to the fact that pores are filled with a highly saline solution. Refilling of the karstic cavities with collapsing and flushed soil slows down sinkhole development in the area. The sinkhole formation cycle at the site is estimated at 10 years. Sinkhole development throughout the studied area is triggered by a drop in the level of the DS, which reduces the head of the confined aquifer and the strength of the overlain sediments.

Evidence of multiple thermokarst lake generations from an 11 800‐year‐old permafrost core on the northern Seward Peninsula,Alaska

Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site‐specific palaeo‐records are needed. Here we present a multi‐proxy study of a 350‐cm‐long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain‐size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, δ¹³C_org) and stable water isotopes (δ¹⁸O, δD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre‐lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post‐drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core‐based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice‐rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst‐affected regions of the Arctic.     

Dolomite-calcite textures in early carbonatites of the Kovdor ore deposit,Kola peninsula,Russia: their genesis and application for calcite-dolomite geothermometry

In early calcite carbonatites of the Kovdor ore deposit four morphological types of dolomite are represented. In the first type, dolomite microcrystals occur as lamellae enclosed by optically continuous calcite. In the second, dolomite microcrystals occur as segmented rods, plates and xenomorphic grains, enclosed by optically discontinuous calcite, and in the third, dolomite is represented by grains of various morphologies, situated along calcite grain boundaries. The fourth type of dolomite occurs as a fine-grained aggregate, which develops along grain boundaries and cleavage cracks of calcite. From microscopic, scanning electron microscope and microprobe studies of these different types of dolomite microcrystals, as well as the calcite associated with them, it can be concluded that the first type of dolomite was exsolved from magnesian calcite during cooling. The second, and the third types of dolomite microcrystals were formed by recrystallization. The fourth type of dolomite was formed by metasomatic dolomitization. As the result of these two processes-recrystallization and metasomatic dolomitization-early dolomite microcrystals seldom occur. The composition of the early-formed primary magnesian calcite yielded temperatures of exsolution of dolomite from magnesian calcite between 665 and 700°C.     

Methane fluxes and gas hydrates as well as seismic activity in the Okhotsk Sea

The research works of methane concentration in water column of the Okhotsk Sea from 1984 to 2005 were reviewed.And some regularities of methane distribution in water column in the North-East Sakhalin slope of the Okhotsk Sea were concluded.     

El'gygytgyn impact crater,Russia: Structure,tectonics, and morphology

Abstract— The 3.6 Myr old El'gygytgyn impact crater is located in central Chukotka, northeastern Russia. The crater is a well‐preserved impact structure with an inner basin about 15 km in diameter, surrounded by an uplifted rim about 18 km in diameter. The flat floor of the crater is in part occupied by Lake El'gygytgyn, 12 km in diameter, and surrounding terraces. The average profile of the rim is asymmetric, with a steep inner wall and a gentle outer flank. The rim height is about 180 m above the lake level and 140 m above the surrounding area. An outer ring feature, on average 14 m high, occurs at about 1.75 crater radii from the center of the structure. El'gygytgyn crater is surrounded by a complex network of faults. The density of the faults decreases from the bottom of the rim to the rim crest and outside the crater to a distance of about 2.7 crater radii. Lake El'gygytgyn is surrounded by a number of lacustrine terraces. Only minor remnants are preserved of the highest terraces, 80 and 60 m above the present‐day lake level. The widest of the terraces is 40 m above the current lake level and surrounds the lake on the west and northwest sides. The only outlet of the lake is the Enmivaam River, which cuts through the crater rim in the southeast. In terms of structure, El'gygytgyn is well preserved and displays some interesting, but not well understood, features (e.g., an outer ring), similar to those observed at a few other impact structures.