Superconcentration of photospheric sources of the large-scale open solar magnetic field in the main zone of active longitudes, differential rotation blocking, and origination of the four-sector structure. 1. The field and solar activity dynamics

The phenomena of superconcentration of the large-scale field photospheric sources in the main zone of active longitudes, blocking of regular differential rotation by these sources, and origination of the four-sector structure of the solar magnetic field during the decline phase of cycle 23 have been considered in more detail and taking into account the polar correction. It has been indicated that superconcentration was formed due to the penetration of photospheric sources into the zone from the western surroundings of this zone and owing to the generation of the large-scale field in the zone itself. The dynamics of a blocking-induced complex MHD disturbance with reflected from the zone and reconnecting photospheric sources of negative and positive polarity, respectively, and the transformation of the bisector structure into the four-sector one have been considered. It has been indicated that the dynamics of this MHD disturbance was responsible for that of associated solar activity: the generation of sunspot groups, appearance of flares, and, finally, origination of a powerful heliospheric storm and the solar-terrestrial extrastorm of July 22–27, 2004.     

An application of Karmarkar's interior-point linear programming algorithm for multi-reservoir operations optimization

Optimization of multi-reservoir systems operations is typically a very large scale optimization problem. The following are the three types of optimization problems solved using linear programming (LP): (i) deterministic optimization for multiple periods involving fine stage intervals, for example, from an hour to a week (ii) implicit stochastic optimization using multiple years of inflow data, and (iii) explicit stochastic optimization using probability distributions of inflow data. Until recently, the revised simplex method has been the most efficient solution method available for solving large scale LP problems. In this paper, we show that an implementation of the Karmarkar's interior-point LP algorithm with a newly developed stopping criterion solves optimization problems of large multi-reservoir operations more efficiently than the simplex method. For example, using a Micro VAX II minicomputer, a 40 year, monthly stage, two-reservoir system optimization problem is solved 7.8 times faster than the advanced simplex code in MINOS 5.0. The advantage of this method is expected to be greater as the size of the problem grows from two reservoirs to multiples of reservoirs. This paper presents the details of the implementation and testing and in addition, some other features of the Karmarkar's algorithm which makes it a valuable optimization tool are illuminated.     

Precursors to earthquakes: Seismoelectromagnetic signals

Field measurements in the past several years have documented electromagnetic signals which are attributed to precursory stress and strain changes which were followed ultimately by earthquakes. Precursory electric field changes observed in Greece on multiple dipoles have been used to issue earthquake predictions. While the source of these signals is still unknown, a sufficient number of predictions has been issued to allow some, but not all, statistical analyses to show this method is better than randomly sampling the earthquake catalog. Ongoing efforts to identify the sources of both these signals and the magnetic field variations prior to the Loma Prieta earthquake are focusing on electrokinetic coupling of fluid flow and transient electric fields. A mechanism related to local fluid flow appears to be best suited at this time of explaining the variety of purported precursors. However, much more work is needed to improve the observations and refine the models of precursor generation. Efforts to monitor magnetotelluric transfer functions at longer periods (T>10s) have been hampered by variability of the functions. The use of modern noise reduction techniques such as remote referencing should reduce this variability, but may not reduce errors to a level needed for monitoring. Monitoring of high frequency (81 kHz) seismoelectric emissions may be promising, but lack of simultaneous observations on multiple instruments hinders the utility of this technique.     

Coda Q in the Kachchh Basin, Western India Using Aftershocks of the Bhuj Earthquake of January 26, 2001

Q_C-estimates of Kachchh Basin in western India have been obtained in a high frequency range from 1.5 to 24.0 Hz using the aftershock data of Bhuj earthquake of January 26, 2001 recorded within an epicentral distance of 80 km. The decay of coda waves of 30 sec window from 186 seismograms has been analysed in four lapse time windows, adopting the single backscattering model. The study shows that Q_c is a function of frequency and increases as frequency increases. The frequency dependent Q_c relations obtained for four lapse-time windows are: Q_c=82 f^1.17 (20–50 sec), Q_c=106 f^1.11 (30–60 sec), Q_c=126f^1.03 (40–70 sec) and Q_c=122f^1.02 (50–80 sec). These empirical relations represent the average attenuation properties of a zone covering the surface area of about 11,000, 20,000, 28,000 and 38,000 square km and a depth extent of about 60, 80, 95, 110 km, respectively. With increasing window length, the degree of frequency dependence, n, decreases marginally from 1.17 to 1.02, whereas Q₀ increases significantly from 82 to 122. At lower frequencies up to 6 Hz, Q_c⁻¹ of Kachchh Basin is in agreement with other regions of the world, whereas at higher frequencies from 12 to 24 Hz it is found to be low.     

Reconstructing hydrological variability from testate amoebae analysis in Carpathian peatlands

Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP, 3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe.     

Subglacial bedforms and conditions associated with the 1991 surge of Skeiðarárjökull, Iceland

Much previous research at surge-type glaciers has sought to identify features diagnostic of surge-type behaviour. However, in comparatively little work have subglacial landform–sediment characteristics been used to reconstruct changing basal processes and conditions during surge events. Subglacial bedforms described in this article are associated with the 1991 surge of Skeiðarárjökull, Iceland, and include a series of drumlins with superimposed flutes and basal crevasse-fill ridges. The drumlins were formed by the subglacial erosion of ice-contact fans. Sedimentary evidence indicates a shift from rigid-bed to soft-bed conditions during the surge. The presence of eroded but undeformed fan sediments suggests that they acted as a rigid bed when initially overridden. Subsequent deposition of a layer of deformation till resulted in a change to soft-bed conditions and the generation of flutes and subglacial crevasse-fill ridges. The lack of mixing between this till and the underlying stratified sediments indicates that subglacial sediment deformation was restricted to a thin layer and that its deposition resulted in a cessation of subglacial erosion. The drumlin is therefore a composite of both rigid-bed and soft-bed processes that illustrates changes in basal conditions and processes during the course of the event. The limited time frame in which the drumlin formed and the presence of kettleholes across its surface are distinctive features that may warrant further investigation in the search for features diagnostic of past surge events.     

Manganese ore deposits in Koira-Noamundi province of Iron Ore Group, north Orissa, India: In the light of geochemical signature

Several small Mn–Fe oxide and Mn-oxide ore bodies associated with Precambrian Iron Ore Group of rocks are located within Koira-Noamundi province of north Orissa, India. These deposits are classified into in situ (stratiform), remobilized (stratabound) and reworked categories based on their field disposition. Volcaniclastic/terrigenous shale in large geographic extension is associated with these ore bodies.The in situ ore bodies are characterised by cryptomelane-, romanechite- and hematite-dominating minerals, low Mn/Fe ratio (1.1) and relatively lower abundance of trace (1500–2500 ppm) constituents. In such type of deposits the stratigraphic conformity of oxides with the tuffaceous shale suggests precipitation of Mn and Fe at a time of decreased volcaniclastic/terrigenous contribution. The minor and trace elements were removed from solution by adsorption rather than by precipitation. Both Mn and Fe oxides when precipitated adsorb trace elements strongly but the partitioning of elements takes place during diagenesis. The inter-elemental relationship reveals that Cu, Co, Ni, Pb and Zn were adsorbed on precipitating hydrous Mn oxides and form manganates. Some of these elements probably get desorbed from Fe oxide because of their inability to substitute for Fe³⁺ in the lattice of its oxide. However, P, V, As and Mo were less partitioned and retained in Fe-oxide phase. Positive correlation between Al₂O₃ and SiO₂, MgO, Na₂O, TiO₂ and some traces like Li, Nb, Sc, Y, Zr, Th and U points to their contribution through volcaniclastic/terrigenous detritus of both mafic and acidic composition.The remobilized ore bodies are developed in a later stage through dissolution, remobilization and reprecipitation of Mn oxides in favorable structural weak planes under supergene environment. Increase in average Mn/Fe ratio (8) and trace content (5000–8500 ppm) by 5–2.5 orders of magnitude, respectively, or more above its abundance in adjoining/underlying protore is characteristic of these deposits. The newly formed Mn ores constituting lithiophorite, cryptomelane/romanechite and goethite get quantitatively enriched in traces like Cu, Co, Ni, Pb and Zn. Positive correlation between Mn, Li, Co and Zn is due to the formation of mineral of lithiophorite–chalcophanite group during redistribution and reconcentration of Mn oxide. P and V, which were present in Fe oxide, also get dissolved and reprecipitate with Fe oxyhydroxide in these ores. Some other elements like Y, Th and U show positive relation with Fe. This is probably due to leaching of these elements during chemical weathering of associated shale and getting re-adsorbed in Fe-oxyhydroxide phase.However, under oxidizing environment selective cations like Ba, K, etc. resorb from Mn-structure, resulting in the development of pyrolusite (Mn/Fe>20). In such transformation, trace metals from pyrolusitic structure expels out, resulting thereby in a considerable reduction in total trace value (<3000 ppm).The reworked ore bodies are allochthonous in nature and developed through a number of stages during terrain evolution and lateritisation. Secondary processes such as reworking of pre-existing crust; solution and remobilization; precipitation and cementation and transport, etc. are responsible for their development. Such deposits are usually very low in Mn/Fe ratio (3) and trace content (<2000 ppm).     

Sr isotopic composition of Paleoproterozoic C-rich carbonate rocks: The Tulomozero Formation,SE Fennoscandian Shield

Rb–Sr systematics has been studied in ¹³C-rich carbonate rocks of the Paleoproterozoic (2.09 ± 0.07 Ga) Tulomozero Formation in the northern Onega Lake area, the SE Fennoscandian Shield. The formation is divided into eight members (A–F) consisting of greenschist-facies-grade, variegated sandstones, siltstones, mudstones, stromatolitic dolostones and subordinate crystalline limestones. Samples of carbonate rocks were obtained from two overlapping drillholes intersecting the entire thickness of the Tulomozero Formation. Prior to isotope analysis, the rocks powders were treated with 1N ammonium acetate for partial removal of the late epigenetic carbonate phases. Major resetting of the Rb–Sr systems in the Tulomozero carbonate rocks appears to take place during the Svecofennian regional metamorphic event, and it was screened by using Mn/Sr, Fe/Sr, Mg/Ca, and ¹⁸O/¹⁶O ratios. High Sr content (up to 2080 μg/g in limestones, and 530 μg/g in dolostones) coupled with low Fe/Mn (<0.40) ratios in the Tulomozero carbonate rocks of Members A, B (the lower part), D, F, and E are consistent with accumulation of original carbonate sediments in evaporitic lacustrine, playa, and sabkha environments. A decrease in the Sr content with concurrent increase in the Fe/Mn ratio (>0.40) in dolostones of the upper part of Member B, and of Members G and H is indicative of seawater influxes (sea transgression) into the Tulomozero basin. The ⁸⁷Sr/⁸⁶Sr values in the least altered (Mn/Sr < 2.0) marine dolostones are 0.70418–0.70442 and 0.70343–0.70409 for the earlier and late phases of the marine transgression, respectively. The decrease in the ⁸⁷Sr/⁸⁶Sr ratio in ca. 2.1 Ga seawater is attributable to an increase in hydrothermal flux Sr into the Palaeoproterozoic ocean.     

High‐Arctic climate conditions for the last 7000 years inferred from multi‐proxy analysis of the Bliss Lake record,North Greenland

The Arctic is more vulnerable to climate change than are mid latitudes. Therefore, palaeolimnological studies from the High Arctic are important in providing insights into the dynamics of the climate system. Here we present a multi‐proxy study from one of the world's northernmost lakes: Bliss Lake, Peary Land, Greenland. The early Holocene (10 850–10 480 cal. a BP) is characterized by increased erosion and gradually more marine conditions. Full marine conditions developed from 10 480 cal. a BP until the lake was isolated at 7220 cal. a BP. From its marine isolation at 7220 cal. a BP Bliss Lake becomes a lacustrine environment. Evidence from geochemical proxies (δ¹³C and total organic carbon) suggests that warmer conditions prevailed between 7220 and 6500 cal. a BP, corresponding to the Holocene thermal maximum, and from 3300 until 910 cal. a BP. From 850 to 500 cal. a BP colder climate conditions persisted. The transition from warmer to colder climate conditions taking place around 850 cal. a BP may be associated with the transition from the Medieval Warm Period to the Little Ice Age. Copyright © 2011 John Wiley & Sons, Ltd.     

Diamictic sediments within high Arctic lake sediment cores: evidence for lake ice rafting along the lateral glacial margin

Sediment cores from six small lake basins in the Canadian high Arctic reveal a gravel‐rich (≤30% by weight) to gravel‐poor (≥2%) diamict facies underlying massive, post‐glacial, clayey silt. Ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages. The sedimentology, clast fabrics and fossil remains (diatoms, ostracodes and chironomid head capsules) within both diamict facies suggest that these deposits are not tills. Clast fabrics yielded low S₁ (0·41–0·57) and high S₃ (0·09–0·22) eigenvalues, placing them within the range of ice‐rafted diamictons and glacigenic sediment flows. The high percentage of clast dip angles >45° (15–61%), random clast azimuth and lower diamict contacts conformable to underlying current‐bedded sediment favours an origin as a rain‐out or settling deposit. Samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms, such as are found in the littoral regions of the lakes today. This contrasts sharply with the assemblages within the overlying clayey silt, in which benthic forms predominate. Clasts are thus interpreted to have been rafted from the littoral areas of the lake. The process proposed to explain this is rafting by the lake ice cover in a glacial‐marginal environment. Early season meltwater, impounded along the lateral margin of retreating cold‐based glaciers, would buoyantly lift the lake ice cover and any adfrozen lake sediment. Higher lake levels and increased areal extent of seasonal freeze‐on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up. Incision by meltwater streams into the lateral glacial margins would later isolate the lake, allowing seasonal warming of lake water, enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts.