The Eastern Congo—a beauty spot,rediscovered from a geological point of view

In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area.     

A computer program for interpreting vertical magnetic anomalies of spheres and horizontal cylinders

Summary A common computer program for the interpretation of vertical magnetic anomalies of spheres and horizontal cylinders has been developed. The input consists of the observed anomalies noted against their distances measured from an arbitrary point in the profile and a code number for each model. The program is written so that the positions and magnitudes of the maximum and minimum anomalies are located and their ratios and signs are used to define the initial parameters of the model under consideration. The errors resulting from these approximate values are derived and are solved for the increments to be given to the initial values. The process is repeated until the sum of the squares of the errors is less than 0.25% of the sum of the squares of the observed anomalies. The method has been tested on various theoretical examples and the results justify the validity of the programme.     

Neoproterozoic Volhynia-Brest magmatic province in the western East European craton: Within-plate magmatism in an ancient suture zone

The reasons for the isotopic and geochemical heterogeneity of magmatism of the Neoproterozoic large Volhynia-Brest igneous province (VBP) are considered. The province was formed at 550 Ma in response to the break up of the Rodinia supercontinent and extends along the western margin of the East European craton, being discordant to the Paleoproterozoic mobile zone that separates Sarmatia and Fennoscandia and the Mesoproterozoic Volhynia-Orsha aulacogen. The basalts of VBP show prominent spatiotemporal geochemical zoning. Based on petrographic, mineralogical, geochemical, and isotopic data, the following types of basalts can be distinguished: olivine-normative subalkaline basalts consisting of low-Ti (sLT, < 1.10–2.0 wt % TiO₂; ε_Nd(550) from ?6.6 to ?2.7) and medium-Ti (sMT, 2.0–3.0 wt % TiO₂, occasionally up to 3.6 wt % TiO₂; ε_Nd(550) from ?3.55 to + 0.6) varieties; normal quartz-normative basalts (tholeiites) including low-Ti (tLT, < 1.75–2.0 wt % TiO₂) and medium-to-high-Ti (tHT1, 2.0–3.6 wt % TiO₂, ε_Nd(550) from ?1.3 to + 1.0) varieties. The hypabyssal bodies are made up of subalkaline low-Ti olivine dolerites (LT, 1.2–1.5 wt % TiO₂; ε_Nd(550) = ?5.8) and subalkaline high-Ti olivine gabbrodolerites (HT2, 3.0–4.5 wt % TiO₂; ε_Nd(550) = ?2.5). Felsic rocks of VBP are classed as volcanic rocks of normal (andesidacites, dacites, and rhyodacites) and subalkaline (trachyrhyodacites) series with TiO₂ 0.72–0.77 wt% and ε_Nd(550) of ?12. The central part of VBP is underlain by a Paleoproterozoic domain formed by continent-arc accretion and contains widespread sills of HT2 dolerites and lavas of LT basalts; the northern part of the province is underlain by the juvenile Paleoproterozoic crust dominated by MT and HT1 basalts. MT and LT basalts underwent significant AFC-style upper crustal contamination. During their long residence in the upper crustal magmatic chambers, the basaltic melts fractionated and caused notable heating of the wall rocks and, correspondingly, nonmodal melting of the upper crustal protolith containing high-Rb phase (biotite), thus producing the most felsic rocks of the province. The basalts of VBP were derived from geochemically different sources: probably, the lithosphere and a deep-seated plume (PREMA type). The HT2 dolerites were generated mainly from a lithospheric source: by 3–4% melting of the geochemically enriched garnet lherzolite mantle. LT dolerites were obtained by partial melting of the modally metasomatized mantle containing volatile-bearing phases. The concepts of VBP formation were summarized in the model of three-stage plume-lithosphere interaction.     

How Well Does Chlorophyll Explain the Seasonal Variation in Phytoplankton Activity?

The seasonal variation in phytoplankton activity is determined by analysing 1385 primary production (PP) profiles, chlorophyll a (Chl) concentration profiles and phytoplankton carbon biomass concentrations (C) from the period 1998–2012. The data was collected at six different stations in the Baltic Sea transition zone (BSTZ) which is a location with strong seasonal production patterns with light as the key parameter controlling this productivity. We show that the use of Chl as a proxy for phytoplankton activity strongly overestimates the contribution from the spring production to annual pelagic carbon flow. Spring (February and March) Chl comprised 16–30% of the total annual Chl produced, whereas spring C was much lower (8–23%) compared to the annual C. Spring PP accounted for 10–18% of the total annual PP, while the July–August production contributed 26–33%, i.e. within the time frame when zooplankton biomass and grazing pressure are highest. That is, Chl failed in this study to reflect the importance of the high summer PP. A better proxy for biomass may be C, which correlated well with the seasonal pattern of PP (Pearson correlation, p < 0.05). Thus, this study suggests to account for the strong seasonal pattern in C/Chl ratios when considering carbon flow in coastal systems. Seasonal data for PP were fitted to a simple sinusoidal wave model describing the seasonal distribution of PP in the BSTZ and were proposed to present a better parameterizaton of PP in shallow stratified temperate regions than more commonly applied proxies.     

Precipitation cycles in the middle and lower reaches of the Yellow River （1736-2000）

Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that： the precipitation in the middle and lower reaches of the Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and the 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation （PDO） coincide with the two cycle signals. However, on a 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong （weak） solar activity is generally correlated to the dry （wet） periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on the 70-80a time scale.     

Numerical simulation of the electric field and zonal current in the Earth’s ionosphere: The dynamo field and equatorial electrojet

The work is devoted to the numerical simulation of the dynamo electric field and its effects in the Earth’s ionosphere within the scope of the thermosphere-ionosphere-protonosphere global self-consistent model developed at WD IZMIRAN. The new electric field calculation block, which was used to obtain results of the self-consistent calculations of the electric field potential generated by the dynamo effect of the thermospheric winds (the dynamo field) and the equatorial electrojet for March 22, 1987, is briefly described in this work. A comparison of the obtained results with the experimental data showed a satisfactory agreement. Moreover, the proposed model was used to calculate the diurnal variations in the ionospheric parameters for Jicamarca equatorial station under the same conditions with the help of the new block of the electric field. The results of these calculations are also presented and discussed in this work. It has been indicated that the new model satisfactorily describes the specific features of electric field distribution at the geomagnetic equator and the well-known phenomenon of equatorial electrojet.     

Validating and assessing the sensitivity of the climate model with an ocean general circulation model developed at the Institute of Atmospheric Physics,Russian Academy of Sciences

A new version of the Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS), climate model (CM) has been developed using an ocean general circulation model instead of the statistical-dynamical ocean model applied in the previous version. The spatial resolution of the new ocean model is 3° in latitude and 5° in longitude, with 25 unevenly spaced vertical levels. In the previous version of the oceanic model, as in the atmospheric model, the horizontal resolution was 4.5° in latitude and 6° in longitude, with four vertical levels (the upper quasi-homogeneous layer, seasonal thermocline, abyssal ocean, and bottom friction layer). There is no correction for the heat and momentum fluxes between the atmosphere and ocean in the new version of the IAP RAS CM. Numerical experiments with the IAP RAS CM have been performed under current initial and boundary conditions, as well as with an increasing concentration of atmospheric carbon dioxide. The main simulated atmospheric and oceanic fields agree quite well with observational data. The new version’s equilibrium temperature sensitivity to atmospheric CO₂ doubling was found to be 2.9 K. This value lies in the mid-range of estimates (2–4.5 K) obtained from simulations with state-of-the-art models of different complexities.     

Puu Hou littoral cones,Hawaii

The Puu Hou littoral cones, on the south shoreline of Hawaii, were built in 5 days by steam explosions from two narrow lava streams of the 1868 Mauna Loa lava flows as they entered the sea. Explosions occurred in localized areas of both streams, from foci that migrated seaward as the flow built jetties into the sea. Debris, radially ejected from the migrating explosion centers, fell partly on land and partly at sea, and thus formed crescent shaped rims (half-cones) on land which overlap one another. The half-cones are breached through their centers by debris-free basalt corridors, because fragments that fell onto the flowing lava were carried seaward beyond the accumulating rims.Gray and red clastic layers are draped smoothly over the rim areas; thus the rims resemble anticlinal arches in cross section. Some beds can be traced from clastic layers on the ridges into irregular agglomeratic masses interbedded with basalt units of the source lava near the foci. The lower layers in the clastic sequence contain less olivine than those high in the sequence, which corresponds in time to an increasing olivine content during the 5 day flow, as recognized in the source lava.Fragments are angular to subangular blocks, lapilli and ash of crystalline basalt mixed with more abundant quickly chilled cognate material of similar sizes. The ash is mostly sideromelane in angular particles and rounded droplets (5–95%), tachylite (2–70%), crystalline basalt (1–40%), and broken olivine phenocrysts (1–9%). In some samples, the sideromelane droplets are partly oxidized on their surfaces, and internally are dark brown (R. I.=1.610–1.616), possibly due to dehydration and/or oxidation during the explosions. Samples with externally oxidized glass also contain etched olivine crystals and some iddingsite. Unaltered sideromelane droplets are pale yellowish-brown with R. I.=1.592–1.600, and are associated with unaltered, angular to subangular olivine crystals. The refractive index of the unaltered sideromelane droplets is the same as sideromelane crusts of pahoehoe on the lava flow farther inland, suggesting that the droplets are not hydrated or highly oxidized. None of the sideromelane fragments are palagonitized, presumably because little or no hydration has taken place since 1868.

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Zusammenfassung Die littoralen Spratzkegel von Puu Hou an der Südküste von Hawaii sind innerhalb von 5 Tagen durch Dampfexplosionen in zwei naheliegenden Lavaströmen des Mauna Loa-Ausbruches im Jahre 1868 entstanden, als diese das Meer erreichten. Die Explosionen traten in eng begrenzten Bereichen beider Ströme auf; die Explosionsherde wanderten mit den Lavaströmen seewärts, wobei sich Landzungen in den Ozean bauten. Aus den seewärts wandernden Explosionsherden wurden Fragmente ausgeworfen, die teilweise auf das Land und in den Ozean fielen; es formten sich dabei halbkreisartige Ränder (Halbkegel), die sich am Land überlappen. Die Halbkegel sind in der Mitte von Basaltkorridoren durchbrochen, die frei von Explosionsfragmenten sind, da diese in die strömende Lava fielen und seewärts abtransportiert wurden.Graue und rote pyro-klastische Sedimentlagen legen sich über die Randzonen der Halbkegel, so daß sie im Querschnitt wie Antiklinalstrukturen aussehen. Einige dieser Schichten können mit klastischen Lagen vom randlichen Saum bis zu irregulären Agglomeratmassen verfolgt werden, die zwischen die Basalte nahe der Explosionsherde eingeschaltet sind. Die tieferen Lagen der klastischen Sedimente enthalten weniger Olivin als die höher liegenden. Dieses entspricht einem sich zeitlich vermehrenden Olivingehalt während der fünftägigen Ausbruchszeit, wie er auch in der Originallava erkannt werden kann.Die Bruchstücke bestehen aus angularen bis subangularen Blöcken, Lapilli und Kristallaschen, die mit rasch erkalteten Lavafetzen ähnlicher Korngröße vermischt sind. Die Asche enthält hauptsächlich Sideromelan in eckigen Bruchstücken und gefundeten Tröpfchen (5–95%), Tachylyt (2–70%), Kristallbasalt (1–40%) und zerbrochene Olivineinsprenglinge (1-9%).In einigen Proben sind die Sideromelantröpfchen teilweise auf ihren Oberflächen oxydiert und im Inneren möglicherweise durch Dehydrierung und/oder Oxydation während der Explosionen dunkelbraun gefärbt (R. I.=1.610-1.616).Proben mit äußerlich oxydiertem Glas enthalten auch angeätzte Olivinkristalle und einigen Iddingsit. Unveränderte Sideromelantröpfchen sind blaß gelblichbraun gefärbt (R. I.=1.592–1.600) und mit unveränderten, eckigen bis subangolaren Olivinkristallen vergesellschaftet. Der Brechungsindex der unveränderten Sideromelantröpfchen ist derselbe wie von Sideromelankrusten auf den Lavaströmen Pahoehoes. Daraus kann gefolgert werden, daß die Tröpfchen nicht hydratisiert oder stark oxydiert sind. Die Sideromelanbruchstücke enthalten keinen Palagonit, weil seit 1868 wahrscheinlich wenig oder gar keine Hydratisierung mehr stattgefunden hat.

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Résumé Les cônes littoraux Puu Hou, sur la côte sud d'Hawai' ont été créés en cinq jours par les explosions de vapeur de deux branches étroites de la coulée de lave de Mauna Loa en 1868 lorsqu'elle entrait en contact avec la mer. Les explosions se sont produites dans des points localisés des deux branches de la coulée à partir du centre avançant en direction de la mer à mesure que la lave y construisait des jetées. Les débris projetés à la ronde depuis les centres d'explosion mobiles tombèrement en partie sur terre et en partie en mer formant ainsi sur le sol des bourrelets en forme de croissants (demi-cônes) qui s'entrecoupent. Les demi-cônes sont traversés dans leur centre par des couloirs de basalte dépourvus de débris, les fragments tombés dans la coulée de lave ayant été entraînés vers la mer au delà des bourrelets d'accumulation.Les couches élastiques grises et rouges sont drapées d'une manière égale au-dessus de la zone des bourrelets. Elle ressemble ainsi à des arches anticlinales en coupe. Certains lits peuvent être retracés à partir des couches élastiques sur les crêtes jusqu'à des masses agglomérées irrégulières mélangées à des éléments de basalte de la lave mère. Les couches inférieures de la séquence élastique contiennent moins d'olivine que les couches supérieures ce qui correspond à un accroissement de la proportion d'olivine pendant les 5 jours ue coulée, comme le lit de lave indique.Les fragments sont des blocs angulaires à sous-angulaires, des lapilli et de la cendre de basalte cristallin, mêlés à des matériaux apparentés de taille semblable, plus abondants et rapidement refroidis. La cendre est composée principalement de sidéromélane en particules anguleuses ou en gouttelettes rondes (5–95%), de tachylite (2–70%), de basalte cristallin (1–40%) et d'olivine phénocristale brisée (1–9%). Dans quelques échantillons, les gouttelettes de sidéromélane sont en partie oxydées à la surface et brun-foncé à l'intérieur (R. I.=1.610–1.616), peut-être par suite de déshydratation e/ou oxydation pendant l'explosion. Les échantillons comportant extérieurement du verre oxydé contiennent des cristaux d'olivine attaqués et une certaine proportion d'iddingsite. Les gouttelettes de sidéromélane intactes, sont d'un jaune-brun pâle, R. I.=1.592-1.600, et sont associées à des cristaux d'olivine non-attaquées, angulaires à sous-angulaires. L'indice de réfraction des gouttelettes intactes de sidéromélane est le même que celui de la croûte de sidéromélane du pahoehoe dans la coulée de lave plus à l'intérieur de l'île, suggérant que les gouttelettes ne sont pas hydratées ou très oxydées. Aucun des fragments de sidéromélane n'est palagonisé, sans doute parce que depuis 1868 il n'y a eu que peu ou pas d'hydratation.

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, 1868 Puu Hou . Ha , .

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday     

Sources of uncertainty in exploring rangeland phenology: A case study in an alpine meadow on the central Tibetan Plateau

Global climate change has been found to substantially influence the phenology of rangeland, especially on the Tibetan Plateau. However, there is considerable controversy about the trends and causes of rangeland phenology owing to different phenological exploration methods and lack of ground validation. Little is known about the uncertainty in the exploration accuracy of vegetation phenology. Therefore, in this study, we selected a typical alpine rangeland near Damxung national meteorological station as a case study on central Tibetan Plateau, and identified several important sources influencing phenology to better understand their effects on phenological exploration. We found man-made land use was not easily distinguished from natural rangelands, and therefore this may confound phenological response to climate change in the rangeland. Change trends of phenology explored by four methods were similar, but ratio threshold method (RTM) was more suitable for exploring vegetation phenology in terms of the beginning of growing season (BGS) and end of growing season (EGS). However, some adjustments are needed when RTM is used in extreme drought years. MODIS NDVI/EVI dataset was most suitable for exploring vegetation phenology of BGS and EGS. The discrimination capacities of vegetation phenology declined with decreasing resolution of remote sensing images from MODIS to GIMMS AVHRR datasets. Additionally, distinct trends of phenological change rates were indicated in different terrain conditions, with advance of growing season in high altitudes but delay of season in lower altitudes. Therefore, it was necessary to eliminate interference of complex terrain and man-made land use to ensure the representativeness of natural vegetation. Moreover, selecting the appropriate method to explore rangelands and fully considering the impact of topography are important to accurately analyze the effects of climate change on vegetation phenology.