Holocene environmental evolution of the SE Greenland Shelf North and South of the Denmark Strait: Irminger and East Greenland current interactions

Holocene climatic and paleoceanographic development of the SE Greenland Shelf is studied from cores MD99-2317 and MD99-2322, at sites north and south of the Denmark Strait, respectively. Lithofacies, IRD counts, calcium carbonate percentages, benthic and planktic foraminiferal assemblages and oxygen isotope analyses, and summer SSTs reveal significant climate variations in the Holocene driven by declining solar insolation and its interaction with waning continental ice sheets, and changing atmospheric pressure patterns. Large changes in the East Greenland and Irminger Currents and the Greenland Ice Sheet are manifested as a 4-part division of the Holocene. An early Holocene cold interval dominated by melting of the Greenland Ice Sheet and Polar Front retreat extends from 11.8 to 9.5 cal kyr BP. A cold interval from 9.5 to 8.1 cal kyr BP involved episodic cooling of the Irminger Current resulting from the last phases of Laurentide Ice Sheet deglaciation and delayed the Holocene optimum off East Greenland by 3 kyr relative to peak summer solar insolation, which likely helped to limit the early Holocene melting of the Greenland Ice Sheet. The period 8.1–3.5 cal kyr BP represents a climatic optimum interval of maximum Greenland Ice Sheet retreat and strong Irminger Current inflow to the Denmark Strait. Between 6.8 and 3.5 cal kyr BP, the Irminger Current penetrated further North into the Nordic Seas than has been observed in recent decades. This signal is consistent with diminished northerly winds, a weaker Greenland High and contracted subpolar gyre. By 5 cal kyr BP, periods of increased Polar Water and decreasing salinity in the Irminger Current suggest a transition toward expansion of the subpolar gyre and increased Polar Water in the EGC. The Neoglacial interval from 3.5 to 0.2 cal kyr BP was cold and variable with increased freshwater forcing from the Arctic Ocean, advance of the Greenland Ice Sheet and southward advance of the Polar Front. Enhanced northerly winds and a strengthened Greenland High are consistent with thicker and more extensive Polar Water and greatly diminished northward advection of Irminger Current in the Denmark Strait.     

Rhyacian (2.23–2.20 Ga) juvenile accretion in the southern São Francisco craton,Brazil: Geochemical and isotopic evidence from the Serrinha magmatic suite,Mineiro belt

The Serrinha magmatic suite (Mineiro belt) crops out in the southern edge of the São Francisco craton, comprising the Brito quartz-diorite, Brumado de Cima and Brumado de Baixo granodiorites, granophyres and felsic sub-volcanic and volcanic rocks, part of which intruded into the Nazareno greenstone belt. The suite rocks have petrographic features that are consistent with magma supercooling due to the low water content combined with volatile loss, leading to crystallization of quartz and alkaline feldspar at the rims of plagioclase phenocrysts (granophyric intergrowth). The investigated rocks are sub-alkaline, calc-alkaline and show low content in rare earth elements. The U–Pb zircon crystallization ages for the Brumado de Cima granodiorite [2227 ± 22 (23) Ma] and a coeval granophyre [2211 ± 22 (23) Ma], coupled with available single-zircon Pb evaporation ages for the Brito and Brumado de Baixo plutons, are significantly older than the “Minas orogeny” (ca. 2100–2050 Ga) of Quadrilátero Ferrífero area, eastward from the Serrinha suite. Our data establish an early Rhyacian event tectonically linked with the evolution of the Mineiro belt. The bulk Nd isotopic signature [low negative to positive ε_Nd(t) values] of the Serrinha samples are consistent with the important role of Paleoproterozoic mantle components in the magma genesis. The integrated geologic, geochemical and isotopic information suggests that Paleoproterozoic evolution of the Mineiro belt initiated in a passive continental margin basin with deposition of the Minas Supergroup at ca. 2500 Ma. This stage was succeeded by outboard rupture of the oceanic lithosphere with development and coalescence of progressively younger magmatic arcs during Rhyacian time. One of the earliest arcs formed the Serrinha suite. The tectonic collage of the Serrinha and Ritápolis (2190–2120 Ma) arcs produced the NE–SW Lenheiro shear zone, resulting in mylonitization and recrystallization of both the granitoid intrusions and host rocks. As a matter of fact juxtaposition of distinct magmatic units in age and origin took place along the Lenheiros structure in this sector of the Mineiro belt.     

Collective effects of stellar winds and unidentified gamma-ray sources

We study collective wind configurations produced by a number of massive stars, and obtain densities and expansion velocities of the stellar wind gas that is to be target, in this model, of hadronic interactions. We study the expected γ-ray emission from these regions, considering in an approximate way the effect of cosmic ray modulation. We compute secondary particle production (electrons from knock-on interactions and electrons and positrons from charged pion decay), and solve the loss equation with ionization, synchrotron, bremsstrahlung, inverse Compton, and expansion losses. We provide examples where configurations can produce sources for GLAST satellite, and the MAGIC, HESS, or VERITAS telescopes in non-uniform ways, i.e., with or without the corresponding counterparts. We show that in all cases we studied no EGRET source is expected.     

Field Measurement of Dissolved Oxygen: A Comparison of Methods

The ability to confidently measure the concentration of dissolved oxygen (D.O.) in ground water is a key aspect of remedy selection and assessment. Presented here is a comparison of the commonly practiced methods for determining D.O. concentrations in ground water, including colorimetric, membrane-covered electrode, and modified Winkler techniques. The Winkler titration (azide and permanganate modifications) is the most accurate and precise technique for determining D.O. and is appropriate for applications with stringent data quality objectives. In addition, excellent correlation over a wide range of D.O. concentrations was found between Winkler titrations and colorimetric tests using the rhodazine D (below 1 part per million [ppm]) and indigo carmine reagents (above 1 ppm). Electrode measurements represent the simplest method for determining D.O. concentrations on a continuous basis and electrode determinations positively correlate with Winkler results above 1 ppm. Below 1 ppm, electrodes provide only a qualitative measure of low D.O. level, apparently due to slow electrode response.     

Evidence for constitutional supercooling from orthopyroxene - pigeonite - plagioclase relations in the Borgmassivet suite of western Dronning Maud Land,Antarctica

Summary The Kullen-type sills of western Dronning Maud land are up to 400 m thick and form part of the Meso- to Neoproterozoic Borgmassivet suite. They consist of a Basal, Cumulate, Central and Upper zone. The petrography of the Cumulate zone, with special emphasis on the occurrences at Hammer Heads in the Annandagstoppane area, is described. Microstructures, such as delicate chains of orthopyroxene primocrysts and an increase in grain size of plagioclase chadacrysts from the cores to the margins of postcumulus clinopyroxene oikocrysts, indicatein situ crystallization. Composite grains with orthopyroxene at the core, which is mantled, in turn, by inverted pigeonite, a second generation orthopyroxene and, on the outer margin, clinopyroxene in a reaction relation with the orthopyroxene, are sporadically developed.The relation between the composite structures and plagioclase nucleation and growth is investigated by the study of plagioclase grain size distributions, nucleation density and An compositions of plagioclase cores, which indicate that two periods of plagioclase nucleation occurred. The first period of nucleation, represented by plagioclase chadacrysts enclosed in primocrysts of orthopyroxene, occurred during supercooling following intrusion. Release of latent heat of crystallization resulted in an increase in magma temperature and a normal sequence of fractional crystallization in which orthopyroxene crystallization was succeeded by pigeonite. The second period of plagioclase nucleation depleted the interface liquid in the zone of crystallization of calcium. The composition of the interface liquid was thus changed from the compositional field from which pigeonite crystallized to that from which orthopyroxene crystallized (cf the liquidus boundaries in the system CaMgSi₂O₆-Mg₂SiO₄SiO₂ ofKushiro, 1972). This constitutional supercooling (Chalmers, 1964;Tiller, 1991) resulted in crystallization of orthopyroxene and the reverse crystallization sequence En-rich orthopyroxene -pigeonite - En-rich orthopyroxene, prior to reaction of the last-formed orthopyroxene with the liquid to form clinopyroxene and subsequent inversion of pigeonite. A possible crystallization sequence is discussed by making use of thespeculative Fo-Di-An-SiO₂ (forsterite-diopside-anorthite-silica) system ofMorse (1980).

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Orthopyroxen-Pigeonit-Plagioklas-Beziehungen in der Borgmassivet Suite des westlichen Dronning Maud Landes, Antarktis: Hinweise auf konstitutionelles Supercooling

Zusammenfassung Lagergänge des Kullen-Types im westlichen Dronning Maud Land sind bis zu 400m mächtig und sind Teil der meso- bis neoproterozoischen Borgmassivet-Abfolge. Sie bestehen aus einer basalen, einer Cumulat, einer zentralen und einer oberen Zone. Die Petrographie der Cumulat-Zone wird mit besonderer Betonung der Vorkommen von Hammer Heads im Annandagstoppane-Gebiet beschrieben. Mikrostrukturen, wie z.B. feinkörnige Ketten von Orthopyroxen-Primokristen und eine Zunahme in der Korngröße von Plagioklas-Chadakristen von den Kernen zu den Rändern in postcumulus Klinopyroxen-Oikokristen, weisen aufin situ Kristallisation hin. Zusammengesetzte Körner mit Orthopyroxen im Kern, der von invertiertem Pigeonit umgeben ist, einer zweiten Generation Orthopyroxen, und, am äußeren Rand, Klinopyroxen in Reaktionsbeziehung mit Orthopyroxen, kommen sporadisch vor.Die Beziehung zwischen diesen zusammengesetzten Strukturen und der Nukleation, sowie dem Wachstum von Plagioklas wurde durch das Studium der Plagioklaskorngrößen, der Nukleationsdichte und der An-Zusammensetzung von Plagioklas-Kernen untersucht. Diese weisen darauf hin, daß zwei Perioden von Plagioklas-Nukleation vorgekommen sind. Die erste Nukleationsperiode wird durch Plagioklas-Chadakristen, die in Primokristen von Orthopyroxen eingeschlossen sind repräsentiert, und fand während einer Phase von Supercooling im Anschluß an die Intrusion statt. Das Freiwerden latenter Kristallisationswärme führte zu einer Zunahme der Magmentemperatur und zu einer normalen Abfolge fraktionierter Kristallisation, in der auf die Orthopyroxen-Kristallisation Pigeonit folgte. Die zweite Phase der Plagioklasnukleation führte zu einer Verarmung der Schmelze an Kalzium in der Kristallisationszone. Die Zusammensetzung der Schmelze bewegte sich so aus dem Pigeonitfeld, in das, aus dem Orthopyroxen kristallisierte (siehe die Liquidus Grenzen im System CaMgSi2O₆-Mg₂SiO₄-SO₂ von Kushiro, 1972). Dieses konstitutionelle Supercooling (Chalmers, 1964;Tiller, 1991) führte zur Kristallisation von Orthopyroxen, und der reversen Kristallisationsabfolge En-reicher Orthopyroxen-Pigeonit-En-reicher Orthopyroxen, noch vor der Reaktion des zuletzt gebildeten Orthopyroxenes mit der Schmelze, das zur Entstehung von Klinopyroxen und zur anschließenden Inversion von Pigeonit führte. Eine mögliche Kristallisationsabfolge wird auf der Basis desspekulativen Fo-Di-An-SiO₂ (Forsterit-Diopsid-Anorthit-Quartz) Systems von Morse (1980) diskutiert.

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With 12 Figures     

Planning in Jordan: Coping with uncertainty

Jordan is an Islamic state with planning based on Islamic principles. The execution of plans, though, has been constrained by geopolitical realities. In the last decade Jordan has moved from strictly sectoral planning to a strongly focused system of regional planning in order to achieve more growth in less developed regions. The prospects for these regions and the country as a whole will turn on the success of the peace process in the region.     

Uncertainty assessment in river flow projections for Ethiopia’s Upper Awash Basin using multiple GCMs and hydrological models

ABSTRACT

Uncertainty in climate change impacts on river discharge in the Upper Awash Basin, Ethiopia, is assessed using five MIKE SHE hydrological models, six CMIP5 general circulation models (GCMs) and two representative concentration pathways (RCP) scenarios for the period 2071–2100. Hydrological models vary in their spatial distribution and process representations of unsaturated and saturated zones. Very good performance is achieved for 1975–1999 (NSE: 0.65–0.8; r: 0.79–0.93). GCM-related uncertainty dominates variability in projections of high and mean discharges (mean: –34% to +55% for RCP4.5, – 2% to +195% for RCP8.5). Although GCMs dominate uncertainty in projected low flows, inter-hydrological model uncertainty is considerable (RCP4.5: –60% to +228%, RCP8.5: –86% to +337%). Analysis of variance uncertainty attribution reveals that GCM-related uncertainty occupies, on average, 68% of total uncertainty for median and high flows and hydrological models no more than 1%. For low flows, hydrological model uncertainty occupies, on average, 18% of total uncertainty; GCM-related uncertainty remains substantial (average: 28%).     

Dispersion in sheared Gaussian homogeneous turbulence

By integrating the Fokker-Planck equation corresponding to a Lagrangian stochastic trajectory model, which is consitent with the selection criterion of Thomson (1987), an analytical solution is given for the joint probability density functionp(x_i, u_i, t) for the position (x _i) and velocity (u _i) at timet of a neutral particle released into linearly-sheared, homogeneous turbulence. The solution is compared with dispersion experiments conforming to the restrictions of the model and with a shortrange experiment performed in highly inhomogeneous turbulence within and above a model crop canopy. When the turbulence intensity, wind shear and covariance are strong, the present solution is better than simpler solutions (Taylor, 1921; Durbin, 1983) and as good as any numerical Lagrangian stochastic model yet reported.