Geochemistry and origin of albite gneisses,northeastern Adirondack Mountains,New York

Albite gneisses containing up to 8.7 percent Na₂O and as little as 0.1% K₂O comprise a significant part of the Proterozoic Lyon Mountain Gneiss in the Ausable Forks Quadrangle of the northeastern Adirondacks, New York State. Two distinct types of albite gneisses are present. One is a trondhjemitic leucogneiss (LAG) consisting principally of albite (Ab95–Ab98) and quartz with minor magnetite and, locally, minor amounts of amphibole or acmiterich pyroxene. LAG probably originated by metamorphism of a rhyolitie or rhyodacitic ash-flow tuff with A-type geochemical affinities, following post-depositional analcitization in a saline or saline-alkaline environment. The other type is a mafic albite gneiss (MAG) containing albite and pyroxene along with 0–45 percent quartz, minor amphibole, and titanite. MAG locally displays pinstripe banding and contains albite (Ab98) megacrysts up to 5 cm across. Its precursor may have been a sediment composed of diagenetic analcite or albite, dolomite, and quartz. Both types of albite gneiss are interlayered with granitic gneisses (LMG) of variable composition derived from less altered tuffs. A potassium-rich (up to 9.7% K₂O) microcline gneiss facies may have had a protolith rich in diagenetic K feldspar. We propose that the albite gneisses and associated granitic gneisses are the granulite-facies metamorphic equivalent of a bimodal, dominantly felsic, volcanic suite with minor intercalated sediments, probably including evaporites. The volcanics were erupted in an anorogenic setting, such as an incipient or failed intracontinental rift. Deposition took place in a closed-basin, playa lake environment, where diagenetic alteration resulted in redistribution of the alkalis and strong oxidation.     

Measurement of Kodaikanal White-Light Images – II. Rotation Comparison and Merging with Mount Wilson Data

Sunspot umbral positions and areas were measured for 82 years (1906–1987) of daily, full-disk photoheliogram observations at the Kodaikanal station of the Indian Institute of Astrophysics. The measurement technique and reduction procedures used were nearly identical to those used earlier for the reduction of Mount Wilson daily full-disk photoheliograms, covering an overlapping interval of 69 years. In this paper we compare the differential rotation of the Sun from the analysis of the Kodaikanal data with the Mount Wilson results. In addition, we analyze the data set formed by combining the data from the two sites for differential rotation. While doing this, it has become apparent to us that small, subtle optical effects at both sites produce systematic errors that have an influence on rotation (and other) results from these data. These optical effects are analyzed here, and corrections are made to the positional data of the sunspots from both sites. A data set containing the combined positional data of sunspots from both sites, corrected for these optical aberrations, has been constructed. Results for both sunspot groups and individual sunspots are presented. It is pointed out that optical aberrations similar to those found in the Kodaikanal data may also exist in the Greenwich photoheliograph data, because these two sets of solar images were made with similar telescopes.     

Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.     

Denitrification coupled to pyrite oxidation and changes in groundwater quality in a shallow sandy aquifer

This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating (³H/³He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe²⁺ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. Significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50% lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO₃, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1996 and 2006 show systematic decreases most likely due to declining fertilizer use.     

The Zn abundance and isotopic composition of diatom frustules,a proxy for Zn availability in ocean surface seawater

We have developed cleaning methods for extracting diatomopal from bulk marine sediment samples, for measurement of both zinc (Zn) abundance and isotope composition. This cleaning technique was then applied to a set of Holocene core-top samples from the Southern Ocean. The measured δ⁶⁶Zn (reported relative to the JMC_Lyon standard) and Zn/Si ratios from the Southern Ocean diatom_opal samples range from 0.7 to 1.5‰, and from 14 to 0.9 μmol/mol, respectively. The Zn abundance and isotope composition data show a clear correlation with opal burial rates and other oceanographic parameters. In common with previous work, we interpret the systematic changes in the Zn/Si ratio to be linked to the variability in the concentrations of bioavailable Zn in the ambient surface seawater where the diatom opal is formed. This variability is likely to be primarily controlled by the degree to which Zn is taken up into phytoplankton biomass. The observed systematic pattern in the δ⁶⁶Zn compositions of the diatom_opal core-top samples is, similarly, likely to reflect changes in the δ⁶⁶Zn composition of the ambient Zn in the surface waters above the core-top sites, which is progressively driven towards isotopically heavier values by preferential incorporation of the lighter isotopes into phytoplankton organic material. Thus, the systematic relationship between Zn isotopes and abundance observed in the core-top diatom_opal samples suggests a potential tool for investigating the biogeochemical cycling of Zn in the past surface ocean for down-core diatom_opal material. In this respect, it may be possible to test hypotheses that attribute variations in atmospheric CO₂ on glacial–interglacial timescales to the degree to which trace metals limited primary productivity in HNLC zones.     

Regional and temporal changes in bivalve diversity off the south coast of Portugal

From 2000 to 2006, a total of 75 bivalve species were identified, varying from 29 (spring 2001) to 54 species (spring 2005) per year. Seasonal tendencies in diversity varied according the year, thus the interpretation of long-term and regional scales is essential before drawing any conclusions in other studies. Richness and diversity consistently decreased with depth and increased with sediment grain size (from low in very coarse sand to high in coarse silt). Diversity decreased progressively from 3 to 16 m depth, thus the harsher shallower environments (due to waves and tidal air exposure) showed greater diversity than the most stable areas. Communities in finer sediments were more diverse than those in coarser sand. Evenness showed patterns opposite to diversity, overall.Diversity and evenness maps (produced with multivariate universal kriging), showed that most geographic areas with greater diversity were farer from river outflows and wastewater treatment plants. Two types of geographic pattern were observed: areas with persistently greater bivalve diversity through time and areas that changed locally from year to year. This spatial analysis can be used to establish priority conservation areas for management purposes, and to analyse the persistency of regional diversity patterns. The area with most habitat heterogeneity (Sotavento) corresponded to greatest diversity.There was a positive relationship between Spisula solida and Chamelea gallina landings and bivalve diversity 2 years and 1 year later, respectively. Possibly, local fisheries, by selectively withdrawing the commercial numerically dominant species from the ecosystem, increased diversity 1 to 2 years later, as the ecological niches of the dominants are quickly filled by several other species thereby creating a more even community. On regional scales, no significant impact was found on long-term bivalve diversity in local fisheries,     

Extraction of Solar Coronal Magnetic Loops with the Directional 2D Morlet Wavelet Transform

We present an automated extraction method based on the continuous wavelet transform (CWT) for analyzing solar magnetic loops. The aim of the work is to extract, from the images taken from solar EUV telescopes, the traces of bright loops presumably shaped by the magnetic field of the solar corona. The technique is that of wavelet analysis, using the two-dimensional Morlet wavelet, because of its efficiency in detecting oriented features, which allows us to follow closely the curvature of the loops. Next, we segment the wavelet modulus image and we threshold it, both globally and locally (i.e., adaptively), in order to eliminate the remaining noise. Altogether, our method performs well, it is robust and fast, and could be used as a standard tool for analyzing large data sets expected from missions like SDO.     

The role of marine spatial planning in sea use management: The Belgian case

The expansion of offshore activities and the increasing need to meet international and national commitments to biodiversity conservation have led to an enhanced interest in marine spatial planning (MSP) as a tool for sea use management. Several European countries, on their own initiative or driven by European legislation and policy, have taken global leadership in implementing MSP. This article will discuss the Belgian experiences with MSP. It will give a short historical overview based on legal developments and review the implementation process of a ‘Master Plan’ as a spatial management policy for the Belgian Part of the North Sea. Additionally, this article will reflect on the research that has been done in Belgium to apply a land-use planning approach to the marine environment. The MSP process in Belgium shows that a spatial approach to sea use management is possible despite the lack of a legal zoning framework. However, it concludes that a legal basis for MSP, in addition to the current permit system, would provide a more strategic and integrated framework for ecosystem-based, sea use management.     

Recent precipitation trends over the polar ice sheets

Summary Meteorological and glaciological analyses are integrated to examine the precipitation trends during the last three decades over the ice sheets covering Antarctica and Greenland. For Antarctica, the best data source is provided by glaciologically-measured trends of snow accumulation, and for limited sectors of East Antarctica consistency with precipitation amounts calculated from the atmospheric water balance equation is obtained. For Greenland, precipitation rates parameterized from atmospheric analyses yield the only comprehensive depiction. The precipitation rate over Antarctica appears to have increased by about 5% over a time period spanning the accumulation means for the 1955–65 to 1965–75 periods, while over Greenland it has decreased by about 15% since 1983 with a secondary increase over the southern part of the ice sheet starting in 1977. At the end of the 10-year overlapping period, the global sea-level impact of the precipitation changes over Antarctica dominates that for Greenland and yields a net ice-sheet precipitation contribution of roughly 0.02 mm yr^–1. These changes are likely due to marked variations in the cyclonic forcing affecting the ice sheets, but are only weakly reflected in the temperature regime, consistent with the episodic nature of cyclonic precipitation. These conclusions are not founded on high quality data bases. The importance of such changes for understanding global sea-level variations argues for a modest research effort to collect simultaneous meteorological and glaciological observations in order to describe and understand the current precipitation variations over both ice sheets. Some suggestions are offered for steps that could be taken.With 8 Figures