ALBERT

Description: The Interdecadal Pacific Oscillation (IPO) influences multidecadal drought risk across the Pacific, but there are no millennial-length, high resolution IPO reconstructions for quantifying long-term drought risk. In Australia, drought risk increases in positive phases of the IPO, yet few suitable rainfall proxies and short (~100 y) instrumental records mean large uncertainties remain around drought frequency and duration. Likewise, it is unknown whether mega-droughts have occurred in Australia's past. In this study, an atmospheric teleconnection in the Indian Ocean mid-latitudes linking East Antarctica and Australia is exploited to produce the first accurate, annually dated millennial-length IPO reconstruction from the Law Dome (East Antarctica) ice core. Combined with an eastern Australian rainfall proxy from Law Dome, the first millennial-length Australian mega-drought (〉5 y duration) reconstruction is presented. Eight mega-droughts are identified including one 39 y drought (AD 1174–1212), which occurred during an unprecedented century of aridity (AD 1102–1212).

Description: Subglacial hydrology in East Antarctica is poorly understood, yet may be critical to the manner in which ice flows. Data from a new regional airborne geophysical survey (ICECAP) have transformed our understanding of the topography and glaciology associated with the 287,000 km2 Aurora Subglacial Basin in East Antarctica. Using these data, in conjunction with numerical ice sheet modeling, we present a suite of analyses that demonstrate the potential of the 1000 km-long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin. We present results from our analysis of basal topography, bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures. Although no clear-cut subglacial lakes are found within the Aurora Basin itself, dozens of lake-like reflectors are observed that, in conjunction with other results reported here, support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the Dome C ice divide to reach the coast via the Totten Glacier.

Description: The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling approximately 34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Young, Duncan A -- Wright, Andrew P -- Roberts, Jason L -- Warner, Roland C -- Young, Neal W -- Greenbaum, Jamin S -- Schroeder, Dustin M -- Holt, John W -- Sugden, David E -- Blankenship, Donald D -- van Ommen, Tas D -- Siegert, Martin J -- England -- Nature. 2011 Jun 2;474(7349):72-5. doi: 10.1038/nature10114.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758, USA. duncan@utig.ig.utexas.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21637255" target="_blank"〉PubMed〈/a〉

Description: The Pebble deposit is located ~320 km southwest of Anchorage, Alaska. It is one of the largest porphyry deposits known with a total resource of 10.78 billion tons (Bt). It comprises the East and West zones, which are approximately equal in size, with slightly lower grade mineralization in the center of the deposit where the peripheries of the two zones merge. The West zone was discovered by Cominco America in 1989 and the East zone was discovered by Northern Dynasty Minerals in 2005. The oldest rock in the Pebble district is the Jurassic-Cretaceous Kahiltna flysch unit, which contains basinal turbidites, interbedded basalt flows, and associated gabbro intrusions. These rocks were intruded between 99 and 96 Ma by coeval granodiorite and diorite sills, followed shortly thereafter by alkalic monzonite intrusions and related breccias. Subalkalic hornblende granodiorite porphyry plutons of the Kaskanak batholith were emplaced at ~90 Ma. Similar, smaller granodiorite plutons were emplaced around the margins of the batholith and are related to Cu-Au-Mo mineralization. Re-Os dates on molybdenite are between 89.7 and 90.4 Ma. A Late Cretaceous volcanic and sedimentary "cover sequence" completely conceals the East zone, whereas the West zone is overlain only by glacial sediments and is exposed in one small outcrop. Eocene volcanic rocks and subvolcanic intrusions occur east and southeast of the Pebble deposit and unconsolidated glacial sediments are widespread. The East and West zones represent two coeval hydrothermal centers within a single system. The West zone extends from surface to ~500-m depth and is centered on four small granodiorite plutons emplaced into flysch, diorite, and granodiorite sills, and alkalic intrusions and breccias. The much higher grade East zone extends to at least 1,700-m depth and is hosted by a larger granodiorite pluton and adjacent granodiorite sills and flysch. The granodiorite plutons merge with depth. On the east side of the deposit, high-grade mineralization has been dropped 600 to 900 m into the NE-trending East graben, where the deposit remains undelineated to the east and to depth. Variations in hypogene grade and metal ratios reflect multiple stages of metal introduction and redistribution. Hornfels related to the Kaskanak batholith formed prior to hydrothermal activity at Pebble and is most intensely developed in flysch. Disseminated and vein-hosted Cu-Au-Mo mineralization, dominated by chalcopyrite and locally accompanied by bornite, formed with potassic alteration in the shallow part of the East zone and with approximately coeval sodic-potassic alteration in the West zone and at depth in the East zone. Illite ± kaolinite alteration overprinted potassic and sodic-potassic alteration throughout the deposit and variably redistributed copper and gold. High-grade copper-gold mineralization is related to advanced argillic alteration controlled by a synhydrothermal brittle-ductile fault zone which overprinted potassic, sodic-potassic, and illite ± kaolinite alteration in the East zone. Advanced argillic alteration comprises a core of pyrophyllite alteration associated with chalcopyrite, bounded to the west by an upward-flaring zone of sericite alteration which contains hypogene bornite, digenite, covellite, and trace enargite and tennantite. Late quartz veins introduced additional molybdenum in several parts of the deposit. Grade-destructive quartz-sericite-pyrite alteration forms a halo to the entire deposit and yields outward to propylitic alteration. A quartz-illite-pyrite cap is preserved in the weakly mineralized center of the deposit. Mineralization at Pebble is predominately hypogene. A thin, incompletely developed zone of supergene mineralization occurs in the West zone and is overlain by a thin leached capping. There is no evidence for paleosupergene mineralization or leaching below the cover sequence in the East zone. Molybdenite contains high concentrations of rhenium throughout the deposit. Elevated palladium concentrations are associated with pyrophyllite alteration in the East zone. The Pebble deposit occurs in one of a number of large, deep-seated magnetic anomalies which are located at the intersection of crustal-scale structures both parallel and at high angles to a mid-Cretaceous magmatic arc. This setting is similar to fertile porphyry environments in northern Chile and suggests that southwestern Alaska is highly prospective for porphyry exploration. The large size and high hypogene grades of the Pebble deposit may reflect a combination of multiple stages of metal introduction with vertically restricted, lateral fluid flow induced by hornfels aquitards in flysch.

Description: Ice thickness data over much of East Antarctica are sparse and irregularly distributed. This poses difficulties for reconstructing the homogeneous coverage needed to properly assess underlying sub-glacial morphology and fundamental geometric constraints on sea level rise. Here we introduce a new physically-based ice thickness interpolation scheme and apply this to existing ice thickness data in the Aurora Subglacial Basin region. The skill and robustness of the new reconstruction is demonstrated by comparison with new data from the ICECAP project. The interpolated morphology shows an extensive marine-based ice sheet, with considerably more area below sea-level than shown by prior studies. It also shows deep features connecting the coastal grounding zone with the deepest regions in the interior. This has implications for ice sheet response to a warming ocean and underscores the importance of obtaining additional high resolution data in these marginal zones for modelling ice sheet evolution.

Description: Published

Description: 551-560

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: open

Description: Hydrogenases interconvert H2 and protons at high rates and with high energy efficiencies, providing inspiration for the development of molecular catalysts. Studies designed to determine how the protein scaffold can influence a catalytically active site have led to the synthesis of amino acid derivatives of [Ni(P2RN2R′)2]2+ complexes, [Ni(P2CyN2Amino acid)2]2+ (CyAA). It...

Description: Analysis of the molecular etiologies of SCID has led to important insights into the control of immune cell development. Most cases of SCID result from either X-linked or autosomal recessive inheritance of mutations in a known causative gene. However, in some cases, the molecular etiology remains unclear. To identify the cause of SCID in a patient known to lack the protein-tyrosine phosphatase CD45, we used SNP arrays and whole-exome sequencing. The patient’s mother was heterozygous for an inactivating mutation in CD45 but the paternal alleles exhibited no detectable mutations. The patient exhibited a single CD45 mutation identical to the maternal allele. Patient SNP array analysis revealed no change in copy number but loss of heterozygosity for the entire length of chromosome 1 (Chr1), indicating that disease was caused by uniparental disomy (UPD) with isodisomy of the entire maternal Chr1 bearing the mutant CD45 allele. Nonlymphoid blood cells and other mesoderm- and ectoderm-derived tissues retained UPD of the entire maternal Chr1 in this patient, who had undergone successful bone marrow transplantation. Exome sequencing revealed mutations in seven additional genes bearing nonsynonymous SNPs predicted to have deleterious effects. These findings are unique in representing a reported case of SCID caused by UPD and suggest UPD should be considered in SCID and other recessive disorders, especially when the patient appears homozygous for an abnormal gene found in only one parent. Evaluation for alterations in other genes affected by UPD should also be considered in such cases.

Description: Numerical models are the primary predictive tools for understanding the dynamic behaviour of the Antarctic ice sheet. However, a key boundary parameter, sub-glacial heat flow, remains poorly constrained. We show that variations in abundance and distribution of heat-producing elements within the Antarctic continental crust result in greater and more variable regional sub-glacial heat flows than currently assumed in ice modelling studies. Such elevated heat flows would have a fundamental effect on ice sheet behaviour and highlight that geological controls on heat flow must be considered to obtain more accurate and refined predictions of ice mass balance and sea-level change. Supplementary materials: Heat flow and heat production definitions, heat production data, and details of the 2D model of the gross geometry of the continental lithosphere for a section through Prydz Bay are available at www.geolsoc.org.uk/SUP18690 .