Deep Trough Research Articles

Younger Dryas Comet 12,900 BP

Deep troughs in Lake Superior support the hypothesis of Younger Dryas Boundary (YDB) comet impact 12,900 BP. The impact theory explains the megafauna extinction, a black mat across the Northern hemisphere, nanodiamonds, platinum and iridium, and the enigmatic Carolina Bays (CB). While the CB were thought to predate Clovis cultural remains, but this must now be seen as spurious as the CB occur on Long Island, an LGM terminal moraine & on end-glacial flood plains, according to Allen West. The CB sand rims are exceptionally pure quartz with large phenocrysts, and also they exude hydrogen (H). This suggests origin from deep granitic plutons, the granite typically being over-saturated with silica. When the Russian Kola Peninsula Superdeep Borehole had reached 40,000 ft, H was boiling from the borehole. This H is among volatiles copiously dissolved in the mantle, from the primitive solar nebula. The granite is from the Lake Superior Province. Lakes Superior, Michigan, Huron & Ontario have deep holes, reaching to below sea level. Bathymetry exhibits a ~145 km circular contour in Eastern L. Superior, where deep troughs occur, eroded in breccias infilling impact explosion cavities many kms deep, as much as 15 to 35 km, the comet fragments coming in from the NW, with the holes lined up along the trajectory. This was an oblique impact with an extremely low angle of incidence, so the ejected granite quartz sands ended up in the CB along the Eastern seaboard principally.

Paleogeographic conditions in the West Siberian Basin during the Tithonian–Early Berriasian

Based on facies, structural, and general paleogeographic analyses, new models of the bottom topography and accumulation of the Tithonian–Early Berriasian Bazhenov Formation (West Siberian Basin) are proposed. According to these patterns, quite a low proportion of the terrigenous material in the high-carbon facies of the Bazhenov Formation can be explained by its accumulation in relatively deep troughs that frame the uplifted shallow-water central part of the West Siberian basin. In addition, the structure and dynamics of ocean currents are considered. During the Tithonian–Early Berriasian, these currents were related to the aeration stages of bottom waters enriched in hydrogen sulfide and carbon dioxide. As a result of the convection of the water mass suffocation periods occurred.

Stratigraphic Correlation between Subsurface Maastrichtian Digma Formation and Safra Unit from Outcrop Sections, Western Desert of Iraq

In this work we try to clarify, and correlate between two Maastrichtian aged units, namely Digma and Safra Units from selected sections in western desert of Iraq. Taking in consideration the stratigraphic code of NASCENT (2005), and the results of previous studies, nine criteria have been used for the correlation, as follow: 1- From lithostratigraphic point of view, Digma Formation (Fm.) mostly composed of dark grey to blackish gray, uniform Carbonates-dominated facies, while Safra unit is characterized by light yellowish brown mixed phosphatic- siliceous-siliciclastics and carbonates facies. 2- Digma Fm. is characterized by Benthonic foraminifera assemblages (Bulimmina sp., Siphogerinoides sp. & Bolivinoides sp. ), while Safra phosphatic unit is flourished by macrofossils assemblages and vertebrates (Oyster, fish teeth’s and bones). 3- The upper and lower boundaries of the Digma Fm. are conformable, and vice versa for Safra Unit. 4- Illite/Semctite mixed layers-Illite clays assemblage and Glauconitic are predominates in Digma Fm., while Sepiolite-palygorskite-Montmorillonite, are common in Safra Unit, without any Glauconitic mineralization. 5- Digma Fm. slightly influenced by neomorphism and micritization. On other hand, Safra facies extremely influenced by phosphatization, silicification, dolomitization, and neomorphism and carbonate-silica replacement of the original evaporate minerals. 6- The predominated foraminiferal wackestone and mudstone microfacies, within Digma facies associations, mostly indicate deep trough marine condition (Anah Graben). The mixed phosphatic-carbonates (Oyster coquina band) and siliciclastics facies, (occasionally cross laminated), mostly deposited in shallower water depth, on the Arabian platform and distal steepened ramp towards Rutba flanks. 7- Sequence boundary of type one and three is bounded the Safra Unit respectively from upper and lower parts. 8- Continuously deposited Sequence was detected from the parasequences of the Safra facies, and across Maastrichtian/Danian boundary (Trafawi Unit). 9- The paleo-configuration of the basin almost influenced by the reactivity of the Anah basement faults started in the Late Campanian, and combined by shallowing upwards sequences. The conclusion is that, Digma facies can be considered as local facial changes of the Shiranish Formation, while Safra unit can be considered as a lower Member of (L. Maastrichtian-Danian) Jeed Formation, which is coincides with the whole stratigraphic frame work of the Mediterranean segments of the Tethyan phosphatic realm.

Lady Bird and Lyndon: The Hidden Story of a Marriage That Made a President by Betty Boyd Caroli

Reviewed by: Lady Bird and Lyndon: The Hidden Story of a Marriage That Made a President by Betty Boyd Caroli Elizabeth Hayes Turner Lady Bird and Lyndon: The Hidden Story of a Marriage That Made a President. By Betty Boyd Caroli. (New York and other cities: Simon and Schuster, 2015. Pp. x, 463. $29.99, ISBN 978-1-4391-9122-4.) Betty Boyd Caroli, best known as the author of First Ladies: Martha Washington to Michelle Obama (New York, 2010); Inside the White House: America’s Most Famous Home, the First 200 Years (New York, 1992); and The Roosevelt Women (New York, 1998), has written a biography/history of Claudia “Lady Bird” Johnson and her marriage to Lyndon Baines Johnson. Caroli’s premise is that this successful union was founded on trust. Lyndon trusted Lady Bird to prop him up after bitter disappointments and motivate him to carry on despite his own deep troughs of depression. He could count on her to stand by him even when he raged at others, and he depended on her to look the other way when she discovered his sexual affairs. In effect, Lady Bird’s tolerance of his peccadilloes and his psychological downturns assured Lyndon that he could rely on her to promote, to campaign for, and to protect him. She desired his success in politics as much as he did, and she was willing to do what most women probably would not in order to see him achieve his goals. Caroli discusses the possibility that Lyndon suffered from what at the time was labeled manic depressive disorder, but she also uses the term narcissistic to describe Lyndon’s behavior. That he was prone to serious outbursts of rage using verbal and emotional abuse is undeniable. Caroli is unsparing in her description of LBJ’s mood swings, his depression, and his angry abuse toward those who worked for him, including loyal assistants, press secretaries (like the affable Bill Moyers), ranch hands, and legislative aides. In one particularly painful tirade, Lady Bird was not spared when Lyndon scolded her in front of company while she stoically stared beyond him. Caroli notes that Lyndon smoked until his heart attack in 1955, and then took up the habit again after his retirement from office. He drank too much, he refused to exercise, and he let vituperation control him even after he was no longer in office. Readers may remember that LBJ died at age sixty-four, while Lady Bird lived to be ninety-four. If stress, anger, and disappointment have the potential to stem longevity, then Lyndon’s mental state and his deleterious habits, according to Caroli, could well explain his relatively short life. Lady Bird and Lyndon both suffered from blistering attacks in the press. While journalists described LBJ’s boorishness and his aggressive politicking, these accounts only added to his masculine bravado. In 1964 Lady Bird came under withering appraisals of a personal and sexist nature with Time magazine remarking, “Her nose is a bit too long, her mouth a bit too wide, her ankles a bit less than trim . . . and her voice . . . like a brassy low note on a trumpet” (p. 279). Writers in the 1960s were soon to be upbraided by well-spoken feminists for noting a woman’s physical attributes while ignoring her accomplishments, but Lady Bird neither protested nor seemed to be [End Page 221] bothered by it. It is to Caroli’s credit that she recounts Lady Bird’s reputation as an enormously successful woman in her own right—managing KTBC radio/television station in Austin, challenging Congress to pass the Highway Beautification Act (1965), initiating First Lady projects, serving on the Board of Regents for the University of Texas, and writing her own history, A White House Diary (New York, 1970). She was also a clever partner who knew how to cultivate allies in the House and the Senate, charming Lyndon’s colleagues and winning their support for his legislation. Lady Bird learned to manage Lyndon’s tirades, insults, and overindulgences. This is the crux of Caroli’s argument—Lyndon was a handful, but his wife understood him better than anyone else, tolerated his infidelities, invited the women...

Asymmetric Behavior in Nominal and Real Housing Prices: Evidence from Emerging and Advanced Economies

In this article, we investigate asymmetry in nominal and real housing price series from eleven emerging and twenty advanced economies using the nonparametric Triples test (Randles et al., 1980), which allows identification of different types of asymmetries in economic cycles. We find asymmetry in fewer emerging than advanced economies. In more than half of the latter, nominal prices reach peaks faster than troughs (positive steepness asymmetry), suggesting the presence of downward nominal rigidities. Nominal price asymmetry is found only in slightly over a quarter of the emerging economies. Hence, nominal housing price increases are more likely to be followed by symmetric price falls in emerging than in advanced countries. Regarding real housing prices, peaks are higher than troughs (positive deepness asymmetry) in half of the advanced economies, suggesting the presence of price overshooting during booms, but less undershooting during busts. Weaker evidence of similar asymmetry is found in emerging economies, where high cyclical peaks are more often matched by equally deep troughs than in advanced economies.

Anomalous western Pacific subtropical high during late summer in weak La Niña years: Contrast between 1981 and 2013

Both 1981 and 2013 were weak La Nina years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the western Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.

Is Ekman pumping responsible for the seasonal variation of warm circumpolar deep water in the Amundsen Sea?

Ekman pumping induced by horizontally varying wind and sea ice drift is examined as an explanation for observed seasonal variation of the warm layer thickness of circumpolar deep water on the Amundsen Sea continental shelf. Spatial and temporal variation of the warm layer thickness in one of the deep troughs on the shelf (Dotson Trough) was measured during two oceanographic surveys and a two-year mooring deployment. A hydrographic transect from the deep ocean, across the shelf break, and into the trough shows a local elevation of the warm layer at the shelf break. On the shelf, the water flows south-east along the trough, gradually becoming colder and fresher due to mixing with cold water masses. A mooring placed in the trough shows a thicker and warmer layer in February and March (late summer/early autumn) and thinner and colder layer in September, October and November (late winter/early spring). The amplitude of this seasonal variation is up to 60m. In order to investigate the effects of Ekman pumping, remotely sensed wind (Antarctic Mesoscale Prediction System wind data) and sea ice velocity and concentration (EASE Polar Pathfinder) were used. From the estimated surface stress field, the Ekman transport and Ekman pumping were calculated. At the shelf break, where the warm layer is elevated, the Ekman pumping shows a seasonal variation correlating with the mooring data. Previous studies have not been able to show a correlation between observed wind and bottom temperature, but it is shown here that when sea ice drift is taken into account the Ekman pumping at the outer shelf correlates with bottom temperature in Dotson Trough. The reason why the Ekman pumping varies seasonally at the shelf break appears to be the migration of the ice edge in the expanding polynya in combination with the wind field which on average is westward south of the shelf break.

The Missing Link between Terrain-Induced Potential Vorticity Banners and Banded Convection

AbstractOn 1 February 2014, the southern side of the Alps was affected by a severe snowstorm that forced authorities to issue the highest level of avalanche danger in southern parts of Austria. The northern side of the Alps was mostly dry. Nevertheless, radar imagery captured the evolution of quasi-steady convective cloud bands over the northern Alpine foreland with a remarkable length of up to 300 km. This study illuminates the processes that generated these cloud bands based on numerical simulations. The storm was associated with a deep large-scale trough that caused strong southwesterly cross-Alpine flow, orographic precipitation on the southern side, and foehnlike subsidence on the northern side of the Alps. Orographic potential vorticity (PV) banners developed at small-scale topographic features embedded in the Alps and extended downstream over the northern Alpine foreland. Convective cloud bands were aligned parallel to these PV banners. They formed in an environment of inertial instability (negative absolute vorticity) and conditional instability. Sensitivity experiments reveal that the structure and size of these cloud bands are strongly sensitive to the small-scale terrain roughness. Removing small-scale topographic features suppresses the formation of orographic vorticity banners, which in turn suppresses the development of cloud bands. These results suggest that the release of inertial instability at negative orographic vorticity banners was crucial for establishing circulations and associated uplift that triggered conditional instability. To summarize, inertial instability was most likely responsible for the banded structure and conditional instability for the convective nature of these cloud bands.

Variability of the Antarctic Coastal Current in the Amundsen Sea

The nature of the Antarctic Coastal Current (AACC) and its seasonal and non-seasonal (several-day) variability were investigated using long-term mooring data obtained near the Dotson Ice Shelf in the Amundsen Sea. The moored instruments were operated from February 2012 to January 2014 in the Dotson Trough, which is one of the deep troughs on the Amundsen Sea shelf. The hydrographic structure of sigma density distribution at the ice shelf (27.25 kg m−3 at the surface) was found to be higher than at the continental shelf (27.00 kg m−3), whereas in the middle layer, 27.45 kg m−3 isopycnal extended to 300 m depth near the ice shelf but below 200 m depth in the offshore. The surface mixed layer thickened from the shelf break toward the ice shelf. This thickening was caused partially by coastal downwelling resulting from onshore Ekman transport and by Ekman pumping in the coastal area. The baroclinic component of the AACC near the Dotson Ice Shelf increased from July to October and decreased from January to June in 2013. In comparison with other potential driving forces, the seasonal and non-seasonal (short-term) variation of the AACC correlated well with density variability, determined principally by salinity variation. Therefore, it is suggested that the variability of the isopycnocline by Ekman pumping in the coastal area is one of the important factors controlling the seasonality and non-seasonal variability of the AACC.

The role of blocking system in heavy precipitation of Iran (a case study: southeast of Iran January 2008)

This article concerns the analysis of the heavy precipitation, which allows investigating the effect of the blocking system on the unusual precipitation and temperature occurrence in Iran. The days of January 2008 have been the coldest days during the history of recorded data in Iran. Variation of precipitation during January 2008 compared with long-term data (30 years) shows the maximum positive anomaly in the stations located in southeast of Iran. However, the precipitation in consecutive days, 14–15 and 15–16 of January, produce a more important proportion of the heavy precipitation in this region. In order to study the role of the blocking system related to heavy precipitation in January 2008, the position and movement of the atmospheric systems including cyclones, anticyclones, fronts, and wind fields have been analyzed by the use of synoptic maps by the environment to circulation approach. Consequently, the weather maps indicated that the blocking system over the north of the Caspian Sea has caused the relatively deep low trough on January 5, 7, 14, 15, and 16, 2008, while the thermal and moisture gradients in the warm section of air masses have produced heavy precipitation. As a result, wind field of low levels (850 hPa) provided remarkable moisture fed by the Arabian Sea, Oman Sea, and Persian Gulf in the study area. Furthermore, the speed of wavelength and the position of the blocking system associated with the heavy precipitation can be clearly identified.

Diagnosis of the Source and Evolution of Medium-Range Forecast Errors for Extratropical Cyclone Joachim

AbstractMedium-range forecasts for Cyclone Joachim, an extratropical cyclone that impacted western Europe on 16 December 2011, consistently predicted a high-impact intense cyclone; however, these forecasts failed to verify. The potential source and propagation of forecast errors for this case are diagnosed from the 51-member European Centre for Medium-Range Forecasts Ensemble Prediction System initialized 5 days prior to the cyclone’s landfall. Ensemble members are subdivided into two groups: one that contained the eight members that had the most accurate forecast of Joachim and, the other, the eight members that predicted the most intense cyclone. Composite differences between these two subgroups indicate that the difference between these forecasts originate in tropopause-based subsynoptic waves along a deep trough in the eastern Pacific. These errors move eastward over a northern stream ridge centered on the west coast of North America and modulate the evolution of a trough that dives equatorward out of Canada and is associated with the development of Joachim. Forecast error calculations and relaxation experiments indicate that reducing forecast errors associated with these subsynoptic features leads to more accurate forecasts. These results present further evidence that subsynoptic errors, especially those originating in the warm sector of a cyclone, can be a significant source of downstream forecast errors.

Proportion of Glacially To Fluvially Induced Quartz Grain Microtextures Along the Chitina River, SE Alaska, U.S.A.

Abstract Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specific transport processes. Accordingly, these transport-induced microtextures are used to infer depositional setting in ancient deposits. Multiple transport histories complicate the microtextural record because modification of grain surfaces can reduce or eliminate the signal of earlier transport episodes. This study utilizes scanning electron microscopy to analyze surface microtextures to assess the role of fluvial overprint on glacially derived grains along ∼ 188 km of the proglacial Chitina River, SE Alaska. Results indicate that occurrence frequency of glacially induced microtextures (i.e., straight and curved grooves, deep troughs, and crescentic gouges) negatively correlates to distance downstream, yet these microtextures persist in every sample. Conversely, occurrence frequency of fluvially induced microtextures (i.e., v-shaped cracks and edge rounding) positively correlate to distance downstream. At least in the Chitina River watershed, the ratio of fluvially to glacially induced microtextures (F/G ratio) generally records physiographic variation, including increase in fluvial signal after a major tributary confluence, and decrease downstream from the intersection of valley glaciers. These results suggest that analysis of quartz grain microtextures in ancient fluvial deposits can be used to infer glacial influence when other diagnostic sedimentologic indicators of glaciation are lacking. Other potential uses for the proxy may exist, but need to be assessed after other modern proglacial systems are studied, including: 1) estimates of distance to paleo–ice margins using the respective downstream trends of glacially or fluvially induced microtextures, and 2) paleogeography of ancient glacio-fluvial systems through F/G ratio analysis.

Dynamics of 2013 Sudden Stratospheric Warming event and its impact on cold weather over Eurasia: Role of planetary wave reflection.

In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013.

Propagated rifting in the Southwest Sub-basin, South China Sea: Insights from analogue modelling

How the South China Sea rifted has long been a puzzling question that is still debated, particularly with reference to the Southwest Sub-basin (SWSB). Analogue modelling remains one of the most useful tools for testing rift models and processes. Here, we present and discuss a series of analogue modelling experiments designed to investigate the rifting process of the SWSB. Convincing geophysical results were compiled to provide realistic constraints to test the experimental results and interpretations. A heterogeneous lithosphere model with a varied lithospheric structure showed tectono-morphological features similar to the natural case of the SWSB, indicating that the initial thermal condition and rheological stratification of the lithosphere should have a dominant effect on the rifting process of the SWSB. Rigid tectonic blocks existed in the continental margin, such as the Macclesfield Bank and the Reed Bank, and they played important roles in both the shaping of the continent–ocean boundary and the coupling between the crust and mantle. The initial thermal condition and rheological stratification of the lithosphere under the South China Sea controlled the propagated rifting process of the SWSB. Extension was centred on the deep troughs between the rigid blocks, and the break-up occurred in these areas between them. The westward rifting propagation is best explained with a heterogeneous lithosphere model characterized by varied lithospheric structure, and it was responsible for producing the V-shaped configuration of the SWSB.

Persistent Chaos of Measles Epidemics in the Prevaccination United States Caused by a Small Change in Seasonal Transmission Patterns.

Epidemics of infectious diseases often occur in predictable limit cycles. Theory suggests these cycles can be disrupted by high amplitude seasonal fluctuations in transmission rates, resulting in deterministic chaos. However, persistent deterministic chaos has never been observed, in part because sufficiently large oscillations in transmission rates are uncommon. Where they do occur, the resulting deep epidemic troughs break the chain of transmission, leading to epidemic extinction, even in large cities. Here we demonstrate a new path to locally persistent chaotic epidemics via subtle shifts in seasonal patterns of transmission, rather than through high-amplitude fluctuations in transmission rates. We base our analysis on a comparison of measles incidence in 80 major cities in the prevaccination era United States and United Kingdom. Unlike the regular limit cycles seen in the UK, measles cycles in US cities consistently exhibit spontaneous shifts in epidemic periodicity resulting in chaotic patterns. We show that these patterns were driven by small systematic differences between countries in the duration of the summer period of low transmission. This example demonstrates empirically that small perturbations in disease transmission patterns can fundamentally alter the regularity and spatiotemporal coherence of epidemics.

Size effect in gas forming a hot-bent AA5xxx V-shaped trough trimmed for an airplane strakelet skin panel

Superplastic forming or gas forming is favorable method for the manufacture of sheet metal for making airplane skin panels. However, a major challenge in applying this method is controlling the thickness distribution in the formed product. Here, we explore a hot-bending-assisted process for gas forming of a deep trough with a complex shape for use in airplane wings. We propose the deliberate arrangement of wrinkles to achieve uniform thickness distribution. Because full-scale experiments are costly, sub-scale specimens are preferred for collecting experimental data. In linking sub-scale data to full-scale manufacturing, the size effect on wrinkle formation sites is important. The cause of the pre-form contour and larger-size specimen could be the greater variations in contour modes due to plastic buckling during the pre-forming stage.

SHADOW OF A COLOSSUS: A z = 2.44 GALAXY PROTOCLUSTER DETECTED IN 3D Lyα FOREST TOMOGRAPHIC MAPPING OF THE COSMOS FIELD

ABSTRACT Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at z ∼ 2.3 – 3 ?> within a 11.′5 × 13.′5 area of the COSMOS field ( ∼ 1200 deg - 2 ?> projected area density or ∼ 2.4 h - 1 Mpc ?> mean transverse separation), we reconstruct a 3D tomographic map of the foreground Lyα forest absorption at 2.2 < z < 2.5 with an effective smoothing scale of ϵ 3D ≈ 2.5 h - 1 Mpc ?> comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, we find that the galaxy positions are clearly biased toward regions with enhanced intergalactic medium (IGM) absorption in the tomographic map. We find an extended IGM overdensity with deep absorption troughs at z = 2.45 associated with a recently discovered galaxy protocluster at the same redshift. Based on simulations matched to our data, we estimate the enclosed dark matter mass within this IGM overdensity to be M dm ( z = 2.45 ) = ( 1.1 ± 0.6 ) × 10 14 h - 1 M ⊙ ?> , and argue based on this mass and absorption strength that it will form at least one z ∼ 0 galaxy cluster with M ( z = 0 ) = ( 3 ± 1.5 ) × 10 14 h - 1 M ⊙ ?> , although its elongated nature suggests that it will likely collapse into two separate clusters. We also point out a compact overdensity of six MOSDEF galaxies at z = 2.30 within a r ∼ 1 h - 1 Mpc ?> radius and Δz ∼ 0.006, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Lyα forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM overdensities associated with protoclusters or other features of large-scale structure.

Evidence for Timanian-age basement rocks in North Greenland as documented through U-Pb zircon dating of igneous xenoliths from the Midtkap volcanic centers

Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Greenland that cut through Cambrian-Ordovician deep water trough sedimentary rocks that were subsequently deformed during the south-verging Ellesmerian Orogeny. The xenoliths were characterized geochemically and their zircons dated through the U-Pb technique. This provided ages ranging from 628 to 570 Ma, for xenoliths with granitic and monzonitic compositions, the former apparently older than the latter. These ages, coupled with the geochemical signature compatible with an arc setting, provide evidence for the presence of Timanian like basement in North Greenland. The structural setting suggests that the dated xenoliths belong to an allochthonous unit emplaced during the Caledonian Orogeny and deformed during the Ellesmerian Orogeny. Furthermore, this data provides new evidence for a northwestern extension (through continuation and/or through dispersal) of the late Neoproterozoic Timanide belt, from its type locality, in the Timan-Pechora region in Russia, through Svalbard, into North Greenland, to the Pearya Terrane on Ellesmere Island.

A glacial landform assemblage from an inter-ice stream setting in the eastern Amundsen Sea Embayment, West Antarctica

Large ice streams that drain the West Antarctic Ice Sheet (WAIS) into the Amundsen Sea Embayment (ASE) are currently thinning, accelerating and retreating rapidly (e.g. Rignot et al. 2014). These ice streams are assumed to have reached the continental shelf edge during the Last Glacial Maximum (LGM; c. 23–19 cal ka BP), some 450 km north of the modern grounding line (e.g. Larter et al. 2014). Recent modelling results suggest that the expanded LGM ice sheet was characterized by fast-flowing regions across the entire ASE shelf (Golledge et al. 2013). However, the original geomorphological imprint of former fast ice-flow has usually only been preserved within deep palaeo-ice stream troughs, for example as mega-scale glacial lineations (MSGLs) (Clark 1993). In contrast, the morphological record in inter-ice stream settings is believed to have been subsequently obliterated by ploughing iceberg keels (e.g. Dowdeswell & Bamber 2007). As a result, evidence for palaeo-ice sheet dynamics in these regions, which make up a substantial portion of the former ice-sheet bed, remain largely understudied (Ottesen & Dowdeswell 2009). The undisturbed geomorphological record from a palaeo-inter-ice stream setting in the ASE, north of Burke Island, revealed an assemblage of subglacial landforms that is entirely different from those in the deep troughs (Klages et al. 2013). The geomorphological record therefore provides new insights into basal conditions of the former WAIS in the Amundsen Sea sector that is also relevant to other sectors and to ice-sheet beds outside Antarctica. The seafloor in the inter-ice stream setting between the Pine Island (PIT) and the Abbot (AT) palaeo-ice stream troughs in the ASE (Fig. 1a) is characterized by a unique assemblage of glacial landforms that includes the following features (Klages et al. 2013, 2015). Fig. 1. Multibeam-bathymetry and acoustic sub-bottom profiles of submarine glacial landforms in an inter-ice stream setting …

Spin-polarized transport in hydrogen-passivated graphene and silicene nanoribbons with magnetic transition-metal substituents.

We present a systematic theoretical study of the electronic transport in hydrogen passivated zigzag graphene and silicene nanoribbons with between zero and four neighboring H atoms on one edge replaced by magnetic transition metals (Fe, Co, and Ni). The calculations were performed using equilibrium transport and density-functional theory with the generalized gradient approximation to exchange and correlation. We considered the magnetic moments of the two edges aligned both ferromagnetically (Ferro-F form) and antiferromagnetically (Ferro-A form). The Ferro-A graphene-based ribbons were all semiconducting and would support moderate spin-polarized currents of either sign by applying positive or negative gate voltages. The Ferro-F graphene-based ribbons were all metallic; the most interesting for possible spintronic applications being that with a single Ni atom, in which strong spin-filtering at low bias resulted from a deep trough in the transmission of one spin component around the Fermi level. By contrast, in the Si-based analog this trough was split, partially eliminating the polarization of the current. This splitting was found to be related to the buckled structure of the Si-based nanoribbon, which has its origin in its preference for sp(3)-like hybridization.