Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source

Late Cretaceous (66.2 ± 0.5 Ma amphibole and 66.7 ± 0.2 Ma phlogopite ⁴⁰Ar/³⁹Ar ages) nephelinitic volcanic rocks from Godzilla Seamount in the eastern North Atlantic (34°N latitude) have trace element and Sr–Nd–Pb–Hf-isotope compositions similar to the Enriched Mantle I (EM-I) endmember, except for their low ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb ratios (²⁰⁶Pb/²⁰⁴Pb_in = 17.7, ²⁰⁷Pb/²⁰⁴Pb_in = 15.34) plotting below the Northern Hemisphere Reference Line on the uranogenic Pb isotope diagram. O isotope data on amphibole separates are mantle-like (δ¹⁸O = 5.6–5.8‰). Age and location of the isolated Godzilla Seamount, however, preclude it from being derived from the Madeira or Canary hotspots, making a lower-mantle origin unlikely. Therefore we propose derivation from a shallow (lithospheric/asthenospheric) melting anomaly. As observed in mid-ocean-ridge and ocean-island basalts, there is a systematic decrease of ²⁰⁷Pb/²⁰⁴Pb ratios (and Δ7/4) in the individual EM-I endmember type localities towards northern latitudes with Godzilla lying on the extension of this trend. This trend is mirrored in ultra-potassic volcanic rocks such as lamproites and kimberlites, which reflect the composition of enriched subcontinental lithospheric mantle. Therefore, a global pattern in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 is suggested. The geochemical composition of EM-I endmember type localities, including Godzilla lavas, and the enriched (DUPAL) anomaly in the southern hemisphere could reflect derivation from ancient, metasomatized subcontinental lithospheric mantle. We propose a two-stage model to explain the trace element and isotopic composition of the EM-I mantle endmember localities worldwide: 1) during the early history of the Earth, subcontinental lithosphere was metasomatized by melts from subducted slabs along convergent margins generating high μ (²³⁸U/²⁰⁴Pb) sources, and 2) as the Earth cooled, hydrous fluids replaced hydrous melts as the main slab component metasomatizing the subcontinental lithospheric mantle (generating EM-I sources with lower μ). In accordance with this model, the global variations in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 could reflect geographic differences in μ and/or the age at which the transition from stages 1 to 2 took place in the Archaean lithosphere. The model would require a re-definition of the EM-I endmember to low ²⁰⁶Pb/²⁰⁴Pb, high ²⁰⁸Pb/²⁰⁴Pb (positive Δ8/4) but variable ²⁰⁷Pb/²⁰⁴Pb (positive and negative Δ7/4).     

Three-dimensional calculations of the formation of the presolar nebula from a slowly rotating cloud

The presolar nebula may have formed from the collapse of a very slowly rotating interstellar cloud. The first three-dimensional, hydrodynamical calculations of the collapse of such clouds are presented. The models include radiative transfer in the Eddington approximation, as well as detailed equations of state appropriate for the nonisothermal regime of protostellar evolution. Very slowly rotating clouds, i.e., those with initial ratios of rotational energy to gravitational energy of 10^?3 or less, avoid fragmentation and instead collapse to form single central objects, containing quasistatic cores with densities of about 10^?10 g cm^?3. These cores are, however, surrounded by significantly nonaxisymmetric regions, such that the presolar nebula would have been bar-like over the scale of the present solar system. This nonaxisymmetry, coupled with differential rotation, results in gravitational torques that produce rapid outward transfer of angular momentum. The center of the presolar nebula should then be able to contract and collapse to pre-main-sequence densities without suffering fission or fragmentation.     

The Falkland Islands’ palaeoecological response to millennial‐scale climate perturbations during the Pleistocene–Holocene transition: Implications for future vegetation stability in the southern ocean islands

Oceanic island flora is vulnerable to future climate warming, which is likely to promote changes in vegetation composition, and invasion of non‐native species. Sub‐Antarctic islands are predicted to experience rapid warming during the next century; therefore, establishing trajectories of change in vegetation communities is essential for developing conservation strategies to preserve biological diversity. We present a Late‐glacial‐early Holocene (16 500–6450 cal a bp ) palaeoecological record from Hooker's Point, Falkland Islands (Islas Malvinas), South Atlantic. This period spans the Pleistocene‐Holocene transition, providing insight into biological responses to abrupt climate change. Pollen and plant macrofossil records appear insensitive to climatic cooling during the Late‐glacial, but undergo rapid turnover in response to regional warming. The absence of trees throughout the Late‐glacial‐early Holocene enables the recognition of far‐travelled pollen from southern South America. The first occurrence of Nothofagus (southern beech) may reflect changes in the strength and/or position of the Southern Westerly Wind Belt during the Late‐glacial period. Peat inception and accumulation at Hooker's Point is likely to be promoted by the recalcitrant litter of wind‐adapted flora. This recalcitrant litter helps to explain widespread peatland development in a comparatively dry environment, and suggests that wind‐adapted peatlands can remain carbon sinks even under low precipitation regimes. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

Palaeoenvironmental records in Holocene Spanish tufas: a stable isotope approach in search of reliable climatic archives

Tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information. This study assesses the potential of stable isotopic archives from two closely juxtaposed Holocene tufa sites in SE Spain. The Ruidera site contains deep‐water lacustrine micrites and tufas, whereas the nearby Alcaraz site represents a shallow barrage tufa. Understanding site characteristics is critical to interpreting the stable isotopic variations. These Holocene lacustrine micrites have isotopic compositions consistent with modern European lake shore microbial carbonates, where the isotopic chemistry is strongly influenced by hydrological and residence time effects. All the lacustrine micrite δ¹³C values were influenced by microenvironmental microbial effects to some degree. Because of these effects, stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation, temperature or vegetation composition of an area. In contrast, Holocene tufas that formed in shallow, fast‐flowing riverine settings may contain valuable palaeoclimatic archives. The tufa deposits must be largely autochthonous, as at Alcaraz, where in situ reed stem encrustations are present. Records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the δ¹⁸O data. These interpretations can be verified by other independent climatic data where chronology is constrained. Variations in riverine tufa δ¹³C values probably record changes in local vegetation and/or soil respiration. Covariation between δ¹⁸O and δ¹³C values may be intrinsically linked to climatic factors such as aridity. Tentative palaeoclimatic interpretations for the middle Holocene at Alcaraz based on the isotope data suggest warming (or increasing influence of Mediterranean‐sourced precipitation) between approximately 5000–3000 radiocarbon years BP, accompanied by increased aridity. These interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the Holocene of SE Spain. This study supports the growing evidence that well‐chosen tufa sites could yield valuable palaeoclimatic information.     

CODA Q estimates for Kumaun Himalaya

CodaQ (Q _c) estimates for the Kumaun Himalaya region have been obtained in high frequency range. Local earthquakes, recorded by a digital seismic network in the region, which fall in the epicentral distances range of 10 to 80 km and with a local magnitude range of 1.4 to 2.8, have been used. The coda waves of 30 sec window length, filtered at seven frequency bands centered at 1.5, 3, 6, 9, 12, 18 and 24Hz, have been analysed using the single backscattering model. The values ofQ _c estimates vary from 65 to 283 at 1.5 Hz to 2119 to 3279 at 24.0 Hz which showed thatQ _c is frequency dependent and its value increases as frequency increases. A frequency-dependentQ _c relationship,Q _c = (92 ± 4.73)f^(1.07±.023), is obtained for the region representing the average attenuation characteristics of seismic waves for Kumaun Himalaya region.     

Variability in habitat use by young-of-the-year winter flounder,<Emphasis Type="Italic">Pseudopleuronectes americanus</Emphasis>, in three northeastern U.S. estuaries

We compared distribution and abundance by habitat for age-0, young-of-the-year (YOY) winter flounder,Pseudopleuronectes americanus, in three estuaries (Hammonasset River, Navesink River, and Great Bay-Little Egg Harbor) in the northeastern United States to better define essential fish habitat (EFH). Two replicates of five representative habitats were sampled in most estuaries: eelgrass (Zostera marina), unvegetated areas adjacent to eelgrass, macroalgae, (primarilyUlva lactuca), unvegetated areas adjacent to macroalgae, and tidal marsh creeks. Fish were sampled every two weeks, May through October 1995 and 1996, with a beam-trawl (1-m width, 3-mm mesh net). Abundance of YOY winter flounder was highest in the Navesink River estuary and similar between years, but was significantly lower and differed between years in the Great Bay-Little Egg Harbor and Hammonasset River estuaries. Annual temperature differences appear to influence estuary use by YOY. In the years and estuaries studied, where habitat-related differences in abundance were significant, YOY were found in higher densities in unvegetated areas adjacent to eelgrass. The exception was in the Hammonasset River in 1995 when densities were higher in eelgrass. We conclude that the type of habitat most important to YOY winter flounder varies among estuaries and as a result, care should be taken in defining EFH, based only on limited spatial and temporal sampling.     

Soft X-ray spectroscopy of ferrous silicates

Energy gaps and electrical conductivities in the ferrous silicates, Fe₂SiO₄ and FeSiO₃, depend primarily on Fe-O bonding and may be studied by ultraviolet and soft X-ray spectroscopy. We have measured FeL_II–III X-ray band spectra under conditions of “minimal” (I₄, at 4.0 keV) and “high” (I₁₀, at 10.0 keV) self absorption to determine 3d orbital energy levels, to delineate d states in the valence band, and to construct band gap models. Absorption spectra, I₄/I₁₀, were computed to determine vacant orbital levels in the gap. A difference function (I₄–I₁₀) has been proposed to identify X-radiation at photon energies above the measured L_III absorption edge, including high-energy, double-vacancy satellites and radiative transitions involving the anti-parallel (spin-down) d ⁶ electron in the ground state. The proposed band gap model for Fe₂SiO₄ is consistent with that of Nitsan and Shankland (1976), including an intrinsic transition of 6.5 eV and an energy gap of 7.8 eV. The 3d orbital energy level electronic structures are in general agreement with levels computed by Tossell et al. (1974) for [FeO₆]^10? in FeO using an SCF Xα cluster MO method. A high-energy, double-vacancy satellite was found at ～710.7 eV, and is presumed to originate from an L_IIIM_II,III initial state. The intensity of these satellites for the ferrous silicates and other iron compounds, and corresponding Fe L_II/L_III intensity ratios are correlated with differences in band gap magnitudes and gap structure. Fe L_II/L_III intensity ratios are not well correlated with iron oxidation state.     

Belonging in charlotte: multiscalar differences in local immigration politics and policies

In the context of Charlotte, North Carolina's, emergence as a “globalizing” pre‐emergent immigrant gateway, this paper focuses on a complex and multiscalar set of governmental policies and community‐development dynamics that are shaping localized response to Hispanic/Latino immigration. Specifically, we explore how these policies and dynamics play out spatially in the context of two Charlotte neighborhoods, both of which have similar historical roots and have become magnets for Latino settlement, yet display divergent contemporary place‐making paths. Our exploration reveals the ways in which contexts of receptivity and spaces of both exclusion and inclusion are created by the socio‐spatial components of public policy and the localized response to that policy at the intraurban level. Reinforcing the importance of space and place in the construction of receptivity contexts, the compared stories of Eastside and South Charlotte reveal that neighborhoods are never the product of one transformational force but of many—no matter how they may be perceived in the public imaginary.     

The influence of topography and approach angles on local deflections of airflow within a coastal blowout

The spatial variability of air flow through complex topography is an important, but not fully understood, component of dune development and dynamics. This study examines the spatial variability of the wind field in a linear blowout in coastal dunes at Jockey's Ridge State Park, on the Outer Banks of North Carolina. A spatial array of single‐height anemometers and wind vanes were placed within the blowout. Topography exerted a significant steering effect when onshore winds approached from directions within 50° of the blowout axis. Under those conditions wind flow in the blowout aligned to the axis regardless of approach angle, maximizing the potential for erosion and transport in the trough. In other locations aspect variations caused deflection both proportional and disproportional to changes in the approaching wind. When prevailing winds approached from directions more oblique than 50° to the blowout axis, topographic steering through the blowout trough was reduced and secondary flow generated by flow separation over the trough became more prominent. During those approach angles, wind directions and speeds within the upper blowout trough became erratic as vortices and turbulence dominated the flow, minimizing transport potential. The changing characteristics of airflow in the blowout relative to differing approach angles has implications on dune development and variations in transport potential under changing conditions. Copyright © 2013 John Wiley & Sons, Ltd.