The Tiny-Scale Atomic Structure: Gas Cloudlets or Scintillation Phenomenon?

We present preliminary results from the recent multi-epoch HI absorption measurements toward several pulsars using the Arecibo telescope. We do not find significant variations in optical depth profiles over periods of 4 months and 9 years. The upper limits on the optical depth variations in directions of B0823+26 and B1133+16 are similar on scales of 10–20, 350 and 500 AU. The large number of non detections of the tiny scale atomic structure suggests that the AU-sized structure is not ubiquitous in the interstellar medium.     

Tectonic histories between Alba Patera and Syria Planum, Mars

Syria Planum and Alba Patera are two of the most prominent features of magmatic-driven activity identified for the Tharsis region and perhaps for all of Mars. In this study, we have performed a Geographic Information System-based comparative investigation of their tectonic histories using published geologic map information and Mars Orbiter Laser Altimetry (MOLA) data. Our primary objective is to assess their evolutional histories by focusing on their extent of deformation in space and time through stratigraphic, paleotectonic, topographic, and geomorphologic analyses. Though there are similarities among the two prominent features, there are several distinct differences, including timing deformational extent, and tectonic intensity of formation. Whereas Alba Patera displays a major pulse of activity during the Late Hesperian/Early Amazonian, Syria Planum is a long-lived center that displays a more uniform distribution of simple graben densities ranging from the Noachian to the Amazonian, many of which occur at greater distances away from the primary center of activity. The histories of the two features presented here are representative of the complex, long-lived evolutional history of Tharsis.     

Using stable and radioactive isotopes for the investigation of contaminant metal mobilization in a metal mining district

Naturally occurring stable and radioactive isotopes were used as environmental tracers to investigate contaminant metal mobilization processes in a metal smelter dump mainly consisting of slag. Water emerging from the dump at a spring is heavily contaminated by metals. The smelter dump contains minor amounts of flue dust, a material which shows a high potential for metal mobilization. Nearby dumps mainly consist of low-grade ore. Concentration patterns of ²³⁸U, ²²⁶Ra and ²¹⁰Pb determined in sediment deposited close to the contaminated spring reveal the flue dust to be the major local metal source rather than the slag or the low-grade ore. Contamination pathways inside the dump were investigated using hydrological, chemical and isotopic data. Strong negative correlation between water discharge and metal concentration in the spring water suggests, besides short-term dilution of the metal concentration by direct rainwater runoff, distinct long-term dilution of the spring water by groundwater being discharged at a significantly increased rate as a result of heavy rains. δ¹⁸O and δD signatures of rain, local groundwater and spring water confirm the importance of groundwater derived from the local aquifer. Another hydrological component with importance for metal mobilization was found to be water that is recharged in the dump itself. Tritium analysis allowed an assessment of the probable residence time of that water component in the smelter dump. Since that water component seems to represent a major local contamination pathway the findings of the study are of substantial importance for site remediation planning. As a primary result it could be stated that covering the dump would not result in any noteworthy short-term improvement of the spring water quality. First significant effects would only be visible after 2–3 decades at the earliest.     

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California I: Interpreting rates and controls based on soil concentration-depth profiles

The spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal California are interpreted in terms of chemical weathering rates and processes. In regoliths up to 15 m deep and 226 kyrs old, quartz-normalized mass transfer coefficients indicate non-stoichiometric preferential release of Sr > Ca > Na from plagioclase along with lesser amounts of K, Rb and Ba derived from K-feldspar. Smectite weathering results in the loss of Mg and concurrent incorporation of Al and Fe into secondary kaolinite and Fe-oxides in shallow argillic horizons. Elemental losses from weathering of the Santa Cruz terraces fall within the range of those for other marine terraces along the Pacific Coast of North America.Residual amounts of plagioclase and K-feldspar decrease with terrace depth and increasing age. The gradient of the weathering profile b_s is defined by the ratio of the weathering rate, R to the velocity at which the profile penetrates into the protolith. A spreadsheet calculator further refines profile geometries, demonstrating that the non-linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface-to-volume ratios and at high residual feldspar concentrations, at greater depth, by the approach to thermodynamic saturation. These parameters are of secondary importance to the fluid flux q_h, which in thermodynamically saturated pore water, controls the weathering velocity and mineral losses from the profiles. Long-term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute Cl balances (q_h = 0.025-0.17 m yr⁻¹).During saturation-controlled and solute-limited weathering, the greater loss of plagioclase relative to K-feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics. The steady-state weathering rate under such conditions is defined as

     

Parametric Study of Urban-Like Topographic Statistical Moments Relevant to a Priori Modelling of Bulk Aerodynamic Parameters

For a horizontally homogeneous, neutrally stratified atmospheric boundary layer (ABL), aerodynamic roughness length, \(z_0\), is the effective elevation at which the streamwise component of mean velocity is zero. A priori prediction of \(z_0\) based on topographic attributes remains an open line of inquiry in planetary boundary-layer research. Urban topographies – the topic of this study – exhibit spatial heterogeneities associated with variability of building height, width, and proximity with adjacent buildings; such variability renders a priori, prognostic \(z_0\) models appealing. Here, large-eddy simulation (LES) has been used in an extensive parametric study to characterize the ABL response (and \(z_0\)) to a range of synthetic, urban-like topographies wherein statistical moments of the topography have been systematically varied. Using LES results, we determined the hierarchical influence of topographic moments relevant to setting \(z_0\). We demonstrate that standard deviation and skewness are important, while kurtosis is negligible. This finding is reconciled with a model recently proposed by Flack and Schultz (J Fluids Eng 132:041203-1–041203-10, 2010), who demonstrate that \(z_0\) can be modelled with standard deviation and skewness, and two empirical coefficients (one for each moment). We find that the empirical coefficient related to skewness is not constant, but exhibits a dependence on standard deviation over certain ranges. For idealized, quasi-uniform cubic topographies and for complex, fully random urban-like topographies, we demonstrate strong performance of the generalized Flack and Schultz model against contemporary roughness correlations.     

Quantifying the Effects of Commercial Clam Aquaculture on C and N Cycling: an Integrated Ecosystem Approach

Increased interest in using bivalve cultivation to mitigate eutrophication requires a comprehensive understanding of the net carbon (C) and nitrogen (N) budgets associated with cultivation on an ecosystem scale. This study quantified C and N processes related to clam (Mercenaria mercenaria) aquaculture in a shallow coastal environment (Cherrystone Inlet, VA) where the industry has rapidly increased. Clam physiological rates were compared with basin-wide ecosystem fluxes including primary production, benthic nutrient regeneration, and respiration. Although clam beds occupy only 3 % of the ecosystem’s surface area, clams filtered 7–44 % of the system’s volume daily, consumed an annual average of 103 % of the phytoplankton production, creating a large flux of particulate C and N to the sediments. Annually, N regenerated and C respired by clam and microbial metabolism in clam beds were ～3- and ～1.5-fold higher, respectively, than N and C removed through harvest. Due to the short water residence time, the low watershed load, and the close vicinity of clam beds to the mouth of Cherrystone Inlet, cultivated clams are likely subsidized by phytoplankton from the Chesapeake Bay. Consequently, much of the N released by mineralization associated with clam cultivation is “new” N as it would not be present in the system without bivalve facilitation. Macroalgae that are fueled by the enhanced N regeneration from clams represents a eutrophying process resulting from aquaculture. This synthesis demonstrates the importance of considering impacts of bivalve aquaculture in an ecosystem context especially relative to the potential of bivalves to remove nutrients and enhance C sinks.     

Comparison of regression-based and combined versions of Inverse Distance Weighted methods for spatial interpolation of daily mean temperature data

This paper focuses on the performance of two regression-based and one Inverse Distance Weighted (IDW) and two combined versions of IDW methods for interpolation of daily mean temperature at the Black Sea Region of Turkey. Simple linear regression (SLR) and multiple linear regression (MLR) are used as regression-based methods. Combinations of IDW with TLR (temperature lapse rate) and gradient plus inverse distance squared (GIDS) are used as combined versions of IDW. This study targets to compare five spatial interpolation methods based on RMSE (root-mean-square error) statistics of interpolation errors for daily mean temperatures from 1981 to 2012. In order to compare the interpolation errors of the five methods, the leave-one-out cross-validation method was applied over long periods of 32 years on 52 different sites. The algorithms of the five interpolation methods’ codes were written in MATLAB by the authors of the paper.     

Celebrating the Career of Dr. John R. Garratt: Long-Term Proponent of Boundary-Layer Meteorology and International Man of Mystery

Boundary-Layer Meteorology -     

Zircon SHRIMP U–Pb age of Late Jurassic OIB-type volcanic rocks from the Tethyan Himalaya: constraints on the initial activity time of the Kerguelen mantle plume

This work presents zircon U–Pb age and whole-rock geochemical data for the volcanic rocks from the Lakang Formation in the southeastern Tethyan Himalaya and represents the initial activity of the Kerguelen mantle plume. SHRIMP U–Pb dating of zircons from the volcanic rocks yielded a ²⁰⁶Pb/²³⁸U age of 147 ± 2 Ma that reflects the time of Late Jurassic magmatism. Whole rock analyses of major and trace elements show that the volcanic rocks are characterized by high content of TiO₂ (2.62 wt%–4.25 wt%) and P₂O₅ (0.38 wt%–0.68 wt%), highly fractionated in LREE/HREE [(La/Yb)_N = 5.35–8.31] with no obvious anomaly of Eu, and HFSE enrichment with no obvious anomaly of Nb and Ta, which are similar to those of ocean island basalts and tholeiitic basaltic andesites indicating a mantle plume origin. The Kerguelen mantle plume produced a massive amount of magmatic rocks from Early Cretaceous to the present, which widely dispersed from their original localities of emplacement due to the changing motions of the Antarctic, Australian, and Indian plates. However, our new geochronological and geochemical results indicate that the Kerguelen mantle plume started from the Late Jurassic. Furthermore, we suggest that the Kerguelen mantle plume may played a significant role in the breakup of eastern Gondwanaland according to the available geochronological, geochemical and paleomagnetic data.     

Zircon SHRIMP U-Pb ages and geochemistry of Late Mesozoic granitoids in Western Zhejiang and Southern Anhui: constraints on the model of lithospheric thinning of Southeast China

ABSTRACT

We report geochemical data and zircon SHRIMP U-Pb ages for Late Mesozoic granitoids from the western Zhejiang province and southern Anhui province (the WZSA region) from southeast China. In combination with published geochronological and geochemical data, the granitoids in the region can be divided into three stages: 171–141 Ma, 140–121 Ma, and 120–95 Ma. The first stage of these granitoids is mainly composed of granite porphyry and granodiorite which are similar to I-type granitoids, including having weakly negative Eu anomalies with enrichment in light rare earth elements (LREE), Rb, Th, and U. The second stage of granitoids consists of monzogranite, syenogranite, and granite with the characteristics of both A-type and I-type granitoids including strongly negative Eu anomalies; depletion of Ba, Sr, and Ti; and enrichment of K, Rb, and high field strength elements (HFSEs) (such as Th and U). The third stage of granitoids is mainly composed of granite, quartz monzonite, quartz diorite, and mafic rocks with weakly negative Eu anomalies and also enrichment in LREE, Rb, Th, U, and K. From our work, we propose a transition from compressional to extensional magmatism at ~141 Ma. Based on the geochemical characteristics of these granites and coeval mafic rocks, we propose that the formation of the A-type magmatism in the WZSA region formed as the result of lithospheric extension and asthenospheric upwelling during the Early Cretaceous.