A catalogue of major and trace element data for Icelandic Holocene silicic tephra layers

Tephra layers with Icelandic provenance have been identified across the North Atlantic region in terrestrial, lacustrine, marine and glacial environments. These tephra layers are used as marker horizons in tephrochronology including climate studies, archaeology and environmental change. The major element chemistries of 19 proximally deposited Holocene Icelandic silicic tephra layers confirm that individual volcanic systems have unique geochemical signatures and that eruptions from the same system can often be distinguished. In addition, glass trace element chemistry highlights subtle geochemical variations between tephra layers which appear to have identical major element chemistry and thus allows for the identification of some, if not all, tephra layers previously considered identical in composition. This paper catalogues the compositional variation between the widespread Holocene Icelandic silicic tephra deposits.     

Water quality modeling and sensitivity analysis using Water Quality Analysis Simulation Program (WASP) in the Shenandoah River watershed

This study used the Water Quality Analysis Simulation Program (WASP) to simulate nutrients, dissolved oxygen (DO), and chlorophyll-a dynamics in the Shenandoah River basin and performed an uncertainty analysis to examine the complexity of these variables in water quality estimation and their influence on the Shenandoah River. Significant progress has been made; however, nutrient loads emitted into the Shenandoah River from nonpoint sources remain high. Modeling of three points on the Shenandoah River in Virginia and West Virginia provides an ideal case study since the river is classified by the Virginia Department of Environmental Quality as being impaired. The results of a sensitivity test show that model error decreases with increasing model complexity and sensitivity. The model predicted DO values that tended to be close to the measured data, while total nitrogen and phosphorus tended to be overemphasized. Our results examine the importance of temperature, stream flow, and velocity in influencing water quality between seasons and levels on the different sections of the watershed.     

辽宁盖县梁屯—矿洞沟碱性正长岩杂岩体的U—Pb和Sm—Nd年龄及其地质意义

辽宁梁屯 -矿洞沟杂岩体主要由辉石正长岩、霓辉正长岩和霓辉角闪正长岩等碱性岩石组成 ,具有全岩 Rb- Sr等时线年龄 186 6± 115 Ma和 ISr=0 .70 4 9的同位素特征 ,是我国目前报道的最古老的碱性正长岩类。本文报道了该岩体的锆石U- Pb和全岩 Sm- Nd同位素测试资料 ,获得了锆石 U- Pb同位素年龄为 185 7± 2 0 Ma、Sm- Nd等时年龄为 1787± 180 Ma、εNd(t) =- 4 .8～ - 5 .0的数据。它们反映出该杂岩体形成年龄的上限为 185 7± 2 0 Ma、下限不小于 1787± 180 Ma,来源于富集地幔物质。基于这些数据并结合区域地质资料分析 ,作者提出了华北地台北缘古元古宙存在有富集地幔储库 ,以及辽河群主体形成于 190 0 Ma以前的认识     

Diffusive equilibrium distributions of He+ in the plasmasphere

Recent satellite observations of thermal ion composition in the near-equatorial plasmasphere have shown that He⁺ comprises 5–10% typically and occasionally 25% or more of the total thermal ion density. A steady state diffusive equilibrium model for the distributions of H⁺, He⁺ and O⁺ along a plasmaspheric flux tube is used to elicit effects that may help explain these observed high He⁺ fractional concentrations. The model indicates that both the ionospheric composition and the temperature distribution along the flux tubes are important factors controlling the equatorial He⁺ composition, through the plasma scale height and thermal diffusion effects. Direct comparison of the model results with thermal ion observations by ISEE-1 indicates that the effects incorporated into the model may explain some of the elevated He⁺ concentrations. In some instances, however, effects not included in the model may also be of importance.     

Movement patterns of an endangered fishery species,Lithognathus lithognathus (Sparidae), and the role of no-take marine protected areas as a management tool

Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r² = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.     

Estuarine and coastal connectivity of an estuarine-dependent fishery species,Pomadasys commersonnii (Haemulidae)

Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ～529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.     

A magnetohydrodynamic model of whistler duct structure in the magnetosphere

In this study, the physical structure for the propagation of whistler waves within a duct in the Earth's magnetosphere is investigated by means of magnetohydrodynamic (MHD) theory. Expressions for the current density and induced magnetic field are determined analytically and evaluated in terms of two models for the duct plasma density distribution. It is found that once the duct is formed, forces associated with the current structure will maintain it. MHD instabilities are examined briefly and found to be unlikely to threaten duct maintenance in regions where whistlers are typically observed. Examination of some effects of field-aligned currents suggest that this may be a viable mechanism for duct formation.     

An analysis of auroral E region neutral winds based on incoherent scatter radar observations at Chatanika

Auroral E region neutral winds determined from incoherent scatter radar observations at Chatanika, AK, during geomagnetic disturbances (15 May 1974) are compared with detailed theoretical calculations of neutral velocities for these conditions. The theoretical velocities are obtained by numerically solving the ion and neutral momentum equations in the ion drag approximation, including coriolis and viscous forces, using observed electric fields and electron densities. Large vertical gradients are found in the calculated velocities for altitudes below about 130 km. As a consequence of this structure and fluctuations in the electron density profiles, the data analysis procedure of Brekke et al. (1973) for obtaining neutral winds from radar data is found to underestimate the wind speed by up to 40%, but it determines the direction and temporal structure reasonably well. Comparison of observed neutral velocities with calculated values shows that ion drag alone cannot account for the observations. An equation is derived to estimate the pressure gradients required to resolve the discrepancy between calculated and observed neutral winds. Accelerations due to these pressure gradients are of the same order as those due to ion drag, but at least an order of magnitude larger than those due to solar heating. Directions of the horizontal pressure gradients are consistent with expected locations of auroral heating. During geomagnetic disturbances, ion drag and auroral heating both appear to play important roles in the generation and modification of neutral winds.     

Light requirements of the seagrass,Zostera muelleri,determined by observations at the maximum depth limit in a temperate estuary,New Zealand

The Kaipara Harbour in New Zealand is one of the largest estuarine systems in the world, containing significant areas of subtidal seagrass habitat (Zostera muelleri). Light availability at the maximum depth limit for Z. muelleri was measured at 2.10 (0.19 SEM) and 4.91 (0.53 SEM) mol photons m^?2 d^?1 during the winter and summer monitoring periods, respectively. The primary drivers of benthic light availability were found to be surface light availability, the timing of the low tide and water clarity. Core sampling analysis suggested that biomass of seagrass growing at the maximum depth limit was low, indicative of light limitation. The results of this study suggest that the subtidal distribution of seagrass in the Kaipara Harbour is light-limited and that reductions in water clarity due to changes in land use are likely to result in significant reductions in the extent and productivity of subtidal seagrass habitat.     

Electrical Resistivity Imaging of a Permanganate Injection During In Situ Treatment of RDX‐Contaminated Groundwater

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) and trichloroethene (TCE). Previous treatability experiments confirmed that permanganate could mineralize RDX in NOP aquifer material. The objective of this study was to determine the efficacy of permanganate to transform RDX in the field by monitoring a pilot‐scale in situ chemical oxidation (ISCO) demonstration. In this demonstration, electrical resistivity imaging (ERI) was used to create two‐dimensional (2‐D) images of the test site prior to, during, and after injecting sodium permanganate. The ISCO was performed by using an extraction‐injection well configuration to create a curtain of permanganate. Monitoring wells were positioned downgradient of the injection zone with the intent of capturing the permanganate‐RDX plume. Differencing between ERI taken preinjection and postinjection determined the initial distribution of the injected permanganate. ERI also quantitatively corroborated the hydraulic conductivity distribution across the site. Groundwater samples from 12 downgradient wells and 8 direct‐push profiles did not provide enough data to quantify the distribution and flow of the injected permanganate. ERI, however, showed that the permanganate injection flowed against the regional groundwater gradient and migrated below monitoring well screens. ERI combined with monitoring well samples helped explain the permanganate dynamics in downgradient wells and support the use of ERI as a means of monitoring ISCO injections.