Formation of radical species in photolyzed CH₄:N₂ ices     

Robert Hodyss  Heather R. Howard  Jay D. Goguen 《Icarus》2011,214(2):748-753

We report photochemical studies of thin cryogenic ice films composed of N₂, CH₄ and CO in ratios analogous to those on the surfaces of Neptune’s largest satellite, Triton, and on Pluto. Experiments were performed using a hydrogen discharge lamp, which provides an intense source of ultraviolet light to simulate the sunlight-induced photochemistry on these icy bodies. Characterization via infrared spectroscopy showed that C₂H₆ and C₂H₂, and HCO are formed by the dissociation of CH₄ into H, CH₂ and CH₃ and the subsequent reaction of these radicals within the ice. Other radical species, such as C₂, , CN, and CNN, are observed in the visible and ultraviolet regions of the spectrum. These species imply a rich chemistry based on formation of radicals from methane and their subsequent reaction with the N₂ matrix. We discuss the implications of the formation of these radicals for the chemical evolution of Triton and Pluto. Ultimately, this work suggests that , CN, HCO, and CNN may be found in significant quantities on the surfaces of Triton and Pluto and that new observations of these objects in the appropriate wavelength regions are warranted.  相似文献   

Characteristics of the 2000 fissure eruption and lava flow fields at Mount Cameroon volcano,West Africa: a combined field mapping and remote sensing approach     

M.N. Wantim  C.E. Suh  G.G.J. Ernst  M. Kervyn  P. Jacobs 《Geological Journal》2011,46(4):344-363

This study focuses on the compound pahoehoe lava flow fields of the 2000 eruption on Mount Cameroon volcano, West Africa and it comprehensively documents their morphology. The 2000 eruption of Mount Cameroon took place at three different sites (sites 1, 2 and 3), on the southwest flank and near the summit that built three different lava flow fields. These lava flow fields were formed during a long‐duration (28th May–mid September) summit and flank eruption involving predominantly pahoehoe flows (sites 2 and 3) and aa flows (site 1). Field observations of flows from a total of four cross‐sections made at the proximal end, midway and at the flow front, have been supplemented with data from satellite imagery (SRTM DEM, Landsat TM and ETM+) and are used to offer some clues into their emplacement. Detailed mapping of these lava flows revealed that site 1 flows were typically channel‐fed simple aa flows that evolved as a single flow unit, while sites 2 and 3 lava flow fields were fed by master tubes within fissures producing principally tube‐fed compound pahoehoe flows. Sites 2 and 3 flows issued from ∼ 33 ephemeral vents along four NE–SW‐trending faults/fissures. Pahoehoe morphologies at sites 2 and 3 include smooth, folded and channelled lobes emplaced via a continuum of different mechanisms with the principal mechanism being inflation. The dominant structural features observed on these flow fields included: fissures/faults, vents, levees, channels, tubes and pressure ridges. Other structural features present were pahoehoe toes/lobes, breakouts and squeeze‐ups. Slabby pahoehoe resulting from slab‐crusted lava was the transitionary lava type from pahoehoe to aa observed at all the sites. Transition zones correspond to slopes of > 10°. Variations in flow morphology and textures across profiles and downstream were repetitive, suggesting a cyclical nature for the responsible processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Rapid increase in copper concentrations in a new marina, San Diego Bay     

Biggs TW  D'Anna H 《Marine pollution bulletin》2012,64(3):627-635

Concentrations of copper in water rose rapidly following the introduction of boats to a new marina in San Diego Bay. Two months after the marina reached half its capacity, a majority of water samples exceeded chronic and acute criteria for dissolved copper, and copper concentrations in several samples exceeded the highest concentrations observed in another marina that has been listed as an impaired water body. A box model suggested that a small fraction of the leached copper was sequestered in sediment. Copper concentrations in water entering the marina from the bay was more than half the chronic concentration limit, so only 50% of marina boat capacity could be accommodated without exceeding the chronic criterion more than 50% of the time. Copper concentrations in water may increase rapidly following boat introduction in small marinas, but could return to pre-introduction levels by controlling boat numbers or reducing use of copper-based paints.  相似文献   

Biodiversity in Hudson River shore zones: influence of shoreline type and physical structure     

David L. Strayer  Stuart E. G. Findlay  Daniel Miller  Heather M. Malcom  David T. Fischer  Thomas Coote 《Aquatic Sciences - Research Across Boundaries》2012,74(3):597-610

The shore zones of the Hudson River, like those of many developed waterways, are highly varied, containing a mix of seminatural and highly engineered shores. Our goal was to document the biodiversity supported by different kinds of shore zones in the Hudson. We chose six common types of shore zones, three of them ??natural?? (sand, unconsolidated rock, and bedrock), and three of them engineered (riprap, cribbing, and bulkheads). We measured selected physical characteristics (shore zone width, exposure, substrate roughness and grain size, shoreline complexity) of three examples of each of these shore types, and also sampled communities of terrestrial plants, fishes, and aquatic and terrestrial invertebrates. Community composition of most taxa differed across shore types, and frequently differed between wide, sheltered shores and narrow, exposed shores. Alien plant species were especially well represented along engineered shores. Nevertheless, a great deal of variation in biological communities was not explained by our six-class categorization of shore zones or the physical variables that we measured. No single shore type supported the highest values of all kinds of biodiversity, but engineered shore zones (especially cribbing and bulkheads) tended to have less desirable biodiversity characteristics than ??natural?? shore zones.  相似文献   

PBDEs, methoxylated PBDEs and HBCDs in Japanese common squid (Todarodes pacificus) from Korean offshore waters     

Gi Beum Kim  Heather M. Stapleton 《Marine pollution bulletin》2010,60(6):935-940

Little information is available on the levels of brominated compounds found in biota from the Korean Peninsula. In this study, Japanese common squids (Todarodes pacificus) were analyzed for 38 polybrominated diphenyl ethers, two methoxylated polybrominated diphenyl ethers and three stereoisomers of hexabromocyclododecane (α, β, and γ-HBCD) from the east and western coasts of the Korean Peninsula. Among 38 PBDEs, 10 PBDEs were detected and their total concentrations ranged from 21 to 292 ng/g lipid wt with a mean concentration of 108 ng/g lipid wt, while two MeO-BDEs and three isomers of HBCDs were detected in all samples. BDE47 showed the highest residual level, followed by BDE99, 154, 153, 28/33. Concentrations of PBDEs and MeO-BDEs were not significantly different between the both sides of the Korean Peninsula; however, HBCD concentrations were higher levels in the East/Japan Sea than the Yellow Sea, indicating that HBCD sources possibly exist in Japan.  相似文献   

Settlement and Recruitment Patterns of the Soft-Shell Clam, <Emphasis Type="Italic">Mya arenaria</Emphasis>, on the Northern Shore of the Bay of Fundy,Canada     

Jenna E. Bowen  Heather L. Hunt 《Estuaries and Coasts》2009,32(4):758-772

To examine the roles of settlement and early postsettlement processes in the recruitment of the soft-shell clam, Mya arenaria, abundance of recent settlers and juveniles was monitored over two field seasons at four locations on the northern shore of the Bay of Fundy in New Brunswick, Canada. Results showed great spatial and temporal variability in patterns of settlement. M. arenaria appeared to become highly vulnerable to postsettlement processes at a shell length of approximately 2 mm. Postsettlement processes drastically altered patterns of settlement less than 1 year after they were established. Results suggest that local factors at specific sites within the Bay of Fundy, such as hydrodynamics, larval behavior, and early postsettlement events, likely control the abundance of juvenile clams. Additionally, postsettlement events are extremely important in shaping M. arenaria populations in this area. Very few mature adult clams greater than 50 mm in shell length were found at any sampling sites, and no relationship was found between abundance of setters and density of juveniles and adults.  相似文献   

Modeling Bedload Transport of Juvenile Bivalves: Predicted Changes in Distribution and Scale of Postlarval Dispersal     

Heather L. Hunt  David C. Fugate  Robert. J. Chant 《Estuaries and Coasts》2009,32(6):1090-1102

The potential consequences of bedload transport of postlarvae for patterns of distribution of marine invertebrates were explored by developing a bedload transport model for juvenile bivalves in a small estuary in New Jersey, USA. A simple numerical model of tidal current hydrodynamics was developed based on field measurements of shear stresses near the bottom. Burrowing behavior of bivalves was incorporated into the model of bedload transport by using estimates of entrainment rates of Gemma gemma and Mya arenaria in a laboratory flume, and jump lengths of the bivalves were estimated by methods previously developed for noncohesive particles. Based on the flood domination and strong gradient of shear stresses in the Navesink estuary, our model predicted that juvenile bivalves would accumulate in the center of the estuary, traveling up to several kilometers over 30 days. Field distributions of juvenile bivalves were consistent with the model predictions for other species of bivalves but not for G. gemma, for which field distributions of both <500- and >500-μm individuals were concentrated in the eastern end of the estuary. Differences between the bedload model and G. gemma distributions suggest that spatial variation in burrowing behavior or biological interactions are playing an important role in maintaining distribution patterns of this species in spite of high levels of bedload transport. This modeling approach is applicable to other juvenile benthic invertebrates that disperse as bedload and is a useful model against which to compare field observations of rates of transport and patterns of distribution and abundance.  相似文献   

Assessment of drought over the past two millennia using near-shore sediment cores from a Canadian boreal lake     

Heather A. Haig  Melanie V. Kingsbury  Kathleen R. Laird  Peter R. Leavitt  Robyn Laing  Brian F. Cumming 《Journal of Paleolimnology》2013,50(2):175-190

Lack of long-term studies on drought in the boreal region of northwest Ontario limits our ability to assess the vulnerability of this region to climate change. We investigated changes in diatoms, scaled chrysophytes, and sedimentary pigments in two near-shore cores from Gall Lake to infer limnological and water-level changes over the last two millennia. The two coring locations, at modern water depths of 7.5 and 11.5 m, were selected to contrast inferences for past lake level based on distance from the modern water-depth boundary between predominantly benthic and planktonic diatom assemblages in surface sediments (6.0 m). Diatom-inferred depth inferences were more variable in the core from 7.5-m water depth, consistent with the hypothesis that the greatest changes occurred at water depths closest to the benthic:planktonic boundary. Both sites revealed a pronounced drought from ~AD 950 to 1300, synchronous with the medieval climate anomaly (MCA). This finding suggests a northeast expansion of the arid MCA into northwest Ontario, extending the known spatial extent of this megadrought. Scaled chrysophytes and sedimentary pigments suggest a recent increase in thermal stratification. Our findings indicate this region is more susceptible to changes in moisture than was previously suspected based on the instrumental record for the past century.  相似文献   

Sixty thousand years of magmatic volatile history before the caldera-forming eruption of Mount Mazama, Crater Lake, Oregon     

Heather Michelle Wright  Charles R. Bacon  Jorge A. Vazquez  Thomas W. Sisson 《Contributions to Mineralogy and Petrology》2012,164(6):1027-1052

The well-documented eruptive history of Mount Mazama, Oregon, provides an excellent opportunity to use pre-eruptive volatile concentrations to study the growth of an explosive silicic magmatic system. Melt inclusions (MI) hosted in pyroxene and plagioclase crystals from eight dacitic–rhyodacitic eruptive deposits (71–7.7?ka) were analyzed to determine variations in volatile-element concentrations and changes in magma storage conditions leading up to and including the climactic eruption of Crater Lake caldera. Temperatures (Fe–Ti oxides) increased through the series of dacites, then decreased, and increased again through the rhyodacites (918–968 to ~950 to 845–895?°C). Oxygen fugacity began at nickel–nickel-oxide buffer (NNO) +0.8 (71?ka), dropped slightly to NNO +0.3, and then climbed to its highest value with the climactic eruption (7.7?ka) at NNO +1.1 log units. In parallel with oxidation state, maximum MI sulfur concentrations were high early in the eruptive sequence (~500?ppm), decreased (to ~200?ppm), and then increased again with the climactic eruption (~500?ppm). Maximum MI sulfur correlates with the Sr content (as a proxy for LREE, Ba, Rb, P₂O₅) of recharge magmas, represented by basaltic andesitic to andesitic enclaves and similar-aged lavas. These results suggest that oxidized Sr-rich recharge magmas dominated early and late in the development of the pre-climactic dacite–rhyodacite system. Dissolved H₂O concentrations in MI do not, however, correlate with these changes in dominant recharge magma, instead recording vapor solubility relations in the developing shallow magma storage and conduit region. Dissolved H₂O concentrations form two populations through time: the first at 3–4.6 wt% (with a few extreme values up to 6.1 wt%) and the second at ≤2.4 wt%. CO₂ concentrations measured in a subset of these inclusions reach up to 240?ppm in early-erupted deposits (71?ka) and are below detection in climactic deposits (7.7?ka). Combined H₂O and CO₂ concentrations and solubility models indicate a dominant storage region at 4–7?km (up to 12?km), with drier inclusions that diffusively re-equilibrated and/or were trapped at shallower depths. Boron and Cl (except in the climactic deposit) largely remained in the melt, suggesting vapor–melt partition coefficients and gas fractions were low. Modeled Li, F, and S vapor–melt partition coefficients are higher than those of B and Cl. The decrease in maximum MI CO₂ concentration following the earliest dacitic eruptions is interpreted to result from a broadening of the shallow storage region to greater than the diameter of subjacent feeders, so that greater proportions of reservoir magma were to the side of CO₂-bearing vapor bubbles ascending vertically from the locus of recharge magma injection, thereby escaping recarbonation by streaming vapor bubbles. The Mazama melt inclusions provide a picture of a growing magma storage region, where chemical variations in melt and magma occur due to changes in the nature and supply rate of magma recharge, the timing of degassing, and the possible degree of equilibration with gases from below.  相似文献   

Rapid magmatic processes accompany arc–continent collision: the Western Bismarck arc, Papua New Guinea     

Heather Cunningham  Jim Gill  Simon Turner  John Caulfield  Louise Edwards  Simon Day 《Contributions to Mineralogy and Petrology》2012,164(5):789-804

New U–Th–Ra, major and trace element, and Sr–Nd–Pb isotope data are presented for young lavas from the New Britain and Western Bismarck arcs in Papua New Guinea. New Britain is an oceanic arc, whereas the latter is the site of an arc–continent collision. Building on a recent study of the Manus Basin, contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc–continent collision and possible slab detachment. All three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle. However, the Western Bismarck arc lavas diverge from the Pb isotope mixing array formed by the New Britain and the Manus Basin lavas toward elevated ²⁰⁸Pb/²⁰⁴Pb. We interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision. ²³⁸U and ²²⁶Ra excesses are preserved in all of the lavas and are greatest in the Western Bismarck arc. High-Mg andesites with high Sr/Y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge. Data for two historical rhyolites are also presented. Although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions, both formed from mafic parents within millennia.  相似文献