Modelled and measured concentrations of peroxy radicals and nitrate radical in the U.S. Gulf Coast region during TexAQS 2006     

Roberto Sommariva  Tim S. Bates  Daniel Bon  Daniel M. Brookes  Joost A. de Gouw  Jessica B. Gilman  Scott C. Herndon  William C. Kuster  Brian M. Lerner  Paul S. Monks  Hans D. Osthoff  Alex E. Parker  James M. Roberts  Sara C. Tucker  Carsten Warneke  Eric J. Williams  Mark S. Zahniser  Steven S. Brown 《Journal of Atmospheric Chemistry》2011,68(4):331-362

Measurements of total peroxy radicals (HO₂?+?RO₂) and nitrate radical (NO₃) were made on the NOAA research vessel R/V?Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO₂?+?RO₂ was typically within ??40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO₃ by 60?C70%, possibly because of rapid heterogeneous uptake of N₂O₅. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO₂ in the different regions. The measurements of HO₂?+?RO₂ and NO₃ were also used to calculate the gas-phase budget of NO₃ and quantify the importance of organic peroxy radicals as NO₃ sinks. RO₂ accounted, on average, for 12?C28% of the total gas-phase NO₃ losses in the unpolluted regions and for 1?C2% of the total gas-phase NO₃ losses in the polluted regions.  相似文献   

Aftershock Distribution as a Constraint on the Geodetic Model of Coseismic Slip for the 2004 Parkfield Earthquake     

Ninfa Bennington  Clifford Thurber  Kurt L. Feigl  Jessica Murray-Moraleda 《Pure and Applied Geophysics》2011,168(10):1553-1565

Several studies of the 2004 Parkfield earthquake have linked the spatial distribution of the event’s aftershocks to the mainshock slip distribution on the fault. Using geodetic data, we find a model of coseismic slip for the 2004 Parkfield earthquake with the constraint that the edges of coseismic slip patches align with aftershocks. The constraint is applied by encouraging the curvature of coseismic slip in each model cell to be equal to the negative of the curvature of seismicity density. The large patch of peak slip about 15 km northwest of the 2004 hypocenter found in the curvature-constrained model is in good agreement in location and amplitude with previous geodetic studies and the majority of strong motion studies. The curvature-constrained solution shows slip primarily between aftershock “streaks” with the continuation of moderate levels of slip to the southeast. These observations are in good agreement with strong motion studies, but inconsistent with the majority of published geodetic slip models. Southeast of the 2004 hypocenter, a patch of peak slip observed in strong motion studies is absent from our curvature-constrained model, but the available GPS data do not resolve slip in this region. We conclude that the geodetic slip model constrained by the aftershock distribution fits the geodetic data quite well and that inconsistencies between models derived from seismic and geodetic data can be attributed largely to resolution issues.  相似文献   

Organic sources and carbon sequestration in Holocene shelf sediments from the western Arctic Ocean     

Jessica F. FauxLaura L. Belicka  H. Rodger Harvey 《Continental Shelf Research》2011,31(11):1169-1179

To quantify changes in organic carbon inputs and preservation, sediments from the Northern Chukchi Sea spanning the last 9000 years of the Holocene period were collected during the HOTRAX expedition and analyzed. The multi-proxy approach included molecular organic markers, bulk carbon and isotope measurements plus more recent approaches to terrestrial carbon estimation (the BIT index of Branched and Isoprenoid Tetraethers). The upper 1100 cm of the core, corresponding to the last 7.4 ka, showed a relatively stable total organic carbon content of 1.13-1.38% which decreased below 1100 cm to 0.6%. C:N ratios ranged from 8.4 to 10.83 over the Holocene time period examined. The distribution of n-alcohols and n-alkanes revealed major contributions from long-chain n-alcohols and n-alkanes while minimal contributions were seen from short-chain n-alkanes. The majority of the total fatty acids was comprised of saturated and monounsaturated fatty acids with short-chain and long-chain saturated fatty acids present in similar concentrations throughout most of the core and monounsaturated fatty acids decreasing down-core. Total sterol concentrations showed considerable inputs from marine sterols, C₂₈Δ^5,22, C₂₈Δ^5,24(28) and dinosterol, as well as C₂₉Δ⁵, typically considered a terrestrial marker. The BIT indices for core sediments ranged from 0.021 to 0.216 with minor changes seen in older sequences. Overall, organic biomarkers indicate marine sources as the more dominant input of organic matter with lower but continual contributions from terrestrial sources at this location during the Holocene. The remarkable consistency among multiple molecular organic markers of both marine and terrestrial origin over the Holocene period encompassed by the core suggests that sinking material or surface sediments were heavily influenced by bottom currents or other mixing processes prior to their deposition.  相似文献   

Origin of uranium deposits revealed by their rare earth element signature   总被引：3，自引：0，他引：3  

Julien Mercadier  Michel Cuney  Philippe Lach  Marie‐Christine Boiron  Jessica Bonhoure  Antonin Richard  Mathieu Leisen  Philippe Kister 《地学学报》2011,23(4):264-269

  相似文献   

The Politics of Nature in British Columbia’s Great Bear Rainforest     

Jessica Dempsey 《Geoforum》2011,42(2):211-221

Environmental politics, argues French philosopher Bruno Latour, have been a ‘disappointment’. Rather than trying to bring environmental concerns into a political world split into two - between Nature/Science and politics/society - Latour argues that environmental movements ought to focus on destroying this two-house collective, and develop ‘an understanding of ecological crises that no longer uses nature to account for the tasks to be accomplished’. In this paper I put my research on the politics and science of the Great Bear Rainforest (GBR), a large tract of temperate rainforest on the central and north coast of British Columbia, into direct conversation with Latour’s arguments about science, epistemology and environmental politics. The GBR was a site of intense political struggle focused predominantly on the scale and scope of industrial forestry, a struggle which ‘ended’ in 2006 with what some call a historic compromise between some high-profile environmental groups, First Nations, the Provincial government, and the forest industry. This paper focuses on two interlinked questions: do the environmental organizations at the centre of the struggle demonstrate the maladies identified by Latour; are they too preoccupied with representing Nature through Science? And second, do these maladies help us explain or understand the politics over the GBR? Were the politics of the GBR limited by environmentalist invocations of a singular Nature through Science, what Latour calls ‘Naturpolitik’? The encounter between theory and practice leads to a more cautious and critical assessment of the environmental politics in the GBR, but also tempers Latour’s arguments. Environmentalists in the GBR do exhibit Latour’s maladies, but in tracing the Politics of Nature there, it seems that Naturpolitik is not as powerful as Latour argues.  相似文献   

Characteristics of a Shallow River Plume: Observations from the Saco River Coastal Observing System     

Charles E. Tilburg  Shaun M. Gill  Stephan I. Zeeman  Amy E. Carlson  Timothy W. Arienti  Jessica A. Eickhorst  Philip O. Yund 《Estuaries and Coasts》2011,34(4):785-799

Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge (thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing, and the geography of the coastline and adjacent islands.  相似文献   

A Comparison of Awareness,Attitudes, and Usage of Water Quality Conservation Practices Between Amish and Non-Amish Farmers     

Jessica D. Ulrich-Schad  Caroline Brock  Linda S. Prokopy 《社会与自然资源》2017,30(12):1476-1490

This study provides a unique examination of Amish farmers’ awareness of water quality issues and their attitudes toward and use of agricultural conservation practices compared with small non-Amish farmers in Northeastern Indiana. There is minimal research about the conservation beliefs and behaviors of this growing and highly diverse ethnoreligious minority, who have faith-based technological restrictions and are often hesitant to work with community outsiders, especially the government. We find that, compared with non-Amish farmers, Amish farmers have limited awareness of the linkages between common agricultural practices and broader water quality problems and lower levels of adoption of conservation practices, with the exception of cover crops. This information is essential for conservation practitioners who need to work with a diverse range of agricultural producers to increase the uptake of conservation practices that address critical water quality concerns.  相似文献   

Changing Course: Comparing Emerging Watershed Institutions in River Restoration Contexts     

Eileen S. Johnson  Kathleen P. Bell  Jessica E. Leahy 《社会与自然资源》2017,30(6):765-781

How watershed collaborations adapt to changing conditions is an enduring question in collaborative resource management. Our research examined the goals and structure of collaborations within watersheds subject to the same federal and state regulations, but at different restoration states. We employed semistructured interviews, document analysis, and participant observation to complete our qualitative research. Our results suggest that policy stakeholders’ understandings of ecological and social attributes influence watershed goals. Within the impaired system, collaborations invested in shifting public perception to engender support for longer term biophysical restoration. Within the restored watershed, collaborations achieved dramatic biophysical improvements but were challenged in addressing social benefits of restoration. Redefining restoration to incorporate social and ecological systems at the outset provides the opportunity to set benchmarks for measuring success that incorporate social and ecological factors, and to create institutions adept at responding to shifting restoration states.  相似文献   

Response to comment on “The suburban bias of American society?”     

William B. Meyer  Jessica K. Graybill 《Urban geography》2017,38(2):170-173

  相似文献   

Experimental phase relations of a low MgO Aleutian basaltic andesite at XH2O = 0.7–1     

Erika L. Rader  Jessica F. Larsen 《Contributions to Mineralogy and Petrology》2013,166(6):1593-1611

We conducted melting experiments on a low MgO (3.29 wt.%) basaltic andesite (54.63 wt.% SiO₂) from Westdahl volcano, Alaska, at XH₂O = 0.7–1 and fO₂ ~ Ni–NiO, at pressures = 0.1–180 MPa and temperatures = 900–1,200 °C. We examine the evolution of the melt along a liquid line of descent during equilibrium crystallization at high H₂O and fO₂ conditions, starting from a high FeOt/MgO, low MgO basaltic andesite. Ti-magnetite formed on the liquidus regardless of XH₂O, followed by clinopyroxene, plagioclase, amphibole, and orthopyroxene. We observe slight but significant differences in the phase stability curves between the XH₂O = 1 and 0.7 experiments. Early crystallization of Ti-magnetite and suppression of plagioclase at higher pressures and temperatures resulted in strongly decreasing melt FeOt/MgO with increasing SiO₂, consistent with a “calc-alkaline” compositional trend, in agreement with prior phase equilibria studies on basalt at similar H₂O and fO₂. Our study helps quantify the impact of small amounts of CO₂ and high fO₂ on the evolution of melts formed during crystallization of a low MgO basaltic andesite magma stored at mid- to shallow crustal conditions. Like the prior studies, we conclude that H₂O strongly influences melt evolution trends, through stabilization of Ti-magnetite on the liquidus and suppression of plagioclase at high P–T conditions.  相似文献