Further considerations on combining earth rotation observations from different space geodetic systems     

Brent A. Archinal  Ivan I. Mueller 《Journal of Geodesy》1989,63(1):35-49

Additional results are presented concerning a study that consider improvements over present Earth Rotation Parameter (ERP) determination methods by directly combining observations from various space geodetic systems in one adjustment. Earlier results are extended, showing that in addition to slight improvements in accuracy substantial (a factor of three or more) improvements in precision and significant reductions in correlations between various parameters can be obtained (by combining Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR) to Lageos, and Very Long Baseline Interferometry (VLBI) data in one adjustment) as compared to results from individual systems. Smaller improvements are also seen over the weighted means of the individual system results. Although data transmission would not be significantly reduced, negligible additional computer time would be required if (standardized) normal equations were available from individual solutions. Suggestions for future work and implications for the new International Earth Rotation Service (IERS) are also presented.  相似文献   

Time-based correlation of biogenic,lithogenic and authigenic sediment components with anthropogenic inputs in the Gulf of Mexico NECOP study area     

Terry A. Nelsen  Pat Blackwelder  Terri Hood  Brent McKee  Nidia Romer  Carlos Alvarez-Zarikian  Simone Metz 《Estuaries and Coasts》1994,17(4):873-885

Hypotheses related to variability in seasonal hypoxic conditions, coastal nutrient enhancement, and off-shelf transport of carbon on the Louisiana continental shelf were tested by characterization of biogenic, lithogenic, and authigenic components from two shelf and one Mississippi Canyon sediment cores. The authigenic-phase glauconite occurs above detection limits only in the core from the hypoxic area. A major increase in glauconite concentration was coincident with the onset (≈1940) of the increased use of commercial fertilizers in the United States. In the same hypoxic-area core, benthic foraminifera species diversity decreases upcore from approximately the turn of the century to the present in a manner concurrent with glauconite and fertilizer increases. A subset of opportunistic benthic foraminifera species, known to become more prominent in stressed environments (i.e., hypoxic), increased upcore from ～52% of the total population at core bottom to ≈90% at core top. These benthic foraminifera population and diversity changes were not apparent in a “control” core outside the area of documented hypoxia. Seaward of the shelf, in the Mississippi Canyon, coincident increases in sediment accumulation rate, percentages of coarse fraction and of organic carbon at core top indicate increased offshelf transport of carbon and other components. Quartz percentages indicate that episodic down-canyon transport has been active to core bottom (prior to the mid 1800s).  相似文献   

An assessment of women’s access to natural resources through communal projects in South Africa     

Brent McCusker  Ann M. Oberhauser 《GeoJournal》2006,66(4):325-339

With the passing of the apartheid regime and its multi-faceted mechanisms of exclusion, women in rural South Africa have begun expanding their access to natural resources for livelihood enhancement. One of the ways this has occurred is through community-based organizations that focus on local production as a mechanism to transform natural resources into material goods. While this practice is nearly ubiquitous throughout sub-Saharan Africa, the apartheid regime was particularly effective in limiting access to natural resources, a phenomenon reversed by the current democratic government. In this paper, we assess the impact of organizational design on women’s livelihood systems as a means of alleviating rural poverty. We surveyed women on both more formal, or bureaucratic, organizations and more informal, or socially-embedded, organizations. After locating the discussion in the relevant gender, environment, and livelihoods literatures, we employ four concepts, organizational context, environmental entitlement, livelihood systems, and gender and power relations to assess the impact of organizational design on livelihood enhancement. Having found that women derived no significant material benefit from participation in either type of organization, we conclude that women are straddling two processes, neo-liberalization and neo-traditionalism, that impact gender and power relations. This situation has left women in vulnerable positions within their organizations and with little livelihood enhancement.  相似文献   

Biogeochemical reactive–diffusive transport of heavy metals in Lake Coeur d’Alene sediments     

S. Sevin engr  Nicolas F. Spycher  Timothy R. Ginn  Rajesh K. Sani  Brent Peyton 《Applied Geochemistry》2007,22(12):2569-2594

Decades of runoff from precious-metal mining operations in the Lake Coeur d’Alene Basin, Idaho, have left the sediments in this lake heavily enriched with toxic metals, most notably Zn, Pb and Cu, together with As. The bioavailability, fate and transport of these metals in the sediments are governed by complex biogeochemical processes. In particular, indigenous microbes are capable of catalyzing reactions that detoxify their environments, and thus constitute an important driving component in the biogeochemical cycling of these metals. Here, the development of a quantitative model to evaluate the transport and fate of Zn, Pb and Cu in Lake Coeur d’Alene sediments is reported. The current focus is on the investigation and understanding of local-scale processes, rather than the larger-scale dynamics of sedimentation and diagenesis, with particular emphasis on metal transport through reductive dissolution of Fe hydroxides. The model includes 1-D inorganic diffusive transport coupled to a biotic reaction network including consortium biodegradation kinetics with multiple terminal electron acceptors and syntrophic consortium biotransformation dynamics of redox front. The model captures the mobilization of metals initially sorbed onto hydrous ferric oxides, through bacterial reduction of Fe(III) near the top of the sediment column, coupled with the precipitation of metal sulfides at depth due to biogenic sulfide production. Key chemical reactions involve the dissolution of ferrihydrite and precipitation of siderite and Fe sulfide. The relative rates of these reactions play an important role in the evolution of the sediment pore-water chemistry, notably pH, and directly depend on the relative activity of Fe and SO₄ reducers. The model captures fairly well the observed trends of increased alkalinity, sulfide, Fe and heavy metal concentrations below the sediment–water interface, together with decreasing terminal electron acceptor concentrations with depth, including the development of anoxic conditions within about a centimeter below the lake bottom. This effort provides insights on important biogeochemical processes affecting the cycling of metals in Lake Coeur d’Alene and similar metal-impacted lacustrine environments.  相似文献   

Evidence for a 55-50 ka (early Wisconsin) glaciation of the Cordilleran ice sheet, Yukon Territory, Canada     

Brent C. Ward  Jeffrey D. Bond 《Quaternary Research》2007,68(1):141-150

Cosmogenic ¹⁰Be ages on boulders of 54-51 ka (n = 4) on a penultimate Cordilleran ice sheet (CIS) drift confirm that Marine Oxygen Isotope Stage (MIS) 4 (early Wisconsin) glaciation was extensive in parts of Yukon Territory, the first confirmed evidence in the Canadian Cordillera. We name the glaciation inferred from the mapped and dated drift the Gladstone. These results are in apparent contrast to the MIS 6 (Illinoian) age of the penultimate Reid glaciation to the east in central Yukon but are equivalent to exposure ages on MIS 4 drift in Alaska. Contrasting penultimate ice extents in Yukon requires that different source areas of the northern CIS in Yukon responded differently to climatic forcing during glaciations. The variation in glacier extent for different source areas likely relates to variation in precipitation during glaciation, as the northern CIS was a precipitation-limited system. Causes for a variation in precipitation remain unclear but likely involve the style of precipitation delivery over the St. Elias Mountains possibly related to variations in the Aleutian low.  相似文献   

Effects of Hypoxia on Fish Survival and Oyster Growth in a Highly Eutrophic Estuary     

Rikke Jeppesen  Miguel Rodriguez  Jenna Rinde  John Haskins  Brent Hughes  Laura Mehner  Kerstin Wasson 《Estuaries and Coasts》2018,41(1):89-98

Human land use activities around estuaries can result in high levels of eutrophication. At Elkhorn Slough estuary, a highly eutrophic California estuary, we investigated the effects of impaired water quality on two stress-tolerant estuarine species, a common fish, the staghorn sculpin, Leptocottus armatus and a foundational invertebrate, the Olympia oyster, Ostrea lurida. We caged the two indicator species at six wetlands with different levels of water quality impairment, four of which had restricted tidal flow. We also recorded water quality parameters simultaneously at all sites using YSI sondes, and sampled nutrients and chlorophyll-a monthly, building on the National Estuarine Research Reserve System-wide Monitoring Program. We found that the monitored environmental variables predicted ecological responses by the indicator species. In particular, we found that the duration and severity of hypoxia were negatively correlated with fish survival and oyster growth. Further, our results corroborate previous studies that artificial tidal restriction leads to increased hypoxia stress. We conclude that large diurnal fluctuations in dissolved oxygen and extended nighttime hypoxia can have lethal and sub-lethal effects even on stress-tolerant organisms in the estuary. While laboratory experiments have often shown such effects, it is relatively rare to demonstrate negative effects of oxygen variation with in situ experiments, which provide stakeholders with concrete evidence for impaired water quality at local wetlands. Tidally restricted sites, which experience the largest fluctuations in dissolved oxygen and longest periods of hypoxia, harbor conditions harmful to vertebrates and invertebrates in the estuary. Reversing the anthropogenically induced low oxygen levels, by restoring more natural tidal exchange and by decreasing agricultural runoff, could improve the survival and growth of important estuarine organisms.  相似文献   

“The Coast” is Complicated: A Model to Consistently Describe the Nation’s Coastal Population     

Brent W. Ache  Kristen M. Crossett  Percy A. Pacheco  Jeffery E. Adkins  Peter C. Wiley 《Estuaries and Coasts》2015,38(1):151-155

Our nation’s coast is a complicated management area where no single delineation provides all of the demographic statistics needed to address the full range of policy and management issues. As a result, several different coastal delineations are currently being used, yielding a variety of US coastal population statistics. This paper proposes a simple model for generating and applying coastal population statistics at the national and regional level to increase consistency in coastal policy discussions and improve public understanding of coastal issues. The model includes two major components. The first component is “the population that most directly affects the coast,” represented by the permanent US population that resides in a standard suite of Coastal Watershed Counties, where land use and water quality changes most directly impact coastal ecosystems. The second component is “the population most directly affected by the coast,” represented by the permanent US population that resides in a standard suite of Coastal Shoreline Counties that are directly adjacent to the open ocean, major estuaries, and the Great Lakes, which due to their proximity to these waters, bear a great proportion of the full range of effects from coastal hazards and host the majority of economic production associated with coastal and ocean resources.  相似文献   

Reconstruction of the history of the Palliser Rockslide based on 36Cl terrestrial cosmogenic nuclide dating and debris volume estimations     

Matthieu Sturzenegger  Doug Stead  John Gosse  Brent Ward  Corey Froese 《Landslides》2015,12(6):1097-1106

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Evaluation of the use of a commercially available cavity ringdown absorption spectrometer for measuring NO2 in flight,and observations over the Mid-Atlantic States,during DISCOVER-AQ     

L. C. Brent  W. J. Thorn  M. Gupta  B. Leen  J. W. Stehr  H. He  H. L. Arkinson  A. Weinheimer  C. Garland  S. E. Pusede  P. J. Wooldridge  R. C. Cohen  R. R. Dickerson 《Journal of Atmospheric Chemistry》2015,72(3-4):503-521

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Governing geoengineering research for the Great Barrier Reef     

Jan McDonald  Jeffrey McGee  Kerryn Brent  Wil Burns 《Climate Policy》2019,19(7):801-811

Coral reefs are highly vulnerable to the impacts of rising marine temperatures and marine heatwaves. Mitigating dangerous climate change is essential and urgent, but many reef systems are already suffering on current levels of warming. Geoengineering options are worth exploring to protect the Great Barrier Reef (GBR) from extreme warming conditions, but we contend that they require strong governance and public consultation from the outset. Australian governments are currently funding feasibility testing of three geoengineering proposals for the GBR. Each proposal involves manipulating ocean or atmospheric conditions to lower water temperatures and thereby reduce the threat of mass coral bleaching events. Innovative strategies to protect the GBR and field testing of these is essential, but current laws do not guarantee robust governance for field testing of these technologies. Nor do they provide the foundation for a more coherent national policy on climate intervention technologies more generally. Responsible governance frameworks, including detailed risk assessment and early public consultation, are necessary for geoengineering research to build legitimacy and promote scientific progress.

Key policy insights

• Marine heatwaves pose a serious threat to coral reefs, including Australia’s iconic Great Barrier Reef.

• Australian governments have recognized the threats of warming waters, and are funding research of geoengineering options for the Great Barrier Reef.

• The limited earlier field testing of geoengineering demonstrates the need for specific governance to manage risks, build legitimacy and maintain public support.

• Australia requires a framework to govern geoengineering research and development before deployment of such technologies.

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