Freshwater export from the Labrador Current to the North Atlantic Current at the Tail of the Grand Banks of Newfoundland     

Paula S. Fratantoni  Michael S. McCartney 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):258-283

Historical hydrographic data, spanning the period 1896–2006, are used to examine the annual mean and seasonal variations in the distribution of freshwater along and across the shelf/slope boundary along the Labrador and Newfoundland Shelves and the Grand Banks of Newfoundland. Particular attention is paid to the export of freshwater along the eastern Grand Banks, between Flemish Cap and the Tail of the Grand Banks, as this has long been identified as a preferential region for the loss of mass and freshwater from the boundary. The data are combined into isopycnally averaged long-term annual and monthly mean gridded property fields and the evolving distribution of fresh arctic-origin water is analyzed in fields of salinity anomaly, expressed as departures from the “central water” temperature–salinity relation of the Gulf Stream. The climatology confirms that cold/fresh northern-source waters are advected offshore within the retroflecting Labrador Current along the full length of the boundary between Flemish Cap and the Tail of the Grand Banks. In fact, it is estimated that most of the equatorward baroclinic transport at the boundary must retroflect back toward the north in order to explain the annual mean distribution of salinity in the climatology. While the retroflection of the Labrador Current appears seasonally robust, the freshwater distribution within the retroflection region varies in response to (1) the freshness of the water available for export which is set by the arrival and rapid flushing of the seasonal freshwater pulse at the boundary, (2) seasonal buoyancy forcing at the surface which alters the vertical stratification across the retroflection region, restricting certain isopycnal export pathways, and (3) the density structure along the eastern Grand Banks, which defines the progressive retroflection of the Labrador Current.  相似文献   

Climatic Influences on Autochthonous and Allochthonous Phytoplankton Blooms in a Subtropical Estuary, St. Lucie Estuary, Florida, USA     

Edward J. Phlips  Susan Badylak  Jane Hart  Daniel Haunert  Jean Lockwood  Kathyrn O’Donnell  Detong Sun  Paula Viveros  Mete Yilmaz 《Estuaries and Coasts》2012,35(1):335-352

The St. Lucie Estuary, located on the southeast coast of Florida, provides an example of a subtropical ecosystem where seasonal changes in temperature are modest, but summer storms alter rainfall regimes and external inputs to the estuary from the watershed and Atlantic Ocean. The focus of this study was the response of the phytoplankton community to spatial and temporal shifts in salinity, nutrient concentration, watershed discharges, and water residence times, within the context of temporal patterns in rainfall. From a temporal perspective, both drought and flood conditions negatively impacted phytoplankton biomass potential. Prolonged drought periods were associated with reduced nutrient loads and phytoplankton inputs from the watershed and increased influence of water exchange with the Atlantic Ocean, all of which restrict biomass potential. Conversely, under flood conditions, nutrient loads were elevated, but high freshwater flushing rates in the estuary diminished water residence times and increase salinity variation, thereby restricting the buildup of phytoplankton biomass. An exception to the latter pattern was a large incursion of a cyanobacteria bloom from Lake Okeechobee via the St. Lucie Canal observed in the summer of 2005. From a spatial perspective, regional differences in water residence times, sources of watershed inputs, and the proximity to the Atlantic Ocean influenced the composition and biomass of the phytoplankton community. Long water residence times in the North Fork region of the St. Lucie Estuary provided an environment conducive to the development of blooms of autochthonous origin. Conversely, shorter residence times in the mid-estuary limit autochthonous increases in biomass, but allochthonous sources of biomass can result in bloom concentrations of phytoplankton.  相似文献   

Global tsunami deposits database     

Paula Dunbar  Heather McCullough 《Natural Hazards》2012,63(1):267-278

The National Geophysical Data Center and co-located World Data Center for Geophysics and Marine Geology provide integrated access to historical tsunami event, deposit, and proxy data. Historical events are important for understanding the frequency and intensity of relatively recent tsunamis. Deposit data collected during post-tsunami field surveys provide information on tsunami erosion, sedimentation, flow depths, inundation, and run-up. Deposit data from prehistoric tsunami events extend the record to pre-recorded times, constrain tsunami recurrence intervals, and estimate the minimum magnitude of tsunami inundation. Proxies indicate that an event capable of producing a tsunami occurred, but are not direct evidence of a tsunami. All of these data are used to develop tsunami hazard assessments, provide guidance to warning centers, validate models, inform community preparedness efforts, and educate the public about tsunami risks.  相似文献   

Experimental investigation of shock metamorphic effects in a metapelitic granulite: The importance of shock impedance contrast between components     

Paula OGILVIE  Roger L. GIBSON  W. Uwe REIMOLD  Alexander DEUTSCH  Ulrich HORNEMANN 《Meteoritics & planetary science》2011,46(10):1565-1586

Shock recovery experiments were performed at 12.5, 25, 34, 40, and 56 GPa at 25 °C, and at 18 and 25 GPa at 400 °C, on a high‐grade, migmatitic, garnet‐cordierite metapelite from the Etivé aureole, Scotland. Objectives for this study were to (1) characterize shock effects in a complex polymineralic rock with a significant proportion of hydrous ferromagnesian minerals, both as a function of variable shock pressure and preshock temperature, and (2) to explore the effects of shock impedance contrast between component minerals on the respective abundances and distribution of these features. At any shock pressure, the order of decreasing intensity of shock metamorphic effects in component phases is: cordierite (Crd)→biotite (Bt)→plagioclase (Pl)→K‐feldspar (Kfs)→quartz (Qtz)→garnet (Grt)→orthopyroxene (Opx). Samples shocked to pressures below 40 GPa (25 °C) were typically characterized by marked heterogeneous distribution of shock effects on both intragranular and intergranular scales. Shock heterogeneity is mainly attributed to shock impedance contrast between contiguous phases, and manifests as shock amplification locally where shock impedance contrast is greatest, and shock suppression where impedance contrast is least. The heterogeneous distribution of shock metamorphic effects in both experiments and natural rocks is a signature of extreme disequilibrium at the submillimeter scale. The heterogeneous distribution of shock metamorphic effects mitigates against the use of shock effects in minerals exclusively as regional shock pressure barometers, and ought to be augmented by additional constraints on shock pressure from numerical models.  相似文献   

Conjugated asymmetry of the onset and magnitude of GPS scintillation driven by the vertical plasma drift     

Sousasantos  J.  Abdu  M. A.  de Paula  E. R.  Moraes  A. O.  Salles  L. A.  Affonso  B. J. 《GPS Solutions》2022,26(3):1-9

Traditional intersatellite communications for shared timing information rely on microwave transceivers such as those in Milstar, AEHF, and Iridium constellations. With extensive space heritage and well-established engineering and performance specifications, these methods have typified the field of high-performance satellite synchronization for decades, recently introduced into active GNSS satellite constellations such as BeiDou. Optical crosslinks, currently investigated as an augmentation or alternative to traditional microwave-based methods, can provide enhanced precision to intersatellite ranging and time transfer, performing beyond one-way or uplink/downlink microwave-based communications. The challenges of time transfer through optical links and crosslinks can significantly impact the systems architecture, optical terminal complexity, and agreements on international standards. Orders-of-magnitude precision enhancement can enable novel timing and ranging technologies allowing for advanced navigation capabilities. Additionally, basic scientific studies with a fleet of synchronized satellites could inform fundamental physics studies on a truly global scale. We evaluate the benefits, drawbacks, and potential applications of satellite synchronization through microwave and optical crosslinks for shared timing and ephemeris data in support of enhanced constellation state estimation and reduced range error. The risks and value associated with these technologies are also discussed with an emphasis on challenges for aerospace.

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Evidence for progressive Holocene aridification in southern Africa recorded in Namibian hyrax middens: Implications for African Monsoon dynamics and the ‘‘African Humid Period’’     

Brian M. Chase  Michael E. Meadows  Paula J. Reimer 《Quaternary Research》2010,74(1):36-45

Presented here are stable nitrogen isotope data from a rock hyrax (Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at ca. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the ‘African Humid Period’ (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low-latitude insolation forcing, which requires an anti-phase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low-latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics.  相似文献   

The preservation of fossil biomarkers during meteorite impact events: Experimental evidence from biomarker‐rich projectiles and target rocks     

John PARNELL  Stephen BOWDEN  Paula LINDGREN  Mark BURCHELL  Daniel MILNER  Mark PRICE  Emily C. BALDWIN  Ian A. CRAWFORD 《Meteoritics & planetary science》2010,45(8):1340-1358

Abstract– A Devonian siltstone from Orkney, Scotland, shows survival of biomarkers in high‐velocity impact experiments. The biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5–6 km s^?1, and in projectile fragments from impact experiments into sand and water at 2–5 km s^?1. The associated peak shock pressures were calculated to be in the range of 110–147 GPa for impacts of the steel projectiles into the siltstone target, and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles. Thermally sensitive biomarker ratios, including ratios of hopanoids and steranes, and the methylphenanthrene ratio, showed an increase in thermal maturity in the ejecta, and especially the projectile, fragments. Measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction. Their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts, and that experiments using biomarker‐rich rock have high potential for testing survival of organic matter in a range of impact scenarios.  相似文献   

FPGA computation of the 3D heat equation     

Fernando Pardo  Paula López  Diego Cabello  Marco Balsi 《Computational Geosciences》2010,14(4):649-664

Efficient solution of the heat equation is one of the recursive topics in computational physics. Over the years, different software solutions have been proposed, taking advantage of today’s impressive computing power of parallel machines. In this work, we consider a hybrid software–hardware approach making use of a field-programmable gate array platform as a heat equation solver that can be easily attached to a PC using a PCI bus with the goal of obtaining a portable system to be used during field experiments. The system has been successfully used for the non-destructive inspection of soils in mine detection applications based on infrared thermography techniques.  相似文献   

Long-Term Trends in Intertidal and Subtidal Benthic Communities in Response to Water Quality Improvement Measures     

Paula Chainho  Gilda Silva  Michael F. Lane  José L. Costa  Tadeu Pereira  Carla Azeda  Pedro R. Almeida  Inês Metelo  Maria J. Costa 《Estuaries and Coasts》2010,33(6):1314-1326

Long-term monitoring studies are needed to understand changes in ecosystem status when restoration measures are implemented. A long-term data series (1996–2007) of the Tagus estuary (Portugal) intertidal and subtidal benthic communities was collected in a degraded area where mitigation measures were implemented. Multivariate analysis was used to analyze spatial and temporal patterns in benthic community composition and trends in five benthic community metrics (i.e., taxonomic richness, density, biomass, Shannon–Wiener diversity and the AMBI index) were also examined. The results revealed a clear separation between intertidal and subtidal assemblages, although they had 50% of taxa in common, including the most abundant. Significant positive trends were found for all metrics showing that both intertidal and subtidal communities responded to the restoration measures implemented. Nevertheless, biotic indices need some adaptation before being universally applied to intertidal and subtidal habitats.  相似文献   

Straw Blankets Sewn With Recycled Plastic Threads for Erosion and Urban Sediments Control     

Terezinha Cássia de Brito Galvão  Aloisio Rodrigues Pereira  Arnaldo Teixeira Coelho  Paula Rodrigues Pereira  Joaquim Fernandes Teixeira Coelho 《Geotechnical and Geological Engineering》2011,29(1):49-55

Soil erosion, transport and deposition of sediments represent invisible threats that along time can affect negatively the existing infrastructure of roads and dams, and the quality of air and water resources. In the last decades, a great number of researches were devoted to study erosion and sediments transportation processes. However, they addressed mostly areas of agriculture, water impoundments for dams, and land conservation. A lack of studies for erosion processes in urban areas is evident, in special those aiming to diminish the deposition of sediments originated from urban areas into the rivers and air, in special as airborne particulate. Traditionally, the costs associated in controlling erosion and sediments in urban areas are high and in some case, out of the range for most developing countries. Factors responsible for those high prices are the use of heavy equipments for soil grading and transportation, the use of costly building materials, and the need for employing more specialized personnel. In the case of gullies in urban areas, another concern is to ensure proper equipment access to the area for remediation operations. Hereby, it is presented a cost-effective method to recover an extensive gully erosion area of about 11,000 m² located in urban area. Estimated sediments released from this area to the water resources and air were estimated on about 66,000,000 tons. In this study area, bioengineering works were performed in 60 days, with hardly any sediment generated outside the work area resulting from bioengineering operations. A combination of bioengineering techniques were chosen for this study area, which was a mixture of rigid and biological products including biologs, silt fence, biodegradable straw blankets sewn with plastic threads derived from recycled PET bottles, among others. An efficient drainage system was implemented for preventing upland flow, sub-seepage and seepage. Biologs were used aiming to fulfill a double role, the first as barrier to soil sediments flow, and the second as filler for empty spaces, avoiding expensive grading operations. All engineering works were concluded in about 60 days at a cost of US0.89/m < sup > 2 < /sup > . This price is cost-effective if compared with the traditional engineering cost of approximately US 0.89/m². This price is cost-effective if compared with the traditional engineering cost of approximately US 2.92/m² because it includes extensive use of grading and soil transportation. An environmental advantage of the bioengineering method is the immediate reduction of airborne particulates. Furthermore, the overall visual aesthetics improved shortly after the implementation of the works because the bare ground was substituted by native vegetation. After 6 months the vegetation in the gully erosion area was totally established. Monitoring was performed after 12 months and no erosion and sediment transport was visually noticed. The ease implementation of this technique without the need for specialized workers in combination with low prices makes this method a model for developing countries.  相似文献