A method of evaluating effects of antecedent precipitation on duststorms and its application to Yuma,Arizona, 1981–1988     

David J. Mackinnon  Diana F. Elder  Paula J. Helm  Marlene F. Tuesink  Catherine A. Nist 《Climatic change》1990,17(2-3):331-360

Precipitation causes several short- and long-term effects on wind-induced surface erodibility and subsequent dust emission. Among the principal effects considered by this paper are soil moisture, soil crusts, and vegetation. A quantitative method is developed to assess these effects using differences between the potential and the actual amounts of dust emitted from dust sources as inferred from surface meteorological measurements obtained downwind from those sources. The results of this assessment must be interpreted with caution, however, when the size and location of dust sources are unknown.Using meteorological data recorded near Yuma, Arizona at the Yuma Marine Corps Air Station (YMCAS), the method is applied to calculate the potential and actual amounts of dust emitted from upwind dust sources during the spring and fall/winter seasons between January 1, 1981 and May 31, 1988. (Spring is considered to be the period between February 1 and May 31; fall/winter, between October 1 and January 31.) Because summer precipitation is intermittent and wind patterns are localized, summer meteorological data are not used to evaluate regional correlations between precipitation and dust storms. For the period between 1981 and 1988, a correlation of -0.60 was found between fall/winter precipitation and the actual amount of dust emitted from sources upwind of YMCAS during the following spring. A particularly strong reduction in dust emission was noted during the springs of 1983 and 1984 following the start of an El Nino event in fall/winter 1982. Photographs taken at a geological and meteorological data-collection (Geomet) site, located in the natural desert 25 km southeast of YMCAS, show a correspondence between increased antecedent precipitation recorded at the site and increased vegetation. Whereas the annual precipitation totals at YMCAS and the Geomet site from the beginning of 1982 through 1984 are high, their seasonal totals, especially during the fall/winter seasons, are disparate. This fall/winter precipitation disparity may account for evidence suggesting that significant vegetation growth occurred at dust sources upwind of YMCAS by spring 1983, but that such growth did not occur at the Geomet site until fall/ winter of 1983. Spatial inhomogeneity in fall/winter precipitation probably contributed to the relatively low correlation (-0.60) between fall/winter precipitation recorded at YMCAS and the actual amount of dust emitted from upwind sources during the following spring.  相似文献   

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   

Distribution and vertical dynamics of planktonic communities at Sofala Bank, Mozambique     

M.C. Leal  C. S  S. Nordez  V. Brotas  J. Paula 《Estuarine, Coastal and Shelf Science》2009,84(4):605-616

Coastal ecosystem processes are largely influenced by the interaction of different factors operating at various temporal and spatial scales, specifically those responsible for primary production patterns that modulate zooplankton and subsequent trophic levels. Hydrological processes, such as tidal cycles and coastal currents, nutrients availability, phytoplankton groups (studied through algal pigment signatures analysed by HPLC), and zooplankton abundance and distribution were investigated at the Sofala Bank (Mozambique), with special emphasis on their horizontal distribution and vertical dynamics (48 h). Horizontal distribution has shown inshore–offshore gradients in all analysed parameters, as well as inshore waters intrusion probably related to Zambezi River delta runoff. Tidal currents were responsible for major hydrological vertical variations and for horizontal and vertical advection of phytoplankton biomass in the surface and deepest layers, respectively. Nutrient concentrations were typical from oligotrophic regions, and nutrient ratios were strongly influenced by depleted nitrate + nitrite concentrations, indicating low estuarine discharges typical from the dry season. The very low N:P ratio obtained suggests strong nitrogen limitation to phytoplankton communities, supporting the low phytoplankton abundance observed. Both phytoplankton pigments and zooplankton were found mainly near the bottom (40 m depth), despite the latter displayed vertical migrations triggered by light variations. Phytoplankton community was dominated by microflagellates, specifically prymnesiophyceans, and behaved as a whole, except Cyanobacteria that displayed vertical distribution movements different from other phytoplankton groups, being mainly concentrated at mid-water column depths (10–20 m). This investigation enhances physico-chemical phenomena and their importance determining the planktonic communities vertical dynamics at Sofala Bank, a tropical coastal ecosystem of the Western Indian Ocean where planktonic dynamics are still poorly described and understood.  相似文献   

Effects of naphthalene and phenanthrene on visual and prey capture endpoints during early stages of the dourado Salminus brasiliensis     

Carvalho PS  Kalil Dda C  Novelli GA  Bainy AC  Fraga AP 《Marine environmental research》2008,66(1):205-207

Naphthalene (NAP) and phenanthrene (PHE) effects on Salminus brasiliensis, a carnivorous freshwater fish, were investigated using behavioral tests. Larval stages of S. brasiliensis were exposed to water concentrations of 0, 0.04 mg/l, 0.20mg/l and 0.50mg/l for naphthalene and 0, 0.01 mg/l, 0.05 mg/l and 0.1mg/l for phenanthrene during two developmental phases. The prey fish Prochilodus lineatus were not exposed. Visual acuity was measured at the end of phase 2 in individual S. brasiliensis, which were also tested at the end of each phase for number of attacks on prey, number of prey captured, prey capture efficiency, and distance swam. Vision was impaired by PHE exposure, as acuity angles increased in exposed fish. At Stage I 2.3+/-1.2 prey were captured with 46% efficiency in controls compared to 0.4+/-0.3 prey captured with 13.4% efficiency in fish exposed to 0.05 mg PHEl(-1), the LOEL for both endpoints. At Stage II 4.0+/-1.1 preys were captured in controls compared to 2.5+/-0.9 preys captured in fish exposed to 0.01 mg PHEl(-1), the LOEL. Stage II control fish captured prey with 70% efficiency compared to 30% efficiency at Stage II fish exposed to 0.05 mg PHEl(-1), the LOEL. Distance swam was not affected by either NAP or PHE exposure. The exposure of larval stages of S. brasiliensis to realistic water concentrations of PHE impairs foraging skills and could affect recruitment of the species.  相似文献   

Small-scale fisheries and food security strategies in countries in the Benguela Current Large Marine Ecosystem (BCLME) region: Angola,Namibia and South Africa     

Merle Sowman  Paula Cardoso 《Marine Policy》2010

This paper provides an overview of the small-scale fisheries sector in countries within the Benguela Current Large Marine Ecosystem (BCLME), one of the most productive large marine ecosystems in the world. The study revealed that Angola, Namibia and South Africa have very different legal and policy frameworks, show different levels of compliance with international and regional agreements to protect the livelihoods and food security of small-scale fishers, as well as of integration of fisheries into food security objectives. Angolan law recognises and protects small-scale fishers through legal and institutional mechanisms. In Namibia, this sector of fishers is not legally recognised, while in South Africa traditional fishers have been largely excluded from the new fisheries management framework. Trends in national and regional fish consumption and in the extent of export orientation in fisheries are explored, as well as the potential threats to small-scale producers and food security in the region posed by ongoing drives to incorporate fisheries in the World Trade Organisation (WTO) agreements.  相似文献   

Combined effects of waves and plants on a mud deposition event at a mudflat-saltmarsh edge in the Bahía Blanca estuary     

Paula D. Pratolongo  Gerardo M.E. Perillo  M. Cintia Piccolo 《Estuarine, Coastal and Shelf Science》2010

This study was carried out at the Bahía Blanca Estuary, Argentina, at the seaward edge of a saltmarsh. The saltmarsh-mudflat boundary in the study area shows sediment deposits at a higher elevation immediately seaward of the saltmarsh edge. We compared field determinations of water velocity, bed shear stress, wind wave conditions and variations of the bed elevation in the mudflat and within the Spartina alterniflora canopy at the seaward edge of a saltmarsh, and we evaluated the relative role of vegetation in the observed morphology. A mud deposition event that raised bed elevation in more than 5 cm occurred during the study period, with TSS concentrations > 500 mg l⁻¹, but simultaneous measurements performed on the bed levels confirmed that the sediments deposited did not originate from local resuspension within the edge of the canopy. In similar tidal cycles in terms of local wave activity and bed shear stresses at the sampling site, deposition occurred only with winds aligned with the azimuth of the Canal Principal, reaching a maximum fetch of more than 20 km in front of the sampling site.  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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