The response of reworked aerosols to climate through estimation of inter-particle forces     

A. Assadi Langroudi  I. Jefferson 《International Journal of Environmental Science and Technology》2016,13(4):1159-1168

This paper describes the first use of inter-particle force measurement in reworked aerosols to better understand the mechanics of dust deflation and its consequent ecological ramifications. Dust is likely to carry hydrocarbons and micro-organisms including human pathogens and cultured microbes and thereby is a threat to plants, animals and human. Present-day global aerosol emissions are substantially greater than in 1850; however, the projected influx rates are highly disputable. This uncertainty, in part, has roots in the lack of understanding of deflation mechanisms. A growing body of literature shows that whether carbon emission continues to increase, plant transpiration drops and soil water retention enhances, allowing more greenery to grow and less dust to flux. On the other hand, a small but important body of geochemistry literature shows that increasing emission and global temperature leads to extreme climates, decalcification of surface soils containing soluble carbonate polymorphs and hence a greater chance of deflation. The consistency of loosely packed reworked silt provides background data against which the resistance of dust’s bonding components (carbonates and water) can be compared. The use of macro-scale phenomenological approaches to measure dust consistency is trivial. Instead, consistency can be measured in terms of inter-particle stress state. This paper describes a semi-empirical parametrisation of the inter-particle cohesion forces in terms of the balance of contact-level forces at the instant of particle motion. We put forward the hypothesis that the loss of Ca²⁺-based pedogenic salts is responsible for much of the dust influx and surficial drying pays a less significant role.  相似文献   

Variations in annual snowline and area of an ice-covered stratovolcano in the Cordillera Ampato,Peru, using remote sensing data (1986–2014)     

Bijeesh Kozhikkodan Veettil  Ulisses Franz Bremer  Sergio Florêncio de Souza  Éder Leandro Bayer Maier  Jefferson Cardia Simões 《国际地球制图》2016,31(5):544-556

This research focuses on the recent variations in the annual snowline and the total glaciated area of the Nevado Coropuna in the Cordillera Ampato, Peru. Maximum snowline altitude towards the end of dry season is taken as a representative of the equilibrium line altitude of the year, which is an indirect measurement of the annual mass balance. We used Landsat and IRS LISS3 images during the last 30 years due to its better temporal coverage of the study site. It is found that there was a decrease of 26.92% of the glaciated area during 1986–2014. We calculated the anomalies in precipitation and temperature in this region and also tried to correlate the changes in glacier parameters with the combined influence of El Niño – Southern Oscillation (ENSO) and pacific decadal oscillation (PDO). It is concluded that the snowline of Nevado Coropuna has been fluctuated during ENSO, and maximum fluctuations were observed when ENSO and PDO were in phase.  相似文献   

Zooplankton Grazing during Dinoflagel-late Blooms in a Cape Cod Embayment, with Observations of Predation upon Tin-tinnids by Copepods     

Jefferson T.  Turner Donald M.  Anderson 《Marine Ecology》1983,4(4):359-374

Abstract. The patterns and rates of feeding by the copepod Acartia hudsonica and larvae of the polychaete Polydora sp. were investigated during the spring in an estuarine embayment. These dominant macrozooplankters fed upon the natural particulate assemblages (predominantly dino-flagellates) spiked with the toxic dinoflagellate Gonyaulax tamarensis. G. tamarensis was ingested by both zooplankters, as was Heterocapsa triquetra , the most abundant alternative food item. Ingestion rates generally increased as dinoflagellate concentrations increased, resulting in a relatively constant (and low) filtration rate for each grazer. Dinophysis acuminata , another dominant dinoflagellate, was essentially ungrazed. Thus, the zooplankters did not ingest one dinoflagellate and consumed others in proportion to their availability but at low rates. Based on these low rates and the small number of A. hudsonica observed during the spring, we infer minima! grazing impact on a 1980 G. tamarensis bloom. In contrast, the impact of polychaete larvae may have been substantial, since their extreme numerical abundance more than compensated for low filtration rates.
In one instance, the tintinnid Eutintinnus pectinis was accidentally included in a grazing experiment. Our ingestion data demonstrate that A. hudsonica , when presented with a combination of tintinnids and several species of phytoplankton (G. tamarensis and D. acuminata) ingested the tintinnids at high rates, in proportion to their high abundance. Since the nanoflagellate Chroomonas amphioxea was found within the loricae of many of the surviving tintinnids, this also provided a qualitative demonstration of the often-hypothesized nanoplankton to tintinnid to copepod link in a marine food chain.  相似文献   

Fractal characteristics of loess formation: evidence from laboratory experiments   总被引：3，自引：0，他引：3  

P. Lu  I. F. Jefferson  M. S. Rosenbaum  I. J. Smalley 《Engineering Geology》2003,69(3-4):287-293

The fractal is presented as a method for describing the geometry of particles, with particular reference to the breakdown of granular soils and the formation of loess. The preliminary results are reported: (a) for the extent to which silt due to comminution exhibits a fractal distribution; (b) the tendency of fractal dimension to change with the comminution process; and (c) the relationship between fractal dimension describing particle size distribution and the grinding time. Laboratory simulation confirms the general tendency of fractal characteristics to reflect the size reduction process.  相似文献   

Comparison of a GPS-defined global reference frame with ITRF2000     

Michael Heflin  Donald Argus  David Jefferson  Frank Webb  James Zumberge 《GPS Solutions》2002,6(1-2):72-75

The Global Positioning System is a constellation of 24–28 satellites, which can be used to define a global terrestrial reference frame. Daily offsets between a GPS defined frame and ITRF2000 have been estimated using more than a decade of GPS observations from 1990–2001. A linear fit to the full span of data shows agreement between the two frames at the level of –1 ppb and –0.1 ppb/year for scale, 5 mm and 0 mm/year for the X component of center of mass, –2 mm and –3 mm/year for the Y component, and 4 mm and 6 mm/year for the Z component. GPS is a viable tool for defining the global reference frame either alone, or in combination with other geodetic techniques. Electronic Publication  相似文献   

Hydrogeologic controls on streamflow sensitivity to climate variation     

Anne Jefferson  Anne Nolin  Sarah Lewis  Christina Tague 《水文研究》2008,22(22):4371-4385

Climate models project warmer temperatures for the north‐west USA, which will result in reduced snowpacks and decreased summer streamflow. This paper examines how groundwater, snowmelt, and regional climate patterns control discharge at multiple time scales, using historical records from two watersheds with contrasting geological properties and drainage efficiencies. In the groundwater‐dominated watershed, aquifer storage and the associated slow summer recession are responsible for sustaining discharge even when the seasonal or annual water balance is negative, while in the runoff‐dominated watershed subsurface storage is exhausted every summer. There is a significant 1 year cross‐correlation between precipitation and discharge in the groundwater‐dominated watershed (r = 0·52), but climatic factors override geology in controlling the inter‐annual variability of streamflow. Warmer winters and earlier snowmelt over the past 60 years have shifted the hydrograph, resulting in summer recessions lasting 17 days longer, August discharges declining 15%, and autumn minimum discharges declining 11%. The slow recession of groundwater‐dominated streams makes them more sensitive than runoff‐dominated streams to changes in snowmelt amount and timing. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Effects of root water uptake formulation on simulated water and energy budgets at local and basin scales   总被引：1，自引：0，他引：1  

Ian M. Ferguson  Jennifer L. Jefferson  Reed M. Maxwell  Stefan J. Kollet 《Environmental Earth Sciences》2016,75(4):316

  相似文献   

厦门港的中华白海豚Ⅲ.牙齿和年龄   总被引：7，自引：3，他引：4  

刘文华  黄宗国 《台湾海峡》1999,18(2):210-214

对厦门５头中华白海豚成体和６头哺乳期的幼仔,进行齿的形态、齿式、内部构造和磨损情况的研究;根据齿的切片判断年龄,５头成体９～３０岁,年龄大小和体表颜色及齿的磨损程度密切相关。出生后的幼仔齿包埋在齿龈中,其齿数、齿式和成体一样。  相似文献