Boundary-layer observations over water and arctic sea-ice during on-ice air flow     

Burghard Brümmer  Birgit Busack  Heinrich Hoeber  Gottfried Kruspe 《Boundary-Layer Meteorology》1994,68(1-2):75-108

Observations made on 8 and 9 May 1988 by aircraft and two ships in and around the marginal ice zone of the Fram Strait during on-ice air flow under cloudy and cloud-free conditions are presented.The thermodynamic modification of the air mass moving from the open water to the ice over horizontal distances of 100–300 km is only a few tenth of a degree for temperature and a few tenth of a gram per kilogram for specific humidity. This is due to the small temperature differences between sea and ice surfaces. During the day, the ice surface is even warmer than the sea surface. The stably stratified 200–400 m deep boundary layer is often topped by a moisture inversion leading to downward fluxes of sensible as well as latent heat.The radiation and energy balance at the surface are measured as functions of ice cover, cloud cover and sun elevation angle. The net radiationR _Nis the dominating term of the energy budget. During the day, the difference ofR _Nbetween clear and overcast sky is only a few W/m² over ice, but 100–200 W/m² over water. During the night,R _Nover ice is more sensitive to cloud cover.The kinematic structure is characterized by strong shears of the longitudinal and the transversal wind component. The profile of the latter one shows an inflection point near the top of the boundary layer. Dynamically-driven roll circulations are numerically separated from the mean flow. The secondary flow patterns have wavelengths of about 1 km and contribute substantially to the total variances and covariances.  相似文献   

Characterization of sediments in an abandoned mining area; a case study of Mansfeld region,Germany   总被引：1，自引：0，他引：1  

Rainer?WennrichEmail author  Jürgen?Mattusch  Peter?Morgenstern  Klaus?Freyer  Hanns-Christian?Treutler  Hans-Joachim?St?rk  Lutz?Brüggemann  Albrecht?Paschke  Birgit?Daus  Holger?Weiss 《Environmental Geology》2004,45(6):818-833

The distribution of selected heavy metals, including some radionuclides, metalloids and non-metals was determined in stream sediments in a region influenced by abandoned copper mining and ore processing activities. A considerable amount of the ore processing waste with a very complex composition and highly elevated concentrations of zinc, sulfur, lead, copper, arsenic, and a lot of other elements in the range between 100 and 1,000 mg/kg (Sb, Mn, Ni, Cr, Cd, Hg, and Ag) was piled up on mine dumps. The dispersion of the pollutants originating from this source and their environmental impact were investigated. Both, sediments and original waste material were studied to indicate the pathways and the mobilization behavior of different pollutants. For this purpose, the process of the elution of pollutants by application of different fractionation schemes was studied. The capabilities of different analytical techniques are shown for the analysis of solid samples (X-ray fluorescence spectrometry, Gamma-spectrometry) and liquid ones (ICP-atomic emission spectrometry, ICP-mass spectrometry and different techniques of atomic absorption). Additionally, the coupling of ion chromatography and ICP-MS detection was used to study the distribution of arsenic species in the sediment cores of a lake which acts as a natural sink for the region.  相似文献   

Geomicrobiology of Blood Falls: An Iron-Rich Saline Discharge at the Terminus of the Taylor Glacier, Antarctica   总被引：1，自引：0，他引：1  

Jill A. Mikucki  Christine M. Foreman  Birgit Sattler  W. Berry Lyons  John C. Priscu 《Aquatic Geochemistry》2004,10(3-4):199-220

Blood Falls, a saline subglacial discharge from the Taylor Glacier, Antarctica provides an example of the diverse physical and chemical niches available for life in the polar desert of the McMurdo Dry Valleys. Geochemical analysis of Blood Falls outflow resembles concentrated seawater remnant from the Pliocene intrusion of marine waters combined with products of weathering. The result is an iron-rich, salty seep at the terminus of Taylor Glacier, which is subject to episodic releases into permanently ice-covered Lake Bonney. Blood Falls influences thegeochemistry of Lake Bonney, and provides organic carbon and viable microbes to the lakesystem. Here we present the first data on the geobiology of Blood Falls and relate it totheevolutionary history of this unique environment. The novel geological evolution of thissubglacial environment makes Blood Falls an important site for the study of metabolic strategiesin subglacial environments and the impact of subglacial efflux on associated lake ecosystems.  相似文献   

Salt-water intrusion and nitrate contamination in the Valley of Hermosillo and El Sahuaral coastal aquifers, Sonora, Mexico   总被引：1，自引：0，他引：1  

Birgit Steinich  Oscar Escolero  Luis E. Marín 《Hydrogeology Journal》1998,6(4):518-526

 The Valley of Hermosillo coastal aquifer, state of Sonora, northwestern Mexico, has been over-exploited for the last four decades, in order to maintain agricultural activity in one of the most important irrigation districts of the Mexican Republic. The over-exploitation has resulted in the development of several drawdown cones and in the lowering of the water table to as much as 50 m below mean sea level. Contamination of the aquifer in the form of salt-water intrusion from the Gulf of California and high nitrate concentrations is the consequence of human activities. A hydrogeochemical zonation of the aquifer, based on the presence of different water families, led to the identification of a coastal band approximately 30 km wide that is affected by salt-water intrusion. Conductivity of the sampled water and the interpretation of the ratio Na/Cl×1000 was used to identify the location of three major intrusion plumes in this coastal band. The background nitrate contamination of the aquifer is about 4 ppm, but contents as great as about 17 ppm occur in some wells. Irrigation with raw sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for localized peaks of the nitrate concentration. Received, October 1996 Revised, September 1997, May 1998 Accepted, July 1998  相似文献   

Hydrogeological Investigations in Northwestern Yucatan, Mexico, Using Resistivity Surveys   总被引：4，自引：0，他引：4  

Birgit Steinich  Luis E. Marin 《Ground water》1996,34(4):640-646

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Rare earth element fractionation in magmatic Ca-rich garnets     

Birgit Scheibner  Gerhard Wörner  Lucia Civetta  Heinz-Günter Stosch  Klaus Simon  Andreas Kronz 《Contributions to Mineralogy and Petrology》2007,154(1):55-74

Igneous garnets have the potential to strongly fractionate rare earth elements (REE). Yet informations on partition coefficients are very scant, and criteria for distinguishing between hydrothermal and magmatic garnets are ambiguous. To fill this gap, we present trace element and isotopic data for two types of Ca-rich garnets from phonolites (Mt. Somma-Vesuvius). Both Ca-garnet populations are different in their style and dynamics of fractionation: one population is progressively strongly depleted in HREE from core to rim, reflecting REE fractionation in the host phonolite via earlier-crystallized garnets. Such examples for extreme changes in HREE in garnets are only known for hydrothermal grandites by REE-bearing fluids. The second garnet population is homogeneous and formed in a closed system. Near-flat patterns between Sm and Lu confirm experimental data indicating lower D(Sm)/D(Lu) for Ca-rich garnets than for e.g. pyrope-rich garnets. It follows: D ^Grt/PhMelt for La = 0.5, Sm = 48 and Yb = 110.  相似文献   

Squall lines and rainfall over Western Africa during summer 1986 and 87     

A. Gaye  A. Viltard  P. de Félice 《Meteorology and Atmospheric Physics》2005,90(3-4):215-224

Summary Using digitized IR images from the European satellite Meteosat, 153 squall lines (SLs) were observed over Western Africa during July, August and September 1986 and 87. The SL mean rainfall volume was computed using the daily rainfall amounts of more than 800 raingauges: 15 km³ in 1986 and 22.5 km³ in 1987. A mean amount of 15 mm was collected per rainy episode at a given station, however, as only about half of the stations situated under a SL experienced a rainy episode, the rainfall amount averaged along the total SL’s swath was 6.8 mm. With the help of the 8 daily Meteosat slots the SL’s area daily variation could be estimated: namely a minimum around noon and a maximum around midnight. Using the SLs displacements (east–west) one had access to the daily variation of the rainfall volume, a minimum in the morning and a maximum toward the end of the afternoon, as already found by several authors who used Meteosat images.  相似文献   

Composition of organic matter in subducted and unsubducted sediments off the Nicoya peninsula, Costa Rica (ODP Leg 170, Sites 1039 and 1040)     

Rüdiger Lutz  Birgit Gieren  Andreas Lückge  Heinz Wilkes  Ralf Littke 《Organic Geochemistry》2000,31(12)

Investigation of sediment samples from Sites 1039 and 1040 (ODP Leg 170) drilled off the Nicoya peninsula (Costa Rica) by organic geochemical and organic petrological methods has revealed that subduction has only little influence on the composition of the sedimentary organic matter. Organic carbon contents reached 1.5% in the Pleistocene samples but Miocene and Pliocene sediments had an average organic carbon content of less than 0.5%. Organic carbon/sulfur ratios are generally below 2.8, reflecting an intense sulfate reduction in the uppermost sediments which was enhanced by sulfate supply both from sea water and deeper strata. Microscopical examinations indicate that the organic matter is mainly derived from marine sources. A small amount of terrigenous organic matter is, however, present as well according to n-alkane and fatty acid distributions. The alkenone unsaturation index U₃₇^k′ shows only a slight decrease during the Miocene and Pliocene, and stronger variations in the Pleistocene, probably indicating more stable sea surface temperatures during the Miocene and Pliocene. Variations in the Pleistocene can possibly be related to glacial/interglacial changes.  相似文献   

Rain-based factors of high agricultural impacts over Senegal. Part I: integration of local to sub-regional trends and variability     

S. Salack  B. Muller  A. T. Gaye 《Theoretical and Applied Climatology》2011,106(1-2):1-22

The evolution of seasonal cycle and interannual rainfall, the number of rainy days and daily rainfall types, dry spells frequency of occurrence, onset/cessation/length of rainy season, sowing dates, and the duration of the cropping period, are investigated at local (individual sites) and sub-regional scales (four different rainfall zones) using daily records of station data (83 sites) over Senegal. In the limits of a case study, these analyses complement and update previous studies conducted in the extreme Western Sahel (11?C16° N and 20° W?C10° E). The results unveil noticeable evolution of some of these rain-based factors in the recent periods as compared to the previous dry years. In the regions recording less than 800?mm/year (Sudan and Sahel sub-regions), the positive and statistically significant trends of rainfall amount are associated with new features of increasing frequency of short dry spell category, increasing number of some classes of extreme daily rainfall amounts and shifts in the peak number of rainy days. At sub-regional scales, the starting years (or change points) the magnitude and the signs of the new trends are unevenly distributed in the period post-1990. Earlier and higher amplitude changes are found at local scales and not less than one third of the sites in each sub-regional network are significantly affected. The extreme Southern sub-region exhibits no significant changes. Statistically significant trends are not observed on daily rain records ??10?mm, onset/cessation dates, successful sowing dates, rainy season length, cropping period, medium and extreme dry spell categories. Rather, some of these factors such as the successful sowing date and the cropping season length exhibit significant variability. The onset (cessation) dates of the rainy season are followed (preceded) by extreme dry spell episodes. In the perspectives of climate impact assessments on the local agriculture a sub-regional periodic synopsis of the major rain-based factors of interest to agricultural applications are provided at the end the paper. They document some important internal variability patterns to reckon with in a multi-decadal work over the 1950?C2008 period for this region.  相似文献   

Seasonal fluctuations and mobility of arsenic in groundwater resources, Anchorage, Alaska     

LeeAnn Munk  Birgit HagedornDerek Sjostrom 《Applied Geochemistry》2011,26(11):1811-1817

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