Evaluation of the boundary layer morning transition using the CL-31 ceilometer signals     

Paulina Sokół  Iwona S. Stachlewska  Ioana Ungureanu  Sabina Stefan 《Acta Geophysica》2014,62(2):367-380

The morning transition of the atmospheric boundary layer from nighttime to daytime conditions was investigated using the Vaisala’s CL-31 ceilometer, located at Magurele, Romania (44.35°N, 26.03°E). Based on the 5-days backward trajectories, we rejected those measurements which were related to the intrusions of long-range transported particles. In the several discussed cases, which are representative for the morning transition in spring and summer seasons over Magurele, the increasing depth of the boundary layer related to the local aerosol load was well discernible. The dynamic change of its depth was estimated with errors using a simple method based on finding the minimum of the first derivative of the ceilometer signal. In the summer, the increase of the boundary layer depth due to the morning transition from the nighttime to daytime conditions starts on average of about 80 min earlier and the growth rate of this depth is 143 ± 6 m/h and about 37% slower than in the spring case.  相似文献   

Fate of Point‐Source Pesticide Spill in Clayey Till after 15 Years          下载免费PDF全文

Peter R. Jørgensen  Niels H. Spliid  Troels Laier  Stefan Outzen 《Ground Water Monitoring & Remediation》2016,36(3):33-42

This study investigated the development of pesticide pollution two, three, and 17 years after spills of the herbicides dichlorprop, mecoprop (MCPP), MCPA, 2,4‐D (phenoxy acids), simazine, and terbutylazine (triazines) in a former orchard machinery service yard. The spills had occurred over several decades on a 23‐m thick, mainly anaerobic fractured clayey till aquitard. Angled monitoring wells were installed in the aquitard 3 years after the spills ceased in 1989. In 1993, monitoring revealed that high groundwater concentrations of dichlorprop (677 µg/L) and MCPP (139 µg/L) were accumulated as a zone of maximum pollution in anaerobic and largely immobile pore water at 5 to 6 m depth in the aquitard profile. In contrast, 2,4‐D was determined in only one water sample, and MCPA and simazine and terbutylazine were determined only in low concentrations (below10 µg/L), although these pesticides had been handled at the site in greater amounts than dichlorprop and MCPP according to detailed historic information obtained for the site. Repeated monitoring in the same wells after a further 14 years in 2007 revealed that no identifiable degradation of MCPP had occurred, while dichlorprop had degraded by 75% to 80% (estimated half‐life of approximately 5 years). Furthermore, degradation products related to the phenoxy acids had accumulated, especially 4‐CPP with a maximum concentration of 218 µg/L. In the same zone, MCPA and simazine had almost disappeared. As the pollution was mainly accumulated in largely immobile pore water of the aquitard clayey matrix, and the groundwater recharge was low (30 to 60 mm/year), only minor vertical displacement of the zone with maximum pollution zone had occurred during the 15 years of monitoring. However, concentrations of dichlorprop (0.01 to 0.02 µg/L), MCPP (0.1 to 0.2 µg/L), and 4‐CPP (0.6 to 0.7 µg/L) had spread along textural heterogeneities in the aquitard into the underlying sandy aquifer at 23‐m depth.  相似文献   

Revised palaeoclimatic significance of Mueller Glacier moraines,Southern Alps,New Zealand          下载免费PDF全文

Natalya V. Reznichenko  Tim R. H. Davies  Stefan Winkler 《地球表面变化过程与地形》2016,41(2):196-207

A sequence of Late Holocene moraines on the foreland of the Mueller Glacier, Southern Alps, New Zealand, forms part of a local moraine‐age database used to establish a regional glacier chronology and subsequently to investigate potential intra‐hemispheric and global climate forcing mechanisms. We present new sedimentological and geomorphological evidence that a set of these moraine ridges, previously considered to represent individual advances, constitutes a single moraine complex (the ‘Mueller Memorial Moraine’) formed by supraglacial transport of a large volume of landslide debris to the glacier terminus. Because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event, we question the palaeoclimatic significance of the Mueller Memorial Moraine, as well as that of other moraines in comparable settings. Our findings suggest that the mode of formation and glacio‐dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re‐examined in order to assess the reliability of these reconstructions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Algal-silica cycling and pigment diagenesis in recent alpine lake sediments: mechanisms and paleoecological implications     

William O. Hobbs  Stefan V. Lalonde  Rolf D. Vinebrooke  Kurt O. Konhauser  R. Paul Weidman  Mark D. Graham  Alexander P. Wolfe 《Journal of Paleolimnology》2010,44(2):613-628

The quality and interpretability of the paleobiological record depends on the preservation of morphological and geochemical fossils. Siliceous microfossils and sedimentary pigments are often cornerstones in paleoecology, although the microbial and geochemical processes conducive to their preservation remain poorly constrained. We examined sediments from an alpine lake in Banff National Park (Alberta, Canada) where diatom frustules are completely dissolved within 50 years of deposition. Diatom dissolution, silica recycling, and diagenetic alteration of algal pigments were investigated, in conjunction with porewater geochemistry and microelectrode profiling of the sediment–water interface. Analysis of sediment trap material showed ~90% of biogenic silica (BSi) production is lost prior to burial. Silica flux calculations, based on dissolved silica (as H₄SiO₄) in pore-waters, show a further ~6% of total BSi is returned to the water column from the upper 4 cm of sediments, implying that only ~4% of total BSi is permanently archived in sediments. In situ sediment pH and O₂ profiles reveal that aerobic respiration by bacteria fully consumes oxygen by a depth of 4 mm into the sediment, with associated strong pH and redox gradients. During sedimentation and early diagenesis, diatoms undergo loss of extracellular polymeric substances that coat their frustules, promoting silica dissolution and leading to the loss of the microfossil record by a depth of 3.25 cm. Sedimentary pigments similarly undergo rapid degradation, but diatom-related carotenoids persist below the depth of silica dissolution. This work provides new insights on diagenetic processes in lakes, with broad implications for the interpretation of sedimentary proxies for algal production.  相似文献   

Holocene tephra horizons at Klocka Bog,west‐central Sweden: aspects of reproducibility in subarctic peat deposits     

Jonas Bergman  Stefan Wastegrd  Dan Hammarlund  Barbara Wohlfarth  Stephen J. Roberts 《第四纪科学杂志》2004,19(3):241-249

This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west‐central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja‐1875, Hekla‐3, Kebister, Hekla‐4 and Lairg A tephras respectively. Radiocarbon‐based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west‐central Scandinavia. Long‐lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

A low-order model for the response of the Atlantic thermohaline circulation to climate change   总被引：1，自引：0，他引：1  

Kirsten?ZickfeldEmail author  Thomas?Slawig  Stefan?Rahmstorf 《Ocean Dynamics》2004,54(1):8-26

Concern has been expressed that anthropogenic climate change may lead to a slowdown or even collapse of the Atlantic thermohaline circulation (THC). Because of the possibly severe consequences that such an event could have on the northern North Atlantic and northwestern Europe, integrated assessment models (IAMs) are needed to explore the associated political and socioeconomic implications. State-of-the-art climate models representing the THC are, however, often too complex to be incorporated into an integrated assessment framework. In this paper we present a low-order model of the Atlantic THC which meets the main requirements of IAMs: it (1) is physically based, (2) is computationally highly efficient, (3) allows for comprehensive uncertainty analysis and (4) can be linked to globally aggregated climate models that are mostly used in IAMs. The model is an interhemispheric extension of the seminal Stommel model. Its parameters are determined by a least-squares fit to the output of a coupled climate model of intermediate complexity. Results of a number of transient global warming simulations indicate that the model is able to reproduce many features of the behaviour of coupled ocean–atmosphere circulation models such as the sensitivity of the THC to the amount, regional distribution and rate of climate change.Responsible Editor: Richard Greatbatch  相似文献   

Earthquakes in Switzerland and surrounding regions during 2003     

Nicolas Deichmann  Manfred Baer  Jochen Braunmiller  Cécile Cornou  Donat Fäh  Domenico Giardini  Monika Gisler  Sarah Huber  Stephan Husen  Philipp Kästli  Urs Kradolfer  Martin Mai  Silvio Maraini  Ivo Oprsal  Thomas Schler  Danijel Schorlemmer  Stefan Wiemer  Jochen Wössner  Adrian Wyss 《Eclogae Geologicae Helvetiae》2004,97(3):447-458

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Marine conditions in central Sweden during the early Preboreal as inferred from a stable oxygen isotope gradient     

Kristian Schoning  Fredrik Klingberg  Stefan Wastegrd 《第四纪科学杂志》2001,16(8):785-794

The marine benthic fauna and the δ¹⁸O_c of foraminifers and ostracods from six sites situated on a west–east transect through central Sweden have been analysed in order to estimate the palaeosalinity and palaeocirculation in this shallow‐marine environment. The measurements have been undertaken on material from the early Preboreal, when the Baltic Basin was in contact with the North Sea through straits in central Sweden. The δ¹⁸O_c values have a more negative value towards the east, indicating decreasing salinity. This was the result of limited possibilities for marine water to penetrate into the Baltic Basin and the mixing with freshwater from the melting Fennoscandian ice‐sheet. Four water masses existed in the area: a surface layer of freshwater, marine water from the North Sea, brackish–marine intermediate water on the Swedish west coast and brackish Yoldia Sea water in the Baltic Basin. The chronology is based on radiocarbon dates of marine fossils and, at one site, on the occurrence of the Vedde Ash (10 400–10 300 ¹⁴C yr BP). This is the first record from marine settings in Sweden. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Structural and metamorphic evolution of the Camughera – Moncucco, Antrona and Monte Rosa units southwest of the Simplon line,Western Alps     

Lukas M. Keller  Maurus Hess  Bernhard Fügenschuh  Stefan M. Schmid 《Eclogae Geologicae Helvetiae》2005,98(1):19-49

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Reply to Comment by W. Kurz on “Tectonic map and overall architecture of the Alpine orogen”     

Stefan M. Schmid  Bernhard Fügenschuh  Eduard Kissling  Ralf Schuster 《Eclogae Geologicae Helvetiae》2005,98(1):99-101

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