The response of saltation to wind speed fluctuations   总被引：2，自引：0，他引：2  

Sascha Pfeifer  Hans‐Jürgen Schönfeldt 《地球表面变化过程与地形》2012,37(10):1056-1064

The response time of saltation to spatial or temporal wind speed fluctuations constitutes an important control parameter for aeolian sediment transport and deposition. In this paper, we present direct measurements of the response time obtained from several field experiments. The sand transport was studied using six small microphones arranged in a vertical profile and collocated with a sonic anemometer, a webcam and a cup anemometer tower. The webcam was coupled with the sonic anemometer via a personal computer and provides information on creeping and saltating grains with a sampling rate of 10 Hz. Sediment transport measurements were obtained over four periods. The Wiener filter, a signal processing technique, is used to obtain a discrete transfer function that relates the horizontal wind speed and the non‐intermittent sand transport. The transfer function can be established using an exponential function with a time constant or characteristic response time τ without time shift. The response time fluctuated between zero and 1·5 seconds depending on the turbulence intensity, the saltation activity, the measuring height and sampling rates. The Wiener filter coefficients suggest that the response of saltation to wind speed alterations is determined by more than one process. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Role of Subsurface Brines in Salt Balance: The Case Study of the Caspian Sea and Kara Bogaz Bay     

Norbert Clauer  Marie-Claire Pierret  Sam Chaudhuri 《Aquatic Geochemistry》2009,15(1-2):237-261

The water level of the Caspian Sea fluctuated significantly during recent history, without consensus for the cause. The varied chemistry of the Caspian, Kara Bogaz and sediment a interstitial waters provides a further insight. Element concentrations and ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters were compared to those of Caspian and Kara Bogaz open waters, and of acid-leached extractable components. The ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters are explained by addition of subterranean waters similar to nearby spring waters. These subterranean waters yield chemical characteristics such as a Cl/SO₄, ⁸⁷Sr/⁸⁶Sr, Ca/Sr and K/Rb ratios of respectively 80, 0.7086, 250 and 1,800. However, their addition does not explain the large difference in the K/Rb ratio of the Caspian and Kara Bogaz waters, respectively at 7,630 and 17,550, which implies also a leaching of salt deposits by the upward migrating subterranean waters. The sediments of the southern Caspian basin, with low Na, Cl and SO₄ in their interstitial waters, deposited apparently in an anoxic environment. The related chemical changes in the waters are also indicative of a recent change in the hydrologic regime, possibly induced by a changing morphology of the drainage basin.  相似文献   

Direct terrestrial-marine correlation demonstrates surprisingly late onset of the last interglacial in central Europe     

Mark J. Sier  Wil Roebroeks  Corrie C. Bakels  Enrico Brühl  Dimitri De Loecker  Norbert Hesse  Lutz Kindler  Thomas Laurat  Herman J. Mücher  Kirsty E.H. Penkman  Douwe J.J. van Hinsbergen 《Quaternary Research》2011,75(1):213-218

An interdisciplinary study of a small sedimentary basin at Neumark Nord 2 (NN2), Germany, has yielded a high-resolution record of the palaeomagnetic Blake Event, which we are able to place at the early part of the last interglacial pollen sequence documented from the same section. We use this data to calculate the duration of this stratigraphically important event at 3400 ± 350 yr. More importantly, the Neumark Nord 2 data enables precise terrestrial-marine correlation for the Eemian stage in central Europe. This shows a remarkably large time lag of ca. 5000 yr between the MIS 5e ‘peak’ in the marine record and the start of the last interglacial in this region.  相似文献   

Trophic interactions of the pelagic ciliate Stentor spp. in North Patagonian lakes     

Norbert Kamjunke  Bernhard Vogt 《Limnologica》2009,39(2):107-114

The zooplankton of oligotrophic lakes in North Patagonia is often dominated by mixotrophic ciliates, particularly Stentor amethystinus and Stentor araucanus. Therefore, we tested whether Stentor spp. (i) is an important food for juvenile endemic (Cheirodon australe, Galaxias maculatus, Odontesthes mauleanum, Percichthys trucha) and introduced (Oncorhynchus mykiss) fish species, and (ii) represents a remarkable grazer of bacteria. Ingestion rates of fish estimated by disappearance of Stentor in feeding experiments ranged between 8 (G. maculatus) and 53 (C. australe) ciliates per fish and day, and assimilation rates measured by using radioactively labelled Stentor ranged between 3 (P. trucha) and 52 (C. australe) ciliates per fish and day. However, although we detected the consumption of Stentor by fish, the daily consumption amounted to at most 0.2% of the fish biomass which can not cover the energy requirement of the fish. Furthermore, the daily consumption was equivalent to a maximum of 1.6% of the Stentor standing stock so that fish predation does not seem to be an important mortality factor for the ciliates. The clearance rate of Stentor sp. on natural bacteria was on average 3.8 μl cil⁻¹ h⁻¹. The daily ingestion (mean 3.9 ng C cil⁻¹ d⁻¹) was about 3.5% of the individual biomass of Stentor sp. Therefore, bacteria ingestion might explain a ciliate growth rate of appr. 1% d⁻¹, which was about 17% of the photosynthesis of endosymbiotic algae. The maximum density of Stentor sp. in the lake could ingest about 1 μg C L⁻¹ d⁻¹ bacteria which is only 3% of average bacterial production. Thus, grazing by Stentor sp. does not seem to be a main loss factor for the bacteria.  相似文献   

Estuaries of the northeastern United States: Habitat and land use signatures     

Charles T. Roman  Norbert Jaworski  Frederick T. Short  Stuart Findlay  R. Scott Warren 《Estuaries and Coasts》2000,23(6):743-764

Geographic signatures are physical, chemical, biotic, and human-induced characteristics or processes that help define similar or unique features of estuaries along latitudinal or geographic gradients. Geomorphologically, estuaries of the northeastern U.S., from the Hudson River estuary and northward along the Gulf of Maine shoreline, are highly diverse because of a complex bedrock geology and glacial history. Back-barrier estuaries and lagoons occur within the northeast region, but the domiant type is the drowned-river valley, often with rocky shores. Tidal range and mean depth of northeast estuaries are generally greater when compared to estuaries of the more southern U.S. Atlantic coast and Gulf of Mexico. Because of small estuarine drainage basins, low riverine flows, a bedrock substrate, and dense forest cover, sediment loads in northeast estuaries are generally quite low and water clarity is high. Tidal marshes, seagrass meadows, intertidal mudflats, and rocky shores represent major habitat types that fringe northeast estuaries, supporting commercially-important fauna, forage nekton and benthos, and coastal bird communities, while also serving as links between deeper estuarine waters and habitats through detritus-based pathways. Regarding land use and water quality trends, portions of the northeast have a history of over a century of intense urbanization as reflected in increased total nitrogen and total phosphorus loadings to estuaries, with wastewater treatment facilities and atmospheric deposition being major sources. Agricultural inputs are relatively minor throughout the northeast, with relative importance increasing for coastal plain estuaries. Identifying geographic signatures provides an objective means for comparing the structure, function, and processes of estuaries along latitudinal gradients.  相似文献   

Magnetostratigraphic results from the eastern Arctic Ocean: AMS ¹⁴C ages and relative palaeointensity data of the Mono Lake and Laschamp geomagnetic reversal excursions     

Norbert R. Nowaczyk  & Jochen Knies 《Geophysical Journal International》2000,140(1):185-197

A new high-resolution magnetostratigraphic record from the eastern Arctic Ocean has yielded further evidence for the existence of the Laschamp excursion (37–35  ka), the Mono Lake excursion (27–25.5  ka) and possibly another very short excursion (22  ka) inferred from steep negative inclinations. Ages are based on nine AMS (accelerator mass spectrometry) ¹⁴C dates, oxygen isotope stratigraphy and correlation with ODP site 983. Estimates of relative palaeointensity variations for the time interval from 80 to 10  ka have revealed that the documented geomagnetic excursions are linked to large fluctuations of the relative palaeointensity. The lowest values were obtained for the two excursions and the normal–reversed (N–R) and reversed–normal (R–N) transitions of the Laschamp polarity excursion, which itself is characterized by a slight increase of relative palaeointensity during its reversed state. The results are in general agreement with palaeointensity studies from other regions, indicating that these fluctuations could be global phenomena and that the geomagnetic field of the Brunhes Chron was very variable in amplitude as well as in geometry. The new result is one of the rare records comprising large directional as well as large relative palaeointensity variations.  相似文献   

A watershed nitrogen and phosphorus balance: The upper Potomac River basin   总被引：1，自引：0，他引：1  

Norbert A. Jaworski  Peter M. Groffman  Aimee A. Keller  Jan C. Prager 《Estuaries and Coasts》1992,15(1):83-95

Nitrogen and phosphorus mass balances were estimated for the portion of the Potomac River basin watershed located above Washington, D.C. The total nitrogen (N) balance included seven input tource terms, six sinks, and one “change-in-storage” term, but was simplified to five input terms and three output terms. The phosphorus (P) balance had four input and three output terms. The estimated balances are based on watershed data from seven information sources. Major sources of nitrogen are amimal waste and atmospheric deposition. The major sources of phosphorus are animal waste and fertilizer. The major sink, for nitrogen is combined denitrification, volatilization, and change-in-storage. The major sink for phosphorus is change-in-storage. River exports of N and P were 17% and 8%, respectively, of the total N and P inputs. Over 60% of the N and P were volatilized or stored. The major input and output terms on the budget are estimated from direct measurements, but the change-in-storage term is calculated by difference. The factors regulating retention and storage processes are discussed and research needs are identified.  相似文献   

Basiswerte fossiler Kohlenwasserstoffe im Nordost-Atlantik     

Dr. Norbert Theobald  Wilfried Lange  Kirsten Jerzycki-Brandes 《Ocean Dynamics》1991,44(1):17-33

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International Geographical Union IGU commission on the coastal environment     

Norbert P. Psuty Dr. 《GeoJournal》1990,20(4):423-427

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On the collisional energy transfer between the constituents of the coronal plasma     

Horst Fichtner  Norbert Vormbrock  S. Ranga Sreenivasan 《Solar physics》1995,160(1):105-120

It has been suggested that the distribution functions characterizing the constituents of the solar coronal plasma are non-Maxwellian. If so, an accurate treatment of the collisional momentum and energy exchange between the plasma constituents within the framework of hydrodynamic models requires a re-evaluation of the general transfer integrals in multi-component plasmas. We have evaluated these integrals numerically for both Maxwellian and non-Maxwellian distribution functions of the plasma species avoiding the standard approximation for the collision cross sections frequently employed in the literature. Significant differences are shown to exist in the energy exchange rates for different distributions. We also demonstrate the inadequacy of the assumption of thermodynamic equilibrium in the innermost solar wind and reveal the importance of an accurate evaluation of the transfer integrals for the solar coronal plasma based on more realistic velocity distributions.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献