Synchronous climatic change inferred from diatom records in four western Montana lakes in the U.S. Rocky Mountains     

Brandi Bracht-Flyr  Sherilyn C. Fritz 《Quaternary Research》2012,77(3):456-467

Late-Holocene environmental and climatic conditions were reconstructed from diatom assemblages in sediment cores from four western Montana lakes: Crevice Lake, Foy Lake, Morrison Lake, and Reservoir Lake. The lakes show synchroneity in timing of shifts in diatom community structure, but the nature of these changes differs among the lakes. Two of the sites provide highly resolved records of hydrologic balance, while the other two stratigraphic sequences primarily record temperature impact on lake thermal structure. All four lakes show significant change in five discrete intervals: 2200–2100, 1700–1600, 1350–1200, 800–600, and 250 cal yr BP. The similarities in the timing of change suggest overlying regional climatic influences on lake dynamics. The 800–600 cal yr BP shift is evident in other paleorecords throughout the Great Plains and western US, associated with the transition from the Medieval Climate Anomaly to the Little Ice Age. Large-scale climatic mechanisms that influence these lake environments may result from atmospheric circulation patterns that are driven by interactions between Pacific and Atlantic sea-surface temperatures, which are then locally modified by topography.  相似文献   

Multi-proxy record of postglacial environmental change, south-central Melville Island, Northwest Territories, Canada     

Matthew Peros  Konrad Gajewski  Tara Paull  Brandi Podritske 《Quaternary Research》2010,73(2):247-258

A sediment core from Lake BC01 (75°10.945′N, 111°55.181′W, 225 m asl) on south-central Melville Island, NWT, Canada, provides the first continuous postglacial environmental record for the region. Fossil pollen results indicate that the postglacial landscape was dominated by Poaceae and Salix, typical of a High Arctic plant community, whereas the Arctic herb Oxyria underwent a gradual increase during the late Holocene. Pollen-based climate reconstructions suggests the presence of a cold and dry period ~12,000 cal yr BP, possibly representing the Younger Dryas, followed by warmer and wetter conditions from 11,000 to 5000 cal yr BP, likely reflective of the Holocene Thermal Maximum. The climate then underwent a gradual cooling and drying from 5000 cal yr BP to the present, suggesting a late Holocene neoglacial cooling. Diatom preservation was poor prior to 5000 cal yr BP, when conditions were warmest, suggesting that diatom dissolution may in part be climatically controlled. Diatom concentrations were highest ~4500 cal yr BP but then decreased substantially by 3500 cal yr BP and remained low before recovering slightly in the 20th century. An abrupt warming occurred during the past 70 yr at the site, although the magnitude of this warming did not exceed that of the early Holocene.  相似文献   

The state of Canadian cities: theoretical and applied themes: an introduction     

Laura A. Reese 《GeoJournal》2010,75(6):509-516

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A Modeling and Field Approach to Identify Essential Fish Habitat for Juvenile Bay Whiff (Citharichthys spilopterus) and Southern Flounder (Paralichthys lethostigma) Within the Aransas Bay Complex, TX     

Bridgette F. Froeschke  Gregory W. Stunz  Megan M. Reese Robillard  Jason Williams  John T. Froeschke 《Estuaries and Coasts》2013,36(5):881-892

The goal of this study was to use an ecosystem-based approach to consider the effect of environmental conditions on the distribution and abundance of juvenile bay whiff and southern flounder within the Aransas Bay Complex, TX, USA. Species habitat models for both species were developed using boosted regression trees. Juvenile bay whiff were associated with low temperatures (<15 °C, 20–23 °C), moderate percent dry weight of sediments (25–60 %), salinity >10, and moderate to high dissolved oxygen (6–9 mg O₂/l, 10–14 mg/l). Juvenile southern flounder were associated with low temperatures (<15 °C), low percent dry weight of sediment (<25 %), seagrass habitat, shallow depths (<1.2 m), and high dissolved oxygen (>8 mg O₂/l). Our results indicate that conservation measures should focus along the eastern side of Aransas Bay and the north corner of Copano Bay to protect essential fish habitat. These findings provide a valuable new tool for fisheries managers to aid in the sustainable management of bay whiff and southern flounder and provide crucial information needed to prioritize areas for habitat conservation.  相似文献   

Populating the Galaxy with pulsars – I. Stellar and binary evolution     

Paul D. Kiel  Jarrod R. Hurley  Matthew Bailes  James R. Murray 《Monthly notices of the Royal Astronomical Society》2008,388(1):393-415

The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed     diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.  相似文献   

Global hydrocarbon seep-carbonate precipitation correlates with deep-water temperatures and eustatic sea-level fluctuations since the Late Jurassic   总被引：2，自引：0，他引：2  

Steffen Kiel 《地学学报》2009,21(4):279-284

The anaerobic oxidation of methane (AOM) in marine sediments, most obviously at cold seeps, is a major sink for this important greenhouse gas and is associated with the precipitation of carbonates. The geological record of seep carbonates provides insights into the long-term dynamics of this process. Since the Late Jurassic, rates of seep-carbonate precipitation have been high during times of low sea levels and cold deep-water temperatures, and vice versa. One possibility is that sea-level fall decreases the thickness of the methane hydrate stability zone in the sediment so that gas hydrates decompose in deeper sediments, thereby increasing seepage and carbonate precipitation. Alternatively, low deep-water temperature facilitates gas hydrate formation on continental slopes and may thereby increase methane availability for AOM-performing consortia and associated carbonate precipitation. These correlations and their potential causes may be of interest for the modelling of global carbon budgets and of past and future climates.  相似文献   

Behavioural response of blackfly larvae (Simuliidae, Diptera) to different current velocities     

Ellen Kiel   《Limnologica》2001,31(3)

Video equipment was used to record and to compare the behaviour of different blackfly species at two flow velocities 0.25 m s⁻¹ and 1.35 m s⁻¹. Simulium noelleri Friederichs, Simulium ornatum (complex) Meigen and Simulium variegatum Meigen were studied. Effects of flow velocity on larval locomotive activties were analysed. Looping activity and the time needed to attach for filter feeding again were affectet to some extend, depending on species and flow velocity. While in S. ornatum no differences were recorded in locomotive activity, larvae of S. noelleri and S. variegatum were less active at high flow velocities. Larvae of S. noelleri also moved over shorter distances when exposed to high flow velocities. Consequences of the differences in behavioural response to flow velocities are discussed with respect to drift and silk pad adhesion.  相似文献   

The indication of morphological degradation of streams and rivers using Simuliidae     

Christian K. Feld  Ellen Kiel  Melanie Lautenschlger 《Limnologica》2002,32(3)

Blackfly communities from five German stream types out of two ecoregions (small and mid-sized siliceous gravel-bed mountain streams of the Central mountains, ecoregion 9, and organic type brooks, small and mid-sized sand-bottomed Central lowland streams of ecoregion 14) are compared. Ecoregional, as well as stream type-specific biocoenotic differences are discussed. The presence of Prosimulium sp. was restricted to mountain streams, whereas Simulium lineatum seemed to prefer mid-sized sand-bottomed Central lowland streams, and S. vernum showed a clear preference for Central lowland streams. An Index of Morphological Stress (IMS), derived from 22 geo-hydromorphological parameters recorded during sampling in the field, is presented. According to the IMS values, sites are divided into morphologically ‘unstressed’ sites (high or good morphological quality) and ‘stressed’ sites (moderate, poor or bad morphological quality), and biocoenotic differences of the two categories are discussed. Two stream types and the entire data set showed significantly higher numbers of taxa at ‘unstressed’ sites. Linear Multiple Regression (LMR) was used to identify geo-hydromorphological parameters that significantly explain the variance of the three most constant taxa, Prosimulium sp., P. hirtipes and Simulium sp. in the LMR model.  相似文献   

Gelelectrophoretic studies on labial gland secretions of immature blackflies (Simuliidae, Diptera)     

Ellen Kiel  Thomas Rder 《Limnologica》2002,32(3):201

Any contact of blackfly larvae and pupae to the substrate they colonise relies on the adhesion of the secretion which is produced in their large labial glands. This secretion anchors their filter-feeding position, any locomotive activity, and the pupal cocoon as well. The secretion works as a biological adhesive which adheres to nearly any substrate surface — even to wood or the integument of other aquatic animals. We began analysing the proteinaceaous compounds of the labial gland secretions of Simulium ornatum (complex) Meigen. According to the SDS-PAGE and amino acid analyses, blackfly gland secretion consists of a variety of proteins ranging from high to low molecular weights. The most prominent proteins form broad bands at about 70, 40 and 20 kDa. These main proteins were present in secretions from young to old larvae as well as in pupal cocoon secretion, but their relative amounts change with larval development. Results of N-terminal sequencing of prominent proteins revealed no obvious homologies to protein sequences deposited in the databases up to now.  相似文献   

Deterministic and probabilistic floor response spectra   总被引：1，自引：0，他引：1  

Aleksandar Paskalov  Stefanie Reese 《Soil Dynamics and Earthquake Engineering》2003,23(7):605-618

The paper presents a comparative study for computing floor response spectra (FRS) for complex structures. For the purpose of validation and evaluation of the methods for practical application, a systematic comparison of two concepts, classical deterministic and probabilistic, was carried out as an example of a nuclear power plants structure. The deterministic method utilizes time history analyses compatible with the prescribed design response spectrum. The probabilistic method uses an analysis of random vibrations for defining the probabilistic FRS influenced by random seismic soil movement. The seismic input is a power spectral density function (PSDF) compatible with the design response spectrum. The probabilistic approach based on PSDF provides satisfying FRS with far less effort and time consumption needed for calculation.  相似文献