The patterned peatlands of Minnesota H. E. Wright,Jr., B. A. Coffin and N. E. Aaseng Publisher University of Minnesota Press,Minneapolis. 1992 (XX + 337 pp. and 16 colour plates)     

Nils Malmer 《第四纪科学杂志》1995,10(4):404-406

  相似文献   

Atmospheric CO₂ consumption by chemical weathering in North America     

Nils Moosdorf  Jens Hartmann  Benjamin Hagedorn 《Geochimica et cosmochimica acta》2011,75(24):7829-7854

CO₂ consumption by chemical weathering is an integral part of the boundless carbon cycle, whose spatial patterns and controlling factors on continental scale are still not fully understood. A dataset of 338 river catchments throughout North America was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors. Detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying CO₂ consumption. Extrapolation of the identified empirical model equations to North America allows the analysis of the spatial patterns of the CO₂ consumption by chemical weathering.Runoff, lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated CO₂ consumption. Other influence factors, e.g. temperature, could not be established in the models. Of the distinguished land cover classes, artificial surfaces, dominated by urban areas, increase bicarbonate fluxes most, followed by shrubs, grasslands, managed lands, and forests. The extrapolation results in an average specific bicarbonate flux of 0.3 Mmol km⁻² a⁻¹ by chemical weathering in North America, of which 64% originates from atmospheric CO₂, and 36% from carbonate mineral dissolution. Chemical weathering in North America thus consumes 50 Mt atmospheric CO₂-C per year. About half of that originates from 10% of the area of North America.The estimated strength of individual predictors differs from previous studies. This highlights the need for a globally representative set of regionally calibrated models of CO₂ consumption by chemical weathering, which apply very detailed spatial data to resolve the heterogeneity of earth surface processes.  相似文献   

Compatibility of space and time for modeling fluvial HCO3- fluxes – A comparison     

Nils Moosdorf  Jens Hartmann  Ronny Lauerwald 《Applied Geochemistry》2011

  相似文献   

Hydraulic conditions at the source zone and their impact on plume behavior     

Nils Gueting  Andreas Englert 《Hydrogeology Journal》2013,21(4):829-844

A laboratory sandbox model (105?×?60?×?15 cm) was filled with different types of sediments to arrange different hydraulic conditions at the tracer’s injection zone. Tracer-input functions were monitored at the injection location and tracer breakthrough curves (BTCs) were measured at a downgradient detection plane. Numerical transport simulations analogous to the sandbox experiments were conducted in a numerical model parameterized with the properties of the sediments used in the sandbox. The results of the study demonstrate that the hydraulic conditions at the source zone have a major influence on plume development. Tracer injection into high-permeability zones causes early arrival, and enhanced transverse and reduced longitudinal spreading. Tracer injection into low-permeability zones causes late arrival, and reduced transverse and enhanced longitudinal spreading. It was further found that using simplified tracer-input functions in the analysis of BTCs can lead to biased transport parameters. The results suggest that transport parameter estimation based on tracer experiments can benefit from monitoring of the tracer-input function and subsequent consideration of the measured tracer-input function in the analysis of BTCs.  相似文献   

Weakening AMOC connects Equatorial Atlantic and Pacific interannual variability     

Lea Svendsen  Nils Gunnar Kvamstø  Noel Keenlyside 《Climate Dynamics》2014,43(11):2931-2941

Observations indicate that since the 1970s Equatorial Atlantic sea surface temperature (SST) variations in boreal summer tend to modulate El Niño in the following seasons, indicating that the Atlantic Ocean can have importance for predicting the El Niño–Southern Oscillation (ENSO). The cause of the change in the recent decades remains unknown. Here we show that in the Bergen Climate Model (BCM), a freshwater forced weakening of the Atlantic meridional overturning circulation (AMOC) results in a strengthening of the relation between the Atlantic and the Pacific similar to that observed since the 1970s. During the weakening AMOC phase, SST and precipitation increase in the central Equatorial Atlantic, while the mean state of the Pacific does not change significantly. In the Equatorial Atlantic the SST variability has also increased, with a peak in variability in boreal summer. In addition, the characteristic timescales of ENSO variability is shifted towards higher frequencies. The BCM version used here is flux-adjusted, and hence Atlantic variability is realistic in contrast to in many other models. These results indicate that in the BCM a weakening AMOC can change the mean background state of the Tropical Atlantic surface conditions, enhancing Equatorial Atlantic variability, and resulting in a stronger relationship between the Tropical Atlantic and Pacific Oceans. This in turn alters the variability in the Pacific.  相似文献   

Overcoming skepticism with education: interacting influences of worldview and climate change knowledge on perceived climate change risk among adolescents   总被引：2，自引：2，他引：0  

Kathryn T. Stevenson  M. Nils Peterson  Howard D. Bondell  Susan E. Moore  Sarah J. Carrier 《Climatic change》2014,126(3-4):293-304

Though many climate literacy efforts attempt to communicate climate change as a risk, these strategies may be ineffective because among adults, worldview rather than scientific understanding largely drives climate change risk perceptions. Further, increased science literacy may polarize worldview-driven perceptions, making some climate literacy efforts ineffective among skeptics. Because worldviews are still forming in the teenage years, adolescents may represent a more receptive audience. This study examined how worldview and climate change knowledge related to acceptance of anthropogenic global warming (AGW) and in turn, climate change risk perception among middle school students in North Carolina, USA (n?=?387). We found respondents with individualistic worldviews were 16.1 percentage points less likely to accept AGW than communitarian respondents at median knowledge levels, mirroring findings in similar studies among adults. The interaction between knowledge and worldview, however, was opposite from previous studies among adults, because increased climate change knowledge was positively related to acceptance of AGW among both groups, and had a stronger positive relationship among individualists. Though individualists were 24.1 percentage points less likely to accept AGW than communitarians at low levels (bottom decile) of climate change knowledge, there was no statistical difference in acceptance levels between individualists and communitarians at high levels of knowledge (top decile). Non-White and females also demonstrated higher levels of AGW acceptance and climate change risk perception, respectively. Thus, education efforts specific to climate change may counteract divisions based on worldviews among adolescents.  相似文献   

Numerical analysis of synthetic granulate deposition in a physical model study     

Gabriele HARB  Stefan HAUN  Joséf SCHNEIDER  Nils Reidar B.OLSEN 《国际泥沙研究》2014,29(1):110-117

The current study focuses on the application of a three-dimensional numerical model for the prediction of morphological bed changes. The sediment deposition in a reservoir during a 10-year-flood was investigated and the results of the simulation were validated with data derived from a physical model study. Because of the small grain sizes in the prototype, synthetic granulate was used in the physical model. The numerical computation domain was a reproduction of the physical model, including the grain sizes and the density of the particles, in order to ensure comparability. The CFD code SSIIM, which solves the RANS-equations in three-dimensions, was used for the simulations. The sediment transport in SSIIM is divided into suspended sediment transport, computed by solving the convection-diffusion equation, and bed-load transport, calculated by an empirical formula. The results of the numerical simulation correspond well to the results of the physical model study. The simulated location and the pattern of the sediment deposition in the reservoir are an accurate representation of the observed distribution in the physical model.  相似文献   

Sensitivity of simulated wintertime Arctic atmosphere to vertical resolution in the ARPEGE/IFS model     

Øyvind Byrkjedal  Igor Esau  Nils Gunnar Kvamstø 《Climate Dynamics》2008,30(7-8):687-701

The current state-of-the-art general circulation models, including several of those used by the IPCC, show considerable biases in the simulated present day high-latitude climate compared to observations and reanalysis data. These biases are most pronounced during the winter season. We here employ ideal vertical profiles of temperature and wind from turbulence-resolving simulations to perform a priori studies of the first-order eddy-viscosity closure scheme employed in the ARPEGE/IFS model. This reveals that the coarse vertical resolution (31 layers) of the model cannot be expected to realistically resolve the Arctic stable boundary layer. The curvature of the Arctic inversion and thus also the vertical turbulent-exchange processes cannot be reproduced by the coarse vertical mesh employed. To investigate how turbulent vertical exchange processes in the Arctic boundary layer are represented by the model parameterization, a simulation with high vertical resolution (90 layers in total) in the lower troposphere is performed. Results from the model simulations are validated against data from the ERA-40 reanalysis. The dependence of the surface air temperature on surface winds, surface energy fluxes, free atmosphere stability and boundary layer height is investigated. The coarse-resolution run reveals considerable biases in these parameters, and in their physical relations to surface air temperature. In the simulation with fine vertical resolution, these biases are clearly reduced. The physical relation between governing parameters for the vertical turbulent-exchange processes improves in comparison with ERA-40 data.  相似文献   

Effects of Short‐term and Long‐term Aluminium Stress on Photosynthesis,Respiration, and Reproductive Capacity in a Unicellular Green Flagellate (Euglena gracilis)     

Roman A. Danilov  Nils G. A. Ekelund 《洁净——土壤、空气、水》2002,30(4):190-196

Effects of short‐term (1 h exposure) and long‐term (7 d exposure) aluminium stress on photosynthesis and reproductive capacity have been studied in Euglena gracilis strain Z. Following concentrations of Al_tot (added as AlCl₃) were tested: 0.5 mg L^‐1, 1.0 mg L^‐1, 1.5 mg L^‐1, 2.5 mg L^‐1, 5.0 mg L^‐1, 7.5 mg L^‐1, 10.0 mg L^‐1, and 15.0 mg L^‐1 Al, respectively. Growth rates at different aluminium concentrations did not show significant differences, except at 15.0 mg L^‐1Al. Initial respiration was higher in long‐term than in the short‐term experiments. It is supposed that an energy‐dependent mechanism of excretion of aluminium ions has been active in the stressed cells. Consequently, the cells of E. gracilis after long‐term exposure to aluminium are believed to be more acclimatised to the aluminium stress. Photosynthetic efficiency (PE) has been negatively affected by aluminium in all experiments performed. Differences between control algae and those treated with aluminium were significant in all cases. PE in long‐term experiments was in general significantly higher at all concentrations of aluminium studied, compared to the short‐term experiments. The aluminium concentrations tested led only to a general decrease in PE while the level of decrease was not especially concentration‐dependent. In general, aluminium tolerance of E. gracilis can be estimated as low, especially by short‐term exposure. However, good acclimatisation capacity of this green flagellate to aluminium doses by long‐term exposure can be supposed.  相似文献   

Concentration fluctuation data from dispersion experiments carried out in stable and unstable conditions     

Nils Mole  C. D. Jones 《Boundary-Layer Meteorology》1994,67(1-2):41-74

Experiments have been carried out to investigate the dispersion of plumes at short range in the atmospheric boundary layer during stable and unstable conditions. The experiments and measurement system are described, and the results are compared with those of previous experiments. The slow meandering under stable conditions found by Mylne (1992) is not present here (probably because of topographic effects), so the plume is present on the mean centreline more often, and timescales are shorter, under stable conditions. Associated with this, statistics during stable conditions exhibit greater stability to changes in total sampling time. Intensity is found to be greater under unstable conditions, but there do not appear to be large differences in the shape of the probability density function between stable and unstable conditions. The intermittency is calculated using several variations on the conventional definition. The values obtained vary substantially according to which definition is used (although they are always higher in the stable than in the unstable experiments), demonstrating the sensitivity to both the precise definition and to measurement system characteristics. It is shown that even at very short range the mean and variance of concentration are determined almost entirely by the fluid not emanating from the source. Thus the partition between source and non-source fluid suggested by Chatwin and Sullivan (1989), while providing a more scientifically sound definition of intermittency, does not have an obvious direct practical application.  相似文献