Life under pressure: insights from electronic data-storage tags into cod swimbladder function     

van der Kooij  Jeroen; Righton  David; Strand  Espen; Michalsen  Kathrine; Thorsteinsson  Vilhjalmur; Svedang  Henrik; Neat  Francis C.; Neuenfeldt  Stefan 《ICES Journal of Marine Science》2007,64(7):1293-1301

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Rates of oxygen transfer from air bubbles to aqueous NaCl solutions at various temperatures     

Stefan A Zieminski  Robert M Hume III  Robert Durham 《Marine Chemistry》1976,4(4):333-346

Experiments have been conducted to investigate the effects of temperature on the interfacial surface area and on the rate of oxygen transfer from air bubbles dispersed in aqueous NaCl solutions. Tests were also conducted to estimate the effects of salt concentration on the size of the bubbles. In addition to NaCl solutions, seawater was used in some tests. The temperature effects were investigated at 5, 10, 15, 20, 25, and 30°C. The results showed a pronounced effect of the salt on the size of the bubbles, which first decreased sharply with increasing concentration, but showed no further drop when the concentration was increased beyond 0.6 M. Both in seawater and in the 0.6 M solution, the mass transfer rate, K_LA, increased almost linearly when temperature was increased within the range from 5 to 25°C. The salt solution, as well as the seawater, showed an increase of K_LA of 60–70% over that in pure water at the same temperatures. This effect was the result of increased surface area of bubbles because of decreased coalescence. The increase in surface area was strongly temperature dependent, especially between 15 and 20°C. Contrary to this behavior the surface area in pure water showed, practically, no temperature dependence. The results are explained and discussed on the basis of ion-water interactions.  相似文献   

Lithium isotope composition of ordinary and carbonaceous chondrites, and differentiated planetary bodies: Bulk solar system and solar reservoirs     

Hans-Michael Seitz  Gerhard P. Brey  Jutta Zipfel  Ulrich Ott  Stefan Weyer  Soodabeh Durali  Stephan Weinbruch 《Earth and Planetary Science Letters》2007,260(3-4):582-596

In order to better constrain the Li isotope composition of the bulk solar system and Li isotope fractionation during accretion and parent body processes, Li isotope compositions and concentrations were determined on a number of meteorite falls and finds. This is the first comprehensive study that systematically investigates a representative set of samples from carbonaceous chondrites (CI, CM2, CO3, CV3, CK4 and one ungrouped member), enstatite chondrites (EH, EL), ordinary chondrites (H, L, LL), and achondrites (one eucrite, diogenites, one pallasite, and a silicate inclusion from a IAB iron).

Carbonaceous chondrites have an average isotope composition of δ⁷Li = + 3.2‰ ± 1.9 (2σ) which agrees with the average composition of relatively pristine olivines (representative for the bulk composition) from the Earth primitive upper mantle (PUM). This is lighter than the average δ⁷Li of the basaltic differentiates of the Earth, Moon and Mars and the achondrites. It is an important observation, however, that the lighter end of the isotopic range of the differentiates always coincides with the averages of the mantle olivines and the carbonaceous chondrites. From this we conclude that the bulk of the inner solar system consists mostly of material from carbonaceous chondrites and that the variation seen in the differentiates is due to planetary body processes. Ordinary chondrites are significantly lighter than carbonaceous chondrites. No significant differences in δ⁷Li exist between enstatite chondrites (n = 3) and carbonaceous or ordinary chondrites. The difference between carbonaceous and ordinary chondrites and the variability within the chondrites could indicate the existence of distinct Li isotope reservoirs in the early solar nebula.  相似文献   

Expert judgements on the response of the Atlantic meridional overturning circulation to climate change     

Kirsten Zickfeld  Anders Levermann  M. Granger Morgan  Till Kuhlbrodt  Stefan Rahmstorf  David W. Keith 《Climatic change》2007,82(3-4):235-265

We present results from detailed interviews with 12 leading climate scientists about the possible effects of global climate change on the Atlantic Meridional Overturning Circulation (AMOC). The elicitation sought to examine the range of opinions within the climatic research community about the physical processes that determine the current strength of the AMOC, its future evolution in a changing climate and the consequences of potential AMOC changes. Experts assign different relative importance to physical processes which determine the present-day strength of the AMOC as well as to forcing factors which determine its future evolution under climate change. Many processes and factors deemed important are assessed as poorly known and insufficiently represented in state-of-the-art climate models. All experts anticipate a weakening of the AMOC under scenarios of increase of greenhouse gas concentrations. Two experts expect a permanent collapse of the AMOC as the most likely response under a 4×CO₂ scenario. Assuming a global mean temperature increase in the year 2100 of 4 K, eight experts assess the probability of triggering an AMOC collapse as significantly different from zero, three of them as larger than 40%. Elicited consequences of AMOC reduction include strong changes in temperature, precipitation distribution and sea level in the North Atlantic area. It is expected that an appropriately designed research program, with emphasis on long-term observations and coupled climate modeling, would contribute to substantially reduce uncertainty about the future evolution of the AMOC.  相似文献   

Uncertainties in predicting travel flows: common ground and research needs. A reply to Bigano et al.     

Stefan Gössling  C. Michael Hall 《Climatic change》2006,79(3-4):181-183

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Numerical Modelling of Katabatic Flow Over a Melting Outflow Glacier     

Stefan Söderberg  Oskar Parmhed 《Boundary-Layer Meteorology》2006,120(3):509-534

A realistic simulation of katabatic flows is not a straightforward task for numerical models. One complicating factor is that katabatic flows develop within a stably stratified boundary layer, which is poorly resolved and described in many numerical models. To capture the jet-shaped shallow flow a model set-up with high vertical resolution is also required. In this study, ‘a state of the art’ mesoscale numerical model is applied in a simulation of katabatic flow over a melting glacier. A basic agreement between observations and model results is found. From scale analysis, it is concluded that the simulated flow can be classified as katabatic. Although the background flow varies in strength and direction, the simulated katabatic flow over Breidamerkurjökull is persistent. Two factors vital for this persistence are identified. First, the melting snow maintains the surface temperature close to 0 °C while the air temperature warms adiabatically as it descends the slope. This provides a ‘self enhanced’ negative buoyancy that drives the flow to a balance with local friction. Second, the jet-like shape of the resulting flow gives rise to a large ‘curvature term’ in the Scorer parameter, which becomes negative in the upper jet. This prevents vertical wave propagation and isolates the katabatic layer of the influence from the free troposphere aloft. Our results suggest that the formation of local microclimates dominated by katabatic flow is a general feature over melting glaciers. The modelled turbulence structure illustrates the importance of non-local processes. Neglecting the vertical transport of turbulence in katabatic flows is not a valid assumption. It is also found that the local friction velocity remains larger than zero through the katabatic jet, due to directional shear where the scalar wind speed approaches its maximum.  相似文献   

Uncertainties in Predicting Tourist Flows Under Scenarios of Climate Change   总被引：2，自引：0，他引：2  

Stefan Gössling  C. Michael Hall 《Climatic change》2006,79(3-4):163-173

Tourism is largely dependent on climatic and natural resources. For example, “warmer'' climates generally constitute preferred environments for recreation and leisure, and natural resources such as fresh water, biodiversity, beaches or landscapes are essential preconditions for tourism. Global environmental change threatens these foundations of tourism through climate change, modifications of global biogeochemical cycles, land alteration, the loss of non-renewable resources, unsustainable use of renewable resources and loss of biodiversity (Gössling and Hall, 2005). This has raised concerns that tourist flows will change to the advantage or disadvantage of destinations, which is of major concern to local and national economies, as tourism is one of the largest economic sectors of the world, and of great importance for many destinations. In consequence, an increasing number of publications have sought to analyse travel flows in relation to climatic and socio-economic parameters (e.g. Lise and Tol, 2001; Maddison, 2001; Christ et al., 2003; Hamilton et al., 2003; Hamilton and Tol, 2004). The ultimate goal has been to develop scenarios for future travel flows, possibly including “most at risk destinations'', both in economic and in environmental terms. Such scenarios are meant to help the tourist industry in planning future operations, and they are of importance in developing plans for adaptation.  相似文献   

Sub-Milankovitch climatic cycles in Holocene stalagmites from Sauerland, Germany     

Stefan Niggemann  Augusto Mangini  Detlev K Richter 《Earth and Planetary Science Letters》2003,216(4):539-547

Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ¹⁸O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ¹⁸O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ¹⁸O and Δ¹⁴C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257-1266; 294 (2001) 2130-2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations.  相似文献   

Higher plant vegetation changes during Pliocene sapropel formation     

Diana Menzel  Stefan Schouten  Pim F. van Bergen  Jaap S. Sinninghe Damst 《Organic Geochemistry》2004,35(11-12):1343

The δ¹³C values of higher plant wax C_27–33 n-alkanes were determined in three, time-equivalent Pliocene (2.943 Ma) sapropels and homogeneous calcareous ooze from three different sites forming an east-west transect in the eastern Mediterranean Basin in order to study the composition of the vegetation on the continents surrounding the Mediterranean Sea. A two-end member mixing model transformed the measured δ¹³C values into the contribution of C₄ plants to the terrestrial vegetation. These calculations indicated a high C₄ plant contribution (i.e. 40–50%) in the periods just before and just after sapropel formation. During sapropel deposition the C₄ plant contribution increased by up to 20% at all sites. This is interpreted to record the increased overall plant coverage of the Mediterranean borderlands resulting from the change in formerly barren desert areas into C₄ grass-dominated savannahs as a response to the wetter climate during sapropel deposition. Enhanced accumulation rates (ARs) of long-chain n-alkanes (C_27–33) and n-alkan-1-ols (C_26–30) towards the middle of the sapropel in concert with a decrease in the Ti/Al ratio confirm an increased delivery of terrigenous organic matter at all sites. These biomarkers were probably predominantly fluvially transported to the Mediterranean Sea, not only by the Nile but by fossil wadi river systems on the northern African continent.  相似文献   

Design of sheet pile installation by vibration     

Stefan van Baars Baars 《Geotechnical and Geological Engineering》2004,22(3):391-400

In The Netherlands 70% of the steel sheet piles are installed with vibrators. This is because vibrators have a high production rate and therefore a low installation cost. This method only works for soft peat and clay layers and saturated sand layers which are not densely compacted. During pile installation several problems might occur. In this paper the attention is paid to avoiding jamming of the pile before it has reached its planned depth. In most of these cases this is caused by a design error which has let to a vibrator which is too light. Over the years different design tools, such as computer models, design graphs and design equations, have been developed in order to predict the minimum required vibrator force. In this paper a new design equation is presented, which consists of three parts: the mass of the sheet pile, the friction along the shaft and the soil resistance at the tip of the pile based on the cone penetration resistance. This equation and several other design tools for sheet pile installation, have been compared with 18 field tests. It was found that the general design graphs of the Dutch Union of Foundation Contractors (NVAF), the design equation of the Dutch Civil Engineering Centre for Construction Research and Design Rules (CUR) and the German design equation of the EAU1996 gave very poor results. The computer model Vibdrive from Holeyman (1996), the design graphs for specific locations from the NVAF and the new presented design equation from the author gave reasonable predictions. Since the computer program is, because of its complexity, not regarded as a design tool for daily design work and the local design graphs only exist for a small number of locations in The Netherlands, the new design equation is according to the field tests the best method for the calculation of the vibrator needed for sheet pile installation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献