Constraining ocean diffusivity from the 8.2 ka event     

Alexander Lorenz  Hermann Held  Eva Bauer  Thomas Schneider von Deimling 《Climate Dynamics》2010,34(5):719-734

Greenland ice-core data containing the 8.2 ka event are utilized by a model-data intercomparison within the Earth system model of intermediate complexity, CLIMBER-2.3 to investigate their potential for constraining the range of uncertain ocean diffusivity properties. Within a stochastic version of the model (Bauer et al. in Paleoceanography 19:PA3014, 2004) it has been possible to mimic the pronounced cooling of the 8.2 ka event with relatively good accuracy considering the timing of the event in comparison to other modelling exercises. When statistically inferring from the 8.2 ka event on diffusivity the technical difficulty arises to establish the related likelihood numerically per realisation of the uncertain model parameters: while mainstream uncertainty analyses can assume a quasi-Gaussian shape of likelihood, with weather fluctuating around a long term mean, the 8.2 ka event as a highly nonlinear effect precludes such an a priori assumption. As a result of this study the Bayesian Analysis leads to a sharp single-mode likelihood for ocean diffusivity parameters within CLIMBER-2.3. Depending on the prior distribution this likelihood leads to a reduction of uncertainty in ocean diffusivity parameters (e.g. for flat prior uncertainty in the vertical ocean diffusivity parameter is reduced by factor 2). These results highlight the potential of paleo data to constrain uncertain system properties and strongly suggest to make further steps with more complex models and richer data sets to harvest this potential.  相似文献   

The representation of a synoptic-scale weather system in a thermodynamically adjusted version of the ECHAM4 general circulation model     

H.-S. Bauer  V. Wulfmeyer  L. Bengtsson 《Meteorology and Atmospheric Physics》2008,99(3-4):129-153

Summary In this work, a strong cyclone event is simulated by the general circulation model (GCM) ECHAM4 for studying the representation of weather systems in a climate model. The system developed along the East Coast of the U.S.A. between the 12th and 14th of March 1993. The GCM simulation was started from climatological conditions and was continuously forced to the analyzed state by a thermodynamical adjustment based on the Newtonian relaxation technique (nudging). Relaxation terms for vorticity, divergence, temperature, and the logarithm of surface pressure were added at each model level and time step. The necessary forcing files were calculated from the ECMWF re-analysis (ERA15). No nudging terms were added for the components of the water cycle. Using this forcing, the model was able to reproduce the synoptic-scale features and its temporal development realistically after a spin-up period. This is true even for quantities that are not adjusted to the analysis (e.g., humidity). Detailed comparisons of the model simulations with available observations and the forcing ERA15 were performed for the cyclone case. Systematic errors were detected in the simulation of the thermodynamic state of the atmosphere, which can be traced back to deficiencies in model parametrizations. Differences in the representation of the surface fluxes lead to systematic deviations in near-surface temperature and wind fields. The general situation is very similar in both model representations. Errors were detected in the simulation of the convective boundary layer behind the cold front. The observed strong convective activity is missed both by the adjusted ECHAM4 simulation and ERA15. This is most likely caused by weaknesses in the cloud and convection schemes or by a too strong downdraft compensating the frontal lifting and suppressing the vertical transport of moisture from the boundary layer to higher levels. This work demonstrates for the investigated case the value of simulating single weather events in climate models for validating model physics. Correspondence: Hans-Stefan Bauer, Institute of Physics and Meteorology, University of Hohenheim, Garbenstra?e 30, 70599 Stuttgart, Germany  相似文献   

Toothed whales in the northwestern Mediterranean: insight into their feeding ecology using chemical tracers     

Praca E  Laran S  Lepoint G  Thomé JP  Quetglas A  Belcari P  Sartor P  Dhermain F  Ody D  Tapie N  Budzinski H  Das K 《Marine pollution bulletin》2011,62(5):1058-1065

Risso’s dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso’s dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (δ¹³C, δ¹⁵N) and organochlorines. Significantly different δ¹⁵N values were obtained in Risso’s dolphins (11.7 ± 0.7‰), sperm whales (10.8 ± 0.3‰) and pilot whales (9.8 ± 0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale’s diet. Similar δ¹³C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 μg.g⁻¹ lw) and higher tDDT/tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso’s dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns.  相似文献   

An Antarctic view of Beryllium-10 and solar activity for the past millennium   总被引：1，自引：1，他引：0  

Gilles Delaygue  Edouard Bard 《Climate Dynamics》2011,36(11-12):2201-2218

Beryllium-10 in ice provides a valuable proxy of solar activity. However, complex production pathways, atmospheric transport, and deposition processes impede its quantitative interpretation. Here, we examine the influence of deposition processes on two Be-10 ice core records from Central Antarctica (South Pole and Dome Fuji stations), covering the last millennium. We try to quantify how Be-10 variations in ice relate to variations in Be-10 production, and the bias associated to this relationship. An independent bias estimation is provided by comparing atmospheric radiocarbon variations reconstructed from tree rings and deduced from Be-10 variations. Both techniques suggest an uncertainty of the order of 10% in Be-10 production. This uncertainty estimate does not account for the geographical origin of Be-10, which remains a major issue. Because both Be-10 records are so similar, we propose to average them as a means to decrease the unshared (non solar) variability. This average record provides a new reconstruction of solar modulation parameter ?? and total solar irradiance over the last ~1,300?years. The lowest solar activity is found during the so-called Sp?rer Minimum (around AD 1450). The highest activities are found during the 8th century and over the last decades: as shown in previous studies, our results suggest that the recent solar activity is not exceptionally high for the last millennium.  相似文献   

Monsoon intraseasonal oscillation and land�Catmosphere interaction in an idealized model     

Gilles Bellon 《Climate Dynamics》2011,37(5-6):1081-1096

A simple coupled model is used in a zonally-symmetric configuration to investigate the effect of land?Catmosphere coupling on the Asian monsoon intraseasonal oscillation. The atmospheric model is a version of the Quasi-equilibrium Tropical Circulation Model with a prognostic atmospheric boundary layer, as well as two free-tropospheric modes in momentum, and one each in moisture and temperature. The land model is the simple one-layer model SLand. The complete nonlinear version and a linear version of the model are used to understand how land?Catmosphere interaction influences the northward-propagating intraseasonal oscillation that has been documented in the atmospheric model (Bellon and Sobel in J Geophys Res 113, 2008a, J Atmos Sci 65:470?C489, 2008b). Our results show that this interaction damps the intraseasonal variability in most cases. The small heat capacity of land surfaces is the main factor that intervenes directly in the dynamics of the intraseasonal oscillation and explains the damping of intraseasonal variability. But in a few peculiar cases, the small heat capacity of land can also cause a strong interaction between the intraseasonal oscillation and the mean state via the nonlinearity of precipitation, that enhances the monsoon intraseasonal variability. High land albedo indirectly influences the intraseasonal variability by setting the seasonal mean circulation to conditions unfavorable for the monsoon intraseasonal oscillation.  相似文献   

Measurement and modeling of mercury complexation by dissolved organic matter isolates from freshwater and effluents of a major wastewater treatment plant     

Bogdan Muresan  Benoît Pernet-Coudrier  Daniel Cossa  Gilles Varrault 《Applied Geochemistry》2011,26(12):2057-2063

Dissolved organic matter (DOM) samples were obtained from a low-density urbanized area located upstream of Paris (along the Marne River, France) and from the treated effluents at the Paris main wastewater treatment plant. These samples were then fractionated according to their hydrophobicity. DOM fractions consisted of nanomolar to sub-micromolar fresh organic substances with extremely strong Hg-complexing ligands. The conditional stability constants (i.e. ; pH ∼ 6.8, I_NaCl = 0.5 M, T = 25 °C) of the Hg-DOM complexes formed were greater than 10²⁴ M⁻¹, for the reaction Hg²⁺ + L = HgL (with L as ligand). For upstream of Paris, thermodynamic calculations indicated that the vast majority of Hg-DOM was associated with hydrophobic DOM. In contrast, in the Paris main wastewater treatment plant effluents, Hg-DOM was mainly bound to hydrophilic DOM. Simple dilution calculations highlighted that due to the large DOM loading of urban discharges, the hydrophilic urban DOM ligands may commonly dominate Hg-DOM speciation in the downstream Seine River, except under extreme dilution (i.e. high water episodes or floods).  相似文献   

Age of river basins in Guadeloupe impacting chemical weathering rates and land use     

Sétareh Rad  Olivier Cerdan  Karine Rivé  Gilles Grandjean 《Applied Geochemistry》2011

The Lesser Antilles have very high chemical weathering rates, with values that can reach 1290 t/km²/a. The tropical environment induces high precipitation rates, high temperature, dense vegetation, with sharp relief and thick soils. Because of volcanic activity, frequent pyroclastic flows produce very erodible and porous materials. In addition, agriculture induces important land use changes which replace existing native forest cover with banana and sugar cane plantations. Their surface can cover as much as 40% of the total area of a river basin. The aim of this study is to identify key parameters, either natural or anthropogenic, that control chemical weathering rates. Among the combined impact of all parameters (climate, runoff, slopes, vegetation etc.), basin age seems to be the control parameter: the younger the basin, the higher the weathering rate. A correlation between the chemical weathering rate and the basin age suggests that young volcanic rocks are more easily weathered than old ones: young fresh material is easily mobilized by erosion, while for older rocks with thick soil covers, chemical rates are much lower. A combined effect between the higher erodibility and a higher climate erosivity of the younger relief could be observed. Moreover, a correlation between banana plantations and the chemical weathering rates that can be explained by an increase of infiltration, due to stem flow processes is shown here. Banana plantations also have a correlation with the basin age, older basins being more favorable terrains for cultivation.  相似文献   

Carbonation of lignite fly ash at ambient T and P in a semi-dry reaction system for CO₂ sequestration     

Markus Bauer  Niklas GassenHelge Stanjek  Stefan Peiffer 《Applied Geochemistry》2011,26(8):1502-1512

The global rise in atmospheric greenhouse gas concentrations calls for practicable solutions to capture CO₂. In this study, a mineral carbonation process was applied in which CO₂ reacts with alkaline lignite ash and forms stable carbonate solids. In comparison to previous studies, the assays were conducted at low temperatures and pressures and under semi-dry reaction conditions in an 8 L laboratory mixing device. In order to find optimum process conditions the pCO₂ (10-20%), stirring rate (500-3000 rpm) and the liquid to solid ratio (L/S = 0.03-0.36 L kg⁻¹) were varied. In all experiments a considerable CO₂ uptake from the gas phase was observed. Concurrently the solid phase contents of Ca and Mg (hydr)oxides decreased and CaCO₃ and MgCO₃ fractions increased throughout the experiments, showing that CO₂ was stabilized as a solid carbonate. The carbonation reaction depends on three factors: Dissolution of CO₂ in the liquid phase, mobilization of Ca and Mg from the mineral surface and precipitation of the carbonate solids. Those limitations were found to depend strongly on the variation of the process parameters. Optimum reaction conditions could be found for L/S ratios between 0.12 and 0.18, medium stirring velocities and pCO₂ between 10% and 20%.Maximum CO₂ uptake by the solid phase was 4.8 mmol g⁻¹ after 120 min, corresponding to a carbonation efficiency for the alkaline material of 53% of the theoretical CO₂ binding capacity. In comparison to previous studies both CO₂ uptake and carbonation efficiencies were in a similar range, but the reaction times in the semi-dry process were considerably shorter. The proposed method additionally allows for a more simple carbonation setup due to low T and P, and produces an easier to handle product with low water content.  相似文献   

The metamorphic complex of Beloretzk, SW Urals, Russia — a terrane with a polyphase Meso- to Neoproterozoic thermo-dynamic evolution     

U. A. Glasmacher  W. Bauer  U. Giese  P. Reynolds  B. Kober  V. Puchkov  L. Stroink  A. Alekseyev  A. P. Willner 《Precambrian Research》2001,110(1-4)

An integrated geological study of the tectono-metamorphic evolution of the metamorphic complex of Beloretzk (MCB) which is part of the eastern Bashkirian mega-anticlinorium (BMA), SW Urals, Russia shows that the main lithological units are Neoproterozoic (Riphean and Vendian age) siliciclastic to carbonate successions. Granitic, syenitic and mafic intrusions together with subaerial equivalents comprise the Neo- and Mesoproterozoic magmatic rocks. The metamorphic grade ranges from diagenetic and very low grade in the western BMA to high-grade in the MCB. The N–S trending Zuratkul fault marks the change in metamorphic grade and structural evolution between the central and eastern BMA. Structural data, Pb/Pb-single zircon ages, ⁴⁰Ar/³⁹Ar cooling ages and the provenance signature of Riphean and Vendian siliciclastic rocks in the western BMA give evidence of Mesoproterozoic (Grenvillian) rifting, deformation and eclogite-facies metamorphism in the MCB and a Neoproterozoic (Cadomian) orogenic event in the SW Urals. Three pre-Ordovician deformation phases can be identified in the MCB. The first SSE-vergent, isoclinal folding phase (D₁) is younger than the intrusion of mafic dykes (Pb/Pb-single zircon: 1350 Ma) and older than the eclogite-facies metamorphism. High P/low T eclogite-facies metamorphism is bracketed by D₁ and the intrusion of the Achmerovo granite (Pb/Pb-single zircon: ≤970 Ma). An extensional, sinistral, top-down-to-NW directed shearing (D₂) is correlated with the first exhumation of the MCB. E-vergent folding and thrusting (D₃) occurred at retrograde greenschist-facies metamorphic conditions. The tremolite ⁴⁰Ar/³⁹Ar cooling age (718±5 Ma) of amphibolitic eclogite and muscovite ⁴⁰Ar/³⁹Ar cooling ages (about 550 Ma) of mica schists indicate that a maximum temperature of 500±50 °C was not reached during the Neoproterozoic orogeny. The style and timing of the Neoproterozoic orogeny show similarities to the Cadomian-aged Timan Range NW of the Polar Urals. Geochronological and thermochronological data together with the abrupt change in structural style and metamorphism east of the Zuratkul fault, suggest that the MCB is exotic with respect to the SE-margin of the East European Platform. Thus, the MCB is named the ‘Beloretzk Terrane’. Recognition of the ‘Beloretzk Terrane’ and the Neoproterozoic orogeny at the eastern margin of Baltica has important implications for Neoproterozoic plate reconstruction and suggests that the eastern margin of Baltica might have lain close to the Avalonian–Cadomian belt.  相似文献   

Gewinnung repräsentativer Wassermischproben mit einem einfachen kontinuierlichen Sammelgerät     

G. Bauer 《洁净——土壤、空气、水》1989,17(3):349-351

The sampling device consists of a weighted wide-necked bottle with a siphon pipe inserted in its top through which water enters the bottle while air escapes out of the bottle through a pipe with a valve that is inserted in the top, too. Due to the variable setting of the valve the period of time for the filling of the bottle can be controlled between few minutes and up to 24 h.  相似文献