The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming   总被引：2，自引：0，他引：2  

R. A. Betts  P. M. Cox  M. Collins  P. P. Harris  C. Huntingford  C. D. Jones 《Theoretical and Applied Climatology》2004,78(1-3):157-175

Summary A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO₂ is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO₂ was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO₂ contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO₂ and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.  相似文献   

Calibration of a land-surface model using data from primary forest sites in Amazonia     

P. P. Harris  C. Huntingford  J. H. C. Gash  M. G. Hodnett  P. M. Cox  Y. Malhi  A. C. Araújo 《Theoretical and Applied Climatology》2004,78(1-3):27-45

Summary A land-surface model (MOSES) was tested against observed fluxes of heat, water vapour and carbon dioxide for two primary forest sites near Manaus, Brazil. Flux data from one site (called C14) were used to calibrate the model, and data from the other site (called K34) were used to validate the calibrated model. Long-term fluxes of water vapour at C14 and K34 simulated by the uncalibrated model were good, whereas modelled net ecosystem exchange (NEE) was poor. The uncalibrated model persistently underpredicted canopy conductance (g _c ) from mid-morning to mid-afternoon due to saturation of the response to solar radiation at low light levels. This in turn caused a poor simulation of the diurnal cycles of water vapour and carbon fluxes. Calibration of the stomatal conductance/photosynthesis sub-model of MOSES improved the simulated diurnal cycle of g _c and increased the diurnal maximum NEE, but at the expense of degrading long-term water vapour fluxes. Seasonality in observed canopy conductance due to soil moisture change was not captured by the model. Introducing realistic depth-dependent soil parameters decreased the amount of moisture available for transpiration at each depth and led to the model experiencing soil moisture limitation on canopy conductance during the dry season. However, this limitation had only a limited effect on the seasonality in modelled NEE.  相似文献   

Macroinvertebrate response to land cover, habitat, and water chemistry in a mining-impacted river ecosystem: A GIS watershed analysis   总被引：1，自引：0，他引：1  

Dale A. Bruns 《Aquatic Sciences - Research Across Boundaries》2005,67(4):403-423

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Experimental and theoretical bond critical point properties for model electron density distributions for earth materials     

G. V. Gibbs  D. F. Cox  K. M. Rosso  A. Kirfel  T. Lippmann  P. Blaha  K. Schwarz 《Physics and Chemistry of Minerals》2005,32(2):114-125

Generalized X-ray scattering factor model experimental electron density distributions and bond critical point, bcp, properties generated in recent studies for the earth materials stishovite, forsterite, fayalite and cuprite with high energy single crystal synchrotron X-ray diffraction data and those generated with high resolution diffraction data for coesite and senarmonite were found to be adequate and in relatively good agreement, ~5% on average, with those calculated with quantum chemical methods with relatively robust basis sets. High resolution low energy single crystal diffraction data, recorded for the molecular sieve AlPO₄-15, were also found to yield model electron density distribution values at the bcp points for the AlO and PO bonded interactions that are in relatively good to moderately good agreement with the theoretical values, but the Laplacian values of the distribution at the points for the two bonded interactions were found to be in relatively poor agreement. In several cases, experimental bcp properties, generated with conventional low energy X-ray diffraction data for several rock forming minerals, were found overall to be in poorer agreement with the theoretical properties. The overall agreement between theoretical bcp properties generated with computational quantum methods and experimental properties generated with synchrotron high energy radiation not only provides a basis for using computational strategies for studying and modeling structures and their electron density distributions, but it also provides a basis for improving our understanding of the crystal chemistry and bonded interactions for earth materials. Theoretical bond critical point properties generated with computational quantum methods are believed to rival the accuracy of those determined experimentally. As such the calculations provide a powerful and efficient method for evaluating electron density distributions and the bonded interactions for a wide range of earth materials.Dedicated to Professor Robert F. Stewart of Carnegie Mellon University on his retirement for his brilliant and original work modeling electron density distributions.  相似文献   

Assessing agreement of measurements and predictions in geomorphology     

Nicholas J. Cox   《Geomorphology》2006,76(3-4):332-346

Commonly in geomorphology measurements by different methods are compared to see how far they agree (i.e. are equal), as are predictions from models and corresponding observations. Such assessment usually employs scatter plots, correlation and possibly regression. More appropriate and more effective methods include plotting differences versus means and summary by concordance correlation and other measures of agreement. These methods, some new to geomorphology, are explained and discussed with a variety of examples using fluvial, hillslope, glacial and coastal data.  相似文献   

Assessing catchment-scale spatial and temporal patterns of groundwater and stream salinity     

David L. Poulsen  Craig T. Simmons  Corinne Le Galle La Salle  Jim W. Cox 《Hydrogeology Journal》2006,14(7):1339-1359

Understanding catchment-scale patterns of groundwater and stream salinity are important in land- and water-salinity management. A large-scale assessment of groundwater and stream data was undertaken in the eastern Mt Lofty Ranges of South Australia using geographical information systems (GIS), regional scale hydrologic data, hydrograph separation and hydrochemical techniques. Results of the study show: (1) salts were mostly of marine origin (75%), while sulfate and bicarbonate from mineral weathering comprised most of the remainder, (2) elevated groundwater salinities and stable water isotopic compositions similar to mean rainfall indicated that plant transpiration was the primary salt accumulation mechanism, (3) key factors explaining groundwater salinity were geology and rainfall, with overall catchment salinity inversely proportional to average annual rainfall, and groundwater salinity ‘hotspots’ (EC >8 mS/cm) associated with geological formations comprising sulfidic marine siltstones and shales, (4) shallow groundwater correlated with elevated stream salinity, implying that baseflow contributed to stream salt loads, with most of the annual salt load (estimated to be 24,500 tonnes) occurring in winter when baseflow volume was highest. Salt-load analysis using stream data could be a practical, low-cost technique to rapidly target the investigation of problem areas within a catchment.  相似文献   

Impact of elevated ammonium on reproduction in two Hawaiian scleractinian corals with different life history patterns     

Cox EF  Ward S 《Marine pollution bulletin》2002,44(11):1230-1235

Elevated nutrients have the potential to disrupt reproduction in scleractinian corals, with consequent impacts on population dynamics. Reproduction in broadcast spawning (Montipora capitata) and brooding (Pocillopora damicornis) species was assessed following exposure to elevated ammonium in a microcosm experiment. Planulation in P. damicornis ceased following 4 months of ammonium exposure and did not recover until 3 months after termination of nutrient enrichment. Larval settlement and survivorship were not affected by ammonium enrichment. Few significant changes were found for reproductive parameters of M. capitata. There was a significant but small decrease in egg size (430 microm in control eggs to 408 microm in eggs from ammonium enrichment treatments), but no differences in total fecundity or fertilization success. This may be related to the presence of zooxanthellae in the eggs of M. capitata, in contrast to changes in reproduction previously reported in Acropora species, whose eggs do not contain zooxanthellae.  相似文献   

Comments on J. B. Smith (Climatic Change 32, 313–326) and the Aggregation of Climate Change Damage Costs     

David Demeritt  Dale Rothmans 《Climatic change》1998,40(3-4):699-704

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Fault-valve behaviour in optimally oriented shear zones: an example at the Revenge gold mine, Kambalda, Western Australia   总被引：1，自引：0，他引：1  

Phung T Nguyen  Lyal B Harris  Chris McA Powell  Stephen F Cox 《Journal of Structural Geology》1998,20(12):1625-1640

Quartz vein systems developed in and adjacent to shear zones host major gold deposits in the Kambalda region of the Norseman–Wiluna greenstone belt. At the Revenge Mine, two groups of mineralised reverse shear zones formed as conjugate, near-optimally oriented sets during ESE subhorizontal shortening adjacent to a major transpressional shear system. The shear zones developed at temperatures of about 400°C in a transitional brittle–ductile regime. Deformation was associated with high fluid fluxes and involved fault-valve behaviour at transiently near-lithostatic fluid pressures. During progressive evolution of the shear system, early brittle and ductile deformation was overprinted by predominantly brittle deformation. Brittle shear failure was associated with fault dilation and the formation of fault-fill veins, particularly at fault bends and jogs. A transition from predominantly brittle shear failure to combined shear along faults and extension failure adjacent to faults occurred late during shear zone evolution and is interpreted as a response to a progressive decrease in maximum shear stress and a decrease in effective stresses. The formation of subhorizontal stylolites, locally subvertical extension veins and minor normal faults in association with thrust faulting, indicates episodic or transient reorientation of the near-field maximum principal stress from a subhorizontal to a near-vertical attitude during some fault-valve cycles. Local stress re-orientation is interpreted as resulting from near-total shear stress release and overshoot during some rupture events. Previously described fault-valve systems have formed predominantly in severely misoriented faults. The shear systems at Revenge Mine indicate that fault-valve action, and associated fluctuations in shear stress and fluid pressure, can influence the mechanical behaviour of optimally-oriented faults.  相似文献   

Ethics and intentional climate change   总被引：2，自引：0，他引：2  

Dale Jamieson 《Climatic change》1996,33(3):323-336

In recent years the idea of geoengineering climate has begun to attract increasing attention. Although there was some discussion of manipulating regional climates throughout the 1970s and 1980s, the discussion was largely dormant. What has reawakened the conversation is the possibility that Earth may be undergoing a greenhouse-induced global warming, and the paucity of serious measures that have been taken to prevent it.In this paper I assess the ethical acceptability of ICC, based on my impressions of the conversation that is now taking place. Rather than offering a dispassionate analysis, I argue for a point of view. I propose a set of conditions that must be satisfied for an ICC project to be morally permissible and conclude that these conditions are not now satisfied. However, research on ICC should go forward so long as certain other conditions are met. I do not intend this to be the last word on the subject, but rather the first word. My hope is that others will be stimulated to think through the ethics of ICC.  相似文献