A method for using a fully coupled climate system model to generate detailed surface boundary conditions for paleoclimate modeling investigations: an early Paleogene example   总被引：1，自引：0，他引：1  

Jacob O. Sewall  Matthew Huber  Lisa Cirbus Sloan 《Global and Planetary Change》2004,43(3-4):173-182

Although fully coupled models of the earth system are now common, simpler model architectures maintain significant utility, and scientific investigations aimed at understanding paleoclimates are frequently conducted with fixed sea surface temperature (SST) or slab ocean modeling experiments. One of the challenges facing the paleoclimate community is that the proxy data used to generate SST boundary conditions exist at a finer resolution and with very limited spatial coverage when compared to a climate model. In addition, SST proxy estimates often represent a single season or annual average conditions. This mismatch in coverage and resolution frequently results in paleoclimate modelers using SST distributions that have very limited spatial and temporal variability. In many regions, a spatially and temporally detailed SST distribution may be necessary for the accurate reproduction of paleoclimatic conditions. Here we borrow from the concept of flux correction and, using available proxy estimates of SST as our guide, force a fully coupled earth system model to produce a spatially and temporally detailed SST distribution for the paleoclimate of the early Paleogene (45–65 Ma). The SST values we produce represent a conservative estimate of early Paleogene high latitude SSTs and match tropical temperatures for this time period well. In addition to matching proxy estimates, our model-derived SST distribution has spatial and temporal variability that meshes well with global climate model resolution. This detailed SST distribution is now available to us as we investigate the causes and sensitivities of early Paleogene climate in fixed SST and slab ocean modeling experiments. The method we used to generate this spatially and temporally detailed SST distribution may prove useful for those investigating other time periods in the past, or the future, for which detailed model boundary conditions are unavailable.  相似文献   

Time-dependent thermal convection - a possible explanation for a multiscale flow in the Earth's mantle     

Ulrich Hansen  Adolf Ebel 《Geophysical Journal International》1988,94(2):181-191

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Bacterial transport experiments in fractured crystalline bedrock   总被引：5，自引：0，他引：5  

Becker MW  Metge DW  Collins SA  Shapiro AM  Harvey RW 《Ground water》2003,41(5):682-689

The efficiency of contaminant biodegradation in ground water depends, in part, on the transport properties of the degrading bacteria. Few data exist concerning the transport of bacteria in saturated bedrock, particularly at the field scale. Bacteria and microsphere tracer experiments were conducted in a fractured crystalline bedrock under forced-gradient conditions over a distance of 36 m. Bacteria isolated from the local ground water were chosen on the basis of physicochemical and physiological differences (shape, cell-wall type, motility), and were differentially stained so that their transport behavior could be compared. No two bacterial strains transported in an identical manner, and microspheres produced distinctly different breakthrough curves than bacteria. Although there was insufficient control in this field experiment to completely separate the effects of bacteria shape, reaction to Gram staining, cell size, and motility on transport efficiency, it was observed that (1) the nonmotile, mutant strain exhibited better fractional recovery than the motile parent strain; (2) Gram-negative rod-shaped bacteria exhibited higher fractional recovery relative to the Gram-positive rod-shaped strain of similar size; and (3) coccoidal (spherical-shaped) bacteria transported better than all but one strain of the rod-shaped bacteria. The field experiment must be interpreted in the context of the specific bacterial strains and ground water environment in which they were conducted, but experimental results suggest that minor differences in the physical properties of bacteria can lead to major differences in transport behavior at the field scale.  相似文献   

Separating wheat from chaff: Diatom taxon selection usingan artificial neural network pruning algorithm     

Julien M.J. Racca  Matthew Wild  H.J.B. Birks  Yves T. Prairie 《Journal of Paleolimnology》2003,29(1):123-133

This study addresses the question of what diatom taxa to includein a modern calibration set based on their relative contribution in apalaeolimnological calibration model. Using a pruning algorithm for ArtificialNeural Networks (ANNs) which determines the functionality of individual taxa interms of model performance, we pruned the Surface Water Acidification Project(SWAP) pH-diatom data-set until the predictive performance of thepruned set (as assessed by a jackknifing procedure) was statistically differentfrom the initial full-set. Our results, based on the validation at each5% data-set reduction, show that (i) 85% of the taxa canbe removed without any effect on the pH model calibration performance, and (ii)that the complexity and the dimensionality reduction of the model by theremoval of these non-essential or redundant taxa greatly improve therobustness of the calibration. A comparison between the commonly usedmarginal criteria for inclusion (species tolerance andHill's N2) and our functionality criterion shows that the importance ofeach taxon in an ANN palaeolimnological model calibration does not appear todepend on these marginal characteristics.  相似文献   

Multiport Well Design for Sampling of Ground Water at Closely Spaced Vertical Intervals     

Geoffrey N. Delin  Matthew K. Landon 《Ground water》1996,34(6):1098-1104

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Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): chemical and isotopic evidence   总被引：4，自引：0，他引：4  

P. Spadea  Massimo D’Antonio  Matthew F. Thirlwall 《Contributions to Mineralogy and Petrology》1996,123(2):159-176

 New Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacific, subsequently developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd show that the seafloor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean ridge basalts (MORB), and distinct from East Pacific Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics are different, in that they have distinctly lower ɛ_Nd(T) for a given ɛ_Sr(T), compared to Sulu and Celebes basalts. In the ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high Δ7/4 Pb (5.3–9.3) and D8/4 Pb (46.3–68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type (“normal”) mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental characteristics and low _Nd(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western Pacific region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland, when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources. Received: 23 May 1995/Accepted: 12 October 1995  相似文献   

Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland   总被引：2，自引：0，他引：2  

C. Nordstroem  H. Soegaard  T. R. Christensen  T. Friborg  B. U. Hansen 《Theoretical and Applied Climatology》2001,70(1-4):149-166

Summary  Turbulent fluxes of CO₂ were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74°28′12″N, 20°34′23″W) in NE-Greenland. The measurements started on 1 June, when there was still a 1–2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period with snow cover, fluxes of CO₂ to the atmosphere were small, typically 0.005 mg CO₂ m⁻² s⁻¹ (0.41 g CO₂ m⁻² d⁻¹), wheres during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the onset of vegetation growth, fluxes of CO₂ to the atmosphere were typically 0.1 mg CO₂ m⁻² s⁻¹ in the afternoon, and daily sums reached values up to almost 9 g CO₂ m⁻² d⁻¹. After 4 July, downward fluxes of CO₂ increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about −0.23 mg m⁻² s⁻¹ at midday and max values of daily sums of −12 g CO₂ m⁻² d⁻¹. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO₂ m⁻². Modelling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO₂ balance the calender year 1997 was calculated to be a net-sink of 20 g CO₂ m⁻² yr⁻¹. Received October 6, 1999 Revised May 2, 2000  相似文献   

American Empire and Globalisation: Postcolonial Speculations on Neocolonial Enframing     

Matthew Sparke 《Singapore journal of tropical geography》2003,24(3):373-389

In this paper, I examine the ways in which widely reproduced discourses and theories about globalisation elide American dominance. Drawing on arguments about enframing made by Timothy Mitchell in his postcolonial analysis of Egypt's colonisation, I suggest that one significant cause of this elision relates to a commonplace imagined geography of globalisation that enframes economic interdependency as constitutive of a smooth, decentred and somehow levelled global space of flows. I argue that this imagined geography is structured into dominant political-economic forms of practice and governance, and that in this way it both enables and elides American dominance. Notwithstanding this force in the world, and notwithstanding the tendency of many commentators on globalisation to ignore American dominance, recent events have made such elisions more difficult. I therefore suggest that we need to do more to theorise how American dominance is interwoven with economic globalisation.  相似文献   

The heating duration and provenance age of rocks in the Salton Sea geothermal field, southern California     

Matthew T. Heizler  T.Mark Harrison 《Journal of Volcanology and Geothermal Research》1991,46(1-2)

⁴⁰Ar/³⁹Ar step heating of single K-feldspar crystals ( 500 μg) in a furnace with a low argon blank and accurate temperature control provide constraints on the thermal history of the Salton Sea geothermal field, southern California. Estimates of ⁴⁰Ar loss from detrital K-feldspars, coupled with kinetic information gleaned from laboratory degassing of ³⁹Ar, allow possible thermal histories to be evaluated. Samples from core and cuttings of sandstones from the State 2–14, Landers #1, Dearborn Farms #1, Magmamax #2, Elmore #3 and Sinclair #3 wells have been analyzed for this purpose. No recent ⁴⁰Ar^* loss is recognized in any of the 17 crystals measured, even for samples currently at temperatures greater than 275°C. This observation suggests that the present temperature distributions in these wells have not been maintained for greater than 1000 years. However, aggregates ( 100 mg) of two K-feldspar samples do reveal recent ⁴⁰Ar^* loss from the State 2–14 well, suggesting a time scale of 1000 to 5000 years for near-peak thermal conditions. These estimates of heating duration are broadly consistent with earlier results from thermal modelling, but do not support interpretations that paleotemperatures were once hotter than present.Provenance ages span the Tertiary through Middle Proterozoic but cluster at ages of 25, 70 and 1250 Ma. These age peaks are very common K-feldspar K-Ar ages in detachment terranes of southeastern California and southwestern Arizona, both drained by the Colorado River. This coincidence supports earlier suggestions that the sands of the Salton Trough were derived mainly from the Colorado River.Unrealistically low apparent activation energies (< 20 kcal/mol) for argon transport are observed for several single crystals which yield absurdly low calculated closure temperatures (e.g., -100°C). We infer that this anomalous behaviour results from a combination of the laboratory heating schedule and the distribution of diffusion domain sizes.  相似文献   

On-Line Monitoring mit Biosensoren am Gewässer zur ereignisgesteuerten Probenahme     

P.-D. Hansen 《洁净——土壤、空气、水》1992,20(2):92-95

Biosensors for On-Line Monitoring of Waterways for Sample Taking Aimed at Relieving Disturbances. There is a generally accepted need for rapid, simple and low cost online water quality monitors. Besides the chemophysical analytical methods the biological and biochemical methods are of increasing importance for the integral monitoring of pollutants. Electrodes made up of cyanobacteria, i.e. Synechococcus, for immediate detection of acute toxic effects of pollutants, are used as a biosensor. The measurements of the photosynthetic electron transport system PETS under alternating light–dark conditions, are conducted in a flow-through cell against reference electrodes (Ag/AgCl). A mediator (Fe(II)/Fe(III)) makes the flow of current possible. The time which the electrode takes to react is about two minutes, and a multiple confirmed result is available after ten minutes (Detection limit for Atrazine = <20 μg/L Atrazine). Similar investigations were done with an E. coli-electrode.  相似文献