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O'Neill BC Gaffin SR Tubiello FN Oppenheimer M 《Tellus. Series B, Chemical and physical meteorology》1994,46(5):378-389
Non-steady state timescales are complicated and their application to specific geophysical systems requires a common theoretical foundation. We first extend reservoir theory by quantifying the difference between turnover time and transit time (or residence time) for time-dependent systems under any mixing conditions. We explicitly demonstrate the errors which result from assuming these timescales are equal, which is only true at steady state. We also derive a new response function which allows the calculation of age distributions and timescales for well-mixed reservoirs away from steady state, and differentiate between timescales based on gross and net fluxes. These theoretical results are particularly important to tracer-calibrated "box models" currently used to study the carbon cycle, which usually approximate reservoirs as well-mixed. We then apply the results to the important case of anthropogenic CO2 in the atmosphere, since timescales describing its behavior are commonly used but ambiguously defined. All relevant timescales, including lifetime, transit time, and adjustment time, are precisely defined and calculated from data and models. Apparent discrepancies between the current, empirically determined turnover time of 30-60 years and longer model-derived estimates of expected lifetime and adjustment time are explained within this theoretical framework. We also discuss the results in light of policy issues related to global warming, in particular since any comparisons of the "lifetimes" of different greenhouse gases (CO2, CH4, N2O, CFC's etc.) must use a consistent definition to be meaningful. 相似文献
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A re-evaluation of the threat status of New Zealand's marine invertebrates was undertaken in 2009, following earlier review of New Zealand's Threat Classification System and subsequent refinement of the national criteria for classifying threat of extinction to New Zealand's flora and fauna. Sufficient information was available to enable 295 marine invertebrate taxa to be fully evaluated and assigned to a national threat category. The 10 taxa at most risk of extinction (‘nationally critical’) were the giant seep clam Calyptogena sp., the primitive acorn barnacle Chionelasmus crosnieri, O'Shea's vent barnacle Volcanolepas osheai, the stalked barnacle Ibla idiotica, the four-blotched umbrella octopus Cirroctopus hochbergi, the roughy umbrella octopus Opisthoteuthis chathamensis, the giant squid Idioteuthis cordiformis, the large-egged polychaete Boccardiella magniovata and two gravel maggots, Smeagol climoi and Smeagol manneringi. The key threatening processes identified for marine invertebrates were fishing and land-use associated impacts such as sedimentation. We identified no taxa that had improved in threat status as a result of past or ongoing conservation management action, nor any taxa that had worsened in threat status because of known changes in their distribution, abundance or rate of population decline. We evaluated a small fraction of New Zealand's marine invertebrate fauna for their threat status. Many taxa remain ‘data deficient’ or unlisted. In addition to the most threatened taxa, we recommend these taxa and their habitats as priorities for further survey and monitoring. 相似文献
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In coastal populations of invertebrates and fishes, the distribution of discrete subpopulations is influenced by adult and larval dispersal, as well as by the effects of habitat heterogeneity on site fidelity or connectivity. Here, we examine evidence for spatial structure of sea perch, Helicolenus percoides, populations among four fjords in the Fiordland region of southwestern New Zealand. We examine patterns in adult morphology, length-at-age, δ13C and δ15N of muscle tissue, and trace elemental composition of whole otoliths as proxies for population isolation among the four inner fjord regions. A multivariate analysis of morphometrics reveals significant differences among populations from each of the four sites, suggesting existence of four distinct subpopulations. These patterns are consistent with observed differences in δ13C and δ15N, and length-at-age estimates among the four subpopulations. Differences in whole otolith concentrations of Sr, Ba, Mg and Li, and high classification scores based on the whole otolith elemental fingerprint are also consistent with significant subdivision among areas. Patterns across all four markers are consistent with discrete subpopulation structure of adult sea perch among the four study sites. These data indicate that the newly implemented network of marine protected areas in Fiordland is likely to contain discrete populations of sea perch. 相似文献
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A geochemical investigation of oils in sandstone core plugs and drill stem test oils was carried out on samples from a North Sea reservoir. A sample of diesel used as a constituent of the drilling fluids was also analysed. The aliphatic and aromatic hydrocarbons and polar non-hydrocarbons were isolated using solid phase extraction methods. GC analysis of the hydrocarbon fraction of the core extract indicated that contamination may be diesel derived. From analysis of diesel some compound classes are less likely to be affected by contamination from diesel itself including: steranes, hopanes, aromatic steroid hydrocarbons, benzocarbazoles and C0–C3-alkylphenols. 相似文献
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High spectral resolution spectroscopy enables to have detailed information on chemical and morphological status of crop. An attempt of using space platform for detecting red edge shift during different growth stages of wheat crop is reported. Study was conducted during rabi 1996–97 season using Modular Opto-Electronic Scanner MOS-B Imaging data onboard IRS-P3 satellite. Inverted Gaussian model was fitted for satellite derived reflectances between 650 and 870 nm to derive inflection wavelength and its subsequent change with crop stages i.e. red shift. Red shift of 10 nm observed from crown root initiation stage (703.8 nm) to peak vegetative stage (714.2 nm). A comparative study on temporal behaviour of vegetative indices like NDVI and ARVI with Red edge showed that latter is more atmospherically stable parameter. It is concluded that red edge shift which hitherto has been observed from ground and airborne sensors, can also be detected from space. 相似文献
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Stuart R. Gaffin 《Climatic change》2009,96(1-2):203-218
A distinctive feature of Earth’s sedimentary systems is that they all involve the interaction between a nearly-horizontal “equilibrium line,” controlling mass supply, and a dynamic sedimentary surface. For glacial systems, this is the snow line or firn line, approximating a zero-degree atmospheric isotherm. For sedimentary basin systems it is sea level or baselevel. For deep ocean carbonate sediments it is the calcite compensation depth or lysocline. First-order considerations in each case suggest a positive feedback on mass supply as the surface builds upwards (and negative feedback if the surface drops). In the first two cases, outstanding paleo-climate problems exist wherein recorded past sedimentary cycles have asymmetric amplitudes that appear too large compared to deduced vertical movements of the respective equilibrium lines. These problems are familiarly known as the “100-kiloyear Pleistocene ice age cycle” and the “million year high-order Cretaceous relative sea level cycles.” Here, I discuss the emerging commonalities that surround these two amplified cycles, emphasizing the ubiquitous presence of a relative equilibrium line dynamic, and which for glacial systems has long been seen as providing a mass supply feedback that can reconcile the disparity between the forcing and the response. I suggest that, in the same way that continental ice sheets have been modeled as passive sedimentary systems that can freely oscillate with little or no snowline forcing, sedimentary basin systems may be capable of similar behavior without vertical sea level change and illustrate the concepts with a low-order model. Sedimentary indicators for relative sea level change may be displaying disproportionately large responses to small eustatic sea level changes, due to internal positive feedbacks. 相似文献
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