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Susumu Sakata John M. Hayes Michel Rohmer Alan B. Hooper Myriam Seemann 《Organic Geochemistry》2008,39(12):1725
For the ammonia-oxidizing bacterium Nitrosomonas europaea, grown autotrophically using semicontinuous culturing, average biomass was depleted in 13C relative to CO2 dissolved in the medium by ca. 20‰ and the total-lipid extract was depleted in 13C relative to biomass by 3.7‰. The n-alkyl lipids (weighted average of fatty acids) and isoprenoid lipids (weighted average of hopanoids) were both depleted in 13C relative to biomass by about 9‰. The large depletion in the isoprenoid lipids seems to indicate that isotopic fractionations associated with the biosynthesis of methylerythritol phosphate (MEP) affected at least two carbon positions in each isoprene unit. Among the fatty acids, trans-9-hexadecenoic acid was most depleted (13.0‰ relative to biomass), followed by cis-9- hexadecenoic acid (9.6‰) and hexadecanoic acid (6.9‰). Isotopic relationships between the three acids suggest that significant isotope effects were associated with the desaturation and cis to trans isomerization of fatty acids. Given these observations, hopanoids produced by ammonia-oxidizing bacteria growing in natural waters are likely to be depleted in 13C by 26–30‰ relative to dissolved CO2. Since CO2 at aquatic oxyclines is often depleted in 13C, the range of δ values expected for hopanoids is ca. −34‰ to −55‰. The δ values of geohopanoids observed in numerous studies and attributed to unspecified chemoautotrophs fall within this range. 相似文献
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Michael A. Wulder Trisalyn A. Nelson Chris Derksen David Seemann 《Climatic change》2007,82(1-2):113-130
Twenty-four winter seasons (1978–2002) of mean February snow water equivalent (SWE) values were analyzed in an exploration of the spatial pattern of temporal variability in snow cover across the non-mountainous interior of Canada. The SWE data were derived from space-borne passive microwave brightness temperatures processed with a land cover-sensitive suite of algorithms. Spatial patterns in the frequency and amount of variability were investigated on an annual basis through comparisons with average trends over all 24 years. Changes in temporal variability through time were also investigated by comparing three eight year time periods to general trends. Analyses were synthesized at the ecozone scale in order to link results both to potential land cover influences on algorithm performance and climatological variability in SWE. Prairie and northern ecozones were typically found to be the most variable in terms of SWE magnitude. Analyses indicate that non-treed land cover classes are generally more variable than treed classes. The results also indicate that extreme weather events appear to be occurring with increasing consistency in the Prairie and Arctic regions. Discerning climatologically significant variability in the time series, compared to algorithm-related issues can be a challenge, but in an era of eroding surface observing networks the passive microwave time series represents an important resource for monitoring and detecting trends and variability in terrestrial snow cover. 相似文献
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U. Seemann 《Sedimentary Geology》1978,21(3):189-204
The paper describes some processes and phenomena relating to snow, such as sedimentation and resedimentation, diagenesis and gravity-induced mass transports (avalanches). It is shown that the type of avalanche is largely governed by the bedding sequence within the snow cover. From this it is concluded that snow could act as a valuable correlation model to gain a better understanding of some gravity-induced sediment transport modes, e.g. slumping—sliding and turbidity flow. 相似文献
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Comprehensive risk assessments are fundamental to effective emergency management. These assessments need to identify the range
of hazards (or perils) an entity is exposed to and quantify the specific threats associated with each of those hazards. While
hazard identification is commonly, if not formally, conducted in most circumstances, specific threat analysis is often overlooked
for a variety of reasons, one of which is poor communication with subject matter experts. This poor communication is often
attributable to an adherence to scientific jargon and missed opportunities to simplify information. In Canada, for example,
earthquake hazard calculations have been readily available to engineers and scientists for decades. This hazard information,
however, is expressed in terms of peak ground accelerations (PGA) or spectral accelerations (SA) that are foreign concepts
to most emergency managers, community decision-makers and the public-at-large. There is, therefore, a need to more clearly,
simply and effectively express seismic hazard information to the non-scientific community. This paper provides crustal, sub-crustal
and subduction interface earthquake shaking probabilities, expressed as simple percentages for each of 57 locations across
Vancouver Island, British Columbia, Canada. Calculations present the likelihood of earthquake shaking on Vancouver Island
as the probabilities of exceeding each of three shaking intensity thresholds (“widely felt”; onset of “non-structurally damaging”
shaking; and onset of “structurally damaging” shaking) over four timeframes (10, 25, 50 and 100 years). Results are based
on the latest Geological Survey of Canada hazard models used for the 2010 national building code and are presented in both
tabular and graphic formats. This simplified earthquake hazard information is offered to aid local residents, organizations
and governments in understanding and assessing their risk and to encourage and facilitate sound earthquake preparedness funding
decisions. 相似文献
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E. P. Hamerlynck T. E. Huxman R. S. Nowak S. Redar M. E. Loik D. N. Jordan S. F. Zitzer J. S. Coleman J. R. Seemann S. D. Smith 《Journal of Arid Environments》2000,44(4):425
Of all terrestrial ecosystems, the productivity of deserts has been suggested to be the most responsive to increasing atmospheric CO2. The extent to which this prediction holds will depend in part on plant responses to elevated CO2under the highly variable conditions characteristic of arid regions. The photosynthetic responses ofLarrea tridentata , an evergreen shrub, to a step-increase in atmospheric CO2(to 550 μmolmol−1) were examined in the field using Free-Air CO2Enrichment (FACE) under seasonally varying moisture conditions. Elevated CO2substantially increased net assimilation rate (Anet) in Larrea during both moist and dry periods of the potential growing season, while stomatal conductance (gs) did not differ between elevated and ambient CO2treatments. Seasonal and diurnal gas exchange dynamics in elevated CO2mirrored patterns in ambient CO2, indicating that elevated CO2did not extend photosynthetic activity longer into the dry season or during more stressful times of the day. Net assimilation vs. internal CO2(A/Ci) responses showed no evidence of photosynthetic down-regulation during the dry season. In contrast, after significant autumn rains, Amax(the CO2saturated rate of photosynthesis) and CE (carboxylation efficiency) were lower in Larrea under elevated CO2. In situ chlorophyll fluorescence estimation ofLarrea Photosystem II efficiency (Fv/Fm) responded more to water limitation than to elevated CO2. These findings suggest that predictions regarding desert plant responses to elevated CO2should account for seasonal patterns of photosynthetic regulatory responses, which may vary across species and plant functional types. 相似文献
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Known mineral occurrences in northern Vancouver Island are typically hosted in volcanic units of the Bonanza Group. At a local scale, the mineralization is associated with advanced argillic bedrock alteration and is often intimately related to porphyry intrusions. On a larger scale, faults are thought to exert the most significant control on the distribution of mineralized host rocks. Poor exposures and a complex glacial history limit the use of traditional methods of geological mapping and mineral exploration in this region and to date geophysical methods have been under-utilized. Here we present findings from four standard geophysical (gravity, magnetics, electromagnetics and seismic refraction) methods, recently deployed here to elucidate the subsurface geology, as well as to identify new targets for base metal exploration. Results at two different sites show that the integrated interpretation of geophysical data, constrained by physical rock property measurements, yields detailed images of the subsurface at a fraction of the cost of drilling. At one site, east of Rupert Inlet, the final subsurface model shows that the Bonanza Group is not nearly as extensive as previously presumed. An extension of the Holberg Fault is identified some 50 km east of the visibly mapped outcrop and an extensive zone of alteration around the fault is recognized. Furthermore, a number of the methods provide support for the existence of a porphyry dike at this site. At the second site, north of Rupert Inlet, magnetic and electromagnetic data prove effective at mapping alteration and locating shear zones beneath a relatively thin drift cover. Together, these results help outline a strategy for exploration in drift-covered terrains and show that a redirection of exploration effort is warranted in the case of northern Vancouver Island. 相似文献
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