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71.
Frederick T. Short Robert Coles Miguel D. Fortes Steven Victor Maxwell Salik Irwan Isnain Jay Andrew Aganto Seno 《Marine pollution bulletin》2014
Seagrass systems of the Western Pacific region are biodiverse habitats, providing vital services to ecosystems and humans over a vast geographic range. SeagrassNet is a worldwide monitoring program that collects data on seagrass habitats, including the ten locations across the Western Pacific reported here where change at various scales was rapidly detected. Three sites remote from human influence were stable. Seagrasses declined largely due to increased nutrient loading (4 sites) and increased sedimentation (3 sites), the two most common stressors of seagrass worldwide. Two sites experienced near-total loss from of excess sedimentation, followed by partial recovery once sedimentation was reduced. Species shifts were observed at every site with recovering sites colonized by pioneer species. Regulation of watersheds is essential if marine protected areas are to preserve seagrass meadows. Seagrasses in the Western Pacific experience stress due to human impacts despite the vastness of the ocean area and low development pressures. 相似文献
72.
A new method for estimating high-frequency radar error using data from Central San Francisco Bay 总被引:1,自引:0,他引:1
Maxwell Hubbard Donald Barrick Newell Garfield Jim Pettigrew Carter Ohlmann Matthew Gough 《Ocean Science Journal》2013,48(1):105-116
This study offers a new method for estimating High-Frequency (HF) radar surface current velocity error in data comparisons with other types of instrumentation. A new method is needed in order to remove the zero-mean random spatial and temporal fluctuations present in surface-current measurements from all sensors. Conventional methods for calculating radar error when comparing with another instrument have included their root mean square differences and scatter plots that provide correlation coefficient and slope/intercept of the regression line. It seems that a meaningful estimate of radar error should attempt to remove both sensors’ zero mean random fluctuations, inasmuch as possible. We offer and compare a method that does this. The method was tested on data collected in the Central San Francisco Bay, where GPS surface-drifter deployments were conducted within the coverage of four 42 MHz radars over six days in October of 2008. Drifters were continuously deployed in these areas over the sampling days, providing 525 usable drifter measurements. Drifter and radar measurements were averaged into thirty-minute time bins. The three-day long-term averages from the sampling areas were then subtracted from the thirtyminute averages to remove biases associated with comparisons done with short, disjoint time-sample periods. These were then used to develop methods that give radar error or bias after the random fluctuations have been removed. Results for error estimates in this study are commensurate with others where random fluctuations have been filtered, suggesting they are valid. The estimated error for the radars in the SF Bay is low, ranging from ?7.57 cm/s to 0.59 cm/s. 相似文献
73.
With rising public awareness of climate change, celebrities have become an increasingly important community of non nation-state ‘actors’ influencing discourse and action, thereby comprising an emergent climate science-policy-celebrity complex. Some feel that these amplified and prominent voices contribute to greater public understanding of climate change science, as well as potentially catalyze climate policy cooperation. However, critics posit that increased involvement from the entertainment industry has not served to influence substantive long-term advancements in these arenas; rather, it has instead reduced the politics of climate change to the domain of fashion and fad, devoid of political and public saliency. Through tracking media coverage in Australia, Canada, the United States, and United Kingdom, we map out the terrain of a ‘Politicized Celebrity System’ in attempts to cut through dualistic characterizations of celebrity involvement in politics. We develop a classification system of the various types of climate change celebrity activities, and situate movements in contemporary consumer- and spectacle-driven carbon-based society. Through these analyses, we place dynamic and contested interactions in a spatially and temporally-sensitive ‘Cultural Circuits of Climate Change Celebrities’ model. In so doing, first we explore how these newly ‘authorized’ speakers and ‘experts’ might open up spaces in the public sphere and the science/policy nexus through ‘celebritization’ effects. Second, we examine how the celebrity as the ‘heroic individual’ seeking ‘conspicuous redemption’ may focus climate change actions through individualist frames. Overall, this paper explores potential promises, pitfalls and contradictions of this increasingly entrenched set of ‘agents’ in the cultural politics of climate change. Thus, as a form of climate change action, we consider whether it is more effective to ‘plant’ celebrities instead of trees. 相似文献
74.
Sequential imaging of the temporal changes inP-wave velocity offers a practical tool to monitor a rock mass. Using established correlations between the location of seismic events and velocity structure, the temporal seismic potential characteristics of the rock may be monitored. Furthermore, the temporal velocity differences isolate the time dependent factors effecting velocity such as stress, while cancelling static factors such as lithology. Various sequential imaging techniques were compared with respect to accuracy. Differences between successive velocity images were found to have relatively high associated error estimates. However, images of velocity differences calculated from measured travel time delays between successive velocity surveys were found to have lower error estimates. In particular, travel time delays measured using cross-correlation techniques resulted in the most accurate sequential image. Two 3D sequential imaging studies were carried out at Strathcona Mine in Sudbury, Ontario, Canada. Results of the average static images indicated an association between the location of induced microseismicity and a zone of both high velocity and high gradient. Additional examples are described from the global seismology literature which also show a similar correlation between seismicity and velocity structure. We attribute this association to an interrelated stress and strength effect. The Strathcona Mine sequential images show zones of significantly decreased velocity in regions of concentrated microseismic activity, which are postulated to be indications of localized destressing and relaxation of the clamping forces resulting in the microseismicity. The zones of decreased velocity corresponded to an increase in the velocity gradient. One of the case studies also shows an increase in velocity in a zone of high static velocity, which is later the site of am
N 2.5 mining-induced seismic tremor. The increase in velocity is believed to correspond to a region of stress concentration, resulting in the subsequent seismic tremor. 相似文献
75.
76.
A.S. Mackenzie R.L. Patience J.R. Maxwell M. Vandenbroucke B. Durand 《Geochimica et cosmochimica acta》1980,44(11):1709-1721
The changes in configuration at a number of chiral centres in certain acyclic isoprenoid alkanes, steranes, rearranged steranes and triterpanes of the hopane type in a suite of fourteen Toarcian shales (Paris Basin) have been determined by gas chromatography and combined gas chromatography-mass spectrometry. A sequence of changes in the ratios of various stereoisomers occurs both with increasing maximum depth of burial and in a North-South direction for shallow samples (maximum burial depth < 1000m). These changes cover the full range of maturity shown by the samples. The presence of 5α(H), 14β(H), 17β(H)-steranes in immature samples indicates the presence of a reworked component. The extent of epimerisation at a number of the chiral centres suggests that it relates to the extent of steric hindrance at the centres. 相似文献
77.
78.
C.M. Ekweozor J.I. Okogun D.E.U. Ekong J.R. Maxwell 《Journal of Geochemical Exploration》1981,15(1-3)
The analyses, by gas chromatography and gas chromatography/mass spectrometry, of the triterpane concentrate of crude oils sampled from various oil fields of the Tertiary Niger delta have revealed the ubiquitous presence of a series of C24–C27 tetracyclic alkanes likely to be novel degraded triterpanes. The presence in the crude oils of a C25 tricyclic alkane, apparently structurally related to the tetracyclanes, seemed consistent with the hypothesis of sequential cleavages of the terminal rings of precursor pentacyclic triterpenoid derivatives with increasing thermal transformation of the respective petroleums.The degraded triterpanes might be useful for assessing the stages of thermal evolution of petroleum in the reservoir. A possible application, to oil exploration, of the expected variations in the concentration of the polycyclanes in crude oils with different thermal histories would be in distinguishing primary (immature) oils from mature but biodegraded oils. 相似文献
79.
Biomarker distributions based on GC and GC-MS data supplemented by stable carbon isotopic compositions based on irm (isotope ratio monitoring) GC-MS data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core (Rheinberger Heide) covering the entire deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany). Compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides (1H-pyrrole-2,5-diones). The core has been previously divided into four sections: TI, TIIA, TIIB and TIII based on lithology. The biomarker distributions and the δ13C values of components indicate contributions from cyanobacteria, algae, green sulphur bacteria and higher plants (minor) throughout Kupferschiefer deposition. All of the phytoplanktonic components show 13C enrichment in the lowest section, suggesting a greater productivity. The occurrence of components derived from green sulphur bacteria (Chlorobiaceae) indicates that the entire deposition was characterised by periods of photic zone anoxia. Such conditions were rapidly established after the initial transgression of the Zechstein Sea and may have been productivity-driven, but were less prevalent during deposition of the upper core sections. 相似文献
80.
Certain features of the distributions of sedimentary 4-methyl steroid hydrocarbons have been investigated: (i) competitive dehydration experiments with stanols adsorbed on a shale suggests a possible explanation for the low abundance of 4-methyl sterenes relative to their desmethyl counterparts in immature sediments, (ii) a 4-methyl spirostene which is a minor product of the backbone rearrangement of 4-methylcholest-4-ene in the laboratory has been tentatively assigned; its presence in a Toarcian black shale with a second isomer provides further evidence that the sedimentary backbone rearrangement of 4-methyl sterenes is analogous to that of their desmethyl counterparts and (iii) the major C30 4-methyl steranes in Semécourt shale (Toarcian, Paris Basin) differ from those in an Eocene lacustrine shale from China; this indicates the potential complexity of C30 steroidal alkanes (both 4-methyl and desmethyl) which can occur in sedimentary organic matter and shows that care must be taken in using m/z 217 mass chromatograms alone for routine input and maturity assessment using steroidal alkanes. 相似文献