Colloidally separated samples from Allende residues: Noble gases,carbon and an ESCA-study

A non-colloidal fraction separated by physical means from an $\text{HF}\text{HCl}$-resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” (Q-type) xenon to “anomalous” xenon (X-type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our $\text{HF}\text{HCl}$-residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.     

The Power Spectral Density technique applied to micropulsation analysis

Summary An empirical investigation has been conducted on the practical methods of obtaining the spectra of micropulsation activity, and the interpretational limits which can be applied to the detailed use of spectra computed by the Power Spectral Density (PSD) method. Results indicate that sufficiently high resolution may be obtained reliably from the PSD method for it to be regarded as a useful improvement over handscaling methods. The limitation is shown to remain in the selection of events rather than in computational or instrumental properties.     

Field measurements of fairweather bottom boundary layer processes and sediment suspension on the Louisiana inner continental shelf

Field measurements of bottom boundary layer and sediment-transport processes were made on the Louisiana inner continental shelf in spring 1992 at a depth of 15.5 m, and in spring and summer 1993 at a depth of 20.5 m. Two different wave–current boundary layer/sediment-transport models were applied to the measured near-bed flows. In addition, the log-profile method was applied to estimate hydraulic roughness and bed stress. Consistent with the results of others, our measurements show that near-bed flows were very weak under non-storm conditions. Bed stresses were typically too low to resuspend bed sediments. However, the advection of high-turbidity layers or plumes past the instrumentation apparently caused a sustained period of high suspended sediment concentration throughout the log layer in spring 1993. In the absence of wave activity or high suspended sediment concentrations, boundary layer profiles showed the bed to have been hydraulically very smooth with

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cm. However, wave agitation, combined with increased suspended sediment concentration caused hydraulically rough conditions with

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cm.     

Local community training and education in southern Tanzania—a case study

Local coastal communities are highly dependent upon the marine environment not only for protein but also as a primary source of income. In addition, there are growing economic opportunities offered within the coastal zone. As populations increase in these areas there is an increasing demand on coastal resources. This in turn requires effective management initiatives at regional, national and local levels.The Marine Education and Training Programme in Mtwara, southern Tanzania was a small scale capacity building project that incorporated two elements; a primary schools field day education programme and a marine coastal resources course for fishermen and women from the Mtwara District. The programme ran for a period of 1 year and during that time 14 schools, 198 children, 34 fishermen, 2 women and 14 villages participated. Results from preliminary evaluation indicated that such education is not only welcome by the local government offices, teachers, village chairmen and fishermen as an expansion of the knowledge base, but is also an important and valuable stepping stone for the local communities to become active in issues regarding the management of coastal resources.     

Carbon Isotope Fractionation of PCE and TCE During Dechlorination by Vitamin B12

Reductive dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) by vitamin B12 is an analogue of the microbial reductive dechlorination reaction and is presently being applied as a remediation technique. Stable carbon isotopic analysis, an effective and powerful tool for the investigation and monitoring of contaminant remediation, was used to characterize the isotopic effects of reductive dechlorination of PCE and TCE by vitamin B12 in laboratory microcosms. In laboratory experiments, 10 mg/L vitamin B12 degraded >90% of the initial 20 mg/L PCE with TCE, the primary product of PCE degradation, accounting for between 64% and 72% of the PCE degraded. In experiments with TCE, 147 mg/L vitamin B12 degraded >90% of the initial 20 mg/L TCE with cis -dichloroethene ( c DCE), the primary product of degradation accounting for between 30% and 35% of the TCE degraded. Degradation of both PCE and TCE exhibited first-order kinetics. Strong isotopic fractionation of the reactant PCE and of the reactant TCE was observed over the course of degradation. This fractionation could be described with a Rayleigh model using enrichment factors of −16.5%o and −15.8%o for PCE, and −17.2%o and −16.6%o for TCE. Fractionation was similar in all experiments, with a mean enrichment factor of −16.5%o ± 0.6%o. The occurrence of such large enrichment factors indicates that isotopic analysis can be used to monitor the dechlorination of PCE and TCE by vitamin B12 and remediation of ground water plumes. Evidence indicates that isotopic fractionation is taking place during complexation of the chlorinated ethenes to vitamin B12, as has been suggested for reductive dechlorination by zero valent iron. The differences between e values for this reaction and those observed for anaerobic biodegradation of the chlorinated ethenes suggest that there may be differences in the rate-determining step for these two processes.     

Comparison of carbon cycle between the western Pacific subarctic and subtropical time-series stations: highlights of the K2S1 project

A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.     

The relationship between magnetic field strength and reversal frequency: Preliminary palaeointensity results from the cretaceous quiet zone

Summary It has been predicted that the geomagnetic field strength will be at its highest during periods of low reversal frequency. Using basaltic lavas from Israel and India, which were erupted during the 35 Ma interval of normal polarity in the mid-Cretaceous (the Cretaceous Quiet Zone), we have obtained palaeointensity estimates. The mean virtual dipole moments from the two areas are about 75% of the present value. This suggests that there is no simple relationship between the time averaged strength of the dipole and the frequency of reversals.     

两种亚历L山大藻产毒过程和毒素特征研究

对 2种有毒亚历山大藻——引自台湾的微小亚历山大藻 AMTK- ( Alexandriumminutum AMTK- )和引自美国阿拉斯加的亚历山大藻 KW0 6( Alexandrium sp.KW0 6)——在不同生长阶段的产毒状况、毒素组成和毒性大小进行了研究 ,比较了两者的异同。结果显示 ,2种藻的单位细胞毒素含量与培养阶段的变化趋势是一致的 ,即在对数生长初期达最高 ,之后逐渐下降 ;微小亚历山大藻 AMTK- 主要生产 GTXs毒素 ,从对数生长后期到静止期其毒素组成比有所变化 ,GTX1 ,GTX4比例增高而 GTX2 ,GTX3降低 ,亚历山大藻KW0 6主要生产 STX毒素 ;亚历山大藻 KW0 6的毒性高于微小亚历山大藻 AMTK- 。