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81.
82.
Sardine Sardinops sagax distributed off the west and south coasts of South Africa have traditionally been assumed to comprise a single well-mixed stock for assessment and management purposes. New research, however, lends weight to the possibility of two stocks in this region. A precautionary management approach thus needs to consider the impact of management decisions on the hypothesised two individual stocks as well as on the resource as a whole. As a first step in this process, Bayesian assessments of South African sardine are presented, which compare results for the traditional single-stock hypothesis with those that follow from a new two-mixing-stock hypothesis. Recruits from the west stock are assumed to move to and remain part of the south stock in annual pulses of varying size. This movement is estimated to be appreciable, and to take place from a substantially more productive west stock to the south stock. This immigration makes a greater contribution to the south-stock biomass than do years of above-average south-stock recruitment. Importantly, this two-mixing-stock hypothesis is shown to be consistent with the data available. Further alternative sardine stock-structure hypotheses suggested by the most recent data are discussed. 相似文献
83.
Dissolved organic matter (DOM) in groundwater and surface water samples from the Florida coastal Everglades were studied using excitation–emission matrix fluorescence modeled through parallel factor analysis (EEM-PARAFAC). DOM in both surface and groundwater from the eastern Everglades S332 basin reflected a terrestrial-derived fingerprint through dominantly higher abundances of humic-like PARAFAC components. In contrast, surface water DOM from northeastern Florida Bay featured a microbial-derived DOM signature based on the higher abundance of microbial humic-like and protein-like components consistent with its marine source. Surprisingly, groundwater DOM from northeastern Florida Bay reflected a terrestrial-derived source except for samples from central Florida Bay well, which mirrored a combination of terrestrial and marine end-member origin. Furthermore, surface water and groundwater displayed effects of different degradation pathways such as photodegradation and biodegradation as exemplified by two PARAFAC components seemingly indicative of such degradation processes. Finally, Principal Component Analysis of the EEM-PARAFAC data was able to distinguish and classify most of the samples according to DOM origins and degradation processes experienced, except for a small overlap of S332 surface water and groundwater, implying rather active surface-to-ground water interaction in some sites particularly during the rainy season. This study highlights that EEM-PARAFAC could be used successfully to trace and differentiate DOM from diverse sources across both horizontal and vertical flow profiles, and as such could be a convenient and useful tool for the better understanding of hydrological interactions and carbon biogeochemical cycling. 相似文献
84.
A variety of alkaline lavas from the Dunedin Volcano have been analyzed for the rare earth elements (REE) La-Yb. The compositions analyzed were: basalt-hawaiite-mugearite-benmoreite; basanite, nepheline hawaiite, nepheline trachyandesite and nepheline benmoreite; trachyte; phonolite. The series from basalt to mugearite shows continuous enrichment in the REE, consistent with a crystal fractionation model involving removal of olivine and clinopyroxene. From mugearite to benmoreite there is a depletion in the REE which is explained by the appearance of apatite as a liquidus phase. The chondrite normalized REE patterns for the phonolites are characterized by strong enrichment and fractionation coupled with a sharp depletion in Eu. Removal of plagioclase from benmoreite magma is suggested for the derivation of the phonolites. The series basanite-nepheline hawaiite, and basanite-nepheline hawaiite-nepheline benmoreite appear to be high pH2O analogues of the series basalt-ben-moreite, with enrichment of the REE being achieved by removal of clinopyroxene, kaersutite and olivine. Compared with other lavas the trachyte has low REE abundances and is characterized by a striking positive Eu anomaly. 相似文献
85.
Surface sediments from the South West Africa shelf and the Gulf of California have been analysed for iodine and organic carbon. The iodine contents range from 96 to 1990 ppm. While iodine and organic carbon show certain anomalies on the South West Africa shelf, the trend of the ratios is smooth and decreases from the shelf edge, an area of oxidising surface sediment, shorewards to reducing sediments, formed as a result of intense water upwelling. In the Gulf of California, a similar distribution of ratios with surface sediment type occurs; lowest values occur in the reduced sediments and highest in oxidised sediments. Values of the ratio of the oxidised sediments (~250) are more than an order of magnitude higher than in reduced sediments, and are similar to some other surface oxidised sediments.The high I content of oxidised sediments is mostly due to uptake of I on to plankton seston on the seabed. In reduced sediments, I contained in planktonic matter originating in surface waters forms the bulk of iodine in the sediment.With sediment burial, oxidised sediments lose most of the iodine through degradation of unspecified organic constituents. This does not happen to the same extent in reduced sediments. The geological implications of these reactions are briefly discussed. 相似文献
86.
Micron-sized soil grains from the Luna 20 mission are the most lightly irradiated we have examined, in contrast to micron-sized grains from the Luna 16 soil, which are the most heavily irradiated. Radiation damage in micron-sized grains is inversely correlated with albedo of the soil. The absence of angular, amorphous grains in Luna 20 supports our previous contention that such grains in Luna 16 were produced by intense radiation damage. 相似文献
87.
An in situ sediment pore water sampler is described. It can simultaneously and continuously sample at four discrete 1 cm levels at one location without disturbing the sediment or the sample. The sampler can maintain an anaerobic environment, and can be used over extended periods of time. Laboratory tests indicate 98 to 100 percent recoveries for ammonium, silicate, reactive phosphate, nitrate and nitrite. Vertical profiles for ammonium, reactive phosphate and silicate are shown from field studies. 相似文献
88.
The major and trace element chemistry of phonolites containing spinel Iherzolite xenoliths from Bokkos (Nigeria), Phonolite Hill (northeastern Australia) and Heldburg (East Germany) is consistent with an origin by fractional crystallization of basanitic magmas at upper mantle pressures (10–15 kbar). At Bokkos, spatially associated lavas ranging from hawaiitic nepheline mugearite to nepheline benmoreite can be modeled very well by fractional crystallization of kaersutitic amphibole + olivine + Fe-Ti-spinel + apatite, a crystal extract consistent with experimentally-determined near-liquidus phase relationships for mugearitic liquids. Further fractional crystallization of aluminous clinopyroxene + mica + apatite will yield the phonolites. A similar model relating the unusual Iherzolite-bearing mafic nepheline benmoreite from Pigroot (New Zealand) to basanitic lavas of the East Otago province is not supported by major and trace element data. The Pigroot lava is possibly the product of melting of a mantle source region previously enriched in Sr and light rare earth elements, with subsequent minor fractional crystallization of olivine + kaersutite. Dynamic flow crystallization processes operating within conduit systems from mantle pressures are capable of yielding large volumes of evolved phonolitic liquids from primary basanitic liquids, if magma flow rates are appropriate. This mechanism may provide an explanation for the volumetric bias towards salic differentiates in some alkalic provinces. 相似文献
89.
Empirical relationships between fracture spacing and bed thickness are established for a number of rock types. The influence of the thickness of adjacent incompetent layers and also the lithology of the competent beds on fracture spacing are indicated; and possible mechanisms leading to the development of these relationships are briefly discussed. 相似文献
90.
The rates of solifluction of two lobes in the Ruby Range have been determined by 14C dates of samples taken from buried organic layers in the lobes. Twenty-one dates are available from one lobe, and seven from another. When plotted against distance back from control points at the lobe fronts the dates show considerable scatter. In part the scatter is thought to be due to a potential age range of 340 ± 100 yr in the organic layers. Linear and polynomial regressions were calculated for the time/distance relationships shown by the dates. The rates of lobe advance established by these means for the lobe with seven dates are not thought to be reliable. Reasonably good estimates of movement rate were determined for the second lobe by both the linear and polynomial methods. However, the rates established by the two methods are quite similar. Because of this and other uncertainties it is difficult to draw inferences of climatic change from the changes in movement rate shown by the polynomial solution. 相似文献