Exploring the spatial distribution patterns of South African Cape hakes using generalised additive models     

A Grüss  D Yemane  TP Fairweather 《African Journal of Marine Science》2016,38(3):395-409

We developed delta generalised additive models (GAMs) to predict the spatial distribution of different size classes of South African hakes, Merluccius capensis and M. paradoxus, using demersal trawl survey data and geographical (latitude and longitude) and environmental features (depth, temperature, bottom dissolved oxygen and sediment type). Our approach consists of fitting, for each hake size class, two independent models, a binomial GAM and a quasi-Poisson GAM, whose predictions are then combined using the delta method. Delta GAMs were validated using an iterative cross-validation procedure, and their predictions were then employed to produce distribution maps for the southern Benguela. Delta GAM predictions confirmed existing knowledge about the spatial distribution patterns of South African hakes, and brought new insights into the factors influencing the presence/absence and abundance of these species. Our GAM approach can be used to produce distribution maps for spatially explicit ecosystem models of the southern Benguela in a rigorous and objective way. Ecosystem models are critical features of the ecosystem approach to fisheries, and distribution maps constructed using our GAM approach will enable a reliable allocation of species biomasses in spatially explicit ecosystem models, which will increase trust in the spatial overlaps and, therefore, the trophic interactions predicted by these models.  相似文献   

Pico- and Nanophytoplankton Dynamics in Two Coupled but Contrasting Coastal Bays in the NW Mediterranean Sea (France)     

Floriane Delpy  Bruno Serranito  Jean-Louis Jamet  Gérald Grégori  Christophe Le Poupon  Dominique Jamet 《Estuaries and Coasts》2018,41(7):2039-2055

Due to its ecological context, the Toulon bay represents a site of scientific interest to study temporal plankton distribution, particularly pico- and nanophytoplankton dynamics. A monthly monitoring was performed during a two-year cycle (October 2013–December 2015) at two coupled sampling sites, referred to as Little and Large bays, which had different morphometric characteristics and human pressures. Flow cytometry analyses highlighted the fact that pico- and nanophytoplankton were more abundant in the eutrophic Little bay. Furthermore, it evidenced two community structures across the Toulon bays: at times, a co-dominance of picoeukaryotes, nanoeukaryotes, Synechococcus 1-like cells and Prochlorococcus-like cells was found, and at other times, a Synechococcus 1-like dominated community existed. The alternation of one structure or the other can be explained by a combined action of temperature regime, nutrient conditions and degree of contamination. This study showed that pico- and nanophytoplankton dynamics were mainly driven by temperature in both sites, as in other temperate Mediterranean regions. Thus, the community was mainly composed of picoeukaryotes and Prochlorococcus-like cells in the winter (<?15 °C), while it was dominated by Synechococcus 1-like cells in the summer (>?20 °C). Additionally, the multiple human stressors in the Little bay seemed to affect the increase in abundance of Synechococcus 1-like cells as they were preferentially observed in the Large bay.  相似文献   

The Oeschinensee rock avalanche,Bernese Alps,Switzerland: a co-seismic failure 2300 years ago?     

Patrizia Köpfli  Lorenz M. Grämiger  Jeffrey R. Moore  Christof Vockenhuber  Susan Ivy-Ochs 《Swiss Journal of Geoscience》2018,111(1-2):205-219

Landslide deposits dam Lake Oeschinen (Oeschinensee), located above Kandersteg, Switzerland. However, past confusion differentiating deposits of multiple landslide events has confounded efforts to quantify the volume, age, and failure dynamics of the Oeschinensee rock avalanche. Here we combine field and remote mapping, topographic reconstruction, cosmogenic surface exposure dating, and numerical runout modeling to quantify salient parameters of the event. Differences in boulder lithology and deposit morphology reveal that the landslide body damming Oeschinensee consists of debris from both an older rock avalanche, possibly Kandertal, as well as the Oeschinensee rock avalanche. We distinguish a source volume for the Oeschinensee event of 37 Mm³, resulting in an estimated deposit volume of 46 Mm³, smaller than previous estimates that included portions of the Kandertal mass. Runout modeling revealed peak and average rock avalanche velocities of 65 and 45 m/s, respectively, and support a single-event failure scenario. ³⁶Cl surface exposure dating of deposited boulders indicates a mean age for the rock avalanche of 2.3 ± 0.2 kyr. This age coincides with the timing of a paleo-seismic event identified from lacustrine sediments in Swiss lakes, suggesting an earthquake trigger. Our results help clarify the hazard and geomorphic effects of rare, large rock avalanches in alpine settings.  相似文献   

Modeling and Fitting of Three-Dimensional Mineral Microstructures by Multinary Random Fields     

Teichmann  Jakob  Menzel  Peter  Heinig  Thomas  van den Boogaart  Karl Gerald 《Mathematical Geosciences》2021,53(5):877-904

Mathematical Geosciences - Modeling a mineral microstructure accurately in three dimensions can render realistic mineralogical patterns which can be used for three-dimensional processing...  相似文献   

A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains,Australia     

Stephen P. Carey  Aaron B. Camens  Matthew L. Cupper  Rainer Grün  John C. Hellstrom  Stafford W. McKnight  Iain Mclennan  David A. Pickering  Peter Trusler  Maxime Aubert 《Quaternary Science Reviews》2011,30(5-6):591-610

A diverse assemblage of late Pleistocene marsupial trackways on a lake bed in south-western Victoria provides the first information relating to the gaits and morphology of several megafaunal species, and represents the most speciose and best preserved megafaunal footprint site in Australia. The 60–110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid Diprotodon optatum, a macropodid (probably Protemnodon sp.) and a large vombatid (perhaps Ramsayia magna or ‘Phascolomys’ medius) and possible prints of the marsupial lion, Thylacoleo carnifex. The footprints were imprinted within a short time period, demonstrating the association of the taxa present, rather than the time-averaged accumulations usually observed in skeletal fossil deposits. Individual manus and pes prints are distinguishable in some trackways, and in many cases some digital pad morphology is also present. Several parameters traditionally used to differentiate ichnotaxa, including trackway gauge and the degree of print in-turning relative to the midline, are shown to be subject to significant intraspecific variation in marsupials. Sexual dimorphism in the trackway proportions of Diprotodon, and its potential for occurrence in all large bodied, quadrupedal marsupials, is identified here for the first time.  相似文献   

Oxygen and organic carbon fluxes in sediments of the Bay of Biscay     

Aurélia Mouret  Pierre Anschutz  Bruno Deflandre  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Henri Etcheber  Jean-Marie Jouanneau  Antoine Grémare  Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540

The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O₂ consumption and POC burial rates. Benthic O₂ distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O₂ consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O₂ fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O₂ profiles. The rupture in the gradient of O₂ microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O₂ fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O₂ fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O₂ penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.  相似文献   

The Portuguese bend landslide     

Karl Vonder Linden 《Engineering Geology》1989,27(1-4):301-373

The Portuguese Bend landslide, in coastal southern California, is an active, slow-moving mass of blocks and debris that extends from the shoreline to moderate altitudes along part of the southerly margin of the Palos Verdes Hills. These hills form a peninsula that is underlain by Cenozoic sedimentary and volcanic rocks draped anticlinally over a core of Mesozoic schist. In the southerly parts of the peninsula, inherently weak units in the Altamira Shale Member of the Miocene Monterey Formation dip seaward in general concordance with the ground surface. Ground failure has been widespread in this area. It evidently began in mid- to late-Pleistocene time, and it has continued intermittently to the present.

The Portuguese Bend landslide represents a reactivation of movement of the eastern part of a complex of prehistoric landslides occupying an area of approximately two square miles. This latest episode of movement began in 1956, presumably in response to placement of fill during a road construction project. The active slide subsequently was enlarged by sequential failure of adjoining blocks of ground, and by September 1969 about 54,500,000 metric tons of debris was slowly moving downslope in an area of approximately 104 ha. Movement has been continuous since recent failure began in 1956, although the velocity of the active slide decreased markedly after that year. Between 1962 and 1972 the velocity fluctuated only slightly about an average value of about 1 cm per day.

The active slide is an irregular prism, roughly triangular in plan view. The southern side of the triangle trends approximately 1100 m east-west along a stretch of shoreline that essentially coincides with the toe of the slide. The other two sides of the triangle trend northeast and northwest from the ends of the toe and meet about 1200 m north of the shoreline. The thickness of the moving mass differs considerably from one place to another, reflecting both topographic irregularities and major undulations in the underlying surface of movement. The maximum thickness is approximately 75 m.

Movement is occurring along a distinct basal failure surface. The eastern part of the slide is underlain by bedrock, and is bordered by bedrock with a general structure that limits further deep-seated propagation of failure to the east and northeast. In contrast, the western part of the slide is underlain and bordered by extensive ancient landslide deposits that are marginally stable. Further encroachment of the active slide westward and northwestward into these materials was viewed as a distinct possibility at the time the dissertation was prepared and has occurred since then.

Continued movement of the Portuguese Bend landslide since 1956 has been due to four main factors. A rise in the water table during the period 1957–1968 has been documented in the northwestern part of the moving mass and is attributable mainly to infiltration of surface runoff entering numerous open fissures that cut the surface of the slide. The toe of the active slide daylights along the shoreline and is subjected to storm-wave erosion, so that any natural build-up of resisting forces is prevented in this area. The redistribution of mass as the slide has moved along an undulatory failure surface has been responsible for local fluctuations in the driving and resisting forces. Finally, smoothing of irregularities in the failure surface by the moving slide mass must have decreased some of the forces resisting movement.  相似文献   

Carbon dioxide emissions in a methane economy     

Jesse H. Ausubel  Arnulf Grübler  Nebojsa Nakicenovic 《Climatic change》1988,12(3):245-263

Increasing reliance on natural gas (methane) to meet global energy demands holds implications for atmospheric CO₂ concentrations. Analysis of these implications is presented, based on a logistic substitution model viewing energy technologies like biological species invading an econiche and substituting in case of superiority for existing species. This model suggests gas will become the dominant energy source and remain so for 50 years, peaking near 70 percent of world supply. Two scenarios of energy demand are explored, one holding per capita consumption at current levels, the second raising the global average in the year 2100 to the current U.S. level. In the first (efficiency) scenario concentrations peak about 450 ppm, while in the second (long wave) they near 600 ppm. Although projected CO₂ concentrations in a methane economy are low in relation to other scenarios, the projections confirm that global climate warming is likely to be a major planetary concern throughout the twenty-first century. A second finding is that data on past growth of world per capita energy consumption group neatly into two pulses consistent with longwave theories in economics.  相似文献   

PHYSICAL GEOGRAPHY OF TROPICAL LATIN AMERICA: THE SPATIAL AND TEMPORAL HETEROGENEITY OF ENVIRONMENTS     

Karl S. Zimmerer  Ph.D.  Robert P. Langstroth  M.S. 《Singapore journal of tropical geography》1994,14(2):157-172

For the past 40 years, studies of physical geography in tropical Latin America have concentrated on the spatial and temporal diversity of biophysical environments and biota. Environmental heterogeneity arises from historical and present-day interaction between climatic, geomorphologic, edaphic, and biogeographic systems. Recent research emphasizes three major themes involving these systems: Quaternary climate change; human-altered biophysical environments; and geomorphologic activity. Findings on these themes are evaluated with respect to the tropical highlands, the tropical lowlands and related extra-tropical areas. Research on physical geography in Latin America promises numerous contributions toward a better understanding of environmental conservation.  相似文献   

Development of a rainwater harvesting system for increasing soil moisture in arid rangelands of Pakistan     

Sheikh Suleman  M. Karl Wood  Bashir Hussain Shah  Leigh Murray   《Journal of Arid Environments》1995,31(4)

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