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11.
Stephen K. Donovan Stuart J. Jones Abigail R. King David A.T. Harper 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(3):358-368
The Almería-Níjar Basin is a Neogene, intermontane depression marginal to the Mediterranean in southern Spain in the vicinity of El Argamasón, Andalucia. The Pliocene Cuevas Formation rests unconformably on the Upper Messinian rock succession in the Carboneras Fault Zone. The Cuevas Formation is a coarse-grained, bioclastic-rich, calcarenite to calcirudite shoreface deposit. Oysters, namely Saccostrea cucullata (Born), are locally common and preserve a moderate diversity of borings: Caulostrepsis taeniola Clarke; Entobia isp.; Gastrochaenolites isp. aff. G. lapidicus Kelly and Bromley; Maeandropolydora isp. cf. M. sulcans Voigt; Oichnus paraboloides Bromley; and Talpina isp. aff. T. hirsuta Voigt. All represent domiciles except for the predatory O. paraboloides trace. This suite of ichnotaxa is assigned to the Entobia ichnofacies sensu Bromley and Asgaard; they are comparable, particularly, with the Boulder Assemblage of the Pliocene of Rhodes, Greece. Physical disturbance is an important parameter in favouring this pattern of infestation, whether the bored clasts are boulders or oyster valves. 相似文献
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Abigail McQuatters-Gollop Alison J. Gilbert Laurence D. Mee Jan E. Vermaat Yuri Artioli Christoph Humborg Fred Wulff 《Estuarine, Coastal and Shelf Science》2009,82(4):583-596
Anthropogenic eutrophication affects the Mediterranean, Black, North and Baltic Seas to various extents. Responses to nutrient loading and methods of monitoring relevant indicators vary regionally, hindering interpretation of ecosystem state changes and preventing a straightforward pan-European assessment of eutrophication symptoms. Here we summarize responses to nutrient enrichment in Europe's seas, comparing existing time-series of selected pelagic (phytoplankton biomass and community composition, turbidity, N:P ratio) and benthic (macro flora and faunal communities, bottom oxygen condition) indicators based on their effectiveness in assessing eutrophication effects. Our results suggest that the Black Sea and Northern Adriatic appear to be recovering from eutrophication due to economic reorganization in the Black Sea catchment and nutrient abatement measures in the case of the Northern Adriatic. The Baltic is most strongly impacted by eutrophication due to its limited exchange and the prevalence of nutrient recycling. Eutrophication in the North Sea is primarily a coastal problem, but may be exacerbated by climatic changes. Indicator interpretation is strongly dependent on sea-specific knowledge of ecosystem characteristics, and no single indicator can be employed to adequately compare eutrophication state between European seas. Communicating eutrophication-related information to policy-makers could be facilitated through the use of consistent indicator selection and monitoring methodologies across European seas. This work is discussed in the context of the European Commission's recently published Marine Strategy Directive. 相似文献
13.
Low‐frequency modulation and trend of the relationship between ENSO and precipitation along the northern to centre Peruvian Pacific coast 
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下载免费PDF全文 Luc Bourrel Pedro Rau Boris Dewitte David Labat Waldo Lavado Aude Coutaud Andrea Vera Abigail Alvarado Julio Ordoñez 《水文研究》2015,29(6):1252-1266
The relationship between El Niño Southern Oscillation (ENSO) and precipitation along the Peruvian Pacific coast is investigated over 1964–2011 on the basis of a variety of indices accounting for the different types of El Niño events and atmospheric and oceanographic manifestations of the interannual variability in the tropical Pacific. We show the existence of fluctuations in the ENSO/precipitation relationship at decadal timescales that are associated with the ENSO property changes over the recent decades. Several indices are considered in order to discriminate the influence of the two types of El Niño, namely, the eastern Pacific El Niño and the central Pacific El Niño, as well as the influence of large‐scale atmospheric variability associated to the Madden and Julian Oscillation, and of regional oceanic conditions. Three main periods are identified that correspond to the interleave periods between the main climatic transitions over 1964–2011, i.e. the shifts of the 1970s and the 2000s, over which ENSO experiences significant changes in its characteristics. We show that the relationship between ENSO and precipitation along the western coast of Peru has experienced significant decadal change. Whereas El Niño events before 2000 lead to increased precipitation, in the 2000s, ENSO is associated to drier conditions. This is due to the change in the main ENSO pattern after 2000 that is associated to cooler oceanic conditions off Peru during warm events (i.e. central Pacific El Niño). Our analysis also indicates that the two extreme El Niño events of 1982/1983 and 1997/1998 have overshadowed actual trends in the relationship between interannual variability in the tropical Pacific and precipitation along the coast of Peru. Overall, our study stresses on the complexity of the hydrological cycle on the western side of the Andes with regard to its relationship with the interannual to decadal variability in the tropical Pacific. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Abigail Parcasio Cid Syouhei Urushihara Tomoharu Minami Kazuhiro Norisuye Yoshiki Sohrin 《Journal of Oceanography》2011,67(6):747-764
The distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in seawater was investigated on the Bering Sea shelf (56–64°N,
165–169°W) in September 2000. The unfiltered and filtered seawater samples were used for determination of total dissolvable
(TD) and dissolved (D) metals (M), respectively. The TD-M concentrations were generally higher than in the Pacific Ocean.
TD-Cd was highest in deep water of the outer shelf domain and dominated by dissolved species. The other TD-M were highest
at stations close to the Yukon River delta and had higher fractions of labile particulate (LP) species that were obtained
as the difference between TD-M and D-M. Dissolved Al, Ni, and Cu were characterized by input from the Yukon River. Dissolved
Mn and Co showed maximums on the bottom of the coastal domain, suggesting influence of sedimentary Mn reduction. The correlations
of D-Zn, D-Cd, and macronutrients indicated their distributions were largely controlled through uptake by microorganisms and
remineralization from settling particles. All these three processes (river input, sedimentary reduction, and biogeochemical
cycle) had an influence on the distribution of D-Fe. D-Pb was fairly uniformly distributed in the study area. The stoichiometry
of D-M in the Bering Sea shelf showed enrichment of Co and Pb and depletion of Ni, Cu, Zn, and Cd compared with that in the
North Pacific. The LP-M/LP-Al ratio revealed significant enrichment of the other eight metals relative to their crustal abundance,
suggesting importance of formation of Fe–Mn oxides and adsorption of trace metals on the oxides. 相似文献
16.
Abigail Jiménez 《Acta Geophysica》2013,61(6):1325-1350
Cellular Automata have been used in the literature to describe seismicity. We first historically introduce Cellular Automata and provide some important definitions. Then we proceed to review the most important models, most of them being variations of the spring-block model proposed by Burridge and Knopoff, and describe the most important results obtained from them. We discuss the relation with criticality and also describe some models that try to reproduce real data. 相似文献
17.
Abigail Amissah-Arthur Bernard Mougenot Maud Loireau 《International journal of geographical information science》2013,27(6):583-599
Through the integration of SPOT HRV, biophysical and socioeconomic information, the study identified population carrying capacities and their vulnerability to land degradation. Land use intensification on the landscapes was quantified into expansion, early and late phases based on the Ruthenberg index calculated using a biennial series of SPOT images for the period 1986-96. Subsequently, farmland dynamic on different landscapes was calculated while observed patterns were linked with agricultural intensification and population carrying capacity. Results show a pattern of agricultural land degradation due to increasing pressure of population and agricultural intensification within a system characterised by little or no use of inputs. Fifty-six percent of the study area supports a population density higher than the carrying capacity (≤ 15 pers/km-2). Sixty-three percent of the study area is under early to late phases of agricultural intensification. Between 1986-96, cultivation declined 2-3% annually on landscapes with Low risk of degradation but increased by 1-2% on those with Average/Extreme risks. This emphasises the process of land abandonment as farmers move on to cultivating marginal lands despite above normal seasonal rainfalls observed during most of the period. By 1996, cultivation tended to include fields much farther away from the vicinity of villages, compared with 10 years earlier. Furthermore, by 1996, farmlands in the zones of late intensification declined from 12 to 4% and increased from 6 to 11% in the zone under the expansion phase. Indicating that by 1996 substantial amount of the land area required increasing lengths of fallowing. The spatial GIS modelling approach allowed not only identification of zones but synthesis of the observed pattern of landscape degradation. The paper highlights the need for combining remote sensing, biophysical and socio-economic data in environmental degradation studies in developing countries with their poor data availability. The role of developing countries scientists is stressed in taking the forefront to tackle environmental problems, which affect their region. The paper calls for increased co-operation between these scientists and regional and international data providers to overcome data availability problems and pave the way for better local and regional studies on environmental degradation. 相似文献
18.
Sainan Zhang Abigail M. York Christopher G. Boone Milan Shrestha 《The Professional geographer》2013,65(3):512-526
This article evaluates the effect of moving window (MW) size on observed fragmentation spatial patterns and proposes a method to identify an effective MW size using Simpson's diversity index. To test the robustness of the proposed method, we demonstrate its use in six cities in the Phoenix metropolitan area that have substantial variation in land composition and configuration. Next we explore the effects of gradient observation scale and the role of scale in removing noise. We compare and discuss two popular approaches to measuring urban-to-rural fragmentation gradients—concentric ring- and transect-based approaches—highlighting the usefulness of each approach in an extensive and rapidly urbanizing region. This study provides a new method for selecting window size, offers insights on scale effects, and provides guidance on gradient scale selection to achieve the best representation of land fragmentation patterns for urban analysis. 相似文献
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Cathy J. Busby Yoshihiko Tamura Peter Blum Gilles Guèrin Graham D. M. Andrews Abigail K. Barker 《International Geology Review》2017,59(13):1677-1708
IODP Expedition 350 was the first to be drilled in the rear part of the Izu-Bonin, although several sites had been drilled in the arc axis to fore-arc region; the scientific objective was to understand the evolution of the Izu rear arc, by drilling a deep-water volcaniclastic section with a long temporal record (Site U1437). The Izu rear arc is dominated by a series of basaltic to dacitic seamount chains up to ~100-km long roughly perpendicular to the arc front. Dredge samples from these are geochemically distinct from arc front rocks, and drilling was undertaken to understand this arc asymmetry. Site U1437 lies in an ~20-km-wide basin between two rear arc seamount chains, ~90-km west of the arc front, and was drilled to 1804 m below the sea floor (mbsf) with excellent recovery. We expected to drill a volcaniclastic apron, but the section is much more mud-rich than expected (~60%), and the remaining fraction of the section is much finer-grained than predicted from its position within the Izu arc, composed half of ashes/tuffs, and half of lapilli tuffs of fine grain size (clasts <3 cm). Volcanic blocks (>6.4 cm) are only sparsely scattered through the lowermost 25% of the section, and only one igneous unit was encountered, a rhyolite peperite intrusion at ~1390 mbsf. The lowest biostratigaphic datum is at 867 mbsf (~6.5 Ma), the lowest palaeomagnetic datum is at ~1300 mbsf (~9 Ma), and the rhyolite peperite at ~1390 mbsf has yielded a U–Pb zircon concordia intercept age of (13.6 + 1.6/?1.7) Ma. Both arc front and rear arc sources contributed to the fine-grained (distal) tephras of the upper 1320 m, but the coarse-grained (proximal) volcaniclastics in the lowest 25% of the section are geochemically similar to the arc front, suggesting arc asymmetry is not recorded in rocks older than ~13 Ma. 相似文献
20.
Evidence for climatic and hillslope‐aspect controls on vadose zone hydrology and implications for saprolite weathering 下载免费PDF全文
下载免费PDF全文 Abigail L. Langston Gregory E. Tucker Robert S. Anderson Suzanne P. Anderson 《地球表面变化过程与地形》2015,40(9):1254-1269
Through the delivery of water in snowmelt, climate should govern the rate and extent of saprolite formation in snow‐dominated mountain watersheds, yet the mechanisms by which water flows deeply into regolith are largely unexplored. In this study we link rainfall, snow depth, and water content data from both soil and shallow saprolite to document vadose zone dynamics in two montane catchments over 2 years. Measurements of snow pack thickness and soil moisture reveal strong contrasts between north‐ and south‐facing slopes in both the timing of meltwater delivery and the duration of significant soil wetting in the shallow vadose zone. Despite similar magnitudes of snowmelt recharge, north‐facing slopes have higher sustained soil moisture compared to south‐facing slopes. To help interpret these observations, we use a 2D numerical model of vadose zone dynamics to calculate the expected space–time moisture patterns on an idealized hillslope under two wetting scenarios: a single sustained recharge pulse versus a set of short pulses. The model predicts that the duration of the recharge event exerts a stronger control on the depth and residence time of water in the upper unsaturated zone than the magnitude of the recharge event. Model calculations also imply that water should move more slowly through the subsurface and downward water flux should be substantially reduced when water is applied in several pulses rather than in one sustained event. The results suggest that thicker soil and more deeply weathered rock on north‐facing slopes may reflect greater water supply to the deep subsurface. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献