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591.
592.
沉积物重力流的研究随着深海、深湖环境油气资源的勘探成为现阶段沉积学领域研究的重点课题之一。沉积重力流的分类与命名已不断的完善与细化,浊流与碎屑流成为沉积物重力流的研究重点,沉积学者依据其流态特征、流变学特征、流体浓度与支撑机理对两者进行区分。重力流的的研究手段从野外观察到室内水槽实验,再到区域地震识别。沉积模式从单一浊流形成的"浊积扇"到多种流体相作用的"深海扇"或"海底扇"转变。由于沉积物重力流的控制因素较多,因此在重力流的概念、分类与成因上依然存在许多争议。水槽实验的不断发展,成为沉积物重力流的研究的主要途径,但实验模拟依旧存在很多问题,需不断完善水槽实验的限定因素与控制参量。 相似文献
593.
The capacity of turbidity currents to carry sand and coarser sediment from shallow to deep regions in the submarine environment has attracted the attention of researchers from different disciplines. Yet not only are field measurements of oceanic turbidity currents a rare achievement, but also the data that have been collected consist mostly of velocity records with very limited or no suspended sediment concentration or grain size distribution data. This work focuses on two turbidity currents measured in Monterey Canyon in 2002 with emphasis on suspended sediment from unique samples collected within the body of these currents. It is shown that concentration and grain size of the suspended material, primarily controlled by the source of the gravity flows and their interaction with bed material, play a significant role in shaping the characteristics of the turbidity currents as they travel down the canyon. Before the flows reach their normal or quasi-steady state, which is defined by bed slope, bed roughness, and suspended grain size, they might pass through a preliminary adjustment stage where they are subject to capacity-driven deposition, and release heavy material in excess. Flows composed of fine (silt/clay) sediments tend to be thicker than those with sands. The measured velocity and concentration data confirm that flow patterns differ between the front and body of turbidity currents and that, even after reaching normal state, the flow regime can be radically disrupted by abrupt changes in canyon morphology. 相似文献
594.
An array of four sediment trap moorings recorded the particulate flux across the Antarctic Circumpolar Current (ACC) at 170 °W, between November 1996 and January 1998, as part of the US JGOFS-Antarctic Environment and Southern Ocean Process Study (AESOPS) program. The trap locations represent sampling within the Polar Frontal Zone, the Antarctic Polar Front, the Antarctic Zone and the Southern Antarctic Zone. Here we report observations from 1000 m below the sea-surface compared to seafloor and surface water distributions. Sub-sample splits from each trap were obtained and total diatom flux and species composition were determined. The diatom fluxes were quantified using both a dilution and a ‘spike’ method to allow for the rapid repeatability of measurements. Diatom flux was found to be highly seasonal across the ACC particularly at higher latitudes. Marine snow aggregates of intact diatom cells and chains were the major components of the biogenic flux. Siliceous particle size was noted to decrease with increasing latitude, which could be aligned with a shift of the diatom assemblage to small-size species/sea-ice affiliated species. A ‘double-structured’ diatom flux was recorded at the location of the Antarctic Polar Front trap, with a shift in the diatom assemblage from larger to smaller diatoms in the second flux episode. The sediment trap assemblage shows deviations from the surface water assemblage, while surface sediment samples indicate that significant dissolution occurs after 1000 m and at the sediment–water interface. Estimation of diatom biovolumes across the ACC shows that large diatoms have the potential to greatly impact biogenic fluxes to the ocean interior despite their low fluxes. Small species of the genus Fragilariopsis could potentially export as much Corg as Fragilariopsis kerguelensis near the retreating ice edge. However, their low abundance in the surface sediments also suggests that these diatoms are a shallow export species. 相似文献
595.
Eirik Drift lies on the slope south of Greenland, where it has been formed under the influence of the Western Boundary Undercurrent (WBUC) closely downstream of its origin in the deep-water formation centres of the Nordic Seas. Therefore, the sediment record at Eirik Drift documents modifications in pathways and intensity of the WBUC. These modifications reflect alterations in deep-water formation in the Nordic Seas and are therefore coupled with climate changes. Based on the seismostratigraphic analysis of sedimentary architecture identified in a set of high-resolution seismic reflection data, we have reconstructed the palaeocirculation of the WBUC at Eirik Drift since the early Miocene. We revealed a strong WBUC during warm climate conditions, and in phases of climate cooling with enhanced sea-ice extent we interpreted weak WBUC influence. We suggest a southward shift of the deep-water formation regions along with a shift of the deep current system during the cool phases. This shift implies that the main North Atlantic Deep Water route affected Eirik Drift only during warm phases and that during cool phases weak branches of the circulation system flowed over Eirik Drift. 相似文献
596.
Long-term activity of earthquake-induced landslides: A case study from Qionghai Lake Basin,Southwest of China 总被引:2,自引:0,他引:2
Xue-li Wei Ning-sheng Chen Qian-gong Cheng Na He Ming-feng Deng Javed Iqbal Tanoli 《山地科学学报》2014,11(3):607-624
Earthquake-triggered landslides are a major geological hazard in the eastern Tibetan Plateau, and have prolonged impact on earth surface processes and fluvial system. To determine how long co-seismic landslides affect basins, a massive number of landslides existing in Qionghai Lake Basin were investigated for landslide distribution characteristics and geomorphological evidences, with further comparison and analysis using historic seismic analog method. The landslides found in Qionghai Lake Basin showed clear features of seismic triggering with strongly controlled by Zemuhe fault. These landslides are still active at present. Some new slides generally occur in ancient slope failure zones causing serious secondary hazards in recent years. In this study we strengthen the idea that the landslides triggered by the 185o Xichang earthquake (Ms7.5) have long term activity and prolonged impact on the mountain disasters with a period of more than 16o years. Our results support growing evidence that coseismic landslides have a prolonged effect on secondary disasters in a basin, and invite more careful consideration of the relationship between current basin condition and landslide history for a longer period. 相似文献
597.
Vishwas S. Kale 《Singapore journal of tropical geography》2014,35(2):161-178
South Asia is drained by some of the most flood‐prone rivers in the world. Flooding during the monsoon season is the most recurring, widespread and disastrous natural hazard in South Asia that results in enormous social, economic and environment consequences every year. Several massive floods have occurred in the recent decades causing huge economic losses and human suffering. On average, the total damage is close to USD 1 billion annually. To answer the question whether flooding in South Asia is getting worse and more frequent, all available data were considered: the annual peak discharge data for major rivers, post‐1985 information on floods from the global archive of large floods and palaeoflood records from nine Indian rivers. According to the global archive data, 372 large and 55 extreme flood events have occurred since 1985. Although there is no significant trend, all types of data point to clustering of large floods. Palaeoflood records show that modern floods (post‐1950) have higher flood levels than the late Holocene floods. Notwithstanding the limitations of data, there is enough evidence to conclude that (1) incidences of flood‐generating extreme rainfall event are rising and (2) human interventions have made the recent floods more destructive. 相似文献
598.
Study of the spatial and historical distribution of sediment inorganic contamination in the Toulon bay (France) 总被引:4,自引:0,他引:4
Tessier E Garnier C Mullot JU Lenoble V Arnaud M Raynaud M Mounier S 《Marine pollution bulletin》2011,62(10):2075-2086
This study presents trace elements levels in surface and deep sediments of the Toulon bay (SE France) subjected to anthropogenic inputs (navy base, harbors, etc.). The studied elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) are defined as priority contaminants in aquatic systems. Fifty-five points scattered on the entire bay were sampled, allowing the determination of contaminants distribution with a high resolution. Several approaches were used to assess the degree of contamination and the potential toxicity of the Toulon bay sediments: comparison to the French legislation, surface-weighted average metal concentrations, enrichment factors (EF), geoaccumulation indices (Igeo), trace element stock calculation and comparison to sediment quality guidelines. A principal component analysis was performed to reveal common behavior of the studied contaminants. Results demonstrated the very high contamination of the small bay, especially in Hg (EF up to 1500), Cu, Pb and Zn, with export to the large bay further governed by hydrodynamics. 相似文献
599.
Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil 总被引:1,自引:0,他引:1
Wagener Ade L Carreira RS Hamacher C Scofield Ade L Farias CO Cordeiro LG Luz LG Baêta AP Kalas FA 《Marine pollution bulletin》2011,62(8):1877-1882
Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L−1 for ∑16PAH and 5-10 μg L−1 for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g−1for ∑16PAH and 0.01-5.0 μg g−1 for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin. 相似文献
600.
Izmir Bay is one of the great natural bays of the Mediterranean. The surface sediment and fish samples were collected during 1997-2009. The sediment concentrations of inner bay showed significant enrichments during sampling periods. Outer and middle bays exhibited low levels of metal enrichments except the estuary of Gediz River. The concentrations were generally higher than the background levels from the Mediterranean and Aegean except Cd and Pb levels gradually decreased. Metal EF is used as an index to evaluate anthropogenic influences of metals in sediments. Maximum metal enrichment was found for Hg in the outer bay, while Pb indicated maximum enrichment in the middle-inner bays. Metal levels were evaluated in sediments in accordance with the numerical SQG of the USEPA. The levels of fish tissues were lower than the results reported from polluted areas of the Mediterranean. The highest BAFs were detected for Hg and Cd in fish. 相似文献