50,000 years of vegetation and climate history on the Colorado Plateau, Utah and Arizona, USA     

Larry L. Coats  Kenneth L. Cole 《Quaternary Research》2008,70(2):322-338

Sixty packrat middens were collected in Canyonlands and Grand Canyon National Parks, and these series include sites north of areas that produced previous detailed series from the Colorado Plateau. The exceptionally long time series obtained from each of three sites (> 48,000 ¹⁴C yr BP to present) include some of the oldest middens yet discovered. Most middens contain a typical late-Wisconsinan glaciation mixture of mesic and xeric taxa, evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria. Differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference. The oldest middens from Canyonlands NP, however, differ in containing strictly xeric assemblages, including middens incorporating needles of Arizona single-leaf pinyon, far north of its current distribution. Similar-aged middens from the eastern end of Grand Canyon NP contain plants more typical of glacial climates, but also contain fossils of one-seed juniper near its current northern limit in Arizona. Holocene middens reveal the development of modern vegetation assemblages on the Colorado Plateau, recording departures of mesic taxa from low elevation sites, and the arrival of modern dominant components much later.  相似文献   

北极航道现状与发展趋势及对策   总被引：1，自引：0，他引：1  

孙鲁闽 《海洋工程》2016,34(3):123-132

相比其他航道,北极航道的行程更短,北极航道的通航具有很高的经济性和商业价值。充分调研北极航道的现状,对当前通航北极的商船类型、路线及沿途的冰区环境进行详细分析,并从北极油气资源开采规划上预测未来商船类型和航线的发展趋势。鉴于我国商船在北极航道面临的风险,提出有效地应对措施,并剖析了我国发展极地救助船的必要性。  相似文献   

Sediment delivery,resuspension, and transport in two contrasting canyon environments in the southwest Gulf of Lions     

Andrea S. Ogston  Tina M. Drexler  Pere Puig 《Continental Shelf Research》2008

Multiple canyons incise the continental slope at the seaward edge of the continental shelf in the Gulf of Lions and are actively involved in the transfer of sediment from shelf to deep sea. Two canyons in the southwest region of the Gulf of Lions, Lacaze-Duthiers Canyon and Cap de Creus Canyon, were instrumented with bottom-boundary-layer tripods in their heads to evaluate the processes involved in sediment delivery, resuspension and transport. In both canyons, intense cold, dense-water flows carry sediment across the slope. In the Lacaze-Duthiers canyon head (located ∼35 km from the shoreline), dense-water cascading into the canyon was episodic. Currents were highly variable in the canyon head, and responded to interactions between the along-slope Northern Current and the sharp walls of the canyon. Inertial and other high-frequency fluctuations were associated with suspended-sediment concentrations of ∼5 mg/l. In Cap de Creus canyon head (located ∼14 km from the shoreline), downslope currents were higher in magnitude and more persistent than in Lacaze-Duthiers canyon head. Greater suspended-sediment concentrations (peaks up to 20 mg/l) were observed in Cap de Creus Canyon due to resuspension of the canyon seabed during dense-water cascading events. The similarities and contrasts between processes in these two canyon heads emphasize the importance of the interaction of currents with sharp canyon bathymetry. The data also suggest that cold, dense-water flows have more potential to carry sediment to the slope on narrow shelves, and may more efficiently transfer that sediment to the deep sea where a smooth transition between shelf and slope exists.  相似文献   

论大峡谷生态环境的脆弱性     

杨逸畴 《云南地理环境研究》1999,11(2):1-8

分析了大峡谷的基本特点, 把它看作是内外作用营力的现阶段表现。提出了内营力的地质基础是破碎的、不良的、不稳定的; 外营力的水汽通道带来强大水热作用的负面影响, 它们结合在一起, 组成了生态环境本质极为脆弱的基础。并把历史上的重大山地灾害当作是一面镜子; 而把现实看到的破坏作为人类参与下正在长鸣的警钟, 提醒人们要建立大峡谷生态环境是极为脆弱的基本概念, 一切要以环保为基础, 以可持续发展为根本目标。  相似文献   

世界第一大峡谷--雅鲁藏布大峡谷科学考察新进展   总被引：4，自引：1，他引：3  

张文敬  高登义 《山地学报》1999,17(2):99-103

介绍了首次徒步穿越世界第一大峡谷科学探险考虑活动观察到的新资料和新发现。  相似文献   

国家庄矿-210m北大巷突水原因分析   总被引：2，自引：0，他引：2  

卜昌森  梁明  曲修术 《煤田地质与勘探》2001,29(5):46-48

肥城矿区国家庄煤矿-210 m北大巷曾发生突水量高达32 970 m3/h的突水事件,出水点附近地质构造复杂,含水层互相对口接触,这一大型突水是承压水沿断裂构造薄弱带突入巷道所致。   相似文献   

Influence du Bani sur la variabilité saisonnière et interannuelle de la crue du fleuve Niger dans le delta intérieur au Mali     

Aïda Zaré  Gil Mahé  Jean-Emmanuel Paturel  Bruno Barbier 《水文科学杂志》2017,62(16):2737-2752

Le delta intérieur du fleuve Niger est une zone humide sahélienne dont l’inondation dépend de la pluviométrie des bassins supérieurs du fleuve Niger et de son principal affluent, le Bani. La crise climatique qui a débuté en 1970 a très peu influencé les dates de passage des maximums de crue sur le Niger amont et son principal défluent, le Diaka. L’influence par contre est très forte sur le Bani, à la confluence avec le Niger à Mopti et sur le delta aval avec des dates de passages des maximums plus précoces qu’auparavant. Cela est dû à la faiblesse des superficies inondées au cours des années sèches. Pendant les années humides, l’importance des débordements latéraux ralentit la propagation de la crue avec pour conséquence des dates de passages plus tardives des maximums. Par ailleurs pendant les années humides antérieures à 1970 l’importance des débordements latéraux conférait au delta amont un caractère d’autorégulation par écrêtage des crues au niveau de certaines station.  相似文献   

Description of feeding apparatus and mechanism innemopilema nomurai kishinouye (scyphozoa: rhizostomeae)     

Hye Eun Lee  Won Duk Yoon  Donghyun Lim 《Ocean Science Journal》2008,43(1):61-65

Feeding apparatus, mechanism and passage of ingested prey were described forNemopilema nomurai (Scyphozoa: Rhizostomeae).N. nomurai medusae without central mouths have developed complicated canal systems connecting the tip of the tentacle and oral arm to the gut cavity. The number of junctions in the canal system increases with the bell diameter. The prey is gathered by paralyzing nematocyst at the tentacles and by adhering cirri at the oral arms and scapulets. They are engulfed into the terminal pore located at the oral arms and scapulets, and entered into the gut cavity via the canal system. The estimated digestion time is 1 hour and 20 min. The diameter of terminal pore is always about 1 mm, implying that they could not eat prey larger than that pore size. On the other hand, ephyrae have central mouths and could swallow prey as large as adults could. Exploitation of the same size of food by adult and ephyra implies thatN. nomurai can affect seriously the whole food web, massively ingesting micro-and mesozoopl a n k t o n and cutting the energy transfer toward the higher level of carnivores.  相似文献   

Assessing potential environmental influences on killer whale (Orcinus orca) distribution patterns in the Bremer Canyon,south-west Australia     

Alexandra Jones  Eleanor Bruce  Kevin P. Davies  Michelle Blewitt  Scott Sheehan 《The Australian geographer》2019,50(3):381-405

ABSTRACT

Submarine canyons play an important role in the regional distribution, abundance and dispersal of marine biota and are increasingly being recognised as geomorphic features of high conservation significance along Australia’s continental margin. Certain canyons have been described as foraging ‘hotspots’ attributable to the high abundance of apex cetacean species aggregating in these areas. Anecdotal evidence of large seasonal aggregations of killer whales in the Bremer Canyon, south-west Australia, has attracted significant research attention in the last decade. To identify important environmental drivers influencing aggregation patterns, a predictive spatial habitat model using the Maxent model was developed based on presence-only whale sighting data. In addition, remotely sensed sea surface temperature and chlorophyll-a concentrations were assessed to investigate the spatio-temporal variation in sea surface conditions. Habitat preference was predicted in areas between canyon heads, with the most influential predictor variables being depth and distance from the continental shelf break. Analysis of remote-sensing data highlighted low localised variability in surface waters and illustrated the seasonal trends of the Leeuwin Current. This study demonstrates the influence of bathymetry and submarine geomorphology on enhanced cetacean abundance and highlights the need for recognition of this potential foraging area in marine reserve planning.  相似文献   

准噶尔盆地陆梁地区断裂-不整合面输导体系与油气运聚   总被引：7，自引：3，他引：7  

陈中红  吴孔友  查明  朱筱敏 《地球学报》2006,27(1):63-68

断裂是准噶尔盆地陆梁隆起油气远距离从源(盆1井西凹陷)到藏(陆梁油田)的主要通道,其中基东断裂作为油源断裂起了关键性的作用。不整合面也是该区油气顺利从源到藏的必要条件,不整合面分布的非均质性是造成该区油气分布差异性的一个重要影响因素。断裂与不整合面形成的断裂-不整合面输导体系是一个高效的输导网络,是油气顺利运聚、成藏的重要条件:二叠系顶面的不整合面与深部断裂组成的输导体系是沟通盆1井西凹陷二叠系油源向上部侏罗系运移的主要通道,而白垩系底面的区域不整合面与中浅层正断层组成的输导体系是头屯河组和呼图壁河组油气成藏的主要因素。  相似文献