A year in Barkley Canyon: A time-series observatory study of mid-slope benthos and habitat dynamics using the NEPTUNE Canada network     

《Deep Sea Research Part II: Topical Studies in Oceanography》2013

Understanding long-term trends in species abundance and distribution represents an important challenge for future research in the deep sea, particularly as management of human impacts becomes a more important concern. However, until natural higher frequency variability is better understood, it will be difficult to interpret any long-term trends that may be apparent in data sets. We present here the results of the first year of observations at the NEPTUNE Canada cabled observatory site in Barkley Canyon, off the coast of Vancouver Island, in the northeast Pacific Ocean. Presence/absence and abundance data for 28 faunal groups were extracted from daily video records from an observatory camera. Concurrent CTD and current meter data were collected from co-located instruments. Water mass properties, currents and faunal community composition exhibited notable seasonal trends. Distinct seasonal faunal groupings were observed, together with summer and winter trends in temperature, salinity and current patterns. Variations in abundance of decapod crustaceans and fishes were responsible for most differences between faunal groups. We suggest that faunal composition may have been responding to seasonal variations in food availability, together with direct and indirect physical influences on predator and prey abundance.  相似文献   

EDITING NATURE IN GRAND CANYON NATIONAL PARK POSTCARDS*     

YOLONDA YOUNGS 《Geographical review》2012,102(4):486-509

This research takes a critical look at the interplay of vision and the production of knowledge in the context of cultural constructions of nature and environmental perceptions. The basis for this work is an exploration of the manufacturing process and subject matter in 259 Curt Teich Company postcards of Grand Canyon National Park manufactured from 1936 to 1955. Through a content analysis and interpretation of the postcards, four themes emerge—scenery, vegetation, water, and animals—that reveal the structure of Curt Teich Publishing Company's representation of the Grand Canyon environment. The company employed a printing technique known as “color embellishment” that allowed the manufacturer to alter the postcards with each reprinting and, in the process, create an edited view of nature at the Grand Canyon. This visual shorthand equated a series of selective and repetitive subjects and locations with ideas of scenic, wild, and grand landscapes.  相似文献   

ages of the recent two episodes of glacially dammed lakes along the upstream of the yarlung zangbo gorge     

LI Cui-ping  WANG Ping  QIAN Da  TANG Mao-yun 《地震地质》2015,37(4):1136-1146

There are many episodes of multiple-level lacustrine terraces along the entrance of the Yarlung Zangbo Great Canyon. Besides, very thick fluvio-lacustrine sediments are buried beneath the cover of the riverbed. Optically stimulated luminescence and radiocarbon dating provide an approximate timeline of upper valley deposits and reveal at least two glacially dammed lake events (Ⅰ and Ⅱ) which have deposition ages of 7～9ka (Ⅰ) and 20～30ka(Ⅱ), respectively. The recent two episodes of glacially dammed lakes produced two steps of lacustrine terraces (T₁, T₂) correspondingly, which are of elevations 2906～2 956m and 3100～3 060m. The formation of paleo-dammed lakes reflects that the Zelunglung Glacier in the west slope of Mt. Namche Barwa had progressively advanced to block the Yarlung Tsangpo River during the early Holocene and the Last Glacial Maximum. The glacially dammed lake I has a relatively smaller extent. Its lacustrine sediments are distributed mainly from Datuoka to Mirui with maximum thickness about 5～8m. Its end is roughly at the south of Milin County. The glacially dammed lake Ⅱ occupies a large area with the end roughly nearby Lang County. Its sediments are exposed from Datuoka to Wolong with maximum thickness about 100m. After the later fluvial erosion, the lacustrine sediments of this lake formed 1～3 levels of secondary terraces.  相似文献   

A JÖKULHLAUP FROM A LAURENTIAN CAPTURED ICE SHELF TO THE GULF OF MEXICO COULD HAVE CAUSED THE BØLLING WARMING     

ULF ERLINGSSON 《Geografiska Annaler: Series A, Physical Geography》2008,90(2):125-140

Since the rapid rate of global warming at the onset of the Bølling interstadial became evident, its cause has been under debate. It coincides closely in time with a strong global transgression called meltwater pulse 1a. One attempt at solution says that a meltwater pulse of Antarctic origin could cause an increase in North Atlantic Deep Water formation, and thus give rise to the Bølling interstadial. However, others have disputed that Antarctic meltwater would have that effect, and furthermore, the start of the Bølling interstadial is not even associated with an increase in North Atlantic Deep Water. A controversial hypothesis says that some Laurentian meltwater came from a jökulhlaup (sub-glacial outburst flood), but no study has yet shown unequivocally that sufficient amounts of water could be stored under the ice. Furthermore, according to all available data a melt-water pulse from the Laurentian ice would give rise to strong cooling, not warming. Nevertheless, meg-afloods appear instrumental in accumulating the Mississippi Fan, created entirely during the Quaternary period, and dramatic climate changes are characteristic of this period. This paper presents a hypothetical chain of events, building on the published literature and simple calculations, to investigate whether the order of magnitude is reasonable. The hypothesis is that a jökulhlaup from a Laurentian captured ice shelf flowed out through the Mississippi, boosted the Gulf Stream, reinvigorated the North Atlantic circulation, and as a result triggered the Bølling warm phase.  相似文献   

Origin of Taiwan Canyon and its effects on deepwater sediment     

Shang Xu  YingMin Wang  XueChao Peng  HuaYao Zou  Yan Qiu  ChengLin Gong  HaiTeng Zhuo 《中国科学:地球科学(英文版)》2014,57(11):2769-2780

The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive continental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topographic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transition and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms reworked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding(slumping), faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east–west direction. Large amounts of sediments overflow at the turning, forming sediment waves.  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   

南海北部古河流演变对欧亚大陆东南缘早新生代古地理再造的启示          下载免费PDF全文

邵磊  崔宇驰  乔培军  朱伟林  钟锴  周俊燊 《古地理学报》2019,21(2):216-231

欧亚大陆东南缘早新生代古地理演变包含了华南沿海中生代山脉的逐步消减与南海的逐步扩张形成等重大事件。南海北部始新统—下中新统“源-汇”路径研究发现,南海沉积物物源在该时期发生了巨大改变。在始新世和早渐新世,源自南海西部古隆起的“昆—莺—琼”河流系统向南海东部地区输送了大量沉积物,包括珠二坳陷在内的南海北部南侧大部分地区受南海西部物源的控制,仅在珠一坳陷接受来自华南大陆珠江的沉积物;晚渐新世,南海西部物源逐步被北部珠江物源取代;到早中新世,珠江来源沉积物全面越过番禺低凸起进入珠二坳陷,大量来自华南内陆的沉积物被珠江运输至南海盆地,“昆—莺—琼”古河流进一步萎缩,仅在南海西部琼东南盆地分布,并且由西向东沉积物源区昆嵩地块逐渐被海南岛取代。南海西部自晚中新世以来发育的中央峡谷正是该古河流的残余。南海新生代早期“昆—莺—琼”河流系统的发现及珠江演变过程的构建,对于深刻认识该地区新生代早期古地理特征、整个欧亚大陆东南缘的古地貌重建以及盆地的油气勘探均具有重要意义。  相似文献   

Features and Origin of Turbidity Current Sediment Waves in the Huatung Basin off the Eastern Taiwan Island     

LIU Jie  SUN Meijing  GAO Hongfang  LI Xuejie 《《地质学报》英文版》2019,93(4):1088-1096

Based on numerous high-resolution seismic profiles, sediment waves and their distribution, morphological characteristics, internal structure, and potential origins were revealed in the eastern waters of Taiwan. The sediment waves are located at the junction between the Taitung Canyon and other canyons in the slope. The wave length and the wave height of a single waveform ranged from 0.8 to 7.2 km and from 18 to 75 m, respectively (NE-SW direction). Sediment waves, located inside the bend of the Taitung Canyon, were characterized by an upward migration and showed mass transport deposits (MTDs) at the bottom, while the inner curve of the bend was subdivided into lower and upper wavy transition units. The sediment waves on the outer curve of the bend were characterized by vertical accumulation, and there was no mass flow deposit at the bottom. According to the geometry of the sediment waves, the calculated flow thicknesses across the entire wave field ranged from 196 to 356 m, and the current velocity ranged from 15 to 21 cm/s. The morphological characteristics, the internal structure, and the distribution of sediment waves, as well as the numerical calculations, evidenced that these sediment waves had formed by turbidity currents. The development of the sediment wave field in eastern Taiwan was found to be similar to that in southwestern Taiwan. It was the sedimentary response of the tectonic movement between 3 and ~1 Ma which created the sedimentary systems where gravity flow processes predominated. Turbidity current sediments settled in the place of less topographical constraints or overflowed in the bend section of the Taitung Canyon, which resulted in the formation of sediment wave fields.  相似文献   

Potential for gas hydrate formation at the northwest New Zealand shelf margin - New insights from seismic reflection data and petroleum systems modelling     

《Marine and Petroleum Geology》2017

In this study we provide evidence for methane hydrates in the Taranaki Basin, occurring a considerable distance from New Zealand's convergent margins, where they are well documented. We describe and reconstruct a unique example of gas migration and leakage at the edge of the continental shelf, linking shallow gas hydrate occurrence to a deeper petroleum system. The Taranaki Basin is a well investigated petroleum province with numerous fields producing oil and gas. Industry standard seismic reflection data show amplitude anomalies that are here interpreted as discontinuous BSRs, locally mimicking the channelized sea-floor and pinching out up-slope. Strong reverse polarity anomalies indicate the presence of gas pockets and gas-charged sediments. PetroMod™ petroleum systems modelling predicts that the gas is sourced from elevated microbial gas generation in the thick slope sediment succession with additional migration of thermogenic gas from buried Cretaceous petroleum source rocks. Cretaceous–Paleogene extensional faults underneath the present-day slope are interpreted to provide pathways for focussed gas migration and leakage, which may explain two dry petroleum wells drilled at the Taranaki shelf margin. PetroMod™ modelling predicts concentrated gas hydrate formation on the Taranaki continental slope consistent with the anomalies observed in the seismic data. We propose that a semi-continuous hydrate layer is present in the down-dip wall of incised canyons. Canyon incision is interpreted to cause the base of gas hydrate stability to bulge downward and thereby trap gas migrating up-slope in permeable beds due to the permeability decrease caused by hydrate formation in the pore space. Elsewhere, hydrate occurrence is likely patchy and may be controlled by focussed leakage of thermogenic gas. The proposed presence of hydrates in slope sediments in Taranaki Basin likely affects the stability of the Taranaki shelf margin. While hydrate presence can be a drilling hazard for oil and gas exploration, the proposed presence of gas hydrates opens up a new frontier for exploration of hydrates as an energy source.  相似文献   

The Fish River canyon (Southern Namibia): A record of Cenozoic mantle dynamics?     

François Mvondo  Olivier Dauteuil  François Guillocheau 《Comptes Rendus Geoscience》2011,343(7):478-485

Intracontinental elevated plateaus remain geomorphologic features which are poorly studied. Their genesis requires a coupling between climate and deformation. The Fish River canyon (southern Namibia), the second largest canyon of the Earth, carved the South-African plateau on 550 m along 65 km. This study reveals that the upper and the lower segments are shaped by NE–SW and north-south grabens, respectively. These deformations increased the meandering and the vertical incision mainly in the lower canyon. However the river main trend was not drastically modified attesting that the river was ancient and that the rate of the vertical displacement was slow compared to the erosion rate. The main incision occurred during a NW–SE stretching of Plio-Pleistocene. These stretching episodes belong to two deformation phases previously poorly described in the South-African plateau. These widespread stretching phases are interpreted as a result of deep mantle dynamics affecting the inner African continent.  相似文献