Late Quaternary submarine bedforms and ice‐sheet flow in Gerlache Strait and on the adjacent continental shelf,Antarctic Peninsula     

Jeffrey Evans  Julian A. Dowdeswell  Colm Cofaigh 《第四纪科学杂志》2004,19(4):397-407

Geophysical data from Gerlache Strait, Croker Passage, Bismarck Strait and the adjacent continental shelf reveal streamlined subglacial bedforms that were produced at the bed of the Antarctic Peninsula Ice Sheet (APIS) during the last glaciation. The spatial arrangement and orientation of these bedforms record the former drainage pattern and flow dynamics of an APIS outlet up‐flow, and feeding into, a palaeo‐ice stream in the Western Bransfield Basin. Evidence suggests that together, they represent a single ice‐flow system that drained the APIS during the last glaciation. The ice‐sheet outlet flowed north/northeastwards through Gerlache Strait and Croker Passage and converged with a second, more easterly ice‐flow tributary on the middle shelf to form the main palaeo‐ice stream. The dominance of drumlins with low elongation ratios suggests that ice‐sheet outlet draining through Gerlache Strait was comparatively slower than the main palaeo‐ice stream in the Western Bransfield Basin, although the low elongation ratios may also partly reflect the lack of sediment. Progressive elongation of drumlins further down‐flow indicates that the ice sheet accelerated through Croker Passage and the western tributary trough, and fed into the main zone of streaming flow in the Western Bransfield Basin. Topography would have exerted a strong control on the development of the palaeo‐ice stream system but subglacial geology may also have been significant given the transition from crystalline bedrock to sedimentary strata on the inner–mid‐shelf. In the broader context, the APIS was drained by a number of major fast‐flowing outlets through cross‐shelf troughs to the outer continental shelf during the last glaciation. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Seasonal evolution of the transverse thermohaline asymmetry in the Ria de Pontevedra (northwestern Spain)     

M. deCastro  M. Gmez-Gesteira  I. lvarez  R. Prego 《Estuarine, Coastal and Shelf Science》2006,70(4):673

A quasi-permanent transverse asymmetry in the thermohaline properties of the Ria de Pontevedra (northwestern Spain) was measured from October 1997 to October 1998 during 23 cruises. On average, the density increased form north to south. This asymmetry was maintained by salinity during the wet season, and by salinity and temperature during the dry season. The density difference between coasts (Δσ_t = σ_tsouth − σ_tnorth) and the river discharge were positively correlated (correlation coefficient, approximately 0.6) throughout the year. The density difference was negatively correlated with the upwelling index during the wet season (correlation coefficient, approximately −0.45) and positively correlated during the dry season (correlation coefficient, approximately 0.55).  相似文献   

Influence of upwelling and river runoff interaction on phytoplankton assemblages in a Middle Galician Ria and Comparison with northern and southern rias (NW Iberian Peninsula)   总被引：2，自引：2，他引：2  

Manuel Varela  Ricardo Prego  Yolanda Pazos  ngeles Moroo 《Estuarine, Coastal and Shelf Science》2005,64(4):721-737

The first oceanographic research (hydrography, nutrient salts, chlorophyll, primary production and phytoplankton assemblages) in a Middle Galician Ria was carried out in Corme-Laxe during 2001, just a year before the Prestige oil spill, being the only reference to evaluate eventual changes in the phytoplankton community. Due to the small size of this ria (6.5 km²), oceanographic processes were driven by the continental water supplied by Anllons River during the wet season (20–30 m³ s⁻¹ in winter), and the strong oceanic influence from the nearby shelf during the dry season. The annual cycle showed a spring bloom with high levels of chlorophyll (up to 14 μg Chl-a L⁻¹) and primary production (3 g C m⁻² d⁻¹) and a summer upwelling bloom (up to 8 μg Chl-a L⁻¹ and 10 g C m⁻² d⁻¹) where the proximity of the Galician upwelling core (<13.5 °C at sea surface) favors the input of upwelled seawater (up to 9 μM of nitrate and silicate) to the bottom ria layer, even during summer stratification events (primary production around 2 g C m⁻² d⁻¹). Thus, phytoplankton assemblages form a “continuum” from spring to autumn with a predominance of diatoms and overlapping species between consecutive periods; only in autumn dinoflagellates and flagellates characterized the phytoplankton community. In the Middle Rias as Corme-Laxe, the nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were higher than those reported for the Northern (Ria of A Coruña) and Southern Rias (Ria of Arousa) for year 2001; this suggests the importance of the hydrographic events occurring in the zone of maximum upwelling intensity of the Western Iberian Shelf, where a lack of annual cycles studies exists.  相似文献   

雷州半岛灯楼角海岸地貌演变   总被引：10，自引：0，他引：10  

王丽荣  赵焕庭  宋朝景  袁家义  于红兵 《海洋学报》2002,24(6):135-144

灯楼角岬角位于雷州半岛的西南端,地处热带北缘.过去几次开展的区域地貌和第四纪地质调查及制图,均包括本区1),2),[1～2].宋朝景曾做过涉及本区海底的地貌与浅地层调查3),又指导学生研究本段海岸地貌4).近年赵焕庭等[3]开展该区珊瑚礁研究,使用了1960年版航空照片和1964年版1:10000地形图,结合野外调查,进一步研究了本区海岸地貌的演变.  相似文献   

雷州半岛灯楼角珊瑚礁海区的浮游植物   总被引：8，自引：2，他引：8  

尹健强  黄晖  黄良民  林永水  李开枝  练健生 《海洋通报》2006,25(2):8-14

雷州半岛西南岸的珊瑚礁,是唯一的中国大陆沿岸现代珊瑚礁。根据2004年8月的调查资料研究分析了雷州半岛灯楼角珊瑚礁海区浮游植物的种类组成、生态类群和数量分布等,以期为珊瑚礁生态系的研究提供基础资料。结果显示:浮游植物共有108种(含变种和变型),其中硅藻门34属85种、甲藻门10属21种、蓝藻门1属2种,浮游植物的种数分布由近岸往远岸递增;浮游植物大致划分为近岸低盐类群、近海广布类群和外海高温高盐类群等3个生态类群;优势种有中肋骨条藻Skeletonemacostatum、菱形海线藻Thalassionemanitzschioides、奇异菱形藻Nitzschiaparadoxa等8种;多样性指数和均匀度平均值分别为3.448和0.655,总体分布比较均匀;浮游植物细胞总量平均值为93×104cells/m3,其中硅藻类占绝对优势,浮游植物分布不均匀,密集于灯楼角南面的A断面。  相似文献   

Coastal geomorphic evolution at the Denglou Cape, the Leizhou Peninsula     

Wang Lirong  Zhao Huanting  Song Chaojing  Yuan Jiayi  Yu Hongbing 《海洋学报(英文版)》2002,21(4):597-611

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＤｅｎｇｌｏｕＣａｐｅ ,ｉｎｔｈｅｓｏｕｔｈｗｅｓｔｏｆｔｈｅＬｅｉｚｈｏｕＰｅｎｉｎｓｕｌａ ,ｉｓａｔｔｈｅｎｏｒｔｈｍａｒｇｉｎｏｆｔｒｏｐｉｃａｌｚｏｎｅ .ＳｅｖｅｒａｌｒｅｓｅａｒｃｈｅｓａｎｄｃａｒｔｏｇｒａｐｈｉｅｓｏｆｔｈｅｒｅｇｉｏｎａｌｇｅｏｍｏｒｐｈｏｌｏｇｙａｎｄＱｕａｔｅｒ ｎａｒｙｇｅｏｌｏｇｙ ,ｗｈｉｃｈｗｅｒｅｃａｒｒｉｅｄｏｕｔｉｎｔｈｅｐａｓｔ,ａｌｌｉｎｃｌｕｄｅｔｈｉｓａｒｅａ (ＭＧＬ ,ＳＣＳＩＯ ,ＣＡＳ ,1 978;ＧＰＣＳＧＲＣＺＴ…  相似文献   

Changes in the mesozooplankton community associated with the hydrography off the northwestern Iberian Peninsula   总被引：2，自引：0，他引：2  

Blanco-Bercial  Leocadio; Alvarez-Marques  Florentina; Cabal  Jesus A. 《ICES Journal of Marine Science》2006,63(5):799-810

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New paleomagnetic results from the Aegean extensional province     

Haubold  Herbert  Scholger  Robert  Kondopoulou  Despina  Mauritsch  Hermann J. 《Geologie en Mijnbouw》1997,76(1-2):45-55

Various Oligocene formations from NE Greece (ignimbrites from the Medousa area, rhyolites from Zagradenia, granodiorites from Elatia) show discordant paleomagnetic signatures, in each case indicating small cw (clockwise) rotation and also inclination flattening. Marls from Pithion were partly remagnetized in a present-day field. Samples that contain ancient magnetization components also indicate small cw rotation and inclination flattening. However, the magnetization of andesites from Peplos reflects a considerably larger rotation, likely owing to local tectonics. In the context of previous work in the area, these results are used to propose a subdivision of NE Greece into four structural zones of distinctive rotational behaviour (from east to west): sites in zone 1, east of the Kavala-Xanthi-Komotini fault (KXK), show various cw and ccw (counterclockwise) rotation angles owing to complex kinematics resulting from the interaction of the KXK and the north-Anatolian fault zone. However, zone 2, between the KXK and the Strymon valley, is structurally homogeneous ( 10° cw rotation). The paleomagnetic signature of the Vertiskos massif (zone 3) implies a larger (> 30°) cw rotation, whereas sites in the Vardar basin (zone 4) contain a paleomagnetic signature similar to that of zone 2. This suggests a motion of the Vertiscos massif, a meta-ophiolitic nappe, relative to underlying strata. Indeed, zones 2 and 4 may be parts of the same structural unit which underlies this nappe.  相似文献   

Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context   总被引：38，自引：2，他引：38  

I. Metcalfe 《Gondwana Research》2006,9(1-2):24

East and Southeast Asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments (terranes) together with volcanic arcs, and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the Eurasian, Indo-Australian and Pacific Plates. The former wide separation of Asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation, different palaeoclimates, and biogeographic isolation. The boundaries between Asian terranes are marked by major geological discontinuities (suture zones) that represent former ocean basins that once separated them. In some cases, the ocean basins have been completely destroyed, and terrane boundaries are marked by major fault zones. In other cases, remnants of the ocean basins and of subduction/accretion complexes remain and provide valuable information on the tectonic history of the terranes, the oceans that once separated them, and timings of amalgamation and accretion. The various allochthonous crustal fragments of East Asia have been brought into close juxtaposition by geological convergent plate tectonic processes. The Gondwana-derived East Asia crustal fragments successively rifted and separated from the margin of eastern Gondwana as three elongate continental slivers in the Devonian, Early Permian and Late Triassic–Late Jurassic. As these three continental slivers separated from Gondwana, three successive ocean basins, the Palaeo-Tethys,. Meso-Tethys and Ceno-Tethys, opened between these and Gondwana. Asian terranes progressively sutured to one another during the Palaeozoic to Cenozoic. South China and Indochina probably amalgamated in the Early Carboniferous but alternative scenarios with collision in the Permo–Triassic have been suggested. The Tarim terrane accreted to Eurasia in the Early Permian. The Sibumasu and Qiangtang terranes collided and sutured with Simao/Indochina/East Malaya in the Early–Middle Triassic and the West Sumatra terrane was transported westwards to a position outboard of Sibumasu during this collisional process. The Permo–Triassic also saw the progressive collision between South and North China (with possible extension of this collision being recognised in the Korean Peninsula) culminating in the Late Triassic. North China did not finally weld to Asia until the Late Jurassic. The Lhasa and West Burma terranes accreted to Eurasia in the Late Jurassic–Early Cretaceous and proto East and Southeast Asia had formed. Palaeogeographic reconstructions illustrating the evolution and assembly of Asian crustal fragments during the Phanerozoic are presented.  相似文献   

Middle Weichselian environments on western Yamal Peninsula, Kara Sea based on pollen records     

Andrei A. Andreev  Steven L. Forman  William F. Manley 《Quaternary Research》2006,65(2):275-281

Pollen data from two sections from a coastal cliff on the western Yamal Peninsula (69°43.27′N, 66°48.80′E) document the environmental history during the Karginsky (Middle Weichselian) interstadial. Low pollen concentrations, high amounts of redeposited pollen, and relatively high presence of Artemisia pollen characterize sediments deposited at about 33,000 ¹⁴C yr B.P. Grass-sedge plant associations with few other herbs occupied the area during the late Karginsky interstadial. Artemisia pollen may indicate rather xerophytic vegetation and disturbed soils in the area. The dominance of redeposited pollen reflects scarce (disturbed) vegetation cover and low pollen productivity. The climate was relatively cold and dry. Sediments dated to 32,400 ¹⁴C yr B.P. contain fewer redeposited pollen and concentration of non-redeposited pollen is significantly higher. Pollen contents indicate the dominance of tundra-like grass-sedge vegetation and more humid conditions. Pollen records dated between 30,100 and 25,100 ¹⁴C yr B.P. also reflect scarce tundra-like vegetation during this interval. The presence of Betula nana and Salix pollen may reflect limited presence of shrub communities. This suggests that the climate was somewhat warmer during the latter part of the interstadial. However, generally the pollen records show that harsh environmental conditions prevailed on the Yamal Peninsula during the Karginsky interstadial.  相似文献