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Continental Shelf (continental + shelf)
Selected AbstractsApproaches for derivation of environmental quality criteria for substances applied in risk assessment of discharges from offshore drilling operationsINTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 2 2008Dag Altin Abstract In order to achieve the offshore petroleum industries "zero harm" goal to the environment, the environmental impact factor for drilling discharges was developed as a tool to identify and quantify the environmental risks associated with disposal of drilling discharges to the marine environment. As an initial step in this work the main categories of substances associated with drilling discharges and assumed to contribute to toxic or nontoxic stress were identified and evaluated for inclusion in the risk assessment. The selection were based on the known toxicological properties of the substances, or the total amount discharged together with their potential for accumulation in the water column or sediments to levels that could be expected to cause toxic or nontoxic stress to the biota. Based on these criteria 3 categories of chemicals were identified for risk assessment the water column and sediments: Natural organic substances, metals, and drilling fluid chemicals. Several approaches for deriving the environmentally safe threshold concentrations as predicted no effect concentrations were evaluated in the process. For the water column consensus were reached for using the species sensitivity distribution approach for metals and the assessment factor approach for natural organic substances and added drilling chemicals. For the sediments the equilibrium partitioning approach was selected for all three categories of chemicals. The theoretically derived sediment quality criteria were compared to field-derived threshold effect values based on statistical approaches applied on sediment monitoring data from the Norwegian Continental Shelf. The basis for derivation of predicted no effect concentration values for drilling discharges should be consistent with the principles of environmental risk assessment as described in the Technical Guidance Document on Risk Assessment issued by the European Union. [source] Species richness of marine Bryozoa in the continental shelf and slope off Argentina (south-west Atlantic)DIVERSITY AND DISTRIBUTIONS, Issue 1 2000Juan López Gappa Abstract., A total of 246 marine bryozoan species was recorded within an area of the south-west Atlantic between 35° and 56°S, and between the coast of Argentina and 50°W. The distribution pattern of benthic stations surveyed during the most important cruises in the area shows that the sampling effort has been biased towards southern shelf areas off Santa Cruz and Tierra del Fuego, as well as around the Malvinas (Falkland) islands. The littoral zone, Patagonian gulfs and the continental shelf off Chubut, Río Negro and Buenos Aires state received less attention, and should be surveyed more intensively in the future. Only 2% of the species can be regarded as non-indigenous, all of them inhabiting biofouling communities in harbour environments. With the exception of some thoroughly surveyed localities, the number of species recorded for different areas of the coast, shelf and slope is estimated to be just a small fraction of the actual number of species present. A distinct diversity gradient was found, with species-rich stations located only in the southern shelf. Highest diversity occurred in shelf areas dominated by coarse sediments, and along a high-productivity shelf-break front. A remarkable decrease in species richness was found in inner and middle shelf areas off Chubut, Río Negro and Buenos Aires state. This pattern may be related to the Pacific origin of the Magellanic fauna, since the diversity of bryozoans is higher in the Pacific than in the Atlantic Ocean. The trend of species richness is, however, overemphasized by the fact that the least diverse faunistic assemblage occurs in areas where surveys have been relatively less frequent. An up-to-date checklist of species recorded for the study area is included. [source] Geomorphology of the onset area of a paleo-ice stream, Marguerite Bay, Antarctic PeninsulaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2008John B. Anderson Abstract Geomorphic features indicate that both glacial and melt-water erosion characterize the onset area of the ancestral Marguerite Ice Stream. The large size of these features indicates that they formed over repeated glacial cycles, most recently during the Last Glacial Maximum. Ice drainage within the bay and on the inner continental shelf was strongly influenced by tectonic fabric. Deep, isolated basins surrounded by rugged bedrock bathymetry characterize the innermost part of the bay. Drumlins and other streamlined features occur in the floors of these basins at depths of up to 900 m. The outer bay has three large interconnected basins. Drumlins and megaflutings within these basins indicate ice was grounded at water depths up to 1000 m. The orientations of these features show convergence of drainage from the northeast, east and south into the Marguerite paleo-ice stream. On the inner continental shelf, the ice converged into a single, wide trough dominated by mega-scale glacial lineations. This transition in geomorphic features from drumlins and megaflutings to mega-scale glacial lineations occurs at the location on the continental shelf where sedimentary strata blanket bedrock, and marks a zone of acceleration of the ice stream. The glacially sculptured geomorphic features within Marguerite Bay co-exist with anastomosing, radial and relatively straight channels, which become increasingly focused in a seaward direction. This implies that a well organized subglacial drainage system existed within the bay at some point in the past. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ocean transport paths for the early life history stages of offshore-spawning flatfishes: a case study in the Gulf of AlaskaFISH AND FISHERIES, Issue 1 2008Kevin M Bailey Abstract Offshore- and deepwater-spawning flatfish species face the problem of transport of their planktonic stages to shallow juvenile nursery grounds that are often far shoreward in bays or estuaries. We compare life history attributes of four offshore-spawning flatfish species in the Gulf of Alaska: Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), rex sole (Glyptocephalus zachirus) and Dover sole (Microstomus pacificus) to examine how their larvae get from a spawning location at the edge or beyond the continental shelf to specific inshore nursery zones. We utilize historical records of survey catches of different life stages to characterize the stage-specific changes in distribution of spawning, planktonic stages and juvenile nursery areas. We infer transport mechanisms based on the shifts in distribution of the life stages and in comparison with local physical oceanography. This comparison provides insight into the different mechanisms marine species may use to solve the common ,problem' of planktonic drift and juvenile settlement. [source] Larval fish assemblages and water mass structure off the oligotrophic south-western Australian coastFISHERIES OCEANOGRAPHY, Issue 1 2008B. A. MUHLING Abstract Larval fish assemblages were sampled using replicated oblique bongo net tows along a five-station transect extending from inshore (18 m depth) to offshore waters (1000 m depth) off temperate south-western Australia. A total of 148 taxa from 93 teleost families were identified. Larvae of Gobiidae and Blenniidae were abundant inshore, while larvae of pelagic and reef-dwelling families, such as Clupeidae, Engraulidae, Carangidae and Labridae were common in continental shelf waters. Larvae of oceanic families, particularly Myctophidae, Phosichthyidae and Gonostomatidae, dominated offshore assemblages. Multivariate statistical analyses revealed larval fish assemblages to have a strong temporal and spatial structure. Assemblages were distinct among seasons, and among inshore, continental shelf and offshore sampling stations. Inshore larval fish assemblages were the most seasonal, in terms of species composition and abundance, with offshore assemblages the least seasonal. However, larval fish assemblages were most closely correlated to water mass, with species distributions reflecting both cross-shelf and along-shore oceanographic processes and events. Similarity profile (SIMPROF) analysis suggested the presence of twelve distinct larval fish assemblages, largely delineated by water depth and season. The strength and position of the warm, southward flowing Leeuwin Current, and of the cool, seasonal, northward flowing Capes Current, were shown to drive much of the variability in the marine environment, and thus larval fish assemblages. [source] Horizontal and vertical movements of juvenile bluefin tuna (Thunnus orientalis) in relation to seasons and oceanographic conditions in the eastern Pacific OceanFISHERIES OCEANOGRAPHY, Issue 5 2007TAKASHI KITAGAWA Abstract Electronically tagged juvenile Pacific bluefin, Thunnus orientalis, were released off Baja California in the summer of 2002. Time-series data were analyzed for 18 fish that provided a record of 380 ± 120 days (mean ± SD) of ambient water and peritoneal cavity temperatures at 120 s intervals. Geolocations of tagged fish were estimated based on light-based longitude and sea surface temperature-based latitude algorithms. The horizontal and vertical movement patterns of Pacific bluefin were examined in relation to oceanographic conditions and the occurrence of feeding events inferred from thermal fluctuations in the peritoneal cavity. In summer, fish were located primarily in the Southern California Bight and over the continental shelf of Baja California, where juvenile Pacific bluefin use the top of the water column, undertaking occasional, brief forays to depths below the thermocline. In autumn, bluefin migrated north to the waters off the Central California coast when thermal fronts form as the result of weakened equatorward wind stress. An examination of ambient and peritoneal temperatures revealed that bluefin tuna fed during this period along the frontal boundaries. In mid-winter, the bluefin returned to the Southern California Bight possibly because of strong downwelling and depletion of prey species off the Central California waters. The elevation of the mean peritoneal cavity temperature above the mean ambient water temperature increased as ambient water temperature decreased. The ability of juvenile bluefin tuna to maintain a thermal excess of 10°C occurred at ambient temperatures of 11,14°C when the fish were off the Central California coast. This suggests that the bluefin maintain peritoneal temperature by increasing heat conservation and possibly by increasing internal heat production when in cooler waters. For all of the Pacific bluefin tuna, there was a significant correlation between their mean nighttime depth and the visible disk area of the moon. [source] Impact of freshwater input and wind on landings of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in shelf waters surrounding the Ebre (Ebro) River delta (north-western Mediterranean)FISHERIES OCEANOGRAPHY, Issue 2 2004J. Lloret Abstract Time series analyses (Box,Jenkins models) were used to study the influence of river runoff and wind mixing index on the productivity of the two most abundant species of small pelagic fish exploited in waters surrounding the Ebre (Ebro) River continental shelf (north-western Mediterranean): anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). River flow and wind were selected because they are known to enhance fertilization and local planktonic production, thus being crucial for the survival of fish larvae. Time series of the two environmental variables and landings of the two species were analysed to extract the trend and seasonality. All series displayed important seasonal and interannual fluctuations. In the long term, landings of anchovy declined while those of sardine increased. At the seasonal scale, landings of anchovy peaked during spring/summer while those of sardine peaked during spring and autumn. Seasonality in landings of anchovy was stronger than in sardine. Concerning the environmental series, monthly average Ebre runoff showed a progressive decline from 1960 until the late 1980s, and the wind mixing index was highest during 1994,96. Within the annual cycle, the minimum river flow occurs from July to October and the wind mixing peaks in winter (December,April, excluding January). The results of the analyses showed a significant correlation between monthly landings of anchovy and freshwater input of the Ebre River during the spawning season of this species (April,August), with a time lag of 12 months. In contrast, monthly landings of sardine were significantly positively correlated with the wind mixing index during the spawning season of this species (November,March), with a lag of 18 months. The results provide evidence of the influence of riverine inputs and wind mixing on the productivity of small pelagic fish in the north-western Mediterranean. The time lags obtained in the relationships stress the importance of river runoff and wind mixing for the early stages of anchovy and sardine, respectively, and their impact on recruitment. [source] Recent advances in understanding the circulation and hydrography of the East China SeaFISHERIES OCEANOGRAPHY, Issue 6 2002Heung-Jae Lie Abstract The physical oceanography of the East China Sea (ECS) has been studied extensively through comprehensive observing programmes conducted in the 1990s, allowing clarification of the major oceanographic processes involved in establishing the hydrography and circulation. An overview of the general circulation and hydrography in the ECS is given here, mainly based on the new observational results and with special attention to the Kuroshio bifurcation north-east of Taiwan and south-west of Kyushu and the major currents in the outer continental shelf. A new schematic circulation pattern of the ECS is sketched using these observations. The oceanographic conditions and fisheries environments of the ECS are not only seasonally variable because of the response of the basin to the seasonally varying atmospheric conditions, but also spatially and temporally complicated because of the wide spectrum of phenomena that coexist with various scales. [source] Transport of larval jack mackerel (Trachurus japonicus) estimated from trajectories of satellite-tracked drifters and advective velocity fields obtained from sequential satellite thermal images in the eastern East China SeaFISHERIES OCEANOGRAPHY, Issue 6 2002Hee-Yong Kim Abstract Transport processes of jack mackerel (Trachurus japonicus) larvae in the waters off the west coast of Kyushu in the eastern East China Sea, have been investigated using satellite-tracked surface drifters and consecutive satellite thermal images. Trajectories of drifters describe northward flows over the continental shelf, eastward flows of the Kuroshio south-west of Kyushu, and a weak clockwise gyre off the west coast of Kyushu. In particular, the clockwise gyre causes the entrainment of jack mackerel larvae into the waters off the west coast of Kyushu. Consecutive satellite thermal images help to elucidate the northward warm water intrusion from the Kuroshio front south-west of Kyushu. Particle trajectories using sea surface current fields computed with the Maximum Cross Correlation (MCC) technique also reveal that the transport of jack mackerel larvae into the nursery ground off the west coast of Kyushu caused by the anti-cyclonic gyre and the warm streamers are an important process for successful recruitment. [source] Springtime ichthyoplankton of the slope region off the north-eastern United States of America: larval assemblages, relation to hydrography and implications for larval transportFISHERIES OCEANOGRAPHY, Issue 2 2001Jonathan A. Hare Larval transport in the slope region off north-eastern North America influences recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were made during springtime over the continental slope to provide insights into larval distributions and transport. Ichthyoplankton composition and distribution mirrored the physical complexity of the region. Three larval fish assemblages were defined, each with different water mass distributions. A Gulf Stream assemblage was found predominantly in the Gulf Stream and associated with filaments of discharged Gulf Stream water in the Slope Sea. Larvae of this assemblage originated from oceanic and shelf regions south of Cape Hatteras. Several members of this assemblage utilize habitats in the Middle Atlantic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema, Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi- and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of this assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf-slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that were spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptocephalus cynoglossus). Previous studies have examined the effect of warm-core rings on larval distributions, but this study identifies the importance of smaller-scale features of the MAB shelf/slope front and of filaments associated with Gulf Stream meanders. In combination with these advective processes, the dynamic nature of larval distributions in the Slope Sea appears to be influenced, to varying degrees, by both vertical and horizontal behaviour of larvae and pelagic juveniles themselves. [source] Palaeozoic tropical rainforests and their effect on global climates: is the past the key to the present?GEOBIOLOGY, Issue 1 2005CHRISTOPHER J. CLEAL ABSTRACT Wetland forests, known as coal forests, extended over large areas of the palaeotropics during the Late Carboniferous and the Permian Periods. They were initiated during the Serpukhovian Age as a response to lowering sea levels having exposed large areas of continental shelf. They expanded dramatically during the late Bashkirian Age, but then contracted by over one-half during the Kasimovian Age. The estimated loss of carbon sink probably resulted in an annual increase in atmospheric CO2 of about 2,5 ppm, and coincided with clear evidence of global warming in both the northern and southern high latitudes. A return to cooler conditions in very Early Permian times coincided with an expansion of the palaeotropical coal forests in the Far East, but this was short-lived and most of the rest of the Permian was a time of global warming. The Palaeozoic evidence clearly confirms that there is a correlation between levels of atmospheric CO2 and global climates. However, care must be taken in extrapolating this evidence to the present-day tropical forests, which do not act as a comparable unsaturated carbon sink. [source] Reconstruction of the Ross Ice Drainage System, Antarctica, at the Last Glacial MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2-3 2000George H. Denton We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface. [source] Permo-Triassic development from Ireland to Norway: basin architecture and regional controlsGEOLOGICAL JOURNAL, Issue 6 2009tolfová Abstract Extensive occurrences of Permo-Triassic strata are preserved along the Northwest European Atlantic margin. Seismic reflection and well data are used to describe large-scale Permo-Triassic basin geometries along a swath of the continental shelf more than 2000,km long extending from the Irish to the mid-Norwegian sectors. Successions in the Celtic Sea, the flanks of the Irish Rockall Basin, basins west and north of Scotland, and the Trøndelag and Horda platforms west of Norway are described. The large-scale Permo-Triassic depositional geometries commonly represent erosional remnants of larger basins modified by later rifting episodes, uplift, inversion and continental breakup. However, the interpreted geometries reveal spatial and temporal differences in rifting style. The basins developed above a complex mosaic of petrologically heterogeneous crustal terranes with inherited crustal fabrics, which had a significant impact on the depositional basin geometries. Small Permian basins with growth faulting developed in the southern Celtic Sea region. Extensive, uniformly thick Triassic strata are characteristic of the wide rift basins in the southeastern Rockall Basin and northwest of the Solan Bank High. Thick, fault-controlled basins developed in the Horda and Trøndelag platform regions. The main controls on Permo-Triassic basin architecture are (a) crustal thickness and composition, which determined the development of narrow or wide rift basin geometries, (b) inherited Variscan, Caledonian and Precambrian basement structures and (c) pre-rift palaeotopography. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ostracode faunas of bottom sediments from the continental shelf, south Marmara Sea, NW Turkey, and their comparison with other shelf environments in the Mediterranean and Aegean regionsGEOLOGICAL JOURNAL, Issue 2 2001Atike Nazik Abstract This study describes the ostracode faunal composition and distribution on the continental shelf of the southern Marmara Sea in Turkey. Twenty-three bottom samples were collected from the shelf. These samples are characterized by silt-clay (mud), sand and gravel in the studied area. A total of 46 species belonging to 32 genera were determined from these samples. Seven species were dominant from 46 ostracode species. Three assemblages were identified by their dominant species. These are characterized by: Costa edwardsii (Roemer); a mixed assemblage which consists of Cytheridea neapolitana Kollmann, Pterygocythereis ceratoptera (Bosquet), Tegmenia rugosa (Costa), Acanthocythereis hystrix (Reuss) and Xestoleberis communis (G.W. Müller); and Aurila convexa (Baird). The relations between the dominant species, lithology and CaCO3 concentration have been investigated, and the results are compared with other shelf environments within the Mediterranean and Aegean regions. Pterygocythereis, Costa, Tegmenia and Cytheridea are abundant in muddy substrates; Aurila and Acanthocythereis are abundant in sandy substrates. Acanthocythereis hystrix (Reuss), Aurila convexa (Baird), Buntonia subulata Ruggieri, Carinocythereis antiquata (Baird), Carinocythereis carinata (Roemer), Costa batei (Brady), Costa edwardsii (Roemer), Cytheridea neapolitana Kollmann, Celtia quadridentata (Baird), Loxoconcha rhomboidea (Fischer), Pterygocythereis jonesii (Baird) and Semicytherura acuticostata (Sars) are common, and similar species are recorded from other continental shelves of the Mediterranean. Copyright © 2001 John Wiley & Sons, Ltd. [source] Mechanical deformation model of the western United States instantaneous strain-rate fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Fred F. Pollitz SUMMARY We present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (M, 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific,North America plate boundary along ,1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. [source] Characterization of macrofaunal assemblages associated with sponges and tunicates collected off the southeastern United StatesINVERTEBRATE BIOLOGY, Issue 2 2010Cara L. Fiore Abstract. Sponges can serve as hosts to invertebrate assemblages that live and reproduce within them. Sponges also constitute a major part of the benthic epifaunal community on the continental shelf of the southeastern United States; however, little is known about these sponges and the assemblages they harbor. In this study, the associated fauna from a variety of sponges and one species of tunicate collected by submersible from the continental shelf and slope of the southeastern United States at depths in the range 18,875 m were examined. Seventeen sponges, comprising eight species (Ircinia campana, Topsentia sp., Geodia sp., Characella sp., Erylus sp., Apylsina archeri, Cliona sp., and Pheronema carpenteri), and three tunicate colonies (Didemnidae) were fully dissected and all associated organisms were identified and counted. Additionally, the sponges Pheronema annae (951 m) and P. carpenteri (770 m) represent new records for the region. The diversity (H,) and density of associates varied considerably among hosts; the densities of associates ranged 0.4,11,684 per 1 L of host volume. Polychaete worms were the most common organisms found, with one species, Haplosyllis spongicola, being especially abundant in I. campana, Topsentia sp., and Cliona sp. The amphipods Ericthonius punctatus and Leucothoe cf. spinicarpa, as well as decapods such as snapping shrimp (Synalpheus sp.) and crabs (e.g., Pilumnus floridana, Micropanope urinator), were also common. The number of symbiont taxa did not significantly increase as the sponge size increased. However, weak positive trends were found between the diversity of associates and increasing canal diameter. Sponges and tunicates were judged to represent legitimate ecological communities harboring a complete food web as well as gravid and juvenile individuals. [source] Spatial patterns of benthic diversity: is there a latitudinal gradient along the Norwegian continental shelf?JOURNAL OF ANIMAL ECOLOGY, Issue 3 2002Karie. Summary 1We examined data on soft-sediment macrobenthos (organisms retained on a 1-mm sieve) from a transect of c. 1960 km along the Norwegian continental shelf (56,71°N), covering a range of water depths (65,434 m) and varying sediment properties. 2A total of 809 species was recorded from 101 sites. Of these, 36% were restricted to one or two sites, and 29% were represented by one or two individuals. No species spanned the entire transect. Polychaetes were the dominant taxonomic group, followed by crustaceans, molluscs and echinoderms. 3Alpha diversity (sample species richness) was highly variable (35,148 species) but showed no evidence of a relationship to latitude or other environmental variables. 4Beta diversity was measured as Whittaker's ,W, the number of shared species, complementarity (biotic distinctness) and Bray,Curtis similarity, and there was no evidence of a latitudinal trend on the shelf. Beta diversity increased with the level of environmental variability, and was highest in the southern-central area, followed by the most northern area. Change in environmental variables had a stronger effect on beta diversity than spatial distance between sites. 5Gamma diversity was computed by pooling samples over large areas. There was no convincing evidence of a latitudinal cline in gamma diversity, but gamma diversity increased with the level of environmental heterogeneity. Mean alpha diversity and gamma diversity were not significantly correlated. Whereas mean complementarity and mean Bray,Curtis similarity were related to gamma diversity, ,W was not. [source] Feeding habits and trophic morphology of inshore lizardfish (Synodus foetens) on the central continental shelf off Veracruz, Gulf of MexicoJOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2005V. H. Cruz-Escalona Summary The inshore lizardfish, Synodus foetens, is one of the most common coastal demersal predators on the continental shelf of the Gulf of Mexico (GOM), but the biology and feeding ecology of this species is virtually unknown. Between November 2001 and January 2003 (10 collections), 603 individuals of S. foetens ranging from 112 to 420 mm standard length (SL) and 13 to 630 g (wet weight) were collected from the continental shelf of Alvarado, Veracruz, Mexico. About 60% of the individuals had empty stomachs with the stomach fullness of the remaining individuals being distributed as follows: 5% full (24.8%), 50,75% full (13.5%), and completely full (1.7%). The mean (± SD) wet weight of stomach contents was 12.1 ± 10.8 g during the rainy season, and 19.0 ± 13.0 g during the nortes season. Seventeen prey items were identified, with the majority thereof being fish. The most important prey items were Upeneus parvus, Loligo pealei, Engyophrys senta, Trachurus lathami, and Anchoa hepsetus. Seasonal changes in the diet were observed, with U. parvus and L. pealei being the most important prey during the nortes season, whereas E. senta and L. pealei were the main items during the rainy season. Prey size selection was evident among size classes of S. foetens, although no trophic overlap was observed among size classes (Cik , 0.004). High trophic level values were determined for all size classes by season (rainy season = 4.67, nortes season = 4.84), and indicated this species belongs to the piscivorous trophic guild that preys upon both demersal and pelagic species. [source] Southeast Alaska: oceanographic habitats and linkagesJOURNAL OF BIOGEOGRAPHY, Issue 3 2009Thomas Weingartner Abstract We provide an overview of the physical oceanographic and geological processes that affect marine biological habitats and production in the marine waters throughout the archipelago and continental shelf of Southeast Alaska. Given the paucity of regional data, our overview summarizes work done in adjacent regions of the Gulf of Alaska shelf and basin, and draws on research carried out in similar settings elsewhere. The geological setting, which critically influences the regional meteorology and oceanography, includes a narrow continental shelf, deep channels that permeate the archipelago, fjords, glaciers and a rugged, mountainous coast. The large-scale meteorology is influenced primarily by seasonal variations in the intensity and position of the Aleutian Low. Winds, freshwater runoff, tides and cross-shelf exchange control the regional oceanography. The large-scale flow field advects mass, heat, salt, nutrients and planktonic organisms northward from British Columbia (and even further south) to the northern Gulf of Alaska along the slope, shelf, and within the channels of Southeast Alaska. The deep channels permeating the island archipelago and narrow continental shelf facilitate communication between basin and interior waters. Water properties and flow fields are subject to large annual variations in response to similarly large variations in winds and coastal freshwater discharge. The complex geological setting leads to large spatial heterogeneity in the physical processes controlling the local circulation fields and mixing, thereby creating numerous and diverse marine biological habitats. These various circulation and mixing processes modify substantially Southeast Alaska water masses and thus influence marine ecosystem processes downstream over the northern and western Gulf of Alaska shelf. [source] Abnormal hermaphroditism in the multispine skate Bathyraja multispinis (Chondrichthyes, Rajidae)JOURNAL OF FISH BIOLOGY, Issue 4 2007L. B. Scenna A hermaphroditic individual of the multispine skate, Bathyraja multispinis, caught on the Argentinean continental shelf, is described. This is the first record of hermaphroditism in the genus Bathyraja and one of the very few hermaphroditic specimens reported in the Rajidae. [source] THE STRUCTURAL STYLE OF SEDIMENTARY BASINS ON THE SHELVES OF THE LAPTEV SEA AND WESTERN EAST SIBERIAN SEA, SIBERIAN ARCTICJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2005D. Franke A total of 11,700 km of multichannel seismic reflection data were acquired during three recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas in the Siberian Arctic Ocean. Three seismic marker horizons were defined and mapped in both shelf areas. Their nature and age were predicted on the basis of regional tectonic and palaeoenvironmental events and corroborated using onshore geology. To the north of the Laptev Sea, the Gakkel Ridge, an active mid-ocean ridge which separates the North American and Eurasian Plates, abruptly meets the steep slope of the continental shelf which is curvilinear in plan view. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north-south trending rift basins: the Ust'Lena Rift, the Anisin Basin and the New Siberian Basin. The Ust'Lena Rift has a minimum east-west width of 300km at latitude 75°N and a Cenozoic infill up to 6 s (twt) in thickness. Further to the NW of the Laptev Shelf, the downthrown and faulted basement is overlain by a sub-parallel layered sedimentary succession with a thickness of 4 s (twt) that thins towards the west. Although this area was affected by extension as shown by the presence of numerous faults, it is not clear whether this depression on the NW Laptev Shelf is continuous with the Ust'Lena Rift. The Anisin Basin is located in the northern part of the Laptev Shelf and has a Cenozoic sedimentary fill up to 5 s (twt) thick. The deepest part of the basin trends north-south. To the west is a secondary, NW-SE trending depression which is slightly shallower than the main depocentre. The overall structure of the basin is a half-graben with the major bounding fault in the east. The New Siberian Basin is up to 70 km wide and has a minimum NW-SE extent of 300 km. The sedimentary fill is up to 4.5 s (twt) thick. Structurally, the basin is a half-graben with the bounding fault in the east. Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, as manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick. [source] Seafloor glacial features reveal the extent and decay of the last British Ice Sheet, east of Scotland,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2009Alastair G. C. Graham Abstract Three-dimensional (3D) seismic datasets, 2D seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf, offshore eastern Scotland (58° N, 1,2° W). The relic features are related to the activity of the last British Ice Sheet (BIS) in the Outer Moray Firth. A landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor. The assemblage comprises: (i) large seabed banks (interpreted as end moraines), coeval with the Bosies Bank moraine; (ii) morainic ridges (hummocky, push and end moraine) formed beneath, and at the margins of the ice sheet; (iii) an incised valley (a subglacial meltwater channel), recording meltwater drainage beneath former ice sheets; and (iv) elongate ridges and grooves (subglacial bedforms) overprinted by transverse ridges (grounding line moraines). The bedforms suggest that fast-flowing grounded ice advanced eastward of the previously proposed terminus of the offshore Late Weichselian BIS, increasing the size and extent of the ice sheet beyond traditional limits. Complex moraine formation at the margins of less active ice characterised subsequent retreat, with periodic stillstands and readvances. Observations are consistent with interpretations of a dynamic and oscillating ice margin during BIS deglaciation, and with an extensive ice sheet in the North Sea basin at the Last Glacial Maximum. Final ice margin retreat was rapid, manifested in stagnant ice topography, which aided preservation of the landsystem record. Copyright © 2008 John Wiley & Sons, Ltd. [source] The deglaciation of Clyde Inlet, northeastern Baffin Island, Arctic Canada,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2007Jason P. Briner Abstract The behaviour of ice sheets as they retreated from their Last Glacial Maximum (LGM) positions provides insights into Lateglacial and early Holocene ice-sheet dynamics and climate change. The pattern of deglaciation of the Laurentide Ice Sheet (LIS) in arctic fiord landscapes can now be well dated using cosmogenic exposure dating. We use cosmogenic exposure and radiocarbon ages to constrain the deglaciation history of Clyde Inlet, a 120,km long fiord on northeastern Baffin Island. The LIS reached the continental shelf during the LGM, retreated from the coastal lowlands by 12.5,±,0.7,ka (n,=,3), and from the fiord mouth by 11.7,±,2.2,ka (n,=,4). Rapid retreat from the outer fiord occurred 10.3,±,1.3,ka (n,=,6), with the terminus reaching the inner fiord shortly after 9.4,ka (n,=,2), where several moraine systems were deposited between ca. 9.4 and ca. 8.4,ka. These moraines represent fluctuations of the LIS during the warmest summers since the last interglaciation, and this suggests that the ice sheet was responding to increased snowfall. Before retreating from the head of Clyde Inlet, the LIS margin fluctuated at least twice between ca. 7.9 and ca. 8.5,ka, possibly in response to the 8.2,ka cold event. Copyright © 2006 John Wiley & Sons, Ltd. [source] Deglacial seasonal and sub-seasonal diatom record from Palmer Deep, Antarctica,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2005Eleanor J. Maddison Abstract The Antarctic Peninsula is one of the most sensitive regions of Antarctica to climate change. Here, ecological and cryospheric systems respond rapidly to climate fluctuations. A 4.4,m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core (ODP Site 1098) recovered from Basin I, Palmer Deep, western Antarctic Peninsula. This deglacial laminated interval was deposited directly over a glaciomarine diamict, hence during a globally recognised period of rapid climate change. The ultra-high-resolution deglacial record is analysed using SEM backscattered electron imagery and secondary electron imagery. Laminated to thinly bedded orange-brown diatom ooze (near monogeneric Hyalochaete Chaetoceros spp. resting spores) alternates with blue-grey terrigenous sediments (open water diatom species). These discrete laminae are interpreted as austral spring and summer signals respectively, with negligible winter deposition. Sub-seasonal sub-laminae are observed repeatedly through the summer laminae, suggesting variations in shelf waters throughout the summer. Tidal cycles, high storm intensities and/or intrusion of Circumpolar Deep Water onto the continental shelf introduced conditions which enhanced specific species productivity through the season. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)JOURNAL OF QUATERNARY SCIENCE, Issue 6 2004C. Giraudi Abstract The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic,environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central-southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd. [source] Chronology of the last recession of the Greenland Ice SheetJOURNAL OF QUATERNARY SCIENCE, Issue 3 2002Ole Bennike Abstract A new deglaciation chronology for the ice-free parts of Greenland, the continental shelf and eastern Ellesmere Island (Canada) is proposed. The chronology is based on a new compilation of all published radiocarbon dates from Greenland, and includes crucial new material from southern, northeastern and northwestern Greenland. Although each date provides only a minimum age for the local deglaciation, some of the dates come from species that indicate ice-proximal glaciomarine conditions, and thus may be connected with the actual ice recession. In addition to shell dates, dates from marine algae, lake sediments, peat, terrestrial plants and driftwood also are included. Only offshore and in the far south have secure late-glacial sediments been found. Other previous reports of late-glacial sediments (older than 11.5 cal. kyr BP) from onshore parts of Greenland need to be confirmed. Most of the present ice-free parts of Greenland and Nares Strait between Greenland and Ellesmere Island were not deglaciated until the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd. [source] Rhythmic diel movements of pandalid shrimps in the western Mediterranean continental shelf and upper slopeJOURNAL OF ZOOLOGY, Issue 4 2007J. Aguzzi Abstract In marine ecosystems, information on diel rhythmic movements of species is of importance to characterize temporal changes in the community structure. In this sense, patterns of bottom trawl catches of the pandalid caridean shrimps Chlorotocus crassicornis, Plesionika gigliolii and Plesionika martia were analysed, as a proxy of the timing and duration of their presence on the seabed, close to the autumn equinox (October) and the summer solstice (June) on the continental shelf (100 m) and the upper slope (400 m). The size structure of catches was also studied for each species to assess the possible occurrence of a modulation of rhythmic movements during ontogeny. Data showed marked diel patterns of catchability on the bottom in association with light intensity cycles in both sampling seasons and depths. Chlorotocus crassicornis on the shelf showed nocturnal peaks in catches. On the slope, Pl. gigliolii showed mainly a higher catchability at dusk and dawn, whereas the catchability of Pl. martia was mainly higher during the day time. Juveniles and adults of Pl. gigliolii and Pl. martia showed ontogenetic differences in their occurrence patterns. This phenomenon is discussed by comparing the reported catchability patterns with those of some prey species that also show rhythmic behaviour in association with the day,night cycle. [source] Particulate Matter in the Ross Sea: a Spreading ModelMARINE ECOLOGY, Issue 2002Sergio Tucci Abstract. Within the framework of the C.L.I.M.A. Project, a part of the Italian Research Program in Antarctica, the Total Particulate Matter (TPM) was used as a natural marker to characterise the water masses. The dynamics of TPM was estimated by using a numerical model capable of following the evolution of the basin during the ice absence in summer. The first numerical simulation, with horizontally constant initial conditions and the absence of TPM source areas, merely reveals how TPM passive dispersion is strongly influenced by the Ross Ice Shelf and bathymetry. The second simulation, with TPM concentration horizontally variable and vertically decreasing layers, shows a dynamic evolution of TPM that is in agreement with experimental data. On the surface, in correspondence with the shelf-break, an out-flowing flux with particulate matter contribution coming from Ross Ice Shelf is recognised. The TPM concentration may be linked to the ice melting due to the Antarctic Surface Water, with production of Shallow Ice Shelf Water. The numerical model produces, near the Drygalski area, two cells with high concentration. This numerical evolution is confirmed by the 1990 data (Spezie et al, 1993) that clearly show these two areas and their correlations with the Drygalski contributions (the inner area) and with the thermo-haline front (the external one). This condition is evident in the 1994-1995 data too (Bu-dillon et al, 1999). In this case the authors observed that the Circumpolar Deep Water penetrates onto the shelf at about 174°E; then, modifying its properties, it follows a southward path for about 200 km. The Antarctic Shelf Front (ASF) separates CDW from the colder shelf water with a high concentration of suspended matter. At the 300-meter level, the diffusion of the particulate matter directed under the RIS, towards the continental shelf, seems to be an important feature. Very high TPM values are also present in the deep water in the area off the Drygalski Glacier; this evolution agrees with the ,400 m data collected during the 1990,1991 cruise (Spezie et al., 1993). [source] Stomach contents of mass-stranded short-finned pilot whales (Globicephala macrorhynchus) from North CarolinaMARINE MAMMAL SCIENCE, Issue 2 2008Vanessa J. Mintzer Abstract We examined the stomach contents of 27 short-finned pilot whales (Globicephala macrorhynchus) that mass stranded on the North Carolina coast on 15 January 2005. Eleven whales had prey parts in their forestomachs. We used frequency of occurrence and numerical abundance to assess the relative importance of prey. Brachioteuthis riisei (numerical abundance 28%), an oceanic species, was the most important cephalopod prey, but Taonius pavo (12%) and Histioteuthis reversa (9%) also represented a substantial part of the diet. A large number of otoliths belonging to the fish Scopelogadus beanii were present (25%). These results differ from reports of the stomach contents of short-finned pilot whales from the Pacific coast in which neritic species dominate the diet. Our findings also suggest that there is a considerable difference between the diet of short- and long-finned pilot whales (Globicephala melas) in the western North Atlantic. The latter feed predominantly on the long-finned squid (Loligo pealei) whereas the former feed on deep-water species. Our results indicate the whales fed primarily off the continental shelf prior to stranding. [source] Coexistence patterns of benthic gastropods on the Uruguayan shelfOIKOS, Issue 8 2010Alvar Carranza Community assembly rules theory attempt to understand the processes that determine the composition of local communities from a regional species pool. Nestedness and negative co-occurrence are two of the most commonly reported meta-community patterns, but almost exclusively from terrestrial and freshwater ecosystems. Here we analyzed the structure of species coexistence in six datasets containing presence/absence data for 120 marine benthic gastropod species in 249 sampling units on the Uruguayan continental shelf and Río de la Plata estuary. The ecological features of this system, such as the idiosyncratic nature of the biogeographic and oceanographic realms, are clearly different from those observed in other systems previously targeted by studies on coexistence structure. Community patterns were evaluated using null models and four structure indices. The existence of patterns in community assembly, and in particular segregated co-occurrence, was verified only when analyzing the number of checkerboard units (CH index). This indicates more mutually exclusive species pairs than expected by chance. Nestedness, on the other hand, was not detected in any dataset. Storage and rescue effects related to overall high immigration and low local extinction rates are plausible mechanisms to account for the general pattern of random species coexistence, while the segregated co-occurrence pattern depicted by the CH index may be related to differential habitat requirements within species pairs. Our study highlights the importance of analyzing metacommunity structures in alternative biological, environmental, and historical contexts in order to advance on the construction of a general ecological theory, relating patterns with the processes dominating in particular ecosystems. [source] | ||||||||||||||||||||||||||||