The discovery of new galaxy members in the NGC 5044 and 1052 groups     

N. P. F. MKay  C. G. Mundell †  S. Brough  Duncan A. Forbes  D. G. Barnes  P. A. James  P. Goudfrooij  V. Kozhurina-Platais  R. Whitaker 《Monthly notices of the Royal Astronomical Society》2004,352(4):1121-1134

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Geography in the Universities     

Craig Duncan 《New Zealand geographer》1967,23(1):50-56

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FRONTIERS IN GEOGRAPHICAL TEACHING. Edited by R. J. Chorley and P. Haggett.     

C. Duncan 《New Zealand geographer》1966,22(2):203-204

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Three-dimensional swimming behavior of individual zooplankters: observations using the acoustical imaging system FishTV     

McGehee  Duncan; Jaffe  Jules S. 《ICES Journal of Marine Science》1996,53(2):363-369

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Impact of sediment organic matter quality on the fate and effects of fluoranthene in the infaunal brittle star Amphiura filiformis     

Selck H  Granberg ME  Forbes VE 《Marine environmental research》2005,59(1):19-45

Hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) readily adsorb to organic matter. The aim of this study was to determine the importance of the quality of sedimentary organic matter for the uptake, biotransformation and toxicity of the PAH, fluoranthene (Flu), in the infaunal brittle star Amphiura filiformis. Brittle stars were exposed to a base sediment covered by a 2 cm Flu-spiked top layer (30 microg Flu/g dry wt. sed.), enriched to the same total organic carbon content with either refractory or labile organic matter. The labile carbon source was concentrated green flagellate: Tetraselmis spp. The refractory carbon source was lignin from a paper mill. Tissue concentrations of Flu both in disk and arm-fractions were determined as total Flu, parent Flu (i.e. untransformed), aqueous Flu-metabolites, polar Flu-metabolites and tissue residue Flu (i.e. unextractable). Our results showed that sediment particle ingestion is a pathway by which Flu can enter benthic food webs. Flu toxicity (measured as arm-regeneration), but not net accumulation, was dependent on the nutritional quality of the ingested sediment particles. Flu bioaccumulation could not be attributed solely to equilibrium partitioning between organism lipid content and organic content of the sediment. Biotransformation of Flu by brittle stars was very limited and unaffected by organic matter quality. A. filiformis contributed to the downward transport of Flu from the surface sediment to the burrow lining. The limited breakdown of parent Flu by brittle stars and/or microorganisms was relatively higher in burrows compared to surface sediment, and highest in the presence of labile organic matter. Tissue concentrations were higher in disk than in arms, but the proportion of metabolic products relative to parent Flu was higher in arms than in the disk fraction. We estimate that the yearly mobilization of sediment-associated Flu by arm-regeneration in A. filiformis is in the range of 3.8-29.4 microg total Flu eq. m(-2) year(-1) at a sediment concentration of 30 microg Flu/g dry wt. sed.  相似文献   

Holocene sedimentation of a wave-dominated barrierisland shoreline: Cape Lookout, North Carolina     

S.Duncan Heron Jr.  Thomas F. Moslow  William M. Berelson  John R. Herbert  George A. Steele III  Kenneth R. Susman   《Marine Geology》1984,60(1-4):413-434

The sedimentary record of 130 km of microtidal (0.9 m tidal range) high wave energy (1.5 m average wave height) barrier island shoreline of the Cape Lookout cuspate foreland has been evaluated through examination of 3136 m of subsurface samples from closely spaced drill holes. Holocene sedimentation and coastal evolution has been a function of five major depositional processes: (1) eustatic sea-level rise and barrier-shoreline transgression; (2) lateral tidal inlet migration and reworking of barrier island deposits; (3) shoreface sedimentation and local barrier progradation; (4) storm washover deposition with infilling of shallow lagoons; and (5) flood-tidal delta sedimentation in back-barrier environments.

Twenty-five radiocarbon dates of subsurface peat and shell material from the Cape Lookout area are the basis for a late Holocene sea-level curve. From 9000 to 4000 B.P. eustatic sea level rose rapidly, resulting in landward migration of both barrier limbs of the cuspate foreland. A decline in the rate of sea-level rise since 4000 B.P. resulted in relative shoreline stabilization and deposition of contrasting coastal sedimentary sequences. The higher energy, storm-dominated northeast barrier limb (Core and Portsmouth Banks) has migrated landward producing a transgressive sequence of coarse-grained, horizontally bedded washover sands overlying burrowed to laminated back-barrier and lagoonal silty sands. Locally, ephemeral tidal inlets have reworked the transgressive barrier sequence depositing fining-upward spit platform and channel-fill sequences of cross-bedded, pebble gravel to fine sand and shell. Shoreface sedimentation along a portion of the lower energy, northwest barrier limb (Bogue Banks) has resulted in shoreline progradation and deposition of a coarsening-up sequence of burrowed to cross-bedded and laminated, fine-grained shoreface and foreshore sands. In contrast, the adjacent barrier island (Shackleford Banks) consists almost totally of inlet-fill sediments deposited by lateral tidal inlet migration. Holocene sediments in the shallow lagoons behind the barriers are 5–8 m thick fining-up sequences of interbedded burrowed, rooted and laminated flood-tidal delta, salt marsh, and washover sands, silts and clays.

While barrier island sequences are generally 10 m in thickness, inlet-fill sequences may be as much as 25 m thick and comprise an average of 35% of the Holocene sedimentary deposits. Tidal inlet-fill, back-barrier (including flood-tidal delta) and shoreface deposits are the most highly preservable facies in the wave-dominated barrier-shoreline setting. In the Cape Lookout cuspate foreland, these three facies account for over 80% of the sedimentary deposits preserved beneath the barriers. Foreshore, spit platform and overwash facies account for the remaining 20%.  相似文献   

Prolonged Magmatic and Tectonic Development of the Caribbean Igneous Province Revealed by a Diving Submersible Survey     

Mauffret  Alain  Leroy  Sylvie  Vila  Jean-Marie  Hallot  Erwan  Mercier de Lépinay  Bernard  Duncan  Robert A. 《Marine Geophysical Researches》2001,22(1):17-45

Using the diving submersible survey NAUTICA we investigated the central part of the Caribbean large igneous province (CLIP) to observe and sample internal portions of this proposed oceanic plateau. Most of the samples are gabbroic and doleritic rocks; basalts are scarce. Radiometric dating by ⁴⁰Ar/³⁹Ar incremental heating experiments indicate that the intrusive rocks are Campanian in age (81–75 Ma). In some places these intrusive rocks underlie older Santonian (85–83 Ma) extrusive basaltic rocks, suggesting that the Campanian rocks represent a sill injection and an underplating episode. Results of the diving program supplemented by information from ODP and DSDP drilling sites document a 20 m.y. period (94–75 Ma) of igneous activity in the submerged portion of the Caribbean large igneous province (CLIP). In the northern part of the Beata Ridge late Campanian and/or post Campanian uplift is documented by prominent Maastrichtian (71–65 Ma) erosion and the establishment of a Paleocene-middle Eocene (65–49 Ma) carbonate platform. During and after the uplift an extensional period is indicated by seismic images and the subsidence (3 km depth) of the carbonate platform. Paleocene ages (55–56 Ma) determined on some volcanic samples are attributed to localised decompression mantle melting that accompanied the extension. We document a prolonged period of magmatic and tectonic events that do not fit with the current models of short-lived plateau formation during mantle plume initiation but shares many similarities with the constructional histories of other oceanic large igneous provinces.  相似文献   

An evaluation of systems for the integrated assessment of capture fisheries     

Duncan Leadbitter  Trevor J. Ward 《Marine Policy》2007

Integrated fishery assessments are intended to take an integrated and wholistic view of fisheries management, to provide comprehensive systems-based evaluations of the sustainability of individual fisheries and their products. Using guidance derived from decision theory and management science, we develop 18 criteria to evaluate the likely effectiveness of nine integrated fishery assessment systems. The assessment systems do not consistently consider four key criteria: the socio-economic impacts of fisheries, the provision of food security, the local relevance of the assessment to the fishery under assessment, and the independent peer review of assessment outcomes. Other important areas of weakness include the lack of appropriate consultation processes relating to both the design of the assessment system and the outcomes of fishery assessments, and limitations in the quality of data and information used in assessments. Improvements will be needed in these areas across all the systems we evaluated if fishers, consumers, managers and other stakeholders are to be provided with consistently reliable assessment outcomes, and an assurance of the sustainability of capture fisheries.  相似文献   

Storms and shoreline retreat in the southern Gulf of St. Lawrence   总被引：1，自引：0，他引：1  

Donald L. Forbes  George S. Parkes  Gavin K. Manson  Lorne A. Ketch 《Marine Geology》2004,210(1-4):169-204

Storms play a major role in shoreline recession on transgressive coasts. In the southern Gulf of St. Lawrence (GSL), southeastern Canada, long-term relative sea-level rise off the North Shore of Prince Edward Island has averaged 0.3 m/century over the past 6000 years (>0.2 m/century over 2000 years). This has driven long-term coastal retreat at mean rates >0.5 m/a but the variance and details of coastal profile response remain poorly understood. Despite extensive sandy shores, sediment supply is limited and sand is transferred landward into multidecadal to century-scale storage in coastal dunes, barrier washover deposits, and flood-tidal delta sinks. Charlottetown tide-gauge records show mean relative sea-level rise of 3.2 mm/a (0.32 m/century) since 1911. A further rise of 0.7±0.4 m is projected over the next 100 years. When differenced from tidal predictions, the water-level data provide a 90-year record of storm-surge occurrence. Combined with wind, wave hindcast, and sea-ice data, this provides a catalogue of potentially significant coastal storms. We also document coastal impacts from three recent storms of great severity in January and October 2000 and November 2001. Digital photogrammetry (1935–1990) and shore-zone surveys (1989–2001) show large spatial and temporal variance in coastal recession rates, weakly correlated with the storm record, in part because of wave suppression or coastal protection by sea ice. Large storms cause rapid erosion from which recovery depends in part on local sand supply, but barrier volume may be conserved by washover deposition. Barrier shores with dunes show high longshore and interdecadal variance, with extensive multidecadal healing of former inlet and overwash gaps. This reflects recovery from an episode of widespread overwash prior to 1935, possibly initiated by intense storms or groups of storms in the latter half of the 19th century. With evidence from the storms of 2000–2001, this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability, as well as the need for a long-term, large-scale perspective in assessing coastal stability. The expected acceleration in relative sea-level rise, together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern GSL, implies a significant increase in coastal erosion hazards in future.  相似文献   

The emplacement of intermediate volume ignimbrites: A case study from Roccamonfina Volcano,Southern Italy     

P. D. Cole  J. E. Guest  A. M. Duncan 《Bulletin of Volcanology》1993,55(7):467-480

A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km³ volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front.We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement.  相似文献