Mezen Bay—a key area for understanding Weichselian glaciations in northern Russia     

Kurt H. Kjr  Igor N. Demidov  Eiliv Larsen  Andrew Murray  Jan K. Nielsen 《第四纪科学杂志》2003,18(1):73-93

Sediment successions in coastal cliffs around Mezen Bay, southeastern White Sea, record an unusually detailed history of former glaciations, interstadial marine and fluvial events from the Weichselian. A regional glaciation model for the Weichselian is based on new data from the Mezen Bay area and previously published data from adjacent areas. Following the Mikulinian (Eemian) interglacial a shelf‐centred glaciation in the Kara Sea is reflected in proglacial conditions at 100–90 ka. A local ice‐cap over the Timan ridge existed between 75 and 65 ka. Renewed glaciation in the Kara Sea spread southwestwards around 60 ka only, interrupted by a marine inundation, before it advanced to its maximum position at about 55–50 ka. After a prolonged ice‐free period, the Scandinavian ice‐sheet invaded the area from the west and terminated east of Mezen Bay about 17 ka. The previously published evidence of a large ice‐dammed lake in the central Arkhangelsk region, Lake Komi, finds no support in this study. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

On the structure of oscillatory boundary layers     

Peter Nielsen 《Coastal Engineering》1985,9(3):261-276

An empirical analysis is performed on the most detailed, recent measurements of turbulent oscillatory boundary layer flow. The measurements show that throughout elevations where the flow can be considered horizontally uniform, one deficit model is sufficient for describing the fundamental mode. Some general properties of the non dimensional velocity deficit D₁(z) appear with striking consistency. First of all the identity $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦ ≡}\text{Arg}\text{D}{}_{\mathrm{<mtext>1</mtext>}}$, which is a theoretical result for smooth laminar flow, seems to hold with great accuracy for a large range of turbulent flow conditions as well. This is of principal theoretical interest because all previous analytical eddy viscosity models as well as numerical mixing length models predict a consistent and fairly large difference between Arg D₁ and $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦}$. If the identity between $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦}$ and Arg D₁ extends all the way to the bed, it means that the bed shear stress leads the free stream velocity by 45 degrees. It is also found that the structure of smooth turbulent oscillatory flows as measured by Kalkanis (1964) corresponds to a sharp maximum in the normalized energy dissipation rate.  相似文献   

A Pliocene mega-tsunami deposit and associated features in the Ranquil Formation,southern Chile     

J.P. Le Roux  Sven N. Nielsen  Helga Kemnitz  Álvaro Henriquez 《Sedimentary Geology》2008,203(1-2):164-180

An exceptionally large tsunami affected the coastline of southern Chile during the Pliocene. Its backflow eroded coarse beach and coastal dune sediments and redistributed them over the continental shelf and slope. Sandstone dykes and sills injected from the base of the resulting hyperconcentrated flow into underlying cohesive muds, assisted in plucking up large blocks of the latter and incorporating them into the flow. Locally, the rip-up intraclasts were fragmented further by smaller-scale injections to form a distinct breccia of angular to rounded mudstone clasts within a medium to coarse sandstone matrix. Sandstone sills in places mimic normal sedimentary beds, complete with structures resembling inverse gradation, planar laminae, as well as ripple and trough cross-lamination. These were probably formed by internal sediment flow and shear stress as the semi-liquefied sand was forcefully injected into cracks. In borehole cores, such sills can easily be misinterpreted as normal sedimentary beds, which can have important implications for hydrocarbon exploration.  相似文献   

Linkages between Alaskan sockeye salmon abundance, growth at sea, and climate, 1955–2002     

G.T. Ruggerone  J.L. Nielsen  J. Bumgarner 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2776

We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976–1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976–1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean.  相似文献   

Morphodynamics of a bar-trough surf zone   总被引：3，自引：0，他引：3  

L.D. Wright  P. Nielsen  N.C. Shi  J.H. List 《Marine Geology》1986,70(3-4):251-285

A field study was made of the distinguishing morphodynamic processes operating in a surf zone which perennially exhibits accentuated bar-trough topography (the “longshore-bar-trough” and “rhytmic-bar-and-beach” states as described by Wright and Short, 1984). Characteristic features of the morphology include a shallow bar with a steep shoreward face, a deep trough, and a steep beach face. This morphology, which is favored by moderate breaker heights and small tidal ranges, strongly controls the coupled suite of hydrodynamic processes. In contrast to fully dissipative surf zones, the bar-trough surf zone is not at all saturated and oscillations at incident wave frequency remain dominant from the break point to the subaerial beach. The degree of incident wave groupiness does not change appreciably across the surf zone. Infragravity standing waves which, in dissipative surf zones, dominate the inshore energy, remain energetically secondary and occur at higher frequencies in the bar trough surf zone. Analyses of the field data combined with numerical simulations of leaky mode and edge wave nodal—antinodal positions over observed surf-zone profiles, indicate that the frequencies which prevail are favored by the resonant condition of antinodes over the bar and nodes in the trough. Standing waves which would have nodes over the bar are suppressed. Sediment resuspension in the surf zone appears to be largely attributable to the incident waves which are the main source of bed shear stress. In addition, the extra near-bottom eddy viscosity provided by the reformed, non-breaking waves traversing the trough significantly affects the vertical velocity profile of the longshore current. Whereas the bar is highly mobile in terms of onshore—offshore migration rates, the beach face and inner regions of the trough are remarkably stable over time.  相似文献   

Commentary on “Fisheries co-management: A comparative analysis”     

Sevaly Sen  Jesper Raakjoer Nielsen 《Marine Policy》1997,21(6):545-546

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Spawning season of the Atlantic halibut (Hippoglossus hippoglossus) in northern Norway     

Kjorsvik  Elin; Haug  Tore; Tjemsland  Jonas 《ICES Journal of Marine Science》1987,43(3):285-293

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Exposure of phytoplankton to ekofisk crude oil     

Kjetill Østgaard  Ingvar Eide  Arne Jensen 《Marine environmental research》1984,11(3):183-200

Solutions of Ekofisk crude oil in sea water were prepared by slow stirring for 21h in a closed system. Headspace and GC/MS techniques were applied to establish dose composition and levels. The standardized test medium produced in a closed system contained approximately 14 mg oil per litre and was dominated by low molecular weight aromatic hydrocarbons and phenols.The toxicity of the standarized oil-containing medium to three marine diatoms was studied in a cage culture turbidostat and by conventional batch culture technique. The three algal species differed in sensitivity to the oil compounds, but showed identical ranking in both test systems.Standardized test medium diluted to 50% with respect to oil content stopped the growth of the most sensitive alga, Skeletonema costatum. For comparison naphthalene was applied and gave 50 % growth reduction at a concentration of 400 μg litre^?1. The growth of Chaetoceros ceratosporum was only slighty affected by the full strength standard test medium, which had no influence on the growth of Phaeodactylum tricornutum, the least sensitive organism. The presence of an oil layer on the surface of the standard test medium during the growth test greatly increased its toxicity and blocked completely the photosynthesis even of P. tricornutum after 4 days.  相似文献   

A brief catalogue of failures: Framing evaluation and learning in fisheries resource management     

Kre Nolde Nielsen  Petter Holm 《Marine Policy》2007,31(6):669-680

We propose a framework for enabling a systematic evaluation of a fisheries resource management system, which we define as a feed-back mechanism coupled to a fishery. The resource management system includes four basic functions: diagnostics, intervention, goal setting, and decision making. This model allows for the development of an evaluation framework for fisheries resource management by facilitating a typology of failures. We suggest that the potential for systemic and interdisciplinary learning will be significantly enhanced through the process of developing such a framework.  相似文献   

Time changes in fishing power in the Danish cod fisheries of the Baltic Sea     

Marchal  Paul; Nielsen  J. Rasmus; Hovgard  Holger; Lassen  Hans 《ICES Journal of Marine Science》2001,58(1):298-310

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