The 1999 Flatfish Symposium: where to go from now?     

Henk W. van der Veer  Richard D. M. Nash 《Journal of Sea Research》2001,45(3-4)

A summary report of the 1999 Flatfish Symposium is presented. The Symposium was built on the themes of the previous Symposia, whereby the link is through processes related to recruitment. As in the previous Symposia, the papers presented have a strong focus on temperate species and basic information on (sub)tropical species is still lacking. The lack of insight into (sub)stock structure is still a problem and more insight is necessary into the methodologies for determining and describing stock structure. Another important unresolved issue concerns the quantitative understanding of the physical processes that affect the cross-shelf transport and exchange of eggs and larvae. Finally, there is a need for bioenergetic approaches to habitat quality and quantity both at the individual and population level to assess the qualitative and quantitative use of habitats in space and time. Applying global information systems (GIS) might be promising in this respect. With respect to management issues two items are of utmost importance: the collapse and recovery of stocks and the problems relating to re-stocking.  相似文献   

A comparison of management planning and implementation in three Indonesian marine protected areas     

Jackie Alder  N. A. Sloan  Henk Uktolseya 《Ocean & Coastal Management》1994,24(3)

A comparison of three marine protected areas in Indonesia illustrates many of the problems in management planning and implementation. Major factors influencing management are proximity to urban areas, the protected area's economic potential, current uses and the resolution of jurisdictional disputes. Isolation does not prevent resource depletion. Improving the economic conditions of local residents and gaining their commitment to environmentally sustainable commercial and subsistence resource uses within and near protected areas are vital to implementing area management.  相似文献   

Cenozoic alongslope processes and sedimentation on the NW European Atlantic margin     

Jan Sverre Laberg  Martyn S. Stoker  K.I. Torbjrn Dahlgren  Henk de Haas  Haflidi Haflidason  Berit O. Hjelstuen  Tove Nielsen  Pat M. Shannon  Tore O. Vorren  Tjeerd C.E. van Weering  Silvia Ceramicola 《Marine and Petroleum Geology》2005,22(9-10):1069

Based on studies of sediment accumulations deposited from-and erode by-alongslope flowing ocean currents on the European continental margin from Porcupine (Ireland) to Lofoten (Norway), the evolution of the Cenozoic paleocirculation was reconstructed as part of the STRATAGEM project. There is evidence of ocean current-controlled erosion and deposition in the Rockall Trough, in the Faeroe-Shetland Channel and on the Vøring Plateau since the late Eocene, although the circulation pattern remains ambiguous. The late Palaeogene flow in the Rockall Trough was almost probably driven by southerly-derived Tethyan Outflow Water. The extent and strength of any northerly-derived flow is uncertain. From the early Neogene (early-mid-Miocene), there was a massive regional expansion of contourite drift development both in the North Atlantic and in the Norwegian-Greenland Sea. This was most probably related to the development of the Faroe Conduit, the opening of the Fram Strait and the general subsidence of the Greenland-Scotland Ridge. These may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the Arctic and Atlantic Oceans. An early late Neogene (late early Pliocene) regional erosional event has been ascribed to a vigorous pulse of bottom-current activity, most probably the result of a global reorganisation of ocean currents associated with the closure of the Central American Seaway. During the late Neogene, contourites and sediment drifts developed in deep-water basins, between units of glacigenic sediments as well as infill of several paleo-slide scars. These sediments were derived from areas of bottom-current erosion as well as from the development of Plio-Pleistocene prograding sediment wedges, incorporating the extensive sediment supply derived from shelf-wide ice sheets. Presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of Atlantic water. Depocentres of sediments derived from the winnowing are located (locally) in lower slope embayments and in slide scars.  相似文献   

Oblique sand ridges in confined tidal channels due to Coriolis and frictional torques     

Hepkema  Tjebbe M.  de Swart  Huib E.  Nnafie  Abdel  Schramkowski  George P.  Schuttelaars  Henk M. 《Ocean Dynamics》2020,70(12):1505-1513

Ocean Dynamics - The role of the Coriolis effect in the initial formation of bottom patterns in a tidal channel is studied by means of a linear stability analysis. The key finding is that the...  相似文献   

Simulating ground water-lake interactions: approaches and insights   总被引：4，自引：0，他引：4  

Hunt RJ  Haitjema HM  Krohelski JT  Feinstein DT 《Ground water》2003,41(2):227-237

Approaches for modeling lake-ground water interactions have evolved significantly from early simulations that used fixed lake stages specified as constant head to sophisticated LAK packages for MODFLOW. Although model input can be complex, the LAK package capabilities and output are superior to methods that rely on a fixed lake stage and compare well to other simple methods where lake stage can be calculated. Regardless of the approach, guidelines presented here for model grid size, location of three-dimensional flow, and extent of vertical capture can facilitate the construction of appropriately detailed models that simulate important lake-ground water interactions without adding unnecessary complexity. In addition to MODFLOW approaches, lake simulation has been formulated in terms of analytic elements. The analytic element lake package had acceptable agreement with a published LAKI problem, even though there were differences in the total lake conductance and number of layers used in the two models. The grid size used in the original LAKI problem, however, violated a grid size guideline presented in this paper. Grid sensitivity analyses demonstrated that an appreciable discrepancy in the distribution of stream and lake flux was related to the large grid size used in the original LAKI problem. This artifact is expected regardless of MODFLOW LAK package used. When the grid size was reduced, a finite-difference formulation approached the analytic element results. These insights and guidelines can help ensure that the proper lake simulation tool is being selected and applied.  相似文献   

Quantification strategies for human-induced and natural hydrological changes in wetland vegetation, southern Florida, USA   总被引：2，自引：0，他引：2  

Timme H. Donders  Friederike Wagner  Henk Visscher 《Quaternary Research》2005,64(3):333-342

An accurately dated peat profile from a mixed cypress swamp in the Fakahatchee Strand Preserve State Park (FSPSP, Florida, USA) has been examined for pollen and spores. The near-annual resolved pollen record shows a gradual shift from a wet to a relatively dry assemblage during the past 100 years. Timing of drainage activities in the region is accurately reflected by the onset and duration of vegetation change in the swamp. The reconstructed vegetation record has been statistically related to pollen assemblages from surface sediment samples. The response range of the FSPSP wetland to environmental perturbations could thus be determined and this allows better understanding of naturally occurring vegetation changes. In addition, the human impact on Florida wetlands becomes increasingly apparent. Superimposed high-frequency variation in the record suggests a positive correlation between winter-precipitation and pollen productivity of the dominant tree taxa. However, further high-resolution analysis is needed to confirm this relation. The response range of the FSPSP wetland to environmental perturbations on both annual- and decadal-scales documented in this study allows recognition and quantification of natural hydrological changes in older deposits from southwest Florida. The strong link between local hydrology and the El Niño Southern Oscillation makes the palynological record from FSPSP highly relevant for studying past El Niño—variability.  相似文献   

Evolution and structure of the Upper Rhine Graben: insights from three-dimensional thermomechanical modelling     

Michael Schwarz  Andreas Henk 《International Journal of Earth Sciences》2005,94(4):732-750

The evolution and geometry of the Tertiary Upper Rhine Graben were controlled by a continually changing stress field and the reactivation of pre-existing crustal discontinuities. A period of WNW-ESE extension in the late Eocene and Oligocene was followed by lateral translation from the early Miocene onwards. This study utilizes 3D finite element techniques to simulate extension and lateral translation on a lithospheric scale. Brittle and creep behaviour of lithospheric rocks are represented by elastoplasticity and thermally activated power-law viscoplasticity, respectively. Contact elements allocated with cohesion and frictional coefficients are used to describe pre-existing zones of weakness in the elastic-brittle field. Our results suggest that (1) extension is accommodated along listric border faults to midcrustal depth of 15–16 km. Beneath, pure shear stretching occurs without a need for localized shear zones in lower crust and upper mantle. (2) Ductile flow at midcrustal depth across the graben accounts for the pronounced halfgraben morphology. Thereby, the shape of the border faults, their frictional coefficients, and sedimentary loads have profound effects on the rate of ductile flow across the graben. (3) Horizontal extension of 8–8.5 km and sinistral displacement across the rift of 3–4 km are needed to accommodate the observed sediment thickness.  相似文献   

Author Index     

Henk De Bruin 《Boundary-Layer Meteorology》2002,104(3):507-507

Authors Index

Author Index  相似文献   

The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island     

Henri J. Dumont  Christine Cocquyt  Michel Fontugne  Maurice Arnold  Jean-Louis Reyss  Jan Bloemendal  Frank Oldfield  Cees L.M. Steenbergen  Henk J. Korthals  Barbara A. Zeeb 《Journal of Paleolimnology》1998,20(4):409-422

We reconstruct aspects of the history of Easter Island over the last 4-5 centuries based on the study of a core from Rano Raraku Lake, situated in the crater that contains the quarry of the island's giant statues or moai. We use microfossils of plants and animals to identify five zones. The last three of these are separated by waves of immigration from South America and from the subantarctic. We argue that the first or South American wave, dated to the second half of the 14th century, may represent a visit by South American Indians. Magnetic information, pollen, diatoms, chrysophyte stomatocysts and fossil plant pigments reveal a synchronism between the South American contact and the cessation of moai quarrying. We therefore suggest that Amerindians contributed to the cultural collapse of the island. The second or subantarctic wave may reflect an early European visit to the island, possibly by Cpt. James Cook in 1774, or by Jacob Roggeveen in 1722.  相似文献   

Gravitational orogenic collapse vs plate-boundary stresses: a numerical modelling approach to the Permo-Carboniferous evolution of Central Europe     

Andreas Henk 《International Journal of Earth Sciences》1997,86(1):39-55

A two-dimensional thermo-mechanical finite element model is used to study the Permo-Carboniferous evolution of Central Europe along a lithosphere-scale transect from the Variscan Internides to the undeformed foreland. The study concentrates on a quantitative evaluation of the processes controlling late-orogenic extension and destruction of the Variscides, particularly the gravitational instability of thickened crust. Modelling results suggest that gravitational forces along cannot reproduce the observed timing and amount of Permo-Carboniferous crustal thinning. Tensile plate-boundary forces are required in addition to gravitation to restore a crustal thickness of approximately 30?km in the Variscan Internides. Stresses as little as 10?MPa result in up to 28% extension and a good fit between observed data and model predictions. It is concluded that the Stephanian to Rotliegend evolution in the vicinity of the modelled traverse resulted not from gravitational forces inherited from Variscan crustal thickening, but was related to a change in orientation of the plate-boundary stresses at the end of the Westphalian.  相似文献