The 8th International Conference on Coastal Dynamics,Helsingør,Denmark, 12-16 June, 2017     

Aagaard  Troels  Kroon  Aart  Fuhrman  David R. 《Ocean Dynamics》2020,70(2):289-290

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Respiration partitioning in contrasting subtidal sediments: seasonality and response to a spring phytoplankton deposition     

Maria de Assunção Franco  Jan Vanaverbeke  Dick Van Oevelen  Karline Soetaert  Maria José Costa  Magda Vincx  Tom Moens 《Marine Ecology》2010,31(2):276-290

Biomass and respiration rates of bacteria, nematodes and macrobenthos were estimated in relation to the deposition of the spring phytoplankton bloom at two contrasting sites in the Southern North Sea: one with fine‐grained sediment close to the coastline and another with highly permeable sediments. Sediment community oxygen consumption (SCOC) was also measured. Bacterial biomass was relatively similar at both stations, whereas nematode and macrobenthic biomass were higher in fine‐grained sediment. In fine sediments, bacterial biomass increased quickly after deposition of the phytoplankton bloom, whereas the response of nematodes and macrobenthos was delayed. In coarser sediments, nematodes and macrobenthos also showed a fast response in terms of density and biomass. Respiration in permeable sediments was mainly dominated by bacteria at all periods of the year. Hence, nematode and macrobenthic respiration did not contribute strongly to SCOC. This is in contrast to the patterns observed in finer sediments, where both macrofauna and nematodes were important oxygen consumers as well. Macrobenthos contributed more to total SCOC than did nematodes in winter. However, shortly after the arrival of phytodetritus at the sea floor, nematodes and macrobenthos contributed equally to the total SCOC, indicating that all benthic size classes should be taken into account when investigating marine benthic respiration rates.  相似文献   

Effects of acoustic alarms, designed to reduce small cetacean bycatch in gillnet fisheries, on the behaviour of North Sea fish species in a large tank     

Kastelein RA  van der Heul S  van der Veen J  Verboom WC  Jennings N  de Haan D  Reijnders PJ 《Marine environmental research》2007,64(2):160-180

World-wide many cetaceans drown incidentally in fishing nets. To reduce the unwanted bycatch in gillnets, pingers (acoustic alarms) have been developed that are attached to the nets. In the European Union, pingers will be made compulsory in some areas in 2005 and in others in 2007. However, pingers may effect non-target marine fauna such as fish. Therefore in this study, the effects of seven commercially-available pingers on the behaviour of five North Sea fish species in a large tank were quantified. The species tested were: sea bass (Dicentrarchus labrax), pout (Trisopterus luscus), thicklip mullet (Chelon labrosus), herring (Clupea harengus), and cod (Gadus morhua). The fish were housed as single-species schools of 9-13 individuals in a tank. The behaviour of fish in quiet periods was compared with their behaviour during periods with active pingers. The results varied both between pingers and between fish species. Sea bass decreased their speed in response to one pinger and swam closer to the surface in response to another. Thicklip mullet swam closer to the bottom in response to two pingers and increased their swimming speed in response to one pinger. Herring swam faster in response to one pinger, and pout and cod (close relatives) showed no behavioural responses to any of the pingers. Of the seven pingers tested, four elicited responses in at least one fish species, and three elicited no responses. Whether similar responses would be elicited in these fish species in the wild, and if so, whether such responses would influence the catch rate of fisheries, cannot be derived from the results of this study. However, the results indicate the need for field studies with pingers and fish. Based on the small number of fish species tested, the present study suggests that the higher the frequency of a pinger, the less likely it is to affect the behaviour of marine fish.  相似文献   

A weight-of-evidence approach to assessing the ecological impact of organotin pollution in Dutch marine and brackish waters; combining risk prognosis and field monitoring using common periwinkles (Littorina littorea)     

Schipper CA  Smit MG  Kaag NH  Dick Vethaak A 《Marine environmental research》2008,66(2):231-239

In the present study an integrated ecological risk assessment based on multiple lines of evidence (LOEs) was evaluated in order to better assess the risk from TBT in Dutch harbours and open coastal waters. On the basis of spatial distributions of measured tributyltin (TBT) concentrations in sediments and suspended matter, predictions of the intersex index (ISI) in Littorina littorea and the ecological risk expressed as the Potentially Affected Fraction (PAF) of species were made. The results were compared to actual ISI measurements and presence of L. littorea in the field. The PAF calculated on the basis of TBT levels for open coastal waters ranged from 4.2% to 15.3%; for harbours it ranged from 3.5% to 26.9%. Significant intersex levels were observed only in waters where the risk was calculated above 10% PAF. This study suggests that the absence of L. littorea from some harbours with high ecological risk values can be explained by high TBT concentrations. A call is made for the use of integrated approaches like weight-of-evidence (WOE) to help practitioners improve ecological risk assessment.  相似文献   

慢速扩张脊下的复杂熔- 岩相互作用：来自大西洋北纬14°97′区段洋中脊含铬铁矿纯橄岩的记录     

周翔  郑建平  熊庆  刘文龙  Henry J B Dick 《地质学报》2022,96(12):4242-4256

在大西洋洋中脊北纬14°97′附近贫岩浆型慢速扩张脊区段的洋底岩石调查中，拖网取样及洋底钻探均发现蛇纹石化地幔岩石中有脉状纯橄岩。纯橄岩中的铬铁矿粒度以毫米级为主，个别颗粒直径接近厘米级别，成分上显示中等程度的铬值与镁值(Cr#=52. 2~56. 1；Mg#=44. 6~51. 5)较高的TiO2含量(0. 60% ～0. 91%)。铬铁矿内部包裹体中大量出现韭闪石+金云母组合，并发现自形磷灰石包裹体。这些特征与“俯冲带型铬铁矿”的成分特征及矿物包裹体组合非常类似。本文的样品观察说明在洋中脊下方的熔体通道内，高度演化的熔体可以形成小体积的富水岩浆并参与铬铁矿的形成。拖网调查与钻探研究证实，研究区的纯橄岩、异剥橄榄岩、富橄榄石橄长岩、辉石岩、辉长岩及橄榄辉长岩等均以脉体形式产于难熔的大洋岩石圈橄榄岩质地幔中。这些脉状岩石共同记录了洋中脊玄武质熔体向上迁移过程中与围岩方辉橄榄岩间的熔- 岩反应，属于“交代橄榄岩”的范畴，揭示了慢速扩张洋脊之下熔体迁移诱发的复杂熔- 岩相互作用。  相似文献   

Improving carrier-phase ambiguity resolution in global GPS network solutions   总被引：7，自引：5，他引：7  

M. Ge  G. Gendt  G. Dick  F. P. Zhang 《Journal of Geodesy》2005,79(1-3):103-110

Integer carrier-phase ambiguity resolution is one of the critical issues for precise GPS applications in geodesy and geodynamics. To resolve as many integer ambiguities as possible, the ‘most-easy-to-fix’ double-difference ambiguities have to be defined. For this purpose, several strategies are implemented in existing GPS software packages, such as choosing the ambiguities according to the baseline length or the variances of the estimated real-valued ambiguities. Although their efficiencies are demonstrated in practice, it is proven in this paper that they do not reflect all effects of varying data quality, because they are based on theoretical considerations of GPS data processing. Therefore, a new approach is presented, which selects the double-difference ambiguities according to their probability of being fixed to the nearest integer. The probability is computed from estimates and variances of wide-lane and narrow-lane ambiguities. Together with an optimized ambiguity fixing procedure, the new approach is implemented in the routine data processing for the International GPS Service (IGS) at GeoForschungsZentrum (GFZ) Potsdam. Within a sub-network of about 90 IGS stations, it is demonstrated that more than 97% of the independent ambiguities are fixed correctly compared to 75% by a commonly used method, and that the additionally fixed ambiguities improve the repeatability of the station coordinates by 10–26% in regions with sparse site distribution.  相似文献   

On the mechanics of basin formation in the Pannonian basin: Inferences from analogue and numerical modelling     

Gbor Windhoffer  Gbor Bada  Dick Nieuwland  Gza Wrum  Ferenc Horvth  Sierd Cloetingh 《Tectonophysics》2005,410(1-4):389-415

We present the results of a thrust fault reactivation study that has been carried out using analogue (sandbox) and numerical modelling techniques. The basement of the Pannonian basin is built up of Cretaceous nappe piles. Reactivation of these compressional structures and connected weakness zones is one of the prime agents governing Miocene formation and Quaternary deformation of the basin system. However, reactivation on thrust fault planes (average dip of ca. 30°) in normal or transtensional stress regimes is a problematic process in terms of rock mechanics. The aim of the investigation was to analyse how the different stress regimes (extension or strike-slip), and the geometrical as well as the mechanical parameters (dip and strike of the faults, frictional coefficients) effect the reactivation potential of pre-existing faults.

Results of analogue modelling predict that thrust fault reactivation under pure extension is possible for fault dip angle larger than 45° with normal friction value (sand on sand) of the fault plane. By making the fault plane weaker, reactivation is possible down to 35° dip angle. These values are confirmed by the results of numerical modelling. Reactivation in transtensional manner can occur in a broad range of fault dip angle (from 35° to 20°) and strike angle (from 30° to 5° with respect to the direction of compression) when keeping the maximum horizontal stress magnitude approximately three times bigger than the vertical or the minimum horizontal stress values.

Our research focussed on two selected study areas in the Pannonian basin system: the Danube basin and the Derecske trough in its western and eastern part, respectively. Their Miocene tectonic evolution and their fault reactivation pattern show considerable differences. The dominance of pure extension in the Danube basin vs. strike-slip faulting (transtension) in the Derecske trough is interpreted as a consequence of their different geodynamic position in the evolving Pannonian basin system. In addition, orientation of the pre-existing thrust fault systems with respect to the Early to Middle Miocene paleostress fields had a major influence on reactivation kinematics.

As part of the collapsing east Alpine orogen, the area of the Danube basin was characterised by elevated topography and increased crustal thickness during the onset of rifting in the Pannonian basin. Consequently, an excess of gravitational potential energy resulted in extension (σ_v > σ_H) during Early Miocene basin formation. By the time topography and related crustal thickness variation relaxed (Middle Miocene), the stress field had rotated and the minimum horizontal stress axes (σ_h) became perpendicular to the main strike of the thrusts. The high topography and the rotation of σ_h could induce nearly pure extension (dip-slip faulting) along the pre-existing low-angle thrusts. On the contrary, the Derecske trough was situated near the Carpathian subduction belt, with lower crustal thickness and no pronounced topography. This resulted in much lower σ_v value than in the Danube basin. Moreover, the proximity of the retreating subduction slab provided low values of σ_h and the oblique orientation of the paleostress fields with respect to the master faults of the trough. This led to the dominance of strike-slip faulting in combination with extension and basin subsidence (transtension).  相似文献   

Water transport and mixing in the North Frisian Wadden Sea — Results of numerical investigations     

Stephan Dick  Wolfgang Schönfeld 《Ocean Dynamics》1996,48(1):27-48

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High temperature alteration of Abyssal ultramafics from the Islas Orcadas Fracture Zone,South Atlantic     

K. L. Kimball  F. S. Spear  H. J. B. Dick 《Contributions to Mineralogy and Petrology》1985,91(4):307-320

Ultramafic rocks dredged from the Islas Orcadas Fracture Zone, along the SW Indian Ocean Ridge (6° E and 54° S), show evidence of progressive hydration beginning at temperatures greater than 600° C (and perhaps as high as 900° C) and continuing to less than 50° C. There are two principal types of alteration present in the ultramafic rocks, both of which are the result of hydration reactions. The first type of alteration involves hydration of original clinopyroxene, orthopyroxene and olivine to amphibole, talc, secondary olivine, and serpentine. The second is a vein type of alteration and results in the formation of veins of amphibole, chlorite, talc and serpentine. — The alteration appears to be episodic. The sequence of events suggested by the petrography is: 1) clinopyroxene altering to amphibole; 2) orthopyroxene altering to talc, or talc + olivine; 3) supersolvus hornblende veining; 4) coexisting actinolite + hornblende veining; 5) chlorite, chlorite + actinolite, or chlorite + secondary clinopyroxene veining; 6) talc veining; 7) serpentine veining; and 8) pervasive serpentinization. — The alteration fluid is most likely seawater. It is suggested that the high temperature alterations may reflect seawater circulation into the upper mantle.  相似文献   

Mineralogic variability of the uppermost mantle along mid-ocean ridges     

Henry J.B. Dick  Robert L. Fisher  Wilfred B. Bryan 《Earth and Planetary Science Letters》1984,69(1):88-106

Modal analyses of 273 different peridotites representing 43 dredge stations in the Atlantic, Caribbean, and Indian Oceans define three separate melting trends. Peridotites dredged in the vicinity of “mantle plumes” or hot spots have the most depleted compositions in terms of basaltic components, while peridotites dredged at locations removed from such regions are systematically less depleted. The modal data correlate well with mineral compositions, with the peridotites most depleted in pyroxene also having the most refractory mineral compositions. This demonstrates that they are the probable residues of variable degrees of mantle melting. Further, there is a good correlation between the modal compositions of the peridotites and the major element composition of spatially associated dredged basalts. This demonstrates for the first time that the two must be directly related, as is frequently postulated. The high degree of depletion of the peridotites in basaltic major element components in the vicinity of some documented mantle plumes provides direct evidence for a thermal anomaly in such regions—justifying their frequent designation as “hot spots”. The high incompatible element concentrations in these “plume” basalts, however, are contrary to what is expected for such high degrees of melting, and thus require either selective contributions from locally more abundant enriched veins and/or contamination by a volatile-rich metasomatic front from depth.  相似文献