压载水管理履约及我国应对措施研究

由船舶排放压载水引发的外来生物入侵问题,已经给各大航运国造成严重的损害,正成为一个世界性难题.文章结合我国现有立法及压载水管理现状,对我国加入<国际船舶压载水和沉积物控制与管理公约>的履约措施进行深入分析,并提出有关履约建议.     

超宽带技术在短距离无线接入中的应用

介绍了超宽带无线通信技术的特点,着重阐述了基于OFDM的超宽带通信技术,提出该技术在短距离无线接入的应用模式,给出其应用中的关键技术,并就超宽带无线通信技术应用前景作了简要介绍。     

The relevance of international transport costs on food prices: Endogenous and exogenous effects

The paper addresses the problem of transport costs and their influence on food prices for South American imports. While transport does not seem to be in the focus of existing analyses, its impact on food prices might be underestimated and even closely linked to the development of commonly mentioned drivers of food prices. Since transport price formation is a function of demand and supply, drivers of food prices are also expected to impact on transport prices. The authors argue that a number of relevant factors that drive transport costs - and in consequence food prices - can be influenced by policy makers. Based on empirical analysis, the authors explain the functioning of the determinants of transport costs in the segment of international shipping, trying to describe their exogenous and endogenous components. These results are discussed in reference to policy development in the region.     

The structure of dissipation in the western Irish Sea front

We report on an intensive campaign in the summer of 2006 to observe turbulent energy dissipation in the vicinity of a tidal mixing front which separates well mixed and seasonally stratified regimes in the western Irish Sea. The rate of turbulent dissipation ε was observed on a section across the front by a combination of vertical profiles with the FLY dissipation profiler and horizontal profiles by shear sensors mounted on an AUV (Autosub). Mean flow conditions and stratification were obtained from a bed mounted ADCP and a vertical chain of thermistors on a mooring. During an Autosub mission of 60 h, the vehicle, moving at a speed of ~ 1.2 m s^− 1, completed 10 useable frontal crossings between end points which were allowed to move with the mean flow. The results were combined with parallel measurements of the vertical profile of ε which were made using FLY for periods of up to 13 h at positions along the Autosub track. The two data sets, which show a satisfactory degree of consistency, were combined to elucidate the space–time variation of dissipation in the frontal zone. Using harmonic analysis, the spatial structure of dissipation was separated from the strong time dependent signal at the M₄ tidal frequency to yield a picture of the cross-frontal distribution of energy dissipation. A complementary picture of the frontal velocity field was obtained from a moored ADCP and estimates of the mean velocity derived from the thermal wind using the observed density distribution. which indicated the presence of a strong (0.2 m s^− 1) jet-like flow in the high gradient region of the front. Under neap tidal conditions, mean dissipation varied across the section by 3 orders of magnitude exceeding 10^− 2 W m^− 3 near the seabed in the mixed regime and decreasing to 10^− 5 W m^− 3. in the strongly stratified interior regime. The spatial pattern of dissipation is consistent in general form with the predictions of models of tidal mixing and does not reflect any strong influence by the frontal jet.     

Quasi-two-dimensional flow on the polar β-plane: Laboratory experiments

Geophysical turbulence is strongly affected by the variation of the Coriolis parameter with latitude. This variation results in the so-called β-effect, which forces energy from small-scales to be transferred preferentially into zonal motions. This effect results in the formation of narrow jet-like zonal flows that dominate the dynamics and act as transport barriers. Here, laboratory experiments are used to reproduce this effect in decaying turbulent flows. An electromagnetic cell is used to generate an initial field of vorticity in a rotating tank. Under conditions of quasi-geostrophic flow, the β-effect is produced by depth variation of the flow instead of variation of the Coriolis parameter. The effects of changing the container geometry and the overall fluid depth on the production of jets are investigated. The results suggest that this laboratory configuration can be used to model jet formation in the oceans and that increasing fluid depth is a practical way to decrease viscous effects.     

Analysis of velocity fluctuations and their intermittency properties in the surf zone using empirical mode decomposition

We consider here surf zone turbulence measurements, recorded in the Eastern English Channel using a sonic anemometer. In order to characterize the intermittent properties of their fluctuations at many time scales, we analyze the experimental time series using the Empirical Mode Decomposition (EMD) method. The series is decomposed into a sum of modes, each one narrow-banded, and we show that some modes are associated with the energy containing wave breaking scales, and other modes are associated with small-scale intermittent fluctuations. We use the EMD approach in association with a newly developed method based on Hilbert spectral analysis, representing the probability density function in an amplitude–frequency space. We then characterize the fluctuations in a stochastic framework using a cumulant generating function for all scales, and compare the results obtained from direct and classical structure function analysis, to EMD–Hilbert spectral analysis results, showing that the former method saturates at large scales, whereas the latter method is more precise in its scale approach. These results show the strength of the new EMD–Hilbert spectral analysis method for data presenting a strong forcing such as found in shallow water, wave dominated situations.     

Impact of macrozoobenthic structures on near-bed sediment fluxes

Sandy sediments in shallow coastal waters of the Baltic Sea are often characterised by large numbers of biogenic structures which are produced by macrozoobenthos species. A series of experiments was devised to quantify how the interaction of such structures with the near-bed flow regime affects the sediment flux. Most experiments were done with simplified replicates of structures generated by typical species commonly found in the Mecklenburg Bight, starting with solitary structures and regularly-spaced arrays in a range of characteristic population densities, followed by a complex benthic macrofauna community, both artificial and alive. A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a topography scanning laser, was used for high-resolution measurements (2 mm horizontal step size and 0.3 mm vertical resolution) of sand erosion (220 µm median grain size, at 20 cm s^− 1) and fine particle deposition (8 µm grain size, at 5 cm s^− 1). Sediment transport threshold values were measured for each layout. As a rule-of-thumb, both the erosion fluxes and the deposition of suspended matter increased considerably at low population densities (below 2%, expressed as percent of the sediment surface covered, i.e. roughness density RD). Above densities of 4%, erosion almost stopped inside the test arrays, and deposition remained well below the level of unpopulated areas. An attempt to extrapolate these findings to field conditions (using field current velocity data from 2001) showed that the net flux switched from erosion to deposition for densities above 5%. These parameters can now be integrated into a numerical sediment transport model coupling waves, currents, sediment dynamics and biological processes, which is currently under construction at the Baltic Sea Research Institute (IOW), Rostock, Germany.     

The importance of oceanographic fronts to marine birds and mammals of the southern oceans

During the last 30 years, at-sea studies of seabirds and marine mammals in the oceans south of the Subtropical Front have described an association with major frontal areas. More recently, the advancement in microtechnology has allowed the tracking of individuals and investigations into how these marine predators actually use the frontal zones. In this review, we examine 1) the relative importance to apex predators of the different frontal zones in terms of spatial distribution and carbon flux; 2) the processes that determine their preferential use; and 3) how the mesoscale dynamics of frontal structures drive at-sea foraging strategies of these predators. We review published results from southern waters and place them in a broader context with respect to what has been learned about the importance of fronts in oceans farther north.Some fronts constitute important boundaries for seabird communities in southern waters. At a mesoscale the maximum values of seabird diversity and abundance correspond to the location of the main fronts. At-sea surveys show a strong curvilinear correlation between seabird abundance and sea surface temperatures. High mean species richness and diversity for whales and seabirds are consistently associated with the southern water mass boundary of the Antarctic Circumpolar Current, the Subtropical Front and the Subantarctic Front; in the case of the Polar Front mean seabird densities are more variable. At small-scales, variation in seabird occurrence has been directly related to the processes at fronts in a limited number of cases. A significant positive relation was found between some plankton feeding species and frontal temperature gradient–phytoplankton variables.Telemetric studies have revealed that several apex predators (penguins, albatrosses, seals) perform long, directed foraging trips either to the Subtropical front or Polar Front, depending on locality. Seabirds with low flight costs, such as albatrosses, are able to reach fronts at long distances from colonies, showing variable foraging strategies as a function of the distances involved. Diving birds such as King penguins, that travel at a higher cost and lower speed, rely on the predictable spatial distribution of mesopelagic fish found close to the Polar Front. They may use the currents associated with eddies as oceanographic cues in the active search for frontal zones. Once in these areas they dive preferentially in and below the depth of the thermocline where catches per unit effort are high. Elephant seals concentrate foraging activity principally inside or at the boundary of cyclonic eddies. These mesoscale features appear to offer exceptional productivity favourable for foraging by various diving top predators.The connection between biophysical parameters at fronts and predators is likely to be made through biological enhancement. Top predators appear to forage at locations where prey are advected by physical processes and others where prey are produced locally. Long-term research on at-sea distributions and demographic parameters of top predators are essential to assess the consequences of potential shift in front distributions in relation to global warming. Such environmental changes would add to the impact of fish extraction by the industrial fisheries on the southern food webs.     

Egg production and associated losses of carbon, nitrogen and fatty acids from maternal biomass in Calanus finmarchicus before the spring bloom

We present concurrent data on ingestion, egg production and the loss of maternal biomass in pre-spring bloom female Calanus finmarchicus incubated under conditions representative of those in situ in the North Atlantic. A balanced metabolic budget was constructed and used to examine the relative importance of ingestion and biomass for fuelling egg production during the incubations. Ingested carbon was not sufficient to meet the observed demands for egg production. More than 80% of the carbon utilised by the females was instead derived from their biomass. Fatty acid analysis demonstrated that the storage reserves, 20:1 (n−9) and 22:1 (n−11), were virtually absent before experimentation began, and therefore could not have been used to supply the carbon required for egg production during the incubations. The C:N mass-specific ratio of the biomass utilised was 4.1, suggesting that the females had instead catabolised protein in order to meet their metabolic demands. These results suggest that C. finmarchicus adopts a sacrificial reproductive strategy when food availability is low.     

Characteristic flow patterns generated by macrozoobenthic structures

A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a bottom scanning laser, was used for detailed, non-intrusive flow measurements (at 2 cm s^− 1 and 10 cm s^− 1) around solitary biogenic structures, combined with high-resolution mapping of the structure shape and position. The structures were replicates of typical macrozoobenthic species commonly found in the Mecklenburg Bight and with a presumed influence on both, the near-bed current regime and sediment transport dynamics: a worm tube, a snail shell, a mussel, a sand mound, a pit, and a cross-stream track furrow. The flow was considerably altered locally by the different protruding structures (worm tube, snail, mussel and mound). They reduced the horizontal approach velocity by 72% to 79% in the wake zone at about 1–2 cm height, and the flow was deflected around the structures with vertical and lateral velocities of up to 10% and 20% of the free-stream velocity respectively in a region adjacent to the structures. The resulting flow separation (at flow Reynolds number of about 4000 and 20,000 respectively) divided an outer deflection region from an inner region with characteristic vortices and the wake region. All protruding structures showed this general pattern, but also produced individual characteristics. Conversely, the depressions (track and pit) only had a weak influence on the local boundary layer flow, combined with a considerable flow reduction within their cavities (between 29% and 53% of the free-stream velocity). A longitudinal vortex formed, below which a stagnant space was found. The average height affected by the structure-related mass flow rate deficit for the two velocities was 1.6 cm and 1.3 cm respectively (80% of height and 64%) for the protruding structures and 0.6 cm and 0.9 cm (90% and 127% of depth) for the depressions. Marine benthic soft-bottom macrozoobenthos species are expected to benefit from the flow modifications they induce, particularly in terms of food particle capture due to altered particle pathways and residence times, but also for the exchange of gases, solutes and spawn. The present results confirm previous studies on flow interaction effects of various biogenic structures, and they add a deeper level of detail for a better understanding of the fine-scale effects.