Dissolved organic matter in shelf waters off the Ría de Vigo (NW Iberian upwelling system)

Net in situ production and export of dissolved organic carbon (DOC) and nitrogen (DON) have been studied in shelf waters off the Ría de Vigo (NW Spain), as part of a comprehensive hydrographic survey carried out from September 1994 to September 1995 with a fortnight periodicity. DOC and DON correlated well (r=+0.78), the slope of the regression line being 12.0±0.7 mol-C mol-N⁻¹, about twice the Redfieldian slope of particulate organic matter, 6.5±0.2 mol-C mol-N⁻¹ (r=+0.95). Labile DOC and DON accumulated in the upper 50 m during the upwelling season (March–September), mainly after prolonged periods of wind relaxation, when horizontal flows were reduced. This labile material represented 50% and 35% of the total (dissolved+particulate) organic carbon and nitrogen susceptible of microbial utilisation, which assert the key contribution of dissolved organic matter (DOM) to the export of new primary production in the NW Iberian upwelling system. This surface excess in shelf waters appeared to be formed into the highly productive Ría de Vigo (a large coastal indentation) at net rates of 4.4 μM-C d⁻¹ and 1.3 μM-C d⁻¹ in the inner and outer segments of the embayment respectively, and subsequently exported to the shelf. Once in the shelf, simple dilution with the inert DOM pool of recently upwelled Eastern North Atlantic Central Water (ENACW) occurred. Eventually, the DOM excess produced during the upwelling season is exported to the adjacent open ocean waters by the coastal circulation. Conversely, during the unproductive downwelling season (October–February), the lowest DOC and DON levels were recorded and export was prevented by the characteristic downwelling front associated to the seasonal poleward slope current.     

Preview-Based Control of Suspension Systems for Commercial Vehicles

An active suspension with preview is developed for the rear axle of a commercial vehicle. The obtained improvements are promising and justify further investigation of the more feasible semi-active suspensions with preview. The inherent non-linearity of semi-active suspensions with switching shock absorbers and the need for controllers that can handle a broad class of control objectives has led to the development of several numerical control methods for both multi-level and continuously variable shock absorbers. The most promising control method and shock absorber type are selected and mounted in a test vehicle. Some first experimental results are discussed.     

Optimization for Vehicle Suspension II: Frequency Domain

The objective of this study is optimizing the components design of a vehicle suspension system under excitation due to road roughness. The vehicle is modelled as a dynamic system made of masses interconnected by, linear, springs and dampers. The optimizing code provides values corresponding to the caracteristics of masses, dampers and springs which, within a range, minimize the objective function for a defined excitation. This objective function auantifies the vehicle comfort level.

The optimization method used is the sequential linear programming by iteratively applying the Simplex algorithm. The model response is obtained in frequency domain and the vehicle excitation can be either random or deterministic.

The exact nature of the optimization problem, objective function and restrictions, depend on the type of excitation considered.

In succeeding paragraphs, the problem formulation together with a comparison with other authors is presented.     

Force Control of a Semi-Active Damper

Two strategies are investigated for controlling a semi-active damper to track a prescribed force demand signal: (i) 'open loop' control, using a model of the damping force versus velocity characteristics; and (ii) force feedback (closed loop) control.

The damping characteristics and switching transients of a prototype damper were measured, and used to develop a mathematical model of the dynamics of the damper. The two control strategies were investigated using an idealised (constant velocity) test. Their performance was also simulated and measured under realistic operating conditions using the Hardware-in-the-Loop testing method.

Open loop damper control was generally found to give superior performance to force feedback control, due to its smaller phase lag at high frequencies.     

Editorial: Young maritime researchers—a note of respect

Globalization, liberalization, competition and spatial interaction are significant factors affecting the transformation of manufacturing industries worldwide. In the transportation and logistics industry, however, cooperation is becoming even more critical than competition in determining firms' efficiency. Cooperation has always characterized the liner sector in which strategic alliances, mergers and acquisitions have generated twin effects: notable increases in ship size and falls in freight rates. Meanwhile, the stevedoring industry is undergoing privatization-driven consolidation and the emergence of global pure terminal operators. This article focuses on vertical integration between global carriers and terminal operators. We address the following key current issues: 1. dedicated terminals as a strategy for cutting costs and controlling integrated transport chains;

2. the struggle for supply chain control, involving global carriers versus global terminal operators, driven by financial power and technical and managerial capability.

We close analysing one of the core problems of the market, namely the evolving role of the dedicated terminals. For the pure stevedores they represent an opportunity to secure a cargo, while in the hands of the liners they enable cost stability and the possibility to put pressure on pure terminal operators.     

The Potential Economic Benefits of Coastal Ocean Observing Systems: The Southeast Atlantic Region

The Southeast Atlantic Coastal Ocean Observing System (SEACOOS) collects, manages and disseminates coastal oceanic and atmospheric observation information along the Atlantic coast of the southeastern United States. This article estimates the benefits of SEACOOS information in eleven benefit categories. Following a methodology used in similar studies of other U.S. coastal regions, we evaluate the impacts of conservative changes in economic activity in each benefit category. The annual economic benefit of SEACOOS information is $170 million (2003 $), an estimate that falls between annual benefits of $33 million for the Gulf of Maine region and $381 million for the Gulf of Mexico.     

Maritime transport and international seaborne trade

Drawing upon over four decades of the United Nations Conference on Trade and Development (UNCTAD) Review of Maritime Transport, this article considers selected key trends that have shaped the maritime transportation of today. Over the review period, a fundamental shift in the geography of trade has been observed, with developing countries increasingly driving growth in the world economy and seaborne trade, and becoming important players in global value chains. The specialization of countries, including in developing regions, in the provision of the maritime goods and services for which they have established a comparative advantage constitutes another major trend, a move away from previous patterns where developing countries were typically users of maritime transport services. The article also observes that bilateral freight sharing agreements between countries which were prominent in 1970s have largely lost their practical relevance, leading to a further liberalization of markets and resulting in overall relatively lower freight costs.     

Evaluation of manatee habitat systems on the northwestern Florida coast

Abstract

Threats to the survival of West Indian manatees (Trichechus manatus) vary throughout their range so that protection of this endangered species requires careful planning on a regional and local basis. The importance and vulnerability of various components of manatee habitats in the Crystal River area of northwestern Florida were assessed, using an ordinal‐combination mapping technique similar to procedures practiced in urban and regional planning. Habitat components were mapped and evaluated in juxtaposition with relevant characteristics of human use of the area, to identify areas of existing and potential manatee/human conflicts in need of reconciliation. Areas evaluated as the most important manatee habitats within this region include Crystal Bay and River, Homosassa River, and the Suwannee River estuary. Existing overlap of human activities with important manatee habitats is most critical near the urban communities of Crystal River and, to a lesser degree, Homosassa Springs. The need for integration of this ecological information into coastal land‐use planning is discussed.     

Investment strategies in market uncertainty

The nature of the global economy is one of dynamic change. Shipping is a service industry with its demand related to changes in international trade levels and patterns. As a consequence shipping is subject to sometimes unpredictable swings in demand so that the operator is required to make strategic planning decisions while navigating through boom or bust environments. While boom economies generate rising freight rates which are welcomed and encourage investment, ship operators may also have to face falling freight demand and declining freight rates that may have significant impact on profitability, often falling to uneconomic levels for extended periods. In such a period of uncertainty and declining profitability management will make operational decisions to reduce costs. However, shipping lines operate in a market environment so any decisions made to rationalize the trade may have significant long-term competitive implications. For example, traditional micro economic theory might suggest that the prudent strategy to adopt would be to close down the operation and reopen when the market conditions improve. In a world of certainty or when costs of taking this action are zero, this would be a valid strategy. However, because of fear of competitors taking up a line's market share if the shipping company exits, even temporarily, this strategy cannot be valued simply in terms of shut-down and start-up costs. A further consideration is the fact that standard capital budgeting techniques, such as Net Present Value (NPV), cannot incorporate the flexibility to respond to new information and strategic responses explicitly into their investment analysis. This paper will demonstrate the use of Real Option Analysis (ROA) to provide guidelines for decisions about closing operations in adverse market conditions.     

Effects of closed trawl fishery areas on some elasmobranch species in the Cantabrian Sea

This study examines the effects of certain closed areas to the trawl fishery on some Rajidae species and small-spotted catshark in the southern area of the Bay of Biscay. The results are based on abundance index (number/haul) and catch length composition obtained from a series of bottom trawl surveys carried out in the area (1993–2005). Abundance trends are similar considering or not closed areas, but with much lower values excluding closed areas. The length distributions revealed that in some of the species like Scyliorhinus canicula the larger specimens were the most affected by this decrease in number. Finally, the effects and consequences of one of these marine protected areas (MPAs), an artificial reef were examined in more detail for all the fishes and invertebrates. The analysis of the yield series showed an increase in total biomass after the placement of the reefs not only for S. canicula and rays but also teleosts fishes like Pagellus acarne, Trachurus trachurus, Mullus surmuletus and Trachinus draco and particularly invertebrates (sea urchins). On the contrary, the main target species of the trawl fishery (hake, monkfish and megrim among others) did not increase.