Kai Myrberg

The use of Lagrangian trajectories for the identification of the environmentally safe fairways.

We propose and test a method for the optimisation of marine fairways to minimise the risk to high-value areas, based on statistical analysis of Lagrangian trajectories of current-driven pollution transport. The offshore areas are quantified according to the probability of pollution released in these areas to reach vulnerable regions. The method contains an eddy-resolving circulation model, a scheme for tracking of Lagrangian trajectories, a technique for the calculation of quantities characterising the potential of different sea areas to supply adverse impacts, and routines to construct the optimum fairway. The gain is expressed in terms of the probability of pollution transport to the nearshore and the associated time (particle age). The use of the optimum fairway would decrease the probability of coastal pollution by 40% or increase the average time of reaching the pollution to the coast from 5.3 to about 9 days in the Gulf of Finland, the Baltic Sea.

Recent Change—Marine Circulation and Stratification

This chapter describes recent change in the circulation and stratification of the Baltic Sea. A recent warming trend in sea-surface waters has been clearly demonstrated by in situ measurements, remote sensing data and numerical models. Trends in sea-surface temperature (SST) for the past three to four decades based on remote sensing data generally agree with trends determined from in situ observations. Models suggest the current warming within the Baltic Sea lies within the range experienced during the past 500 years. The salinity and stratification of the deep waters are strongly linked to the major inflows of North Sea water that occur sporadically and bring high-saline water into the deep layers of the Baltic Sea. The major inflows normally occur during winter and spring and bring cold oxygen-rich waters into the deep basins. Since 1996, large inflows have also occurred during summer, bringing in warm low-oxygen water.

A future technology of environmental management of semi-enclosed seas

We give an overview of the principles of and recent developments in the new technique that employs the potential for a systematic decrease in the environmental risk to the nearshore by means of optimization of the offshore locations of the release of adverse impacts. The gain may be an increase in the time until an adverse impact (for example, an oil spill) reaches a nearshore or a corresponding decrease in the probability of the impacting such an area. The “ability” of different offshore domains to provide risk of coastal pollution in terms of current-induced drift of pollution is quantified based on the analysis of a large pool of numerically simulated Lagrangian trajectories of water particles in the surface layer of the sea. Environmental gain is achieved by placing the dangerous activities into sea areas (or redirecting ship traffic accordingly), from which the transport of the adverse impact to the nearshore is less likely or takes the most time. We provide several examples of implementation of this technique and estimates of the resulting gain from the use of the corresponding optimal fairways for the Gulf of Finland and for the south-western the Baltic Sea.