Particle camera and settling chamber measurements at site PC (GeoB11834-3) and SC (GeoB12914-4) off Cape Blanc/Mauritania

Particles sinking out of the euphotic zone are important vehicles of carbon export from the surface ocean. Most of the particles produce heavier aggregates by coagulating with each other before they sink. We implemented an aggregation model into the biogeochemical model of Regional Oceanic Modelling System (ROMS) to simulate the distribution of particles in the water column and their downward transport in the Northwest African upwelling region. Accompanying settling chamber, sediment trap and particle camera measurements provide data for model validation. In situ aggregate settling velocities measured by the settling chamber were around 55 m d**-1. Aggregate sizes recorded by the particle camera hardly exceeded 1 mm. The model is based on a continuous size spectrum of aggregates, characterised by the prognostic aggregate mass and aggregate number concentration. Phytoplankton and detritus make up the aggregation pool, which has an averaged, prognostic and size dependent sinking. Model experiments were performed with dense and porous approximations of aggregates with varying maximum aggregate size and stickiness as well as with the inclusion of a disaggregation term. Similar surface productivity in all experiments has been generated in order to find the best combination of parameters that produce measured deep water fluxes. Although the experiments failed to represent surface particle number spectra, in the deep water some of them gave very similar slope and spectrum range as the particle camera observations. Particle fluxes at the mesotrophic sediment trap site off Cape Blanc (CB) have been successfully reproduced by the porous experiment with disaggregation term when particle remineralisation rate was 0.2 d**-1. The aggregation-disaggregation model improves the prediction capability of the original biogeochemical model significantly by giving much better estimates of fluxes for both upper and lower trap. The results also point to the need for more studies to enhance our knowledge on particle decay and its variation and to the role that stickiness play in the distribution of vertical fluxes.

Limits of the Southern Ocean

The knowledge about processes concerning perception and understanding is of paramount importance for designing means of communication like maps and charts. This is especially the case, if one does not want to lose sight of the map-user and if map-design is to be orientated along the map-users needs and preferences in order to improve the cartographic product's usability. A scientific approach to visualization can help to achieve useable results. The insights achieved by such an approach can lead to modes of visualization that are superior to those, which have seemingly proved their value in praxis - so-called "bestpractices" -, concerning their utility and efficiency. This thesis shows this by using the example of visualizing the limits of bodies of waters in the Southern Ocean. After making some introductorily remarks on the chosen mode of problem-solution in chapter one, which simultaneously illustrate the flow of work while working on the problem, in chapter two the relevant information concerning the drawing of limits in the Southern Ocean is outlined. Chapter 3 builds the theoretical framework, which is a multidisciplinary approach to representation. This theoretical framework is based on "How Maps Work" by the American Cartographer MacEachren (1995/2004). His "scientific approach to visualization" is amended and adjusted by the knowledge gained from recent findings of the social sciences where necessary. So, the approach suggested in this thesis represents a synergy of psychology, sociology, semiotics, linguistics, communication theory and cartography. It follows the tradition of interdisciplinary research getting over the boundaries of a single scientific subject. The achieved holistic approach can help to improve the usability of cartographic products. It illustrates on the one hand those processes taking place while perceiving and recognizing cartographic information - so-called bottom-up-processes. On the other hand it illuminates the processes which happen during understanding this information in so-called top-down-processes. Bottom-up- and top-down-processes are interdependent and inseparably interrelated and therefore cannot be understood without each other. Regarding aspects of usability the approach suggested in this thesis strongly focuses on the map-user. This is the reason why the phenomenon of communication gains more weight than in MacEachren's map-centered approach. Because of this, in chapter 4 a holistic approach to communication is developed. This approach makes clear that only the map-user can evaluate the usability of a cartographic product. Only if he can extract the information relevant for him from the cartographical product, it is really useable. The concept of communication is well suited to conceive that. In case of the visualization of limits of bodies of water in the Southern Ocean, which is not complex enough to illustrate all results of the theoretical considerations, it is suggested to visualize the limits with red lines. This suggestion deviates from the commonly used mode of visualization. So, this thesis shows how theory is able to ameliorate praxis. Chapter 5 leads back to the task of fixing limits of the bodies of water in the area of concern. A convention by the International Hydrographic Organization (IHO) states that those limits should be drawn by using meridians, parallels, rhumb lines and bathymetric data. Based on the available bathymetric data both a representation and a process model are calculated, which should support the drawing of the limits. The quality of both models, which depends on the quality of the bathymetric data at hand, leads to the decision that the representation model is better suited to support the drawing of limits.