Lagrangian Studies of Vertical Sedimentation in the Ocean

For a certain range of densities higher than that of seawater and sizes, the velocity of sinking particles in a flow can be well approximated by the velocity of the fluid in which they are immersed, plus a vertical settling constant accounting for the effect of gravity. Starting from a common initial condition near the surface, a Lagrangian integration is performed using a realistic submesoscale velocity field of the Algero-Balearic Basin. When the particles are deposited in virtual horizontal layers at different depths, they exhibit non-homogeneous clustering. This Master’s Thesis provides a mathematical characterization of these inhomogeneities using the correlation dimension in strongly stratified (Summer) and weakly stratified (Winter) waters. The results show that, in both seasons, the fractal dimension decreases with depth. With respect to settling velocity, in the summer integration, the correlation dimension increases continuously, whereas in winter it exhibits a non-monotonic dependence with a minimum. The dependence on settling time and periodic boundary conditions is also analysed.

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