Mathematical Modeling of Vortex Interaction Using a Three-Layer Quasigeostrophic Model. Part 1: Point-Vortex Approach

The theory of point vortices is used to explain the interaction of a surface vortex with subsurface vortices in the framework of a three-layer quasigeostrophic model. Theory and numerical experiments are used to calculate the interaction between one surface and one subsurface vortex. Then, the configuration with one surface vortex and two subsurface vortices of equal and opposite vorticities (a subsurface vortex dipole) is considered. Numerical experiments show that the self-propelling dipole can either be captured by the surface vortex, move in its vicinity, or finally be completely ejected on an unbounded trajectory. Asymmetric dipoles make loop-like motions and remain in the vicinity of the surface vortex. This model can help interpret the motions of Lagrangian floats at various depths in the ocean.

Beach debris in the Azores (NE Atlantic): Faial Island as a first case study

Marine debris is widely recognised as a global environmental problem. This study assesses density, type, and temporal trends of marine debris in two sandy beaches of Faial Island (Azores, NE-Atlantic). During seven months (six days per month) the beaches were surveyed by performing 10 random transects at each site. Recorded items within the range 2-30 cm were organised into seven categories. Densities of total debris varied from 0 to 1.940 items m(-2), with plastics dominating both areas. Both beaches, presented the highest debris abundance in February, most probably related to prevailing winds and swell. Location and/or time of year also seemed to influence the type of debris present. These findings provide new insights into debris accumulation rates in the Azores, where no previous studies were made. It also confirms the global trend of increased plastics accumulation on shorelines, highlighting the need for further research in remote islands.