Distribuzione delle microplastiche e microfibre nella colonna d'acqua del Mar Mediterraneo occidentale

Plastic production has dramatically increased in recent years and, consequently, plastic waste. After the media outbreak on the topic or just observing the ocean, everybody has become aware of the pervasive presence of plastic in the ocean, especially on sea surface and beaches. The ratio between waste production and estimate of debris in the seawater indicates that a large portion of plastic is lost and hidden somewhere in the ocean. A large amount of plastic is expected to be in the Mediterranean Sea, as it is a highly populated and extremely touristic area, heavily trafficked by cargo and fishing ships. Furthermore, the semi-enclosed conformation of this basin prevents water mass movements to and from the Atlantic Ocean. There are comprehensive estimates of debris in surface waters, but information about the vertical distribution along the water column is lacking in the Mediterranean Sea as well as in the other oceans. The Ichnussa17 and Infra-Oce expeditions, carried out by the Italian National Research Council, took place in October-November 2017 in the Western Mediterranean Sea. During this campaign, microplastics and microfibers were sampled from the sea surface to the bottom depth, using respectively a stainless-steel bucket and the Rosette sampler system. Parallel, relevant environmental variables (i.e. temperature, oxygen and salinity) were measured using a CTD probe, deployed along the entire water column. RStudio was used to validate the statistical correlation between the vertical distribution of microparticles and the environmental variables. Results were graphically represented using Ocean Data View and QGIS software. In our samples, the concentration of microfibers was significantly higher than that of microplastics in most of the water column samples. Generally, the highest values of microplastics were found in the surface layers, decreasing with increasing depth. On the contrary, microfibers had no specific vertical trend, being usually distributed homogeneously along the entire water column. Microfiber accumulation areas were found in the deepest sampling stations that exceed 1500 meters. Environmental variables did not explain microfiber distribution whereas microplastics generally followed the trend of temperature and oxygen in some areas. This thesis is the first snapshot ever about the vertical distribution of microplastics and microfibers in Western Mediterranean waters, from the surface to the bottom. Future research of this field could exploit this baseline data, better explaining the mechanisms behind microplastics sinking and vertical distribution, improving at the same time spatial resolution and sampling time scale.