Tracking plastics in the Mediterranean: 2D Lagrangian model

Modelling plastics exposure for the marine biota: Risk maps for fin whales in the Pelagos Sanctuary (North-Western Mediterranean)

“…We note that this region is relatively poorly resolved in the oceanographic circulation reanalyses we exploited. Our results are also comparable with the simulation results by (7), (36) and (30), while there are some dissimilarities with the work by (28), probably because of the use of different oceanographic grids. In addition, our analyses confirm a known feature of the summer oceanography of the Pelagos area: the Capraia gyre.…”

“…Removal of plastic fragments from the surface layer has been included in the model by characterizing Lagrangian particles with a certain source-independent permanence period in the surface layer, corresponding in fact to the duration of their transport. Assuming that particle removal is a Poissonian process, the permanence period of each particle can be extracted from an exponential distribution with an average decay rate of 50 d −1 (see 30). The distribution of the permanence times was then approximately discretized into three classes with relative frequency of 1/3 each.…”

“…Then, to obtain an aggregated picture of plastic within the study area, daily outputs of the single-source simulations have been normalized by dividing the number of particles in each cell of the oceanographic grid by the maximum number of particles registered in all cells. To account for the different magnitude of the plastic input from coastlines, rivers and shipping routes, the aggregated mapping was obtained by attributing different weights to the particles according to their source, with the coast-to-rivers-to-shipping lanes ratio of 50%:30%:20% proposed by (30). In terms of the temporal dimension of particles concentration, at first the simulation outputs from the three source types were averaged over the eleven summer seasons simulated.…”

“…For this reason, sampling campaigns are key to provide a temporal snapshot of the concentrations of plastic items, but might not be repre-sentative of their long-term distribution. Ocean circulation models and oceanographic reanalyses are commonly applied when studying marine litter distribution both for the global oceans (6) and for the Mediterranean Sea (28)(29)(30). They allow us to account not only for the transport of particles within ecologically relevant seasons, but also for its interannual variability.…”

Technical note: On the importance of a three-dimensional approach for modelling the transport of neustic microplastics

“…All these findings may be transferable to (1) the other hydrodynamic conditions of this bay which are also dominated by baroclinic processes (coastal trapped waves, upwelling, cooling events; e.g. Wang and Symonds, 1999;Sun et al, 2017;Liao and Wang, 2018), (2) other stratified coastal systems such as estuaries characterized by a density circulation, but also (3) to oceanic water characterized by vertical current shear induced by wind and wave-driven Ekman flow or density-driven processes, for instance (Lund et al, 2015;Lanotte et al, 2016). Besides the microplastics, these results can also be applied for other floating "young" objects.…”