Fig 1.
Size distribution and aspect of the floating plastic debris collected in the Mediterranean Sea.
The size distribution of plastic debris in the Mediterranean (n = 3,901 plastic items; this study) is compared to those measured for plastic accumulation regions in the open ocean (n = 4,184 plastic items; [5]). Both plastic size distributions were obtained using the same methodology. Horizontal axis shows the size limits of the bins in logarithmic scale. Because the width of the bins is not uniform, the vertical axis (i.e., normalized abundance of plastic) is shown as number of plastic items divided by the width of the bin (in millimeters). In the comparison of the plastic size distributions in Mediterranean and open-ocean waters, note the logarithmic scale of the vertical axis. The percentages (in abundance) of plastic types (pellets/granules, films, fishing threads, foam, fragments) found in the Mediterranean Sea are shown in the chart at the top right corner.
Fig 2.
Concentrations of plastic debris in surface waters of the Mediterranean Sea at basin scale (zoomed in the top right corner inset), and compared to the plastic concentrations reported for the global ocean.
Gray-scale base map in the Mediterranean basin shows the relative surface plastic concentrations predicted by numerical modeling [8]. Darker areas are predicted to have higher concentrations. Major areas of deep-water formation in the Mediterranean are also shown with black circles [24]. In the global map, dark and light gray areas represent inner and outer accumulation zones, respectively, modeled for the five subtropical gyres; white oceanic areas represent non-accumulation zones [7]. Mediterranean map compiles data from the present study and from ref. [20, 21], while open-ocean map compiles measurements of plastic concentrations from ref. [1–5, 10, 11]. Outside the inner accumulation zones, the open-ocean also includes concentrations reported without correction by wind effect (see details in ref. [5]).
Fig 3.
Ranges of surface plastic concentrations measured in the Mediterranean Sea, and reported for the open ocean.
A) Frequency distribution of the measurements of plastic concentrations in the Mediterranean Sea (n = 72) and in the global ocean (n = 1760). Mediterranean measurements (blue line) are from the present study and ref. [20, 21]; ocean measurements (red line), including the five plastic accumulations in the subtropical gyres, were compiled from ref. [1–5, 10, 11]. All these data are mapped in Fig. 2. Size limits of the bins, shown in the horizontal axis, followed a 2.5-log series of plastic concentration (in g km2). B) Surface plastic concentrations measured in the Mediterranean Sea, and reported for the inner accumulation zone of the five subtropical gyres (dark gray areas in Fig. 2) [1–5]. Ranges of concentrations outside the convergence zone of each subtropical gyre (white areas in Fig. 2) are also shown for comparative purposes. The boundaries of the boxes indicate the 25th and 75th percentiles, the whiskers above and below the boxes indicate the 95th and 5th percentiles, and the black and white dots mark mean and median respectively. All data in this analysis include correction by wind effect.