The dashed line in Fig. 2 and Fig. 3 represents the recorded sea state at each station, using the Beaufort Scale and measured by visual observation of multiple observers. These data suggest a possible inverse relationship

between plastic count/weight and the sea state. More data are needed to examine this relationship more thoroughly. However such a relationship has been tentatively identified in Kukulka et al. (2012) from MEK inhibitor review the North Atlantic. In general, changes between some pairs of samples can be explained by changes in sea surface conditions. For example, lower (compared to adjacent samples) counts in samples 27 and 28 coincide in time with the brief and sharp increase in winds. Analogously, high counts and weights in samples 22 and 23 were

obtained during a short period of weaker wind. The statistical model used herein (Maximenko et al., 2012), based on observed trajectories of drifting buoys, was successfully used to find an accumulation zone of plastic pollution in the SPSG. While this model identifies regions of maximum aggregation of the floating debris, it fails to predict the relative abundance of plastic between different gyres. For example, it predicts the maximum density in the South Pacific to be as much as ten times higher than the maximum density in the North Atlantic. The actual selleck screening library particle abundance in the central region of the North Atlantic, reported between 29 and 31°N, was 20,328 ± 2324 pieces km−2 (Law et al., 2010), i.e. the abundance was 1.3 times higher in the South Pacific (26,898 ± 60,818 pieces km−2 in this study). This is explained by the setup of the model experiment.

The relative maximum in the model South Pacific is dictated by the larger amount of tracer “injected” there in the model due to the larger size of this subtropical gyre. In reality, northern gyres appear to contain more plastics, corresponding to higher rates of production, consumption and loss of plastic to the marine environment in the northern hemisphere (Lebreton et al., 2012). Law et al. (2010) observed no significant increase in plastic marine pollution in a 22-year survey second of the North Atlantic subtropical gyre, while during a similar time frame Goldstein et al. (2012) observed a dramatic increase of microplastics in the NPSG. Overall, the densities of microplastics found in the SPSG are comparable with those observed in other areas of the world (Hidalgo-Ruz et al., 2012). They are, however, lower than those reported for the North Pacific Subtropical Gyre (NPSG). Using a similar approach as Moore et al. (2001), herein we found a mean of ∼25,000 microplastics km−2 compared to ∼330,000 microplastics km−2 in the NPSG. The maximum density in the NPSG was ∼970,000 microplastics km−2 (Moore et al.