Ocean circulation

Within the ocean the source of pollution does not always determine where the plastics end up. The target pathways of marine pollutants are determined by a combination of the circulatory patterns of the world’s oceans and the pollutant source, as shown in the above video. 

The oceans circulate due to the Earths rotation and winds (Easterlies and Westerlies) moving surface water. The convergence of currents leads to the formation of gyres, where velocity decreases and suspended debris such as pollutants accumulate.

Several attempts have been made within science to map the spatial distribution of plastic pollution in the worlds oceans.

One initial attempt to map the spatial distribution of plastics was computed using the trajectories of surface buoys of the Global Drifter Program by Van Sebille et al (2012). The source distribution and variation of plastic was simulated via this method, utillizing the produced matrix of ocean circulation patterns the evolution of plastic from any point within the oceans can be modelled.

As shown in the model there are high concentrations of plastic in areas where ocean currents converge such as the northern Atlantic and Pacific gyres. High concentrations are also evident in coastal areas due to their proximity to source and the deposition of material on beaches by the oceans. Within coastal industrial areas there is variation in plastic accumulation as a result of the areas relative proximity to industrial areas (Browne, 2011).

Cozar et al present a map of plastic debris on the open ocean (Cozar et al, 2013), the map shows the ships route whilst the coloured circles indicate volume of plastics at sample sites. They grey zones indicate the presence of gyres and correlate with high plastic concentrations as shown by the large red circles.

(Above map is sourced in Cozar et al, 2013)