Impact of microplastic pollution on breaking waves

Anthropogenic plastic waste heavily pollutes global water systems. In particular, micron-sized plastic debris can have severe repercussions for the ocean flora and fauna. Microplastics may also affect physical processes such as wave breaking, which are critical for air–sea interaction and albedo. Nevertheless, the effects of micron-sized plastic debris on geophysical processes are widely unexplored. Herein, we investigate the effect of microplastic collected from the North Pacific and a surfactant mimicking surface active materials present in the ocean on the stability of foam generated by breaking wave experiments. We found that microplastic particles increase foam stability. In particular, an increased foam height was found in a column foaming setup, while an increased foam area was observed in a laboratory-scale breaking wave channel. We propose that microplastic particles assemble at the air–water interface of foam bubbles, form aggregates, presumably decrease the liquid drainage in the liquid film, and thus change the lifetime of the liquid film and the bubble. The effect of surfactants is generally larger due to their higher surface activity but still in a range where synergistic effects can be observed. Our results suggest that microplastic could influence oceanic processes essential for air–sea interaction, sea spray formation, and albedo.