Bad News for Microplastics and Deep Sea Biodiversity Hotspots

News to watch: Ocean plastics are known to reach the deep sea. It turns out they are piling up in all the wrong places.

99% of ocean plastic pollution exists between the surface and the seafloor. While it might seem logical that plastics float aimlessly from their polluting source and then sink to the bottom, new research says otherwise. News from Science finds that plastic pollution hitches rides on essential bottom currents and, worse, lands in biodiversity hotspots.

To understand how the plastics are moving around researchers in Europe and the UK looked at data from the Tyrrhenian Sea. This area of the Mediterranean Sea, with its known topography and well-studied water circulation patterns, is a good place to track how plastic pollution from both land and marine (fishing and shipping) sources reaches the seafloor.

Previous studies had proposed that microplastics were transported across surface currents and then settled vertically, making microplastic accumulation somewhat predictable. This study suggests something different. “In our study area there is no relationship between microplastic concentrations and distance from terrestrial plastic sources,” they said.

Instead, this study analyzed the relationship between deep water currents known for their role in creating a healthy underwater ecosystem and microplastic distribution. What it found was that the highest concentrations of microplastics were in contourite drifts, sediment drifts that are directly formed by these currents. The bad news is that these same bottom currents, critical for moving oxygen and nutrients to deep sea biodiversity hotspots, are in fact also transporting and concentrating microplastics to areas rich with life and at the base of the marine food web.

Source: Science