The vertical distribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre

[摘要] Millimetre-sized plastics are numerically abundant and widespread across theworld's ocean surface. These buoyant macroscopic particles can be mixedwithin the upper water column by turbulent transport. Models indicatethat the largest decrease in their concentration occurs within the first fewmetres of water, where in situ observations are very scarce. In order toinvestigate the depth profile and physical properties of buoyant plasticdebris, we used a new type of multi-level trawl at 12 sites within the NorthAtlantic subtropical gyre to sample from the air–seawater interface to adepth of 5 m, at 0.5 m intervals. Our results show that plasticconcentrations drop exponentially with water depth, and decay rates decreasewith increasing Beaufort number. Furthermore, smaller pieces presented lowerrise velocities and were more susceptible to vertical transport. Thisresulted in higher depth decays of plastic mass concentration (milligrams m⁻³) than numerical concentration (pieces m⁻³). Further multi-levelsampling of plastics will improve our ability to predict at-sea plastic load,size distribution, drifting pattern, and impact on marine species andhabitats.

[学科分类] 地球化学与岩石