Exploring Trends and Characteristics of Plastic Debris in the North Atlantic Ocean

Abstract

Much research over the past two decades demonstrates the ubiquity of that ocean plastic pollution across the world’s oceans. Through these works, some of the environmental consequences of plastic pollution have been well detailed while others remain un-quantified. Though public awareness of ocean plastic debris has increased over the same period, much is misunderstood. Many people still only think of this pollution as large “islands” of trash and focus solely on the effects of large pieces of plastic on larger animals. In reality, much of the plastic ocean debris consists of confetti-sized pieces distributed throughout the oceans, with higher concentrations in the center of the major ocean gyres at the convergence of the ocean surface currents. This study, as part of a larger NSF-funded project, investigates a large dataset of smaller plastic pieces collected from the North Atlantic between 1991 and 2007. It tracks how the size parameters (e.g. area and mass) of different plastics found in the ocean vary with time and geographic location. In a previous marine plastics study, Moret-Ferguson et al (2010) measured longest-edge particle size, mass, and density of individual plastic fragments from 50 tows taken throughout the North Atlantic Ocean by Sea Education Association (SEA). They found that for each sample area, both longest edge particle size and mass decreased from the 1990s into the 2000s. This project extends the Moret-Ferguson study to several other characteristics of individual plastic fragments, revisiting the same large dataset of over 1000 plastic pieces collected from the same 50 net tows over 16 years. A reevaluation of the data shows that Polyethylene (PE) dominates the assemblages over all other polymer types in ratios unexplained by plastic production data. It hints at a possible preferential breakdown of Polypropylene (PP) over PE to sizes smaller than the mesh size of collection nets. A slight decrease in mass over the time period between 1991-1995 and 2004-2007 is seen, but a firm conclusion on this point is not yet possible. An analysis of the shape of plastic pieces demonstrates that the assumptions of a near-spherical or cubic shape to microplastics in debris-tracking models can be reasonable. Tracking plastic debris over geographic space shows a non-uniform mixture of plastic polymer and form types within the North Atlantic, and a significant difference in size of plastic assemblages north and south of 30°N. It also hints at changes in the makeup of plastic assemblages with proximity to land. Finally, a descriptive analysis and glossary of terms was developed to help classify plastic debris, and proved useful in identifying polymer types under the microscope. Hopefully this framework can become a standard applied throughout future analyses of ocean plastic debris.