SEA Abstracts
A 22-year Record of Plastic Marine Debris in the Atlantic Ocean
Kara Lavender Law, Skye Morét-Ferguson, Christopher M. Reddy, Emily Peacock, Nikolai A. Maximenko
Presented at the Ocean Sciences Meeting, Portland, OR, 24 Feb. 2010.
Plastic marine debris is increasingly abundant in the global ocean. Because of its long residence time this debris accumulates in regions of oceanic convergence, such as subtropical gyres. We present a 22-year time series of surface plastic distribution in the western North Atlantic Ocean and Caribbean Sea collected by the Sea Education Association (SEA). Since 1986 more than 6100 neuston net tows have been conducted from SEA’s sailing research vessels on annually-repeated cruise tracks. No other comparable data set exists in the Atlantic or any other ocean. The floating plastic debris collected in these tows is both pre- and post-consumer plastic that is typically millimeters in size, with a material density (specific gravity) less than that of seawater.
These ship surveys allow the first large-scale quantification of the spatial and temporal distribution of plastic microdebris in the North Atlantic Ocean. The region of highest plastic concentration is found between roughly 24°N and 37°N, and is strongly associated with the North Atlantic subtropical convergence as described by mean surface currents. Surprisingly, despite increases in plastic production during this time period, no statistically significant temporal trends are observed in the high concentration region. Possible loss terms will be discussed, including variability in surface circulation, physical degradation of plastic, and changes in buoyancy due to biological growth.
Physical Characterization of Plastic Debris in the North Atlantic Ocean
Skye Morét-Ferguson, Kara Lavender Law, Emily Peacock, Giora Proskurowski, Christopher M. Reddy
Presented at the Ocean Sciences Meeting, Portland, OR, 24 Feb. 2010.
Plastic marine debris is now present on the surface of every ocean on Earth. Studying the physical properties of individual plastic pieces provides a baseline understanding of what types persist on the open sea. Sea Education Association has collected more than 64,000 plastic pieces from surface net tows in the North Atlantic over the past 22 years. Here, we analyze 750 of these plastic pieces for size, mass, and material composition. This subset of pieces selects from tows at every 5th parallel between 15-40°N. More than 85% of particles are less than 10mm in size, and the majority of particles have a mass less than 0.25g. Material densities of individual pieces greater than 1g/ml are rare, and over half of the sample densities ranged between 0.96-0.99g/ml. Densities are unexpectedly higher at 30°N in the subtropical convergence zone. Geographic trends in particle form (i.e. fragment, pellet, line) will also be discussed. The large spatial and temporal scales of this study offer a compelling and unique insight into environmental implications, persistence, and sources of plastic marine debris.
The Impact of Wind Stress on the Concentration of Plastic Debris in the Open Ocean
Giora Proskurowski, Kara Lavender Law, Skye Morét-Ferguson, Christopher M. Reddy
Presented at the Ocean Sciences Meeting, Portland, OR, 24 Feb. 2010.
Millimeter-sized plastic debris in the world’s oceans is subject to the physics of mixing in the surface boundary layer. While the density of plastic debris is generally less than the density of seawater, the resulting upward buoyancy force can readily be overcome by turbulent mixing due to wind forcing and surface heat loss. The extension of this logic suggests that as the wind stress increases, plastic debris can be mixed downwards meters to 10’s of meters to the base of the boundary layer. As a fraction of the total plastic debris is likely mixed down into the water column under many environmental conditions, surface layer (neuston) net tows (e.g. Sameoto, Manta, MARMAP) that sample the upper ~20 cm cannot account for all the plastic mixed throughout the surface boundary layer.
On an annual basis since 2003, the Sea Education Association (SEA) has conducted plastic marine debris research on a cruise-track from Hawaii to the west coast of North America. These expeditions occur in the early summer (May-June-July), and typically include twice daily neuston net tows over the course of the month-long expedition. Coincident with each sample tow are continuous shipboard measurements of true wind speed, air temperature, surface water temperature, and hourly measurements of relative humidity. Results show persistent high concentrations of plastic debris in two areas, within a band north of Hawaii between 26-28°N, and within a large region of east and north of Hawaii between 33-40°N and 136-155°W. Preliminary results clearly show that the highest measured plastic concentrations correspond with wind speeds of less than 15 knots. The results from a handful of experimental sampling efforts where a surface net and a net submerged 3-5 meters below the surface were towed simultaneously showed that plastic concentrations below the neuston layer are up to 25% of the surface concentrations. A basic understanding of the relationship between wind stress and the distribution of plastic debris dispersed throughout the boundary layer is important in determining the total plastic debris in the world’s oceans, as the true amount is undoubtedly higher than the value calculated from neuston tow observations.
Establishing a Robust Characterization of Beach Plastics
Christopher M. Reddy, Emily Peacock, Skye Morét-Ferguson, Ellen Murphy, Kara Lavender Law
Presented at the Ocean Sciences Meeting, Portland, OR, 24 Feb. 2010.
As part of a major effort to understand the sources and transport of plastic pieces collected in the western North Atlantic Ocean and Caribbean Sea by the Sea Education Association (SEA), we initiated a series of surveys for plastic pieces collected along northeastern beaches of the USA. In particular, we measured the densities of over 500 plastic pieces collected in the summer of 2009. This approach can provide invaluable information, especially for pieces that are otherwise unidentifiable, as different manufactured plastics can vary widely in density (0.9 to 1.4 g/cc). In addition, we also employed carbon/hydrogen/nitrogen analyses to identify certain plastic pieces, especially Nylon, which contains nitrogen while other plastics are limited to carbon and hydrogen, and for some, oxygen. These studies reveal that all known post-consumer plastics can be found on beaches. Direct comparisons of these samples to those found in the open ocean will be presented.
