The Great Pacific Garbage Patch is rapidly accumulating plastic

New study published last week in the journal Scientific Reports reveals that the Great Pacific Garbage Patch (GPGP) could be four-to-sixteen times more massive than previously estimated. The comparison of the new data with historical observations also suggests that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.

Floating marine debris collection, seen from below (credit: NOAA)

Floating marine debris collection, seen from below (credit: NOAA)

The annual plastic consumption has reached over 320 million tons worldwide. Around 60% of the plastic we produce is less dense than sea water, which means that a large fraction of the plastic accidentally introduced into the marine environment ends up floating on the oceans’ surface. A portion of it is recaptured by coastlines, degrades into smaller pieces or loses buoyancy and sinks; yet another fraction is transported offshore and enters oceanic gyres (large systems of circulating ocean currents). The Great Pacific Garbage Patch located halfway between Hawaii and California, is one of those accumulation zones of buoyant plastic—it is, in fact, the largest on Earth.

The actual mass of the GPGP is unknown, with estimates swinging from ~4.8k metric tons to ~21k metric tons depending on the method used to produce the estimates. Up to now, the available data on quantities and characteristics of buoyant ocean plastic derived from samples collected with small sea surface trawls initially developed to collect neustonic plankton. The problem with these survey methods though, is that due to the small aperture of the trawls used (0.5–1 m width, 0.15–1 m depth) and the limited surface area covered, the surveys were prone to underestimate loads of rarer and larger plastic objects such as bottles, buoys and fishing nets.

In an effort to overcome this limit, an international team of scientists affiliated with The Ocean Cleanup Foundation, six universities and an aerial sensor company, embarked in the most comprehensive sampling effort of the GPGP, to date. As many as 30 vessels crossed simultaneously the GPGP with sampling nets, while two aircrafts surveyed it from the sky. The analysis was also supplemented by the fleet’s mothership RV Ocean Starr which trawled specific devices to sample medium and large objects.

The data shows that the sea surface environment of the GPGP is dominated by polyethylene and polypropylene pieces, substantially outweighing other artificial and natural floating debris. Based on these new observations and mathematical modeling the team of scientists was able to conclude that the 1.6 million km2 accumulation zone of the GPGP is currently holding around 42k metric tons of megaplastics (e.g. fishing nets, which represented more than 46% of the GPGP load), ~20k metric tons of macroplastics (e.g. crates, eel trap cones, bottles), ~10 k metric tons of mesoplastics (e.g. bottle caps, oyster spacers), and ~6.4 k metric tons of microplastics (e.g. fragments of rigid plastic objects, ropes and fishing nets) for a total of ~79 k metric tons of plastic. “We were surprised by the amount of large plastic objects we encountered,” said Dr. Julia Reisser, Chief Scientist of the expeditions. “We used to think most of the debris consists of small fragments, but this new analysis shines a new light on the scope of the debris.”

By comparing the amount of microplastics with historical measurements of the GPGP, the researchers also concluded that plastic pollution levels within the GPGP have been growing exponentially since the 1970s. “Although it is not possible to draw any firm conclusions on the persistency of plastic pollution in the GPGP yet, this plastic accumulation rate inside the GPGP, which was greater than in the surrounding waters, indicates that the inflow of plastic into the patch continues to exceed the outflow,” Laurent Lebreton, lead author of the study, concluded.

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Carlo Bradac

Carlo Bradac

Dr Carlo Bradac is a Research Fellow at the University of Technology, Sydney (UTS). He studied physics and engineering at the Polytechnic of Milan (Italy) where he achieved his Bachelor of Science (2004) and Master of Science (2006) in Engineering for Physics and Mathematics. During his employment experience, he worked as Application Engineer and Process Automation & Control Engineer. In 2012 he completed his PhD in Physics at Macquarie University, Sydney (Australia). He worked as a Postdoctoral Research Fellow at Sydney University and Macquarie University, before moving to UTS upon receiving the Chancellor Postdoctoral Research and DECRA Fellowships.

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