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How has the amount of plastic in the ocean changed over time?

Posted on October 21 2012

Question submitted by Pacific Boychoir Academy

During class onboard the ship, we learned that plastics were first produced in the late 1800s.  There was very little plastic used in American households before 1940.  As it became more useful, easily disposable, and households and industry depended on it, the amount of plastic used and disposed of grew.  People thought nothing of dumping plastics in the ocean.  The United Nations International Maritime Organization (IMO) became aware of the polluting of the oceans and in 1970 it ratified the "International Convention for the Prevention of Pollution from Ships".  It was known as MARPOL (MARine POLlution) but it wasn't put into force until 1980.  Annexes were added to it over the years and with the fifth one in 1988, the dumping of plastics from ships was banned.

SEA data from the North Atlantic Ocean, collected by students over the past 25 years, do not show an increase or decrease in annually-averaged plastic concentrations in the region where floating plastic accumulates.  This was a surprising result to researchers, because it is very likely that the total amount of plastic in the ocean has increased during this time period.  Where has the plastic gone?  There are a number of hypotheses, but as of now we don't understand why we do not see an increasing trend in the concentration of floating plastic pieces.

The Seamans is reflected in the ocean studded with tiny pieces of plastics. Most of the plastics SEA has collected over the years are the size of these tiny pieces.
Photo by Zora McGinnis.