School Email Exchange

How will you be measuring the extent of the “patch”?

Posted on October 14 2012

Question submitted by King Philip Regional High School

Zora McGinnis looks for pieces of plastic visible from the deck during one of her hour-long observations.

What I most want you to understand is plastic concentrations are not uniform in the gyre.  In other words, there are small areas within the gyre that can accumulate more plastic than others because of eddies, wind, and wave action.  Also, most of the plastic is in small pieces, some even microscopic so you can’t actually see them from the ship!  You have to put a net in the water and drag it on the surface, bring it onboard, and look at the contents of the net.  We will collect plastic below the surface of the water with a net called a MOCNESS.  The samples from the surface will be collected using a manta net and a neuston net.  To look at macroplastic, or large plastic objects that can be seen with the naked eye from the deck of the ship, we will do visual surveys.  Zora McGinnis is onboard to document macroplastic during four one-hour-long watches per day.  She counts and records data for each piece of large floating debris that she observes in a 90 degree arc off the bow on one side of the ship.  She will use these data in an equation that will give her an idea of the total amount of macroplastic in the area that the Seamans has sailed through.

We will be doing a transect of the eastern part of the North Pacific subtropical gyre, sailing across it from the eastern edge off California to 145°W longitude, then we will head south towards Hawaii.

(See the Oct. 8 Expedition Journal at and watch the "Science of Plastics at SEA" video (Day 11 video))