Microplastics in the Ocean

Caitlin collected surface samples using a bucket on a rope.
You can see the CTD A-frame deployed in the background.

Caitlin Kelly was onboard Agulhas II for the entire cruise collecting surface water samples for a microplastics study. The professor in charge of the project, Dr. Peter Ryan, was also on the ship, but was part of the turnover crew that went to Gough Island for a few weeks. He has been studying the effects of plastic on seabirds since his master’s project in the 1980s.

Plastic pollution in the ocean is probably something you've heard about before, and it's in the news more and more with the discovery of huge "garbage patches" around the world. Tiny pieces of plastic (microplastics) can be found in the surface waters of oceans all over the planet. 

The group came onboard with a vacuum filtration rig, but one of the glass components got broken in the first few days when we experienced bad weather. Not willing to sacrifice the opportunity to collect data, the team reverted to the low-tech approach developed on the Antarctic Circumnavigation Expedition by SAEON (South African Environmental Observation Network) biologist, Dr Tommy Bornman. Caitlin collected samples using a bucket on a rope, and then filtered that water through a 25 micron mesh filter using plastic cartons held together with duct tape.

Filter with fibers and particles clearly visible.

I was amazed that with my own eyes, no magnification, I could see fibers and colored particles on the filters after just 10 liters of water had been run through them. But it's perhaps not too surprising, because we were traveling through the edge of the South Atlantic gyre, where floating plastics and other debris accumulates. The filters will be analyzed by a lab in Italy, which uses a micro-FTIR spectrometer to pinpoint the type of material. 

Caitlin processed each sample by pouring the water
into a carton. The filter was held in place by the cap. 

Talking with Peter Ryan over dinner one night, I learned more about the huge threat that plastic poses our oceans. Since it does not biodegrade, most of the plastic ever made is still on the planet (unless it is incinerated or converted into fuel). Plastics slowly degrade through UV exposure and are battered into tiny pieces and distributed by surface currents. Some plastics are more dense than seawater and sink fairly quickly. Less dense plastics also sink once they become fouled with algae, barnacles, bacteria, etc. Which suggests that plastic ends up on the ocean floor, where it is harder to quantify and study. If you've ever been snorkeling, you've probably seen some trash tangled up in coral or floating by.


I have never been on a cruise with microplastic sampling, and it was interesting to see it in person. But also disheartening. Here we were in some of the most remote areas on the planet, and still surrounded by negative human impact. Understanding the distribution of microplastics is an important step to acknowledging the impact, and will hopefully lead to protections and a change in our behavior.