**This blog entry orginally appeared on the website oceanspaces.org.**/p>
In this second piece of my experience sailing the ocean blue, I describe the research methods we used to document levels of plastic marine pollution across the subtropical and subpolar gyres in the North Atlantic during my 2014 voyage with 5Gyres Institute. Last spring I was invited to be a guest scientist with the 5Gyres on a research cruise that would traverse two gyres in the North Atlantic Ocean sailing from Bermuda to Iceland. This turned out to be a unique cruise indeed. Instead of boarding a diesel powered research vessel on June 9th 2014, we boarded a 72-foot sailing vessel, the SV Sea Dragon. Sailing from Bermuda to Iceland is no easy task and challenging because when the sails are up the vessel actually tilts to one side or the other. Along our voyage, we braved chilly winds, rain, intense fog, choppy seas, and the possibility of dodging icebergs. Day and night, my fellow crewmates and I worked as a team to steer the boat, hoist and lower sails, learned to read instruments, and record log entries. We also cooked, cleaned and most importantly, conducted marine pollution research all while keeping ones balance on a boat tilted at a 45 degree angle moving through wave sets and wind.
I had had a few experiences on day cruises on diesel boats collecting oceanographic data and conducting marine mammal surveys but this trip was well beyond any long scale research or adventure I had participated in to date. To find out how much litter is in our oceans we deployed multiple methods to document plastic presence and abundance both on the sea surface and below. Our research questions were simple, 1) Does plastic abundance vary between two gyres? 2) Does abundance vary at depth as sea-state changes? We had to adhere to limited space onboard, so the onboard survey equipment comprised of three different types of trawls, which I briefly described in my previous blog on Oceanspaces.org Blog Part 1.
The crew deployed the Manta trawl daily for one hour off the Sea Dragon’s port side during each morning and evening shift, regardless of rain or shine, calm, or moderate seas. All trawl equipment was rigged to a spinnaker pole mounted horizontally to the mast. The purpose of the Manta was to measure the surface abundance of plastics along our route requiring us to sail between 2-4 knots per hour while it was deployed. This meant we moved quite slowly and upright for that hour (the crew was very happy about that). Once the hour was up, crewmembers quickly brought in the trawl, used a hose to spray down the collection net with saltwater, scrape out all biota and plastics into a sieve, and pour the contents into a labeled bottle to be analyzed later in a laboratory for abundance, size, and chemical composition.
A hi-speed trawl which could collect data while travelling at speed (8 -12 knots per hour) was also tested on this voyage. Its purpose was to measure surface abundance of plastic quickly, unfortunately, after a week and a half of similar deployment to the Manta, we had to retired it due to the moderate sea conditions as we progressed on our journey northward. I have described our methods for sampling the surface of the ocean for plastics thus far, yet the vertical distributions of plastic in the ocean are less known. The third trawl known as the Multi-Depth Trawl did just that, collected plastics at eleven depth levels below the surface simultaneously. Its performance showed promise in documenting less understood sub-surface plastic. Lastly, we used visual observations three times a day to document the presence of larger plastics that may be floating by the vessel. I saw several litter items floating by the Sea Dragon during each daily observation shift; plastic items such as bottles, fishing rope, and even balloon string were documented. In the next blog, I will share more of what daily life and routines where like on the boat, weather, friendships, and my conclusions from sailing an unforgiving ocean in the calmest month of the year.