13 June 2019
It’s common knowledge that climate change has been causing a series of profound transformations in the Arctic Ocean. But until recently, it was believed that marine litter was primarily a concern in temperate and tropical regions. Not anymore. ANDRÉS CÓZAR CABAÑAS explains the changes that are making the Arctic more susceptible to plastic pollution.
THE ARCTIC’S REMOTE LOCATION and hostile environment have helped preserve it as one of the most pristine places on Earth. But in recent years, human voracity has led governments and businesses to turn a speculative eye toward this untapped piece of our planet. The polar regions are warming much more quickly than the rest of the Earth, and a shrinking ice cap is opening the door to unprecedented development.
THE SCIENCE BEHIND “GARBAGE PATCHES”
There are virtually no human settlements north of the Arctic Polar Circle, located above Iceland at 66.34 degrees latitude. The biggest sources of marine litter are far from there, and a powerful system of ocean currents works to retain the floating litter at mid-latitudes: the Earth’s wind patterns mean that marine litter accumulates at around 30 degrees’ latitude.
In each hemisphere, from the equator to 60 degrees, two steady wind belts blow in opposite directions south and north of the 30th parallel. When these crosswinds interact with the ocean surfaces, they generate convergence zones in the middle of each ocean basin. The results are the great subtropical gyres, more commonly known today as the “great plastic garbage patches.”
In 2013, the research vessel Tara completed a five-month expedition around the North Pole. I was responsible for leading the team that assessed plastic pollution in the waters around the Arctic ice cap. The researchers sampled floating debris by towing nets with meshes as fine as one-third of a millimetre wide and measured the concentration of the particles caught.
This expedition changed our understanding of the isolation of the Arctic Ocean. As expected, most of the ice-free surface waters in the Arctic Polar Circle were only slightly polluted with plastic debris—a situation that seemed consistent with the low population settled there. However, we were surprised to find that plastic debris was plentiful in the Greenland and Barents seas to the east of Greenland and north of Scandinavia. Our study concluded that most of the plastic found in this part of the Arctic was coming from faraway sources, including the coasts of northwest Europe, the UK and the east coast of the United States.
THE ARCTIC: A “DEAD END” FOR FLOATING DEBRIS
In addition to the wind-induced system of subtropical gyres, there is a second large-scale ocean circulation at work. This one is driven by differences in the densities of polar and tropical waters. The surface water in the Greenland and Barents seas becomes progressively more dense by cooling, ultimately moving downward. This sink of ocean waters pulls surface water from the North Atlantic, collecting buoyant plastic from highly populated latitudes and delivering it to the Arctic, where the landmasses, together with the ice cap, constitute a dead end for all floating debris.
This poleward migration of plastic involves the so-called thermohaline circulation, a global conveyor belt currently known for redistributing heat across the global ocean and now connecting remote sources of marine litter with the Arctic.
Most of the hundreds of tons of plastic found in Arctic waters appears in the form of aged fragments about the size of a grain of rice. A total of 300 billion plastic pieces are estimated to be present in surface waters alone, and it’s likely there is even more plastic on the sea floor. These tiny fragments are nearly impossible to remove.
There is no way out for the plastic entering the Arctic. It will stay there for a long time, interacting with one of the Earth’s wildest ecosystems. While we still don’t fully understand the consequences of so much plastic for the Arctic, it is troubling that plastic pollution has made its way into the marine food chain.
The migration of floating debris to the Arctic is a non-stop process. A massive accumulation of plastic is just beginning: years’ worth of plastic already disposed into the oceans is now in transit to the Arctic, and more and more plastic litter enters the oceans every year.
The Arctic is more vulnerable to remote sources of pollution than ever before. Plastic particles also have the potential to act as vectors for contaminants added during plastic manufacturing or acquired from seawater. As well, invasive species are hitching rides across the oceans on these long-ranging plastic vehicles. Our study confirms that the Arctic is indeed connected to the rest of the world. More than ever before, preserving the Arctic requires preserving the planet.
ANDRÉS CÓZAR CABAÑAS is an ecology professor at the University of Cadiz, Spain.