This is not the first time researchers from the University of Basel and the Alfred Wegener Institute (AWI) have studied microplastics in Antarctica. However, analysis of data from the spring 2021 expedition shows that environmental pollution from these tiny plastic particles is a bigger problem in the remote Weddell Sea than previously known.

All 17 seawater samples showed higher concentrations of microplastics than previous studies. “This is due to the type of sampling we did,” says Klara Leistenschneider, a doctoral candidate at the Department of Environmental Sciences at the University of Basel and lead author of the study.

The current study focused on particles ranging in size from 11 to 500 micrometers. The researchers collected them by pumping water into tanks, filtering it, and then analyzing it with infrared spectroscopy. Previous studies in the region have mostly collected microplastic particles from the ocean using fine mesh nets with a mesh size of approximately 300 micrometers. Smaller particles will easily pass through these planktonic networks.

The results of the new study show that 98.3 percent of the plastic particles found in the water were less than 300 micrometers in size, meaning they were not collected in previous samples. “The level of pollution in the Antarctic Ocean far exceeds what has been reported in past studies,” says Leistenschneider. The study was published in the journal Total Environmental Science.

What is the role of ocean currents?

Individual samples were contaminated to varying degrees. Marine samples collected north of the continental slope and the Antarctic Slope Current contained the highest concentrations of microplastics. The reasons for this are not fully known. It is possible that the ice that forms near the shore traps small pieces of plastic, which can only return to the water when the ice melts. Ocean currents may also play a role. “They can act as a barrier, reducing water exchange between north and south,” says Gunnar Gerdts from AWI in Helgoland, Germany.

Of course, ocean currents are an important factor and are the subject of many open questions in this field. So far, researchers have only examined water samples taken from the ocean surface, but not from shallower depths. First of all, this is due to the limited duration of the voyage on ships to take samples and the insufficient production of equipment. “However, it may be interesting to analyze such data, since deep currents are very different from those at the surface, and thermohaline circulation leads to exchanges with water masses from northern regions,” says Leistenschneider.

It is also still unclear how microplastics entered the Weddell Sea and whether they left the area. The strong Antarctic Circular Current, which flows around the Antarctic Ocean at about 60° south latitude, may prevent them from leaving. Researchers also can’t yet say for sure where microplastics come from. Possible sources include regional ship traffic from the tourism, fishing and research industries, as well as land-based research stations. However, microplastics can also enter Antarctica from other regions via ocean currents or atmospheric transport.

Research raises awareness

Clara Leistenschneider then plans to focus on analyzing the rainfall samples she collected during the same expedition. This should provide insight into how microplastics accumulate on the seafloor, which is home to unique and sensitive organisms and a breeding ground for Antarctic ice fish (Bovichtidae).

With the increase in tourism in the Antarctic Ocean, pollution may increase in the future, further affecting the environment and the food chain.

Despite all this, Leistenschneider remains cautiously optimistic: “Research on this topic in recent years has significantly increased awareness of the problems that microplastics cause to the environment and all living organisms.” While there is no one-size-fits-all solution, he notes that various stakeholders around the world are working hard to better understand the problem and develop innovative ideas to reduce plastic pollution. And of course, “everyone who demonstrates environmentally responsible behavior can make a positive difference.”