The Colossal Pollution on the Move! Mapping the Global Distribution of Marine Debris — An Interview with Ming-Shiou Jeng

Marine Debris Is Drifting Toward Tropical and Polar Regions

Marine debris has drawn considerable attention in recent years. Researcher Ming-Shiou Jeng of Academia Sinica's Biodiversity Research Center assembled a team that used big-data analysis to examine 25 years of ocean-drifting debris across the world's seven major ocean zones. The team found that windage effects and ocean currents both influence debris distribution, which is gradually shifting from subtropical waters toward tropical and polar regions. The accumulation of marine debris is most severe in the Pacific, and 50% of debris continues to drift at sea. The findings were published on 6 October 2020 in Environmental Research Letters.

Where Does Drifting Marine Debris Come From?

Having grown up alongside the sea, Jeng is deeply pained by the degradation of our oceans. "In the past, when we went out diving or by boat, the sea surface was very clean — people only watched for dolphins or seabirds. It's different now. Wherever you look, the surface is almost entirely covered in garbage!" The problem is especially severe in certain zones. The Pacific Garbage Patch, for instance, now covers an area nearly 50 times the size of Taiwan and is still growing. The debris sits half-submerged in the water and is completely invisible from an aircraft.

Marine debris comes in many forms: 20% floats and 80% sinks, including fishing nets. It is estimated that 4.8 million to 12.7 million tonnes of floating waste enter the ocean globally each year. About 50% of that may be washed ashore by wind and waves, while the rest continues to drift. Under sunlight and wave action, it gradually weathers, breaks down, and crumbles into microplastics — or even nano-sized particles — which are consumed by tiny zooplankton, then eaten by small fish, small shrimp, and larger fish. Through the food chain, these particles accumulate in the organs and muscle tissue of marine animals, and may ultimately end up being consumed by humans.

Many scientists are studying the impact of plastic debris and microplastics on marine life. A well-known example is Midway Atoll in the Hawaiian Islands, where albatrosses mistake plastic for food and swallow it, and parent birds feed plastic to their chicks. Scientists who have dissected dead albatrosses have found their stomachs stuffed with garbage. The carcasses of whales, sea lions, seals, and other animals have also been found full of debris.

In addition, plastics contain plasticizers that dissolve into the sea and harm marine organisms. These compounds also act as environmental hormones, causing shrinkage of male molluscs' reproductive organs and feminization in various animals. "Because plasticizers are not acutely toxic and microplastics don't kill immediately, many people feel nothing about marine debris — they don't even know to be afraid," says Jeng.

Building an Analytical Model from Dongsha Island

The marine debris research team consists of Academia Sinica researcher Ming-Shiou Jeng, associate researcher Yi-Chia Hsin, and National Taiwan University Institute of Fisheries Science associate professor Chia-Yin Ko. They began building their analytical model starting from Dongsha Island. Why choose Dongsha Island as the survey site? "I've been to Dongsha Island more than 50 times," Jeng explains. "Twenty-something years ago it was still very clean. Now the amount of drifting debris is terrifying. I became very curious about where all this garbage was coming from."

Furthermore, although Dongsha Island has a military garrison, littering is strictly prohibited. Jeng's team concluded that all the debris on Dongsha Island must have drifted in from elsewhere, making it an ideal site for developing a marine debris tracking model. On beaches on both the north and south sides of the island, monthly surveys were conducted with the assistance of staff from the Marine National Park Headquarters, visiting research teams, and Coast Guard soldiers. The debris was analysed for its composition, and after identification, the majority was found to originate from China or Southeast Asian countries.

The team also gathered data online from governments and relevant agencies around the world — collecting 25 years of global ocean current and wind-direction data from the National Oceanic and Atmospheric Administration (NOAA), sea-surface temperature data from the Central Weather Bureau, and fishing vessel operation locations from the Fisheries Agency — for big-data analysis.

At Dongsha Island, the northeast monsoon prevails in winter and the southwest airflow in summer. More debris from China arrives in winter; more from Vietnam arrives in summer. The team fed all the collected ocean current and wind-direction data into computers, built a model, and performed back-tracking of drifting debris at Dongsha Island. When compared against the actual debris origins identified on-site, the results matched — confirming that the theoretical model was valid.

A Global Analysis of Drifting Marine Debris

With the Dongsha Island model proven successful, the team noticed that marine debris was arriving from all directions, which sparked the motivation to understand drifting marine debris on a global scale. They immediately applied data simulations to analyse the trajectories of marine debris worldwide. Dividing each degree of latitude and longitude into 3 grid cells, they simulated the release of 10 pieces of debris in every ocean grid cell around the globe, then observed where ocean currents and wind would carry them between 1993 and 2017. Associate researcher Yi-Chia Hsin explains that windage is a key factor in pushing marine debris onto shores and coastlines — and this study marks the first time windage effects have been incorporated globally into the analysis of marine debris trajectories.

As shown in the figure below, marine debris discarded in open-ocean areas with a low windage coefficient — heavier than seawater — accumulates mainly between 30°N and 25°–50°S latitude. Medium- to high-windage debris such as EPS foam and plastic bottles, which are lighter than seawater, drifts readily with the wind and accumulates around 10°N and poleward of 60°S. Coastal debris, meanwhile, is less affected by wind regardless of windage coefficient and concentrates in the tropical zone between 10°N and 5°–15°S.

The research team not only identified hotspots for drifting marine debris, but also used three colours to indicate different degrees of overlap between marine debris hotspots and marine ecosystem service hotspots (Note 1). The marine ecosystem service hotspots include: chlorophyll-a concentration (assessing ocean primary productivity), total annual fishing effort (assessing fisheries), and marine biodiversity.

Based on the model simulation results, the distribution of marine debris has already shifted from subtropical to tropical and high-latitude regions, and is expected to shift further from the eastern Pacific to the western Pacific — meaning Taiwan and the broader Asian region may face enormous harm from marine debris. In addition, because plastic debris is less dense than seawater, it can be transported over vast distances and is easily carried toward the poles. The Arctic and Antarctic Oceans may become another hotspot for marine debris accumulation.

This massive migration of drifting marine debris has already severely impacted global marine biodiversity and is encroaching on fishing grounds. If the volume only continues to grow, the entire marine ecosystem and human economic activities will suffer serious consequences.

Is Recycling or Beach Cleanup Only a Stopgap?

Now that we know the problem, how do we solve it? Can plastic recycling, for example, eliminate the issue at its root? "Although plastic can be recycled and reprocessed, at present only highly industrialised nations with high living standards can achieve high recycling rates. In Scandinavia, there are dedicated recycling machines: you simply put a plastic bottle into the machine and receive a cash reward. In Taiwan, the incentives are shrinking, and public willingness is low."

In addition, local governments across Taiwan regularly organise beach cleanup or beach adoption events, with the aim of letting the public see firsthand that coastlines are strewn with garbage, and inspiring change starting from themselves. However, Jeng points out that most participants head to easily accessible beaches and bathing areas. For remote, hard-to-reach spots, the government still has to spend enormous sums on cleanup — for instance, at the Penghu South Islands, special task forces are deployed, with workers dangling in the air to collect debris from cliff faces, sometimes hauling up just a single large piece of EPS foam per trip. Fishing communities have also formed environmental fleets, dispatching fishing boats specifically to collect debris at sea — but these efforts can only operate on a small scale and require substantial funding.

The large volumes of discarded fishing gear, EPS foam (used as oyster-farming buoys), floats, and fishing nets in recent years have become a major problem in their own right. In the past, fishing nets were expensive, so fishers would mend and reuse them when they were damaged; now that nets are cheap, broken ones are simply thrown away, and the same goes for other fishing gear. It is estimated that there are more than 100,000 abandoned fishing nets on the ocean floor worldwide. They frequently become entangled around coral reefs and ensnare marine life, causing serious ecological damage. The Taiwanese government is now promoting a real-name registration system for fishing gear, asking fishers to return discarded nets and equipment and offering incentives for doing so.

Calling on Governments to Address the Problem at Its Source

Jeng speaks with deep feeling: "I believe we should stop trying to deal with garbage already in the ocean — we'll never finish cleaning it up. We need to eliminate the problem at the source." Plastic was invented only a few decades ago, yet it has already been widely abused. Something so difficult to decompose is routinely discarded after fewer than 10 minutes of use. "The global plastics economy must change. Governments everywhere must enact relevant policies — such as making plastic products more expensive, banning them outright, or replacing them with alternatives — to bring things under control from the source."

In recent years, economically less developed African nations have taken some of the boldest action. "In many African countries, drainage systems have been blocked by plastic bags, causing flooding. They concluded that since they cannot manage plastic waste, they might as well ban it altogether." More than 60% of African countries have now implemented plastic bag bans — shutting down plastics factories, and prohibiting the import of plastic bags nationwide.

"Wastewater treatment is also extremely important! Every time clothes are washed, synthetic-fibre garments shed enormous quantities of microplastics that flow with wastewater into the ocean," Jeng adds. "Although the wastewater treatment rate in Taipei is 86%, Taiwan's overall rate is only 37% — meaning that 63% of wastewater is discharged directly into the sea without treatment. There is still enormous room for improvement."

Marine debris knows no borders. "All the world's oceans are connected. Microplastics have now been detected even at the most remote North and South Poles and in the Mariana Trench, the deepest point on Earth. Only when the global marine environment is healthy will Taiwan's ocean truly be healthy." Jeng hopes more people will pay attention and continue conducting research, and urges governments around the world to recognise the severity of the marine debris problem.

Throughout his career, Jeng has been driven by a deep sense of mission, tirelessly championing marine conservation in Taiwan — instrumental in establishing the Dongsha Atoll and Penghu South Islands National Parks. He continues to travel widely, explaining the issues to the public and pressing relevant authorities. "If I know about it and don't speak up, that would be my fault! I always keep one saying in mind: success need not be mine — that's the only way to keep doing this with joy." His passion, drive, and optimism are what have allowed Jeng to keep moving forward on this difficult path.

Note 1: "Hotspot" here refers to grid cells in the global ocean that rank in the top 25% of values for each assessed indicator.

Interviews & Writing│Ou Yu-Tian
Art Direction│Lin Xun-An

Reproduced from Academia Sinica's Research Matters (研之有物). URL: https://research.sinica.edu.tw/ocean-litter-windage/