How much plastic is really entering the ocean?

The Data Puzzle & Plastic Mystery

Knowledge is built in layers. Scientific research is not about finding facts, but testing and questioning them². The seminal 2015 Jambeck paper was built on large datasets and models, and so field researchers rolled up their sleeves and got to work testing the outputs and assumptions. The search was on for empirical evidence: data from on the ground (and in the ocean) that shows where the predictions were right, and where they were wrong.

Some of the original country-level estimates turned out to be too high. Researchers measured actual plastic flows in rivers and along coastlines and found that the real numbers didn’t always match the modeled ones³. Institutions working on capacity development and new monitoring tools found they needed to correct some of the over-estimations through direct measurement. Models were fine-tuned to account for on-the-ground waste realities, such as informal dump sites and burning of waste⁴.

Then there was the ocean itself. If tens of millions of tonnes of plastic had been entering the sea every decade, where was it all? When scientists went looking for plastic in the oceans, they didn’t find as much as they expected⁵. Even in the gyres, the vast circulating currents that trap floating debris, they saw hardly anything. Instead, the ocean resembles a plastic soup of tiny fragments – far harder to see and track – raising fundamental questions about where all the plastic ends up.

The gap between how much plastic should be in the ocean (based on models) and how much is actually in the ocean (based on measurements) is one of the defining puzzles of the field⁶. We now know that some plastic sinks deep to the ocean floor⁷. Much of it fragments into tiny particles (microplastics) that are difficult to measure⁸, and can even be incorporated into marine organisms⁹. For all the floating plastics and beaches covered in waste, there is so much more hidden in the ocean, and we still don’t know where it all is.

Meanwhile, plastic appears in unexpected places. It has been found in Arctic sea ice¹⁰ and in deep-sea sediments¹¹. Microplastics are found in freshwater springs far from any coast¹². The scientific community began to recognize that plastic is moving through the entire earth system, and even our own bodies¹³. As research developed, models have become more complicated – not less – and studies often lead to more questions than answers.

What We Know and What We Don’t

Ten years on from the Jambeck paper, the field has made real progress. We know that plastic is present in every ocean basin, floating on the surface and sinking into the deepest trenches. We have a better understanding of how rivers carry plastic to the sea, but also how mangroves, rivers and estuaries trap plastic, reducing leakage into the ocean¹⁷. We also have more precise models that can predict how ocean currents distribute waste once it enters the marine environment. We understand the processes (fragmentation, biofouling, ingestion by marine life) that remove plastic from the surface and redistribute it through the water column and into sediments.

We also know the original estimates were imprecise, but that the true scale of the problem may be even larger than first thought. Researchers are training their microscopes to study microplastics, a tiny but dangerous pollutant. Compared to the 2015 study, there are many more microplastics entering the ocean – from tire dust, synthetic fibers from laundry and paint chipping off boats – than previously expected¹⁸.

The biggest gaps remain in the places that are hardest to reach. Remote stretches of ocean, deep-sea environments, polar regions, and isolated islands are understudied but not unpolluted. They are often critical habitats, home to unique species and vulnerable ecosystems¹⁹, yet they remain “data deserts”, lacking reliable baseline data and sometimes omitted entirely from global models.

This is why Plastic Odyssey also collects data in the most remote corners of the world. At Henderson Island, we documented one of the highest densities of plastic debris on any beach on Earth, though it is thousands of kilometers from the nearest city. In Saint Brandon, the data that was available was outdated and therefore inaccurate, and the island had over ten tonnes of plastic when only two were predicted. The gap between what models predict and what’s actually there is not just a scientific problem. It is a practical one, with real consequences for cleanup and management programs.

The question of how much plastic is entering the ocean is not yet fully answered. But we are asking it better than ever before, with more powerful tools and with a growing number of people participating. Plastic Odyssey plans to do its part, using its vessel to visit remote, protected islands in partnership with UNESCO. The team is working not only to clean up these ecologically valuable sites, but fill critical data gaps. Because before we can fix the problem, we need to truly understand its scale.