on a sunny summer morning in 2024, i walked along costa rica’s drake bay, my feet sinking into the sand as crabs skittered away, disappearing into burrows below the wet sand. after a three-day storm, wind and waves had tossed not only seaweed and driftwood along the beach, but also flip-flops, dented metal tins, and other pieces of trash onto the shore.

as i scanned the shoreline, helping clean the beach of trash, something caught my eye. i picked up what at first glance looked like just another ordinary plastic bottle, but upon closer inspection, i noticed that the label was in a language totally foreign to costa rica’s predominant spanish. judging by the label, this was a chinese water bottle.

as i examined the bottle, i puzzled over the journey that brought it to costa rica. what did its journey to this beach look like? how long has it drifted through the ocean? finding this chinese bottle 9,000 miles away on a distant central american shore, inspired me to take my own journey to learn more about how trash moves through the oceans and what science can tell us about how long, how far trash travels through the ocean, and how it rides currents across and through the oceans.

an interconnected system

according to the united nations, an estimated 60 to 90% of the trash that litter shorelines, the ocean’s surface, and the seafloor is plastic. eighty percent of this plastic waste comes from land-based sources, with the remaining 20% coming from marine-based sources primarily trash from fishing vessels.

“ocean currents are part of the machinery, the engine that gives us the climate we have… so when we tinker with the atmosphere through greenhouse gas and aerosols, we bring about a whole chain of reactions that are going to change the wind field that’s driving the currents,” said eddy carmack, ph.d., senior research scientist emeritus and head of the drift bottle project, a research project that uses volunteers to throw bottles with identifiable information inside into the ocean to track ocean currents.

ocean currents are everywhere, from the arctic to the five gyres located in the north pacific, south pacific, north and south atlantic, and indian ocean. a gyre is a large system of ocean currents that move circularly. they are continuous and are driven by winds, tides, and water densities that are ever-changing throughout each year.

“it was thought that the arctic ocean was not a player in the game. it was way up north and all the heat exchanges were going on in the equatorial zone,” carmack said. but according to researcher rebecca woodgate, this small ocean that covers only 2% of the global ocean surface area is key in regulating deep ocean currents, also known as thermohaline circulation, all over the world.

“though she be little, she be fierce,” said carmack quoting “a midsummer night’s dream” when referring to this ocean. the global ocean conveyor belt, consisting of both deep and surface currents circulates the earth on a one-thousand-year period, plays a major role in how our oceans and wind function. 

plastic, plastic, everywhere

in the 1950s, plastic became a craving for consumers around the world because of its versatility and affordability. as each individual throws out their bottle, a styrofoam cup of coffee, or a plastic packet, the debris often eventually flows out to the ocean like on a conveyer belt. it then slowly breaks down into smaller fragments and often becomes ingested by marine life for the remainder of its life cycle.

now add in the phenomenon of ocean currents, and the moment plastics reach the ocean, they can hitch a ride on ocean currents worldwide. the large gyre across the globe can sweep in and collect loose trash from nonpoint sources. these five gyres are sometimes assumed to hold floating islands of trash, made up of large pieces of debris such as tires, fishing ropes, shoes, and more. contrary to popular belief however, oceanographer captain charles moore states that they are more like soups of confetti-sized trash.

a 2018 study from the nature journal presented that at least 79,000 tonnes of ocean debris are within an area three times the size of france – that’s 617,763 miles of trash.

although plastic, at its core, pollutes our waters, seeing a floating rubber ducky may seem ordinary. yet, bowling balls, toilets, and scooters have been found by beach cleanup volunteers with sarah weller, senior manager of international coastal cleanup at ocean conservancy.

“fun things that people have found are cash or suitcases,” weller said. over decades, these and millions of bizarre objects of all materials and sizes, have found their way into the ocean where currents sweep them away to gyres or to other countries. a shipping accident known as “the great lego spill of 1997” released nearly 5 million nautically shaped legos off the coast of cornwall, england that still appear throughout the english channel, celtic sea, and north sea today.

using trash to track ocean currents

sometimes identifiable pieces of ocean trash can serve as useful pinpoints to help oceanographers study ocean currents. for example, shigeru fujieda, ph.d., a professor and researcher at kagoshima university in japan, proposed that cigarette lighters can also aid in tracking ocean currents.

when found by someone, each lighter has printed information about the sale address or phone number of the country of origin. contact information has also been key in carmack’s the drift bottle project where students and volunteers threw empty watertight glass bottles with contact information of the research project from up and down the west coast of the americas from alaska down to the panama canal, among some other locations.

a plethora of bottles have been dropped off in these areas and while many are still oceangoing, 1 in every 25 bottles have been recovered in places like brazil, norway, and on kodiak island, alaska.

like this project, my father, stephen carman was about 50 miles out of the coast of cape hatteras in north carolina when he threw a message in a bottle into the gulf stream. about 5 months and 650 miles later, the same bottle was mailed back by a prisoner cleaning the beaches of bermuda.

what can be done?

“i kind of describe (ocean debris) more as like, the more you peel back the layers of it, the more complex it becomes. because you think, ‘why don’t we just go and clean it all up?'” weller said. due to the scale of the problem and the complexity of ocean currents, we can’t fully rid our oceans of trash. but participating in beach cleanups in a community does bring about positive changes. you may even come across a lego or personal note.

seventy percent of earth’s surface  hasn’t been fully mapped out yet meaning there is likely more garbage in those areas. approximately 33 billion pounds of plastic enter our oceans each year, and it’s expected to triple by 2040.

the trash free seas alliance, save our seas 2.0 act, and the trash free waters program are just three organizational and governmental initiatives that support this worldwide issue. the drift bottle project, other people’s attempts at it, and the accidental spills of objects bring us one step closer to understanding the world’s currents and why it’s distressing to find a plastic bottle with an asian brand on it on the shores of costa rica. when coming across trash on a beach, many may not consider its nautical path, but each unsolicited piece of debris like this bottle has a story of where it came from like ours.