How drift bottles and rubber ducks unravelled the mysteries of ocean currents.
Created in plastic toy factories in China, loaded onto a container ship in Hong Kong and toppling overboard in the North Pacific Ocean, close to 29,000 plastic bath toys became both ocean travellers and Internet sensations. How these ducks, beavers, turtles and frogs, designed for nothing more than a quick trip around the bathtub, ended up floating around the world is quite extraordinary. Even more extraordinary is what they taught scientists about ocean currents and the fate of objects at sea.
If we backtrack a little, we’ll find that human beings have been exploring the ocean for millennia. One of the first seagoing voyages was undertaken by the people who would later become Aborigines, as they made their way to Australia for the first time, some 40–60 thousand years ago. These pioneering sea goers really were just setting the trend for the rest of humanity. All across the globe mankind began going to sea. Between two and four thousand years ago Polynesians migrated to many islands of the Pacific. These seafarers often relied on detailed local knowledge and, with no written language, information on local currents, wind and wave patterns were passed on orally.
Research on ocean currents has been going on for at least fifteen hundred years. We’ve all heard of the good old message-in-a-bottle, used by those stranded on desert islands. Well, Greek philosopher Theophrastus utilised these bottles way before they became popular. Back in AD 310 he tried to prove that the water of the Mediterranean had actually travelled all the way from the Atlantic. However, it’s unclear whether Theophrastus’ experiment was successful or whether the bottles were simply lost at sea.
Potentially one of the first oceanographers, Theophrastus was part of an enormous scientific field that would continue to this day. The term oceanography comes from two Greek words: Oceanus, the son of two Titan gods and the father of the sea nymphs, and graphia, which refers to recording and describing. Oceanography is the study of the sea, and oceanographers examine all aspects of the ocean.
Looking at ocean currents is part of oceanography. Ocean currents are bodies of continuously moving seawater, driven by wind, water density, and tide. They can span thousands of kilometres and have large effects on the ecosystems they encounter by moving food, larvae, and animals around the great ocean basins. The Gulf Stream is an example of one of the world’s largest currents. A part of the northern Atlantic gyre, it was discovered in 1513 by Spanish explorer Juan Ponce de Leon. Spanish ships used it as they travelled from the Caribbean to Spain. Benjamin Franklin charted it in 1786. Similar to Theophrastus, Franklin used drift bottles to figure out the approximate size and location of the Gulf Stream and this further increased its usage.
In 1906, another oceanographer, George Parker Bidder, used a drift bottle technique to study the currents of the North Sea. He enclosed a postcard in each of more than 1000 bottles and threw these bottles into the ocean. This postcard promised a shilling to any person who safely returned it to the Marine Biological Association in the UK.
Since then, the understanding of ocean currents has expanded, often relying on a combination of unconventional methods and citizen science. When objects fall overboard, oceanographers can track them and, over the years, anything from Nike shoes to glass ball floats to hockey gloves have been used.
In January 1992, a container ship was making its way from Hong Kong to America when it ran into a storm and one of its containers fell overboard. The content, including nearly 29,000 coloured bath toys, was set adrift in the Pacific. Being brightly coloured, floatable and made from the almost everlasting material that is plastic, these bath toys became ideal objects to track throughout the world’s ocean. They weren’t just the popular yellow rubber duckies, but also red beavers, blue turtles and green frogs. These plastic toys taught oceanographers a thing or two about the North Pacific subtropical gyre whilst, ironically, alerting them to the dangers of plastic pollution.
Beachcombers around the world began finding these toys washed up amongst the flotsam and jetsam of the tides. They were easy to identify given their recognisable shapes and the words, ‘the first years,’ inscribed on their side. A good portion of the bath toys became trapped in the North Pacific Subtropical Gyre. This gyre is a clockwise rotating system of ocean currents that spiral around a centre point. It is made up of four main currents, the North Pacific current, the California current, the North equatorial current and the Kuroshio Current, and is estimated to be between 7 and 9 million square miles.
There are five major ocean gyres around the world, two in the northern hemisphere and three in the southern. These gyres are formed through three major phenomen: global wind patterns, earth rotation and earth’s landmasses. Wind drags on the ocean surface, pushing the water in the direction it’s blowing. The earth’s rotation then changes or deflects this water. Due to the Coriolis effect, ocean currents in the northern hemisphere move right, to form clockwise motions, whereas those in the southern hemisphere move left, to create anticlockwise motions.
Earth’s landmasses will also have an effect on gyres but the extent of this effect will depend on how bounded they are by landmasses. For example, the continents around the northern Indian Ocean gyre constrain it and cause the gyre to be much smaller. At the other end of the spectrum the South Pacific Gyre is huge and includes hundreds of kilometres of open ocean.
It’s not just manmade objects that use these currents for moving across the planet. Marine animals, both vertebrates and invertebrates, will take advantage of these ocean highways for migration purposes — whether it’s to find good foraging areas or suitable breeding sites. The migration of thousands of cownose rays in late spring from the Yucatan Peninsula to Western Florida is a good example of this. They move in a clockwise direction, aided by the the Gulf Stream, which carries warm water north from the Caribbean. Another example is the incredible journey undertaken by juvenile European eels after they hatch in the Sargasso Sea, to the east of Bermuda. Research has found that these young eels may use magnetic fields to find the Gulf Stream, which they then hitch a ride on for some 6000 km to get back to Europe.
Six months after the friendly floatees began their incredible journey a group of enthusiastic oceanographers and beachcombers started tracking them. A website was set up by oceanographer, Curtis Ebbesmeyer, for beachcombers to report to. Over the years this immense collection of data began to yield information.
The bath toys journeyed for quite some time around the gyre, making their way to the four corners of the Pacific. Some washed up on beaches in the tropics — such as Australia, Indonesia and Hawaii — and some headed north, to Alaska and Japan. Using an ocean current simulator, oceanographers were able to correctly predict where other bath toys would wash up. After taking roughly three years to circle the gyre, a portion managed to escape to the Bering Strait, became frozen in the Arctic Ice and then washed up on the shores of the eastern US states and the UK.
These friendly floatees gave oceanographers an understanding of how long water took to do a full circuit of the North Pacific Subtropical Gyre — around three years. This information is important as ocean currents have large effects on our daily lives - from our climate to our ecosystems to the seafood we eat. Understanding how these ocean highways work give scientists an indication of the effects climate change could have, both on the currents and on the organisms they move. There are still believed to be around 2000 friendly floatees left in the ocean and they continue to circle the gyre, having gone round half a dozen times already. The information can also aid with the design of marine protected areas. Ocean currents often disperse fish, eggs and larvae thousands of kilometres from the place of hatching. Understanding the strength and speed of these currents will allow marine biologists to pinpoint where these organisms go, and which areas need to be protected. Finally, this information could be useful for search and rescue operations trying to recover people, or objects, lost at sea.
However, on the flip side of this useful information, these friendly floatees also came with a warning. Two decades after going overboard the bath toys were still washing up in Alaska and were still recognisable. This taught oceanographers a thing or two about the longevity of plastic. A survey, conducted in 2014 by the World Shipping Council, estimated that between 2011 and 2013, 2683 shipping containers were lost overboard every year. Furthermore, around 8 million tonnes of plastic entered the ocean in 2010 alone, made of a material that never truly breaks down. Plastic has now been circling the oceans for centuries and all of it is still somewhere - whether in the form of microplastics, bobbing around the ocean gyres or washed up on some distant beach.
We’ve all seen the photos of straws being extracted from turtles’ noses or whales washing up on the beach with their stomach’s lined with bags, but most of the plastic in the earth’s oceans are unrecognisable — a mixture of chemical waste and microplastics. Convergence zones, often found in the middle of gyres, are perfect areas for accumulating this soupy waste. There are garbage patches in the Indian ocean and the Atlantic ocean but with the Great Pacific Garbage Patch being the biggest, this is the one people tend to talk about. At the size of Western Europe this garbage patch is the world’s largest landfill and most of its garbage is tiny, almost invisible. Although plastic ducks and beavers may tell stories of ocean currents, the breakdown of these objects tell a more foreboding tale. These microplastics can sneak into the food chain of fish, seabirds and marine mammals and, if that’s where they’re going, then they can quite easily end up on our own plate.
Marine rubbish isn’t going anywhere and nothing said this more clearly than in 2015, when a message-in-a-bottle, discovered on an island north of Germany, was declared the oldest one ever found. The woman who found it read the postcard enclosed and, as requested, mailed it back to the Marine Biological Association in the UK. In return, she received the promised shilling. The bottle had been in the ocean for over 108 years, one of the thousand deposited into the North Sea by George Parker Bidder in 1906. As for the friendly floatees, well, they’re now fetching as much as $1000 at auction. So keep your eyes peeled next time you head to the beach, because you never know what you might find.
Edited by Diana Crow