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Physical oceanography

Ghost ships, adorable flotsam, and measuring surface currents

The Flying Dutchman, one of the first recorded ghost ships, occupies a special place in the creepy lore of the seas. The ship made its’ first literary appearance in 1790 and has been regularly featured in stories, paintings, movies, and television. According to legend, the Dutchman was lost waiting to get into harbor off the Cape of Good Hope during a torrential storm. The doomed ship and her crew were condemned to sail the seas for the rest of eternity as punishment for a long forgotten sin. The vessel has appeared to superstitious sailors ever since as a ghostly, glowing light floating just above the horizon. “Fast gliding along, a gloomy bark / Her sails are full, though the wind is still, / And there blows not a breath her sails to fill” — a portent of doom to mariners the world over (poetry from Thomas Moore, 1804).

mary_celeste_as_amazon_in_1861

Figure 1 – Painting of the Mary Celeste c. 1861 (image in the public domain)

Ghost ships, however, are not limited to the realm of the supernatural. Real life ghost ships regularly float the worlds’ oceans and can be just as spooky as their paranormal cousins. The Mary Celeste is one particularly famous and mysterious example (Fig. 1). The ship was discovered afloat off the coast of Portugal in 1872, totally intact, well provisioned, and completely empty. The missing crew of the Mary Celeste was never found, prompting allegations of foul play and countless conspiracy theories. The disappearance of the crew was never fully explained and the ship’s name has become synonymous with unexplained desertion.

The reality (le sigh) is that the majority of derelict ships end up adrift for more ordinary reasons: broken towlines, snapped moorings, and premature abandonment after sustaining damage. Without anyone at the helm, ghost ships wander the seas at the mercy of surface currents and wind. Amazingly, some of these unmanned vessels are rediscovered thousands of miles from their last known location.

The fact that a modern tanker can simply disappear into the great blue yonder is mind-boggling. But, while these vessels are large (some are more than 1000 feet long), they are but a speck on the ocean surface. Without detailed knowledge of surface currents and local wind patterns, it is very difficult to predict where ghost ships may go.

Oceanographers are constantly trying to improve their understanding of how water moves in the ocean. They may use freely floating objects like ghost ships to try to assess how well their models are working. Scientists call such floats by the far less scary terms “passive tracer” or “Lagrangian drifter.” Both are fancy ways of talking about stuff that floats around the ocean without means to propel itself.

Since ghost ships appear rarely and are prone to sinking, oceanographers will instead put hundreds of passive drifters into the water. Researchers will then track the floats and compare their final locations to model results. Dumping more tracers in the ocean would enhance the community’s understanding of currents and physical effects like wind. But scientific drifters are expensive and, due to low recovery rates, often single use. Occasionally, however, scientists get a unique opportunity to see what happens to tens of thousands of drifters.

duckies_toys

Figure 2 – The Friendly Floatees. Below the meter stick are the toys fresh out of the package. Above the stick are some of the drifters found on beaches in Alaska. Notice how the yellow ducks and red beavers are sunbleached after their long journey. (Courtesy of Curtis Ebbesmeyer via Beachcombers’ Alert)

The Friendly Floatees are about the cutest scientific instrument you can dream up. Probably because they were originally intended as bath toys for small children. In 1992, a shipping container of 29000 plastic ducks, beavers, turtles, and frogs was ripped off the deck of a tanker during a storm. The container opened and released a swarm of tiny drifters. The Floatees were released near the international dateline, the imaginary line where the calendar day changes in the Pacific, and began their journey to parts unknown.

Curtis Ebbesmeyer, then an oceanographer at the University of Washington, quickly recognized the unique opportunity presented by the little plastic critters. He spent his career analyzing the movements of flotsam, the floating wreckage of a ship or its cargo, and predicting ocean currents with models. The huge pulse of intrepid rubber ducky explorers was a spectacular data set waiting to be collected.

Ebbesmeyer and his colleague Jim Ingraham quickly ran the Ocean Surface Current Simulations (OSCURS) model to predict where the duckies might go. The OSCURS output showed that the Floatees could end up all over the Pacific basin: Hawaii, Alaska, Australia, Indonesia, and Chile were potential destinations. The model even predicted that some of the toys would end up in the Artic, get frozen in sea ice, and end up in the Atlantic.

Ebbesmeyer sought to validate the model by tapping into his vast network of beachcombers, asking them to collect the toys and report where they were found. The citizen scientists were happy to oblige, eagerly reporting their findings. In fact, Ebbesmeyer got word of Friendly Floatee discoveries for more than a decade!

The rubber duckies are now part of a record of flotsam that has helped oceanographers refine their models of surface currents. But there is still a lot to learn. Remember that ghost ships are often lost for years at a time or never recovered. The development of better models will assist in studies of marine debris, enhance climate models, and aid in searches for shipwrecks and survivors.

But let’s not lose sight of what is important here: how awesome a Friendly Floatee Halloween costume would be! Dress up like a barnacly rubber ducky and enthrall your friends with tales of adventures on the high seas. You can talk about your encounter with the Flying Dutchman

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