By Curtis C. Ebbesmeyer
Using flotsam to study ocean currents
Beachcombers, scientists and reporters ask if flotsam contributes to the understanding of ocean surface currents. Amongst beached debris — plastic bottles, fishing nets, tires, sea-beans, volcanic pumice, sneakers, gloves, toys, light sticks, rope, beer cans, logs, medical waste, lighters, cigarette butts — lie drifters telling from whence they floated. To messages in bottles (MIBs), add traceable debris from container spills, license tags from lobster pots, and flotsam from myriad other sources.
Much can be learned from this accidental oceanography. Of the hundred million cargo containers shipped overseas annually, several thousand fall overboard. Each container may hold 10,000 sneakers. Until the incident in 1990 in which 80,000 Nike sneakers fell overboard in the mid-North Pacific Ocean, I employed two instruments for learning where surface currents transported drifters: 1) satellite-tracked drifters which transmitted positions daily over intervals of months to a few years; and 2) MIBs which requested beachcombers to report where and when they stranded.
The great sneaker spill revealed another tool. Each Nike shoe carries a code as traceable as a MIB. The code 90 04 06 indicated that Nike Company ordered the 1990 sneakers in April (04) for delivery during June (06). Media and beachcomber reporting provided data regarding where and when 2.5% of the lost sneakers washed up, a percentage matching the 2.8% of the 19,449 MIBs released during 1956-1959 upstream of the sneaker spill.
Unmarked container flotsam may also provide instruments. On January 10, 1992, 28,800 plastic tub toys — turtles, ducks, beavers, and frogs— fell overboard in the mid-Pacific upcurrent of the sneaker spill. Amongst the myriad toys adrift, these four critters which were designed by child psychologist T. Barry Brazelton and manufactured by The First Years, Inc. are unique in Charlotte Lee’s Guinness Book of World Records collection o f 1,900 toy ducks.
The number of toys reported totaled about 3.3% of those spilled. Though the toys carried no traceable ID, I received as many reports as if they had. I tracked the tub toys for 14 years, knowing as much about where the toys drifted as if the same number of MIBs had been released.
Traceable flotsam provides the times and positions of the release and recovery points. In the 1800s, these data were pioneering, but the main question we ask today is, can the data garnered from drifters contribute anything of value to modern oceanography?
A comparable answer comes from many drifters for which we know the time and location on both sides of the ocean. Those that strand for a time scatter the elapsed times, whereas those that remain adrift cluster around a mean value within narrow statistical confidence limits. Flotsam contributes to oceanography through the statistics of large numbers.
Point measurements of currents circumscribe the ocean’s global conveyor belts, but do drifters actually go all the way around them? Multiple lines of evidence suggest so. Recently, three colleagues and I focused on a segment of a conveyor belt — the North Pacific Sub arctic Gyre — using the tub toys, infant sandals, pumice, MIBs, computer drifters, and spectra of water properties. We combined flotsam with water properties because we consider the ocean to be comprised of discrete slabs of water, each with differing temperatures and salinities produced by varying atmospheric conditions. Drifting objects and spectra yielded means and standard deviations, which were not statistically different at the 95% confidence level. The combined data indicate that within a nine percent uncertainty, a drifter takes on average three years to circle 12,000 kilometers around the Subarctic Gyre.
To gather and interpret traceable flotsam, I established an international network of beachcombers known as the Beachcombers Alert (www.beachcombers.org). Forty newsletters later, the power of the Alert network became evident in the regular reporting of old drift cards and bottles, debris from container spills and crustacean tags. Each year, lobstermen set 10-20 million traps along the US and Canadian east coasts. Each trap sports a tag, and each decade some 14 million tags float free, exceeding the six million historic MIBs released worldwide during 1825-2000.
The Alert network also contributes to traditional oceanographic studies. Most were funded only for a few years after the last drifter release, leaving beachcombers with nowhere to report. During 1976-1980, for example, the National Oceanic and Atmospheric Administration (NOAA) set out tens of thousands of plastic cards in response to significant oil spills along the East Coast from Florida to Massachusetts. Years later, NOAA entrusted me to be the keeper of their drift card records. After a quarter century, reports continue trickling in, occasionally extending the cards’ endurance record. The coating of slowing-growing bryozoans attested to their decades at sea. As of 2006, NOAA’s three oldest cards drifted 28.6, 27.8 and 26.6 years 7- 9 times around the North Atlantic Subtropical Gyre.
Major blocks of ocean surface current data result from releases of more than 100,000 traceable drifters, or a Traceable Drifter Unit (TDU). A review of historical records reveals on the order of ten TDU from university and governmental organizations. Non-conventional programs include the release of beer bottles by the Guinness Brewing Company (2 TDU, 1950s), MIBs with Biblical tracts by a dozen evangelical churches (3 TDU, 1950s), and bottles full of propaganda from the Taiwanese government (1 TDU, 1980s). In present years, crustacean tags, container spills, and MIBs released by mariners annually contribute 3 TDU.
For centuries, drifters have taught us the broad sweep of ocean currents. In the 1800s, drifting derelict vessels revealed the subtropical planetary gyres in the North Pacific and Atlantic and Oceans (Brooks, 1875; Richardson, 1985). By their endurance for as long as a century, flotsam provides a tool for tracing long planetary drifts. Drifters riding the global conveyor belts, for example, require twenty years to circle the earth. We must develop networks, which remain vigilant to collect this flotsam.
Everything afloat has an important story to tell.
Gyre Planetary vortex connecting continents
Brooks, C. W., 1875. Japanese wrecks stranded and picked up adrift in the North Pacific Ocean. Proceedings of the California Academy of Sciences, 6, 50-66.