Page 453 - Environment: The Science Behind the Stories

the SCIeNCe behINd the StORy

predicting the In 2008, Maximenko partnered
Oceans’ “Garbage with Peter Niiler of the Scripps Institu-
tion of Oceanography to use data from
patches” the Global Drifter program to produce
a more detailed map of surface ocean
In 1997, while sailing across a little- currents. The team combined data on
traveled portion of the Pacific Ocean as drifter movements with satellite altim-
he returned from a recreational yacht etry and wind currents, producing a
race, Captain Charles Moore encoun- highly detailed map of both geostrophic
tered a huge floating mass of debris and Ekman currents. As the issue of
he described as a “soupy” collection of oceanic plastic pollution gained atten-
items including tires, plastics, chemi- tion, Maximenko saw an opportunity to
cal drums, coat hangers, fishing nets, utilize his map to predict the areas of
and other items. This was the first the ocean where floating debris is likely
recorded visual confirmation of what is nikolai Maximenko, international Pacific to accumulate. To do this, he partnered
now called the “Great Pacific Garbage research center at the university of with his colleague, Jan Hafner, and cre-
Patch” and brought firmly into the hawaii at Manoa ated a computer model that predicted
public eye the issue of plastic pollution the movements of drifters over long
in the oceans. Knowing where floating mine patterns in ocean currents. Each time periods in the world’s oceans. He
debris will accumulate in the oceans buoy (Figure 1) is composed of a 30- to then ran a simulation in which he uni-
is important to marine biologists and 40-cm (11.8–15.7 in.) floating drifter, formly distributed drifters in the oceans
oceanographers, but short of stum- which contains sensors for detecting and saw where drifters concentrated
bling upon these areas in the ocean, as ocean temperature, salinity, and other over time.
Captain Moore did, is there any way to properties, as well as a transmitter The simulation’s results, published
know where to look for them? Thanks to send its information to satellites over- in 2012 in Marine Pollution Bulletin,
to the work of Nikolai Maximenko and head. The drifter is tethered to a type revealed that oceanic debris was likely to
his collaborators, the answer is yes. of anchor, called a subsurface drogue, accumulate in portions of five subtropical
Maximenko, a senior researcher of which hangs at a depth of gyres (Figure 2), including the area of
the International Pacific Research Center 15 m (49.2 ft). The drogue keeps the Great Pacific Garbage Patch. The
at the University of Hawaii at Manoa, the drifter upright on the surface and simulation also revealed that 70% of the
studies the movements of currents in provides an underwater “sail” for cur- drifters remained at sea after 10 years,
the oceans. In particular, his work exam- rents to push. Drifters typically operate showing the lengthy life span of floating
ines Ekman drift, wind-driven currents in for about 400 days before they stop debris in the oceans. One of the model’s
the water’s upper layers first modeled by transmitting, and the program aims to predictions, which were first released in
scientist Walfrid Ekman in the early 20th maintain an array of 1250 drifters at any 2008, was verified when a 2010 study
century. Although the ocean currents given time in the world’s oceans. found high concentrations of plastic in
that are driven by pressure gradients
and the Coriolis force (collectively called
geostrophic currents) are fairly well Figure 1 A researcher
described, the movements associated prepares to deploy a buoy
with Ekman currents are not. This lack for the global drifter
of information hinders researchers’ abil- Program. The cylindrical
ity to predict smaller-scale movements sea anchor (or drogue)
of floating material in the oceans—such extends vertically in
as plastics and other debris. the water column after
Data gathered by the Global deployment and is pushed
Drifter Program of the U.S. National along by shallow ocean
Oceanic and Atmospheric Administra- currents.
tion (NOAA) is helping scientists better
understand these currents. Since 1979,
the program has deployed more than
12,000 buoys in the world’s oceans
and tracked their movements to deter-

452

M16_WITH7428_05_SE_C16.indd 452 12/12/14 3:06 PM