26 March 2013

Despite the fact that plastic has existed for just over a century, the threat and seriousness of plastic debris to the marine environment has long been ignored.

A new paper titled Origin dynamics, and evolution of ocean garbage patches from observed surface drifters, released by the ARC Centre of Excellence for Climate System Science, reveals for the first time how ocean garbage patches–some equivalent to the size of NSW–are connected.

As plastic debris is generally lighter than seawater, it floats and accumulates in the regions of the strongest convergence near the surface. The research examines how the winds that set up the ocean currents known as gyres mix garbage into different regions; how ‘leaky’ the garbage patches are; and how they will evolve over the coming centuries.

“There are five known garbage patches, one in each of the subtropical oceans between the continents and some contain so much plastic that if you were to drag a net through these areas you would pull up more plastic than biomass,” said Dr Erik van Sebille, lead author of the paper and Associate Investigator at the Centre.

In fact, the five subtropical gyres known as the ‘deserts of the ocean’ contain water that has been at the surface for a long time, so the nutrients needed to support marine life are almost non-existent. The same currents that move the nutrient-depleted waters toward the centres of the gyres also create the garbage patches. These gyres are essentially the ‘black holes’ of the ocean.

To determine how garbage finds its way to these plastic islands, the researchers used observational data gathered from the Global Drifter Program (GDP), which uses global drifter buoys. Each buoy, which has a battery life of up to five years, sends out a message every six hours on its location, temperature and conditions.

“In the recent study we purposefully disregarded the effects on coastal areas, as we needed to collect and analyse global data before we could even begin to understand how that translated to coastal regions,” Dr van Sebille said.

In 2012, Dr van Sebille received an ARC Discovery Early Career Researcher Award (DECRA) to focus his research on the ocean currents around Australia. In the next stage of his research, he wants to model the pathways of marine debris closer to the coast.

“We are now focused on discovering how plastic gets onto our beaches and how the currents and winds within the shelf region affect the Australian coastline. As we gather dedicated scientific data on all of the unknown variables, we will be able to understand how debris will affect our marine life and other eco-systems in decades to millennia.

“To achieve this we need a ‘fleet’ of drifter buoys to be released around Australia so we can begin to model and assess future risks to the coastal

eco-system. Only then, will we be able to evaluate the impact on our beaches.”“Knowing how fast coastal debris reaches the different garbage patches as well as how leaky these patches are can help with monitoring efforts over the coming decades. 

For more information please email Dr Erik van Sebilleat the ARC Centre of Excellence for Climate System Science.

A presentation of this research is also available on Youtube.