Giant garbage patches help redefine ocean boundaries

Sep 02, 2014
This map shows how researchers from UNSW divided the entire ocean into seven regions whose waters mix very little. The map could yield insights into the formation of giant ocean garbage patches, as well as ocean ecology. Credit: Gary Froyland, Robyn M. Stuart, and Erik van Sebille/UNSW

The Great Pacific Garbage Patch is an area of environmental concern between Hawaii and California where the ocean surface is marred by scattered pieces of plastic, which outweigh plankton in that part of the ocean and pose risks to fish, turtles and birds that eat the trash. Scientists believe the garbage patch is but one of at least five, each located in the center of large, circular ocean currents called gyres that suck in and trap floating debris.

Researchers from the University of New South Wales (UNSW), in Sydney, Australia, have created a that could help determine who's to blame for each garbage patch – a difficult task for a system as complex and massive as the . The researchers describe the model in a paper published in the journal Chaos.

"In some cases, you can have a country far away from a that's unexpectedly contributing directly to the patch," said Gary Froyland, a mathematician at UNSW. For example, the ocean debris from Madagascar and Mozambique would most likely flow into the south Atlantic, even though the two countries' coastlines border the Indian Ocean.

The new model could also help determine how quickly garbage leaks from one patch into another, said Erik van Sebille, an oceanographer who collaborated with Froyland on the Chaos paper. "We can use the new model to explore, for example, how quickly trash from Australia ends up in the north Pacific."

At the heart of the researchers' work on the origins and fate of floating rubbish lies a bigger question – how well do the ocean's surface waters mix?

The anatomy of ocean currents

Fast-moving form due to winds, differences in water temperatures, salinity gradients across the globe, and the forces caused by the spinning Earth. Currents stir ocean waters, but they also serve as barriers that minimize mixing between different ocean regions, much like the blast of fast-moving air at the entrance of an air-conditioned store keeps the cold inside air from mixing with the warm outside air.

Froyland, van Sebille and their UNSW colleague, Robyn Stuart, divided the entire ocean into seven regions whose waters mix very little. Their approach borrowed mathematical methods from a field known as ergodic theory, which has been used to partition interconnected systems like the internet, computer chips and human society, and the new analysis revealed the underlying structure of the ocean without getting bogged down in complex simulations.

"Instead of using a supercomputer to move zillions of water particles around on the , we have built a compact network model that captures the essentials of how the different parts of the ocean are connected," said Froyland.

According to the new model, parts of the Pacific and Indian oceans are actually most closely coupled to the south Atlantic, while another sliver of the Indian Ocean really belongs in the south Pacific.

"The take-home message from our work is that we have redefined the borders of the ocean basins according to how the water moves," said van Sebille. The geography of the new basins could yield insights into ocean ecology in addition to helping track ocean debris. The researchers say their modeling technique could also be applied on a smaller scale – determining for example how much Canadian and American waters mix in the Great Lakes or how an oil spill might spread in the Gulf of Mexico.

Explore further: Climate change does not cause extreme winters, new study shows

More information: "How well-connected is the surface of the global ocean?" by Gary Froyland, Robyn M. Stuart, and Erik van Sebille, Chaos: An Interdisciplinary Journal of Nonlinear Science, September 2, 2014. DOI: 10.1063/1.4892530

add to favorites email to friend print save as pdf

Related Stories

Our plastics will pollute oceans for hundreds of years

Jan 09, 2013

(—Australia's plastic garbage has made its way into every ocean in the world. New research shows that it doesn't matter where in the world plastic garbage enters the ocean, it can end up in any ...

Fukushima radioactive plume to reach US in three years

Aug 28, 2013

The radioactive ocean plume from the 2011 Fukushima nuclear plant disaster will reach the shores of the US within three years from the date of the incident but is likely to be harmless according to new paper ...

How the Pacific Ocean leaks (w /Video)

Apr 17, 2012

A state-of-the-art ocean model has been used in a new study to conduct the first detailed investigation of oceanic water flow between the Pacific and Indian Oceans via the south of Australia. 

Recommended for you

Image: Aral Sea from orbit

Mar 27, 2015

This multitemporal Sentinel-1A radar image shows the Aral Sea, located on the border between Kazakhstan and Uzbekistan in Central Asia.

IceBridge overflies Norwegian camp on drifting sea ice

Mar 27, 2015

Studying sea ice in the Fram Strait, a passage between Greenland and Svalbard that is the main gateway for Arctic sea ice into the open ocean, is not easy. In this area, not only does ice flow southward quickly ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.