Tag Archives: gyre

New model predicts how plastic travels across ocean garbage patches

The impact on human health from ocean garbage is not yet fully known. (Credit: Pixabay)

Every year, approximately eight million tons of plastic find their way to our oceans. The Great Pacific Garbage Patch, a collection of marine debris in the North Pacific, is the poster child of this haphazard waste disposal byproduct. You may have heard it called the Pacific trash vortex. It is comprised of Western Garbage Patch, located near Japan, and the Eastern Garbage Patch, located between the U.S. states of Hawaii and California. The litter spans from the American west coast all the way to Japan. But one may wonder…how did it get there exactly?

Researchers in the U.S. and Germany decided to find out. In a new study published in the journal Chaos, they created a Markov chain model of the oceans’ surface dynamics from historical trajectories of surface buoys. Their model describes the probability of plastic debris being transported from one region of ocean surface to another.

“Surface debris is released from the coast and distributed according to their location’s share of the global land-based plastic waste entering the ocean,” said Philippe Miron, an assistant scientist at the University of Miami and a co-author of the study. “To observe the long-term distribution of floating debris, beached debris is reinjected into the system following the same distribution. We call this model ‘pollution aware,’ because it models the injection, dispersion, and recirculation of debris within the system.”

Their work focused on areas from the coasts to the subtropical gyres — or rotating ocean currents — to try and identify pathways or transition paths that connected the trash sources directly to the areas of the Pacific harboring the waste. It is actually possible to sail through these garbage patches seeing very little, or even no, evidence of this trash.

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The garbage patches of the Pacific are the most famous examples of ocean litter. (Credit: NOAA)

Wind, tides, and differences in temperature and salinity drive ocean currents. The ocean will churn up the different types of currents like eddies, whirlpools or deep ocean currents. Larger, more sustained currents, such as the Gulf Stream located in the Atlantic, go by proper names. Taken together, these larger and more permanent currents make up the systems of currents known as gyres.

There are five major gyres: the North and South Pacific Subtropical Gyres, the North and South Atlantic Subtropical Gyres, and the Indian Ocean Subtropical Gyre.

In some instances, the term “gyre” is used to refer to the collections of plastic waste and other debris which can be found in higher concentrations of certain parts of the ocean. While this use of the term is increasingly common, the name traditionally refers simply to large, rotating ocean currents.

The researchers inferred these debris pathways and searched for garbage patch stability by quantifying the connection between them and their ability to retain the litter. What they found was that generally the gyres they studied were weekly connected or even disconnected altogether.

“We identified a high-probability transition channel connecting the Great Pacific Garbage Patch with the coasts of eastern Asia, which suggests an important source of plastic pollution there,” said Miron. “And the weakness of the Indian Ocean gyre as a plastic debris trap is consistent with transition paths not converging within the gyre…Indeed, in the event of anomalously intense winds, a subtropical gyre is more likely to export garbage toward the coastlines than into another gyre.”

One of the biggest discoveries the group made is while the North Pacific subtropical gyre will attract the most debris, the South Pacific gyre actually stands out as the most enduring, because debris has fewer pathways out and into other gyres.

“Our results, including prospects for garbage patches yet to be directly or robustly observed, namely in the Gulf of Guinea and in the Bay of Bengal, have implications for ocean cleanup activities,” said Miron. “The reactive pollution routes we found provide targets — aside from the great garbage patches themselves — for those cleanup efforts.”

Asian dust fertilizes the ocean with life-supporting nutrients

The vast oceanic gyres (large systems of rotating currents) are thought to be stable and barren. Caused by the Coriolis effect produced by the Earth’s rotation, they cover around a third of the Earth’s surface. They’re also regarded biological deserts, with stratified, nutrient-poor water that just doesn’t favor a thriving ecosystem.

But there’s an exception.

The North Pacific Subtropical Gyre ecosystem features an anomaly which has puzzled oceanographers for years: it changes its chemistry with no clear cause. The new study focused on the North Pacific Subtropical Gyre, using three decades of observation data from Station ALOHA by the Hawaii Ocean Time-series program to characterize this surprising area.

The five major ocean-wide gyres — the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres.

Generally speaking, the more mixing takes place in an oceanic environment, the better it is for life. Sunlight passes through the surface parts of the water column, allowing photosynthetic creatures to do their thing, while nutrient-rich layers from the bottom of the sea are brought to the surface as a fertilizer. In the North Pacific gyre, however, that’s not really the case.

The water is strongly stratified because there’s no real mixing taking place. This means that without deeper murky waters brought in the mix, the surface water is exceptionally clear, supporting photosynthetic activity below 100 meters (or 328 feet). But in order for marine life to thrive, it would need elements such as phosphorous and iron, which are lacking in the area.

Or so we thought.

Over the course of three decades, researchers noticed a surprising variation in the chemistry of these waters, as if something was fertilizing them with phosphorous and iron. They traced the source back to Asian dust, coming from small desert particles, forest fires, and even factory output. These particles are carried over large distances by strong winds, ultimately spreading around the gyre and providing nutrients necessary to sustain life.

The supply of nutrients is a fundamental regulator of oceanic wildlife (and carbon sequestration). These ecosystems are governed by nutrient sources and nutrient sinks, and any change in these parameters could have cascading effects on biodiversity. Researchers were surprised to see just how much of an impact the Asian dust has, and how dynamic and unpredictable its input is.

“We now know that these areas that were thought to be barren and stable are actually quite dynamic,” said Ricardo Letelier, an Oregon State University biogeochemist and ecologist, who in collaboration with David Karl at the University of Hawaii led this study. “Since these areas cover so much of the Earth’s surface, we need to know more about how they work in order to better predict how the system will respond to climate variations in the future.”

Asian dust is transported over the North Pacific Ocean. Image credits: NASA.

This pattern isn’t regular, researchers stress, and it’s not exactly clear how the ecosystem copes with this irregularity.

“Sometimes there are periods of 5-6 years of phosphorus enrichment, and then there are periods when it switches over,” Letelier said. “From 2000 to 2007, there was almost no phosphorus. We have seen some changes in the function of the ecosystem, but we haven’t yet seen significant changes in the biological composition. They may be coming; it’s too early to tell.”

There’s another creeping issue affecting this process: human influence. Rising temperatures (which are especially prevalent in the Arctic) mean that global wind circulation will also change, with consequences that are as of now unforeseen. Additionally, pollution is also an unpredictable factor in the mix. How these aspects will affect the transport of iron- and phosphorous-rich dust from Asia to the Pacific remains a question to be answered by further research.

The study has been published in PNAS.

Just in case you didn’t know, there’s a garbage island twice as big as France in the Pacific Ocean

I was surprised to talk to a bunch of people today and find out they didn’t know about this, so I figured this is definitely something worth knowing. Here’s the deal.

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There’s a whole lot of garbage floating around; a whole lot ! Some are above the surface, some are below. What happens is they get sucked in by oceanic currents, and tangle up with other garbage (mostly plastic). But you shouldn’t think only about bottles and such; most of the times, the plastic particles are hard to see even from a boat, but that doesn’t make them any less dangerous – on the contrary. It’s been proved that albatross and other sea creatures ingest way more plastic this way. The total amount of ‘plastic soup’ is hard to quantify, varying from twice the size of Texas (or France) to twice the size of the USA. It’s also expanding – fast. Stretching from Hawaii to Japan the biggest such patch is estimated to weigh around 100 million tons, according to American oceanographer Charles Moore, who also explains:

“The original idea that people had was that it was an island of plastic garbage that you could almost walk on. It is not quite like that. It is almost like a plastic soup. It is endless for an area that is maybe twice the size as continental United States.”

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There’s also a missconception that it has well defined borders, like an island. There’s just a gradient of particle density, with most particles being as big as 1-3 mm. According to wikipedia, 80% is a result of terrestrial pollution, and the 20% left comes from ships. As you probably guessed, any effort towards cleaning the area is not going to happen any time soon, as it would require massive efforts and collaborations, and an estimated (very rough) cost of 10 billion dollars. No nation has made a step forward in taking responsability, and I can’t see anyone doing this in the near future.

“At this point, cleaning it up isn’t an option. It’s just going to get bigger as our reliance on plastics continues. … The long-term solution is to stop producing as much plastic products at home and change our consumption habits.”, said Chris Parry, public education program manager with the California Coastal Commission in San Francisco.

The effects are hard to estimate, varying from extremely harmful to catastrophic. Without even taking into consideration the long term effects and what will happen when it becomes even bigger (which quite frankly, won’t take that long if things continue to move the way they have), the short and medium term effects are devastating. Marine animals and birds ingest plastic which just doesn’t go away from their stomach. Eventually, it starts filling it up, and if it’s not toxic, and kills them, it fills their stomach and basically causes the animals to starve to death – a quite painful and tragic death. It can be harmful even for humans because we too eat the animals which ingest the plastic.

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In case you’re wondering, no, I don’t think there’s anything you can do to help clean the patch up (even if you wanted to). But you can limit it’s ever growing size, as well as the size of land garbage. Just do the basic stuff:

– Limit your use of plastic whenever possible. Take your canvas bags to the supermarket or just don’t take plastic bags whenever possible.

– Throw your garbage where it should belong; don’t leave it on the beach or on the street or whatever.

– Tell other people. Make it spread. Many people don’t care about this at all; but many do, and they just need a small push to act. Be that push !