There’s no ‘garbage patch’ in the Southern Indian Ocean, so where does all the rubbish go?


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Plastic waste on a remote beach in Sri Lanka.
Author provided

Mirjam van der Mheen, University of Western Australia; Charitha Pattiaratchi, University of Western Australia, and Erik van Sebille, Utrecht University

Great areas of our rubbish are known to form in parts of the Pacific and Atlantic oceans. But no such “garbage patch” has been found in the Southern Indian Ocean.

Our research – published recently in Journal of Geophysical Research: Oceans – looked at why that’s the case, and what happens to the rubbish that gets dumped in this particular area.

Every year, up to 15 million tonnes of plastic waste is estimated to make its way into the ocean through coastlines (about 12.5 million tonnes) and rivers (about 2.5 million tonnes). This amount is expected to double by 2025.




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Some of this waste sinks in the ocean, some is washed up on beaches, and some floats on the ocean surface, transported by currents.

The garbage patches

As plastic materials are extremely durable, floating plastic waste can travel great distances in the ocean. Some floating plastics collect in the centre of subtropical circulating currents known as gyres, between 20 to 40 degrees north and south, to create these garbage patches.

The Great Pacific Garbage Patch.
National Oceanic and Atmospheric Administration

Here, the ocean currents converge at the centre of the gyre and sink. But the floating plastic material remains at the surface, allowing it to concentrate in these regions.

The best known of these garbage patches is the Great Pacific Garbage Patch, which contains about 80,000 tonnes of plastic waste. As the National Oceanic and Atmospheric Administration points out, the “patches” are not actually clumped collections of easy-to-see debris, but concentrations of litter (mostly small pieces of floating plastic).

Similar, but smaller, patches exist in the North and South Atlantic Oceans and the South Pacific Ocean. In total, it is estimated that only 1% of all plastic waste that enters the ocean is trapped in the garbage patches. It is still a mystery what happens to the remaining 99% of plastic waste that has entered the ocean.

Rubbish in the Indian Ocean

Even less is known about what happens to plastic in the Indian Ocean, although it receives the largest input of plastic material globally.

For example, it has been estimated that up to 90% of the global riverine input of plastic waste originates from Asia. The input of plastics to the Southern Indian Ocean is mainly through Indonesia. The Australian contribution is small.

The major sources of riverine input of plastic material into the Indian Ocean.
The Ocean Cleanup, CC BY-NC-ND

The Indian Ocean has many unique characteristics compared with the other ocean basins. The most striking factor is the presence of the Asian continental landmass, which results in the absence of a northern ocean basin and generates monsoon winds.

As a result of the former, there is no gyre in the Northern Indian Ocean, and so there is no garbage patch. The latter results in reversing ocean surface currents.

The Indian and Pacific Oceans are connected through the Indonesian Archipelago, which allows for warmer, less salty water to be transported from the Pacific to the Indian via a phenomenon called the Indonesian Throughflow (see graphic, below).

Schematic currents and location of a leaky garbage patch in the southern Indian Ocean: Indonesian Throughflow (ITF), Leeuwin Current (LC), South Indian Counter Current (SICC), Agulhas Current (AC).
Author provided

This connection also results in the formation of the Leeuwin Current, a poleward (towards the South Pole) current that flows alongside Australia’s west coast.

As a result, the Southern Indian Ocean has poleward currents on both eastern and western margins of the ocean basin.

Also, the South Indian Counter Current flows eastwards across the entire width of the Southern Indian Ocean, through the centre of the subtropical gyre, from the southern tip of Madagascar to Australia.

The African continent ends at around 35 degrees south, which provides a connection between the southern Indian and Atlantic Oceans.

How to follow that rubbish

In contrast to other ocean basins, the Indian Ocean is under-sampled, with only a few measurements of plastic material available. As technology to remotely track plastics does not yet exist, we need to use indirect ways to determine the fate of plastic in the Indian Ocean.

We used information from more than 22,000 satellite-tracked surface drifting buoys that have been released all over the world’s oceans since 1979. This allowed us to simulate pathways of plastic waste globally, with an emphasis on the Indian Ocean.

Global simulated concentration of floating waste after 50 years.
Mirjam van der Mheen, Author provided

We found that unique characteristics of the Southern Indian Ocean transport floating plastics towards the ocean’s western side, where it leaks past South Africa into the South Atlantic Ocean.

Because of the Asian monsoon system, the southeast trade winds in the Southern Indian Ocean are stronger than the trade winds in the Pacific and Atlantic Oceans. These strong winds push floating plastic material further to the west in the Southern Indian Ocean than they do in the other oceans.

So the rubbish goes where?

This allows the floating plastic to leak more readily from the Southern Indian Ocean into the South Atlantic Ocean. All these factors contribute to an ill-defined garbage patch in the Southern Indian Ocean.

Simulated concentration of floating waste over 50 years in the Indian Ocean.

In the Northern Indian Ocean our simulations showed there may be an accumulation of waste in the Bay of Bengal.




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It is also likely that floating plastics will ultimately end up on beaches all around the Indian Ocean, transported by the reversing monsoon winds and currents. Which beaches will be most heavily affected is still unclear, and will probably depend on the monsoon season.

Our study shows that the atmospheric and oceanic attributes of the Indian Ocean are different to other ocean basins and that there may not be a concentrated garbage patch. Therefore the mystery of all the missing plastic is even greater in the Indian Ocean.The Conversation

Mirjam van der Mheen, PhD Candidate in Oceanography, University of Western Australia; Charitha Pattiaratchi, Professor of Coastal Oceanography, University of Western Australia, and Erik van Sebille, Associate Professor in Oceanography and Climate Change, Utrecht University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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There’s a lot of bad news in the UN Global Environment Outlook, but a sustainable future is still possible



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It’s not all doom and gloom – pathways to restore the health of our planet do exist.
wonderisland/Shutterstock

Pedro Fidelman, The University of Queensland

The Sixth Global Environment Outlook (GEO-6), the most comprehensive environmental assessment produced by the UN in five years, brought us both good and bad news.

The environment has continued to deteriorate since the first GEO-6 report in 1997, with potentially irreversible impacts if not effectively addressed. But pathways to significant change do exist, and a sustainable future is still possible.

Launched in March at the fourth session of the United Nations Environment Assembly in Nairobi, the 700-page report involved nearly 200 global experts who collaborated over 18 months.




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It covers, in detail, a range of topics, including air, biodiversity, oceans and coasts, land and freshwater, climate change, human health and energy.

And it assessed the state of the global environment, the effectiveness of policy responses, and possible pathways to achieve the environmental goals of the 2030 Agenda for Sustainable Development.

The good news

There is a fair bit of negative information in the GEO-6, which unfortunately reflects the overall state of environmental affairs globally. But it is not all doom and gloom, the GEO-6 has many positive, solution-oriented messages too.

The GEO-6 advises that pathways and approaches to systemic change exist, which must be scaled up quickly to steer the planet towards more sustainable futures.




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The considerable connections between environmental, social and economic policies can inform multiple goals. So policies addressing entire systems – such as food, energy and waste – are more likely to have beneficial impact.

For instance, reducing our use of fossil fuels leads to health benefits by decreasing outdoor air pollution responsible for premature deaths. And efforts to eliminate hunger (such as changes in agriculture production) can help address climate change, biodiversity loss, land degradation and chemical pollution.

With the window for action closing quickly, given the unprecedented rate of global environmental change, the GEO-6 is calling for more ambitious and innovative policy.

We need significant change leading us to decarbonisation, a circular economy, sustainable agriculture and food systems, and better adapting socio-economic systems to climate change.

The bad news

The GEO-6 warns the overall condition of the global environment continues to deteriorate, driven mainly by population growth, urbanisation, economic development, technological change and climate change.

Here’s what we’re dealing with:

  • air pollution currently causes an estimated 6 to 7 million premature deaths annually
  • we might be witnessing the sixth mass species extinction in the planet’s history
  • 8 million tons of plastic enters the ocean every year as a result of mismanagement of domestic waste in coastal areas
  • warming ocean waters are leading to mass mortality of coral reefs across the world’s tropics
  • 29% of all lands are degradation hotspots
  • pathogen-polluted drinking water and inadequate sanitation cause approximately 1.4 million human deaths annually, with many millions more becoming ill.

These and other issues reported in the GEO-6 will lead to ongoing and potentially irreversible impacts if they are not addressed effectively, and immediately.

Typically, environmental policy efforts are based on individual issues, like air pollution, or industry sectors. But this approach doesn’t address the complexity of contemporary environmental problems that require system-oriented efforts at large scales.

Under current policy scenarios, the environmental dimension of the Sustainable Development Goals, as well as other goals like the Paris Agreement, are unlikely to be achieved.

The GEO-6 calls for urgent, inclusive and sustained action by governments, business and society proportionate to the scale and pace of global environmental change.

What it means for Australia

In Australia, positive action is taking place at state and local levels of government, where support for more ambitious emissions targets is generally stronger than at the Australian government level.

And many sectors of society and business are shifting towards more sustainable practices. The booming uptake of rooftop solar and the development of large-scale renewable projects illustrates such a shift.

But when it comes to sustainable development policies at the national level, Australia lags behind most of the developed world, particularly in relation to energy and climate change policy.




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We don’t yet have long-term certainty for support of the uptake of electric cars, the transition to renewables, the adoption of fuel efficiency standards, and limiting emissions from the manufacturing and resources industry.

Effective strategies to curb land clearing remains to be seen, and only recently Australia has incorporated principles of circular economy into the National Waste Policy.

These do not help Australia meet its agreed commitments under the UN 2030 Agenda for Sustainable Development and associated Sustainable Development Goals.

With long-term environmental, socio-economic and political stability at stake, it is time for commitment, leadership and robust policies that can last beyond the three-year electoral cycle.The Conversation

Pedro Fidelman, Senior research fellow, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.