What is a Gyre and how does it create a trash vortex in the ocean?

Gyre - what are gyres?

What was the first image that came to your mind when you read the title? Was it something like the one below? A floating island of trash. Well, it’s incorrect. Oceanic garbage does not get collected in heaps like that. It gets collected in Gyres. But what is a gyre? Though it is true that marine trash is a result of the reckless dumping of waste, it is also exacerbated by a physical phenomenon that results in the formation of water bodies which are known as a gyre. We will explain this phenomenon and the issue of trash vortex in this post.

trash vortex fake image
This photograph shows debris resulting from a 9.0 magnitude earthquake that struck northern Japan in 2011 and not oceanic trash. This picture was posted by Ripley’s Believe It or Not Facebook page under the misleading title of the Great Pacific Garbage Patch.

What is a gyre?

It is imperative to understand the reason behind the formation of trash vortices in the ocean. Gyres are a big part of it. Gyres are mainly large swathes of the ocean that are constantly moving in a circular motion. This is because of three main reasons

The Coriolis effect: The rotation of the Earth has an influence on the movement of the ocean and air. In the northern hemisphere, it causes the ocean or winds to rotate in an anti-clockwise direction. In the southern hemisphere, it causes them to move in a clockwise direction. This video will give you a better visual explanation.

Air currents: These cause the top layer of the ocean bed to move.

Density: A difference in the density of the water in the ocean also causes the water to move. Water with a higher density is heavier and moves downwards. Water with lower density is lighter and rises. Density is also affected by the salinity.

Landmass: These oceanic movements are restricted by landmasses, which determine the size of the gyre. For example, the South Pacific Gyre is much larger than the northern Indian Ocean Gyre.

The movements of gyres are responsible for the exchange of water between major oceans, creating a well-balanced system of water current trajectories that are collectively termed as the Ocean Conveyor Belt. This movement of water is imperative to regulate the weather on land, salinity in the ocean and, in general, the climate of the earth.

Where are these gyres located and how are they classified?

The five main gyres spread across earth’s surface are the North and South Atlantic Gyres, the North and South Pacific Gyres and the Indian Ocean Gyre.

The five major gyres
The five major gyres

These are a mix of the three primary types of Gyres:

  • Subpolar Gyres: Found near the polar caps, these are nutrient-rich.
  • Tropical Gyres: Found near the equator. The Coriolis effect is less near the equator, so these gyres are formed mostly due to the action of the win
  • Subtropical Gyres: Most of the gyres on earth are of this category. These gyres are formed between the equator and a polar cap. These gyres are a bit different and interesting.

So how do gyres play a role in the formation of a trash vortex?

The movement of the water currents that form gyres, as we have seen above, causes that particular area of the ocean to move in a circular pattern. Take a glass of water and swirl it with a spoon. You will notice a spiral in the center. This is actually quite similar to how a gyre works. The center of a gyre is very stable. The center of a subtropical gyre os more stable than the other two types. This region of the ocean is very calm, and the water remains quite still. Consequently, these areas are classified as having lower nutrient value and sparse aquatic life.

Since the external currents of the gyre move inward towards the static center, any trash spilled into the ocean or picked up from the coasts by the waves gets deposited in these centers. This trash is broken down into small pieces due to the movement of the current and mostly consists of non-degradable materials like plastic. So the images, like the one posted above in the article, don’t accurately depict the real picture.

However, it is important to understand that the small size of the aquatic trash does not downplay the danger presented by it. Trash vortices in our oceans are an issue that needs to be addressed. There are many companies like The Ocean Cleanup Project that are actively working in this domain to make sure that our oceans remain safe and clean.

Here’s marine biologist Miriam Goldstein from the Scripps Institution explaining how the trash is actually quite small and still affects the oceanic ecosystem.

Sources and further reading :

One thought on “What is a Gyre and how does it create a trash vortex in the ocean?

  1. The information that the coriolis effect on the northern hermisphere is anti-clockwise isn’t correct.
    The coriolis effect causes a clockwise rotation on the northern hermisphere and an anti-clockwise rotation on the southern hermisphere.

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