You see, it’s a conveyor belt issue. And a never-really-goes-away kind of issue. Things don’t stay put, and your and my boundary lines on a map mean absolutely nothing in this situation. In many ways, that Spanish hospitality phrase “Mi casa es su casa” (‘my home is your home’) takes on a whole new meaning. It is pretty ugly! (Yes, I realize that that phrase is an oxymoron – an internal contradiction.)

I am talking about plastic.

Everywhere we look around us, we see plastic in splendorous colour and versatility. In many instances, we don’t even realize there is plastic in some of the goods that we use. Plastic has brought us considerable convenience … easier to pack that bisibele bhath without it leaking, to pack those books that I wanted to ship from the USA to India when I returned, and so on.

But it all comes at a terrible, terrible cost.

Your geography textbook probably has a chapter of a few pages (or may be just a section of a chapter) on ocean currents. A few badly drawn maps showing the directions of some warm currents and cool (or cold) currents, some “explanatory” text that gives you a vague idea that water is moving around in them there oceans, and that’s about it. Well, there’s more. A LOT more.

Conveyor Belt

The ocean’s waters are not still. They are constantly moving up and down, forward and sideward, and so on. It’s just like the wind currents above the surface that are always moving around, except here it is water.  Ocean currents are rather like rivers of the oceans.

Water in the oceans is moved around by winds pushing the water  … and by differences in temperature and salt content of the water. The latter is called thermo-haline (thermo – referring to temperature, haline – referring to salt) circulation. Combine all this with the relative position of Earth and sun, and you find the role that latitude plays – depending on the latitude above which the sun is directly overhead, the heating of the oceans is different at different times of the year.

Warming ocean water expands, its salt concentration decreases, this water is lighter, and therefore rises. On the other hand, cooling ocean water contracts, its salt concentration increases, this water is heavier, and therefore sinks. Remember also that the distribution of temperature and salt in the oceans is not uniform. Instead, it occurs in gradients (gradual differences). But this difference is so strong that the waters move in currents (streams) around the world.

Your textbook map shows you nice smooth lines to show which way the currents move (and a few are given names). In reality, the currents are engaged in a very complex twisting, turning movement. Overall, the currents move in the directions that your textbook maps show you.

Also remember: the land on which we live – the continents – continues under water to the edge of the tectonic plates we are on.  Thus, there are many vast mountains and valleys and other topographic features under the ocean waters, too.  So, the waters that are driven around in currents cannot just go in nice simple lines like you go PT class: in a nice single line! Rather, the movement is more like you racing out of school when the final bell of the day rings – seemingly chaotic, but there is a general direction towards the school gates.

Life belt

As the temperatures and salt concentrations vary, life forms that thrive in different parts of the oceans also vary. Different types of microscopic marine plankton thrive, attracting those organisms that feed on them, other organisms that feed on these, and so on up the food chain. It is this that causes those migrations of the magnificent whales. It is also this that causes the diversity of fish (and other marine life) that we humans catch in various places for our food. The great ocean conveyor belt is actually bringing us food!

Also, the ocean currents distribute heat energy around the planet. This makes places where we live, more livable. Hot places get some amount of cooling and cooler places get some amount of warming – they create a lot of comfort for us and we are able to live and feed ourselves because of these currents.

The ocean currents system is like our blood circulation system – regulating and re-distributing heat energy, and circulating nutrients.

Plastic bane

Most plastics do not decompose. They just break down into tinier and tinier pieces. Most of the plastics we use eventually end up in the oceans. The currents carry them to far off places and thus distribute the pollution, too.

In the ocean waters, the plastics disintegrate into tiny particles that look like plankton and get eaten up by sea animals along with the plankton. Another animal may feed on these animals and end up collecting the plastic in a large number of the first feeders. As you go up the food chain, the plastic accumulation is larger and larger. This disrupts the food chain significantly.  (Would you like to have a seafood dinner?)

The plastic that does not disintegrate (for whatever reason) ends up floating around on or near the oceans’ surface. Many marine animals, especially birds such as gulls and albatrosses, mistake these for food and swallow them. Once the plastic enters the stomach, it does not get digested; it just sits there. Over time, the stomach is so full of plastic that the bird can’t get enough food and dies.

The babies of these birds also suffer. When the adult birds feed the babies by regurgitating (vomiting!) the semi-digested food into them, the babies’ stomachs get filled with plastic and they die prematurely.

So, my throwing a plastic bag into the environment does have an impact, and it is not always only on land. And we cannot argue, “I am throwing the bag in my river, in my country, so, what’s it to you?”

Because the Great Conveyor Belt will take it around.

Things you can do:

  1. How ocean currents move around. A generalized animated model. You can see the different levels at which warm and cool currents flow and how underwater topography makes the currents move in certain directions. (1 minute 23 seconds)
  2. NASA’s “perpetual ocean” video showing the actual movements of the ocean currents in a complex dance. This animation is based on decades of satellite data collected by NASA. (10 minutes)
  3. Very powerful and interesting ABCNews report on the “great northern Pacific garbage patch” and how deadly it is. (5 min. 23 sec.)
  4. Documentary about how our addiction to plastic is affecting our environment and our lives. “Addicted to plastic” (1 hr 25 min).
  5. A very interesting interactive that lets you track where your plastic would end up 10 years from now, if you drop it anywhere in the ocean. This is a scientifically designed experiment online that you can try out. Designed by Dr Erik van Sebille, University of New South Wales, Australia.

(A version of this article appeared in the Deccan Herald Student Edition on 11 September 2014.)

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