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Promise in Plankton: The Earth’s Essential Oxygen Emitter

Updated: Jul 4, 2021

Kate Byng-Hall sheds light on one of the planet’s most important but often overlooked organisms.

Photo by Benjamin Sow

We all know that oxygen is essential to support life on this planet, but the biggest contributor of oxygen to our atmosphere is largely overlooked. Where rainforests are responsible for providing 28% of our oxygen, 70% actually comes from the ocean through marine plants, such as kelp, and phytoplankton – in fact, plankton produce 50% of the Earth’s oxygen supply.

Its name derived from the Greek phyto (plant) and planktos (drifter), phytoplankton are microscopic organisms that live in both salt and fresh water. Some plankton are bacteria and some are protists (single-celled organisms), but most are single-celled plants such as kinds of algae. Although small, these organisms are absolutely invaluable to life both in the oceans and on land.

Planktons’ Role

Just like the plants found on land, phytoplankton undergo photosynthesis in the water to keep them alive, using the chlorophyll in their bodies to convert the sun’s rays which filter through the water into chemical energy. Through this process, they simultaneously absorb carbon dioxide and convert it into oxygen on a similar scale to forests and other land plants; plankton absorb roughly 50 billion tonnes of CO2 each year. Some plankton survive solely through this photosynthetic cycle, while some also eat other organisms.

In addition to contributing to the world’s oxygen, plankton are the foundation of the ocean’s food chain, feeding everything from microscopic zooplankton to huge whales. Put simply, without plankton, there would be no sustenance for any of the fish we eat, the seabirds we see near the coast, or some of the planet’s most extraordinary creatures like the baleen whale, the world’s largest mammal.

The Threat to Oxygen

Even a small adjustment in phytoplanktons’ absorption of carbon dioxide affects atmospheric CO2 concentrations, and consequently influences global temperatures. Scientists are concerned this is already happening.

Plankton are incredibly sensitive to slight changes in their environments such as the changes which oceans are undergoing due to rising water temperatures caused by global warming. The fluctuating temperatures have significant ramifications on plankton populations, thus affecting the marine food chain, ocean ecosystems and atmospheric oxygen levels.

Changes in water condition can also cause too many plankton to drift into one area and reproduce en masse, leading to oversaturation of an area known as a ‘bloom’. These mass gatherings of certain types of plankton can release dangerous toxins into the water which cause ‘red tides’ in which other organisms are killed by the toxins and ecosystems are disrupted. On top of this, all the plankton die, thus releasing the carbon dioxide they had absorbed when their bodies break down.

Blooms are more likely to occur when varying sea temperatures affect plankton movement and reproduction. Essentially, global warming is doing even more damage to atmospheric levels of both CO2 and oxygen than we realise. Because of the ocean’s distance from our everyday lives, it’s easy to forget how integral its processes are to the fabric of life on Earth, but the time has come to acknowledge and protect the tiny organisms which quite literally keep us alive.


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