translated from Spanish: Who produces the oxygen we breathe? The response floats in the oceans

The abundance of animal life in the ocean has provided a huge variety of services since time immemorial, from food to adventure and leisure. But none of this would be possible without the single-celled organisms of phytoplankton, which float by thousands in every drop of water in the upper layers of the sea.
Phytoplankton comprises two main groups: photosynthetic cyanobacteria and single-celled algae that move near the sun-lit surface of the oceans. They do it in the so-called euphotic zone, which can reach a depth of up to 200 meters in tropical areas.
As I wrote in a previous article, plants with larger and more complex structures are those with a lower oxygen production balance. Or what is the same, those with a simple structure (much “green” and little “trunk”, to say to simplify) are the ones with the highest production of net oxygen.
Following this reasoning, it seems logical to think that the great oxygen producers are the meadows, the young forests, the crops and almost all the growing plants that surround us, which release more oxygen than they consume. It’s not like that.
Where are plant populations that continually multiply and continue to grow?
The organisms responsible for us being able to breathe are in the oceans; which, let’s not forget, cover 71% of the Earth’s surface. Phytoplankton is at the base of the trophic chain of ocean ecosystems. Without the autotroph microorganisms that make up it, seas and oceans would be lifeless deserts. Thanks to their photosynthetic work, these microscopic creatures produce between 50 and 85% of the oxygen that is released into the atmosphere each year.
Volvox, one of the algae genres that make up phytoplankton. Shutterstock/ChoksawatdikornFor a couple of decades ago, images from Nasa’s Nimbus satellites and the US Meteorological Agency showed that ocean productivity, assessed based on chlorophyll concentrated on the sea surface, could be higher than the productivity of terrestrial ecosystems. This meant that phytoplankton were the great oxygenator of the planet.
The hypothesis was confirmed in 2015 by the international Tara Oceans project, the results of which concluded that phytoplankton generates at least half of the oxygen we breathe (about 270 billion tons per year) and transfers about 10 gigatonnes of carbon from the atmosphere to the depths of the ocean each year.
This is essential to sustain life on Earth and mitigate the effects of climate change.
Phytoplankton has chlorophyll, the pigment that makes photosynthesis possible. In addition to this, it serves as food to zooplankton, which in turn feeds other marine animals. Billions of microscopic plants that inhabit the sine of the oceans carry out their cycle of renewal and death in just a few days.
That infinite universe that is born and dies continuously, phytoplankton, is the bomb that produces most of the O2 we breathe. But, in addition to absorbing light and releasing O2, chlorophyll allows these tiny plants to remove dissolved CO2 to fix it, in the form of carbohydrates, to their biological structures.
Therein lies the crucial role of phytoplankton in the carbon cycle and, as a consequence, in its colossal ability to purify the air. Thanks to photosynthesis, phytoplankton consume scoion on a scale equivalent to terrestrial ecosystems. It is estimated that each year it incorporates between 45 and 50 million tons of inorganic carbon. Ground plants incorporate about 52 million tons of carbon a year, but it returns to the atmosphere in the short to medium term. When the phytoplankton die, some of the captured carbon falls into the depths of the ocean.
All living organisms in the photic zone sink when they die, so there is a constant rain of organic matter into deeper waters. Nutrients are returned to the upper layers of water, especially in places where there are strong updrafts due to the topography of the bottom and the patterns of ocean currents.
A very slow oxygen manufacturer
85% of the organic matter created each year by phytoplankton is recycled among the organisms that live in the illuminated waters, while the remaining 15% is lost in the depths of the ocean. There, where microorganisms have removed oxygen from water, traces of organic matter remain buried under anaerobic conditions. This plant matter buried at the bottom of the ocean is the source of oil and gas.
Only a small fraction, about one thousandth of photosynthesis worldwide, escapes the processes described and is added to atmospheric oxygen. But since the emergence of cyanobacteria, the first photosynthetic organisms, between 3 500 and 3.8 billion years ago, the residual oxygen left by the small imbalance between growth and decomposition has accumulated to form the oxygen reservoir life-long, breathable, the volume of which accounts for 21% of the total atmosphere.
Therefore, although photosynthesis is ultimately responsible for breathable oxygen, only a small fraction of plant growth is added each year to atmospheric oxygen storage. Even if all terrestrial organic matter were burned at once, less than 1% of the oxygen available in the world would be consumed.
How is it possible that phytoplankton mass does not run out if the biomass of pre-predatory organisms is much higher?
The balance sheet is offset by a high renewal rate. The high reproduction rate of phytoplankton causes their populations to renew faster than they are consumed. A whale shark that feeds on millions of these small photosynthetic cells is only able to give birth to one calf a year. Instead, a diatomaceous is able to generate one million descendants every day.
In this way, the balance of life accounts do add up.
Manuel Peinado Lorca, University Professor. Department of Life Sciences and Researcher at Franklin Institute for American Studies, University of Alcalá
This article was originally published in The Conversation. Read the original.

Original source in Spanish