Professor Kevin Haines
April 2021

In two out of every three breaths we take, we inhale oxygen produced in the World’s oceans.

This is not a Briefing Note that is going to suggest, for a second, that protecting the World’s rainforests is unimportant or insignificant (in terms of carbon sequestration, oxygen production or biodiversity – to name just the big three). This is, however, following our thematic hashtag #nostraightlines, a Briefing Note that is going to address the significance of phytoplankton for carbon sequestration and oxygen production (we will set aside, for the time being, the important role phytoplankton plays in maintaining marine ecosystems).

Estimates vary but approximately 50% - 80% of the carbon dioxide produced by anthropogenic activities is absorbed by phytoplankton in the World’s oceans – through photosynthesis. By whatever measure one uses, phytoplankton absorbs (sequesters, i.e. removes from the atmosphere) more carbon dioxide than all plant life on planet Earth, including the rainforests. 

Furthermore, the largest reservoir of the Earth’s Carbon is located in the deep ocean, with 37,000 billion tons of Carbon stored (out of the 65,500 billion tons on Earth). Most of this Carbon comes from the bodies of dead ocean organisms: a process known as the ‘biological carbon pump’ which transfers around 10 gigatonnes of Carbon from the atmosphere to the deep ocean each year (a process intensely sensitive to the changing size of the Phytoplankton biomass).

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Phytoplankton are, of course, plants not animals. These microscopic plants float in the ocean surface and they grow through photosynthesis, converting carbon dioxide using the sun’s energy and releasing oxygen. The exact amount of oxygen produced by phytoplankton varies (as the biomass varies) but despite variations phytoplankton are the single biggest producers of oxygen on Earth.

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There is a problem, however, phytoplankton are in danger due to climate change - as the oceans are getting warmer their population is decreasing. Reducing the biomass of phytoplankton, through anthropomorphic activity or inactivity, reduces the amount of oxygen available to sustain human life. The big problem here is who cares? Who is doing something (anything) about this?

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