Humanity: sailing into a stagnant ocean

“We were the first that ever burst into that silent sea.” – STColeridge, Rime of the Ancient Mariner

Like the mariners of old, humanity has embarked on a deadly voyage into a world unable to support life in its current abundance. A stagnant, dying world where poisons seep amain through ocean and atmosphere.

Life first appeared on Earth around 3.8 billion years ago, not long after the planet itself formed. But for the next 3 billion years it did very little. There was something about those dark, primordial oceans that prevented lifeforms such as we see today, and such as ourselves, from arising. Only bacteria and primitive algae could survive. Then, around 700 million years ago, life burst forth in all its magnificent variety, growing from the simple creatures we see in the Ediacaran rocks of Australia to fish, plants and land-dwelling animals by around 300 million years ago.

The trigger was oxygen. For the first three quarters of the Earth’s history, the oceans were anoxic – a place where only microbes, like those in your gut or compost heap, could survive. Then, gradually, the oceans were flooded with oxygen, and the cycle of life was unleashed in all its rich diversity.

How ironic, then, that human action is now setting the planet on a course back to the primeval ocean, to a planet where very little besides single-celled organisms can make it. To a world where we ourselves cannot endure.

It all begins with the main driver of the planetary thermostat – carbon dioxide. Previously emitted only by vast outbursts of volcanic and tectonic activity, the level of CO2 has driven the Earth’s temperature up and down many times in history, each surge being accompanied by a major wipeout of life, beginning with a dying ocean – a ‘Canfield Ocean’ – named after the scientist who first described it. [i]

The process is complex, but worth understanding:

  • as CO2 is released from the Earth, it traps atmospheric heat which warms the planet. The poles gain heat much faster and begin to melt, eventually becoming ice-free.
  • as the difference in temperature between the equator and poles diminishes, the energy differential that powers the world’s ocean currents also declines, causing them to fail. Oxygen-rich top waters no longer mix with deeper waters, which then become stagnant.
  • Life in the anoxic waters dies out, leaving only its rotting remains, where compost bacteria generate two gases – methane (CH4) and hydrogen sulphide (H2S or rotten egg gas). The methane accelerates the warming process.
  • The yellow H2S gas drifts through the atmosphere, turning the blue sky green, and falling out as acid rain over sea and land. Like the acid rain from coal-fired industry, it poisons lakes, rivers and all the vegetation it falls upon, eventually killing whole forests. Animals that depend on plants or trees for food or shelter also begin to die out, as do their predators. Oxygen in the air we breathe begins to decline.

This process, or one very like it, is what many scientists think drove the great mass extinctions of the past, especially the Permian event 250 million years ago when 96 per cent of all living species, especially in the oceans, perished. (By contrast, the Cretaceous event, 65my  ago, triggered by an asteroid and which removed the dinosaurs, took just 76% of species, mostly on land). The true deadliness begins with the oceans losing their oxygen as they stagnate.

Ironically, the decaying organic matter from dead life on land and sea accumulated in great drifts on the seabed, to become the crude oil deposits that humans now mine and release into the atmosphere again, as if there were no tomorrow, recreating the extinction process.

That the formation of an oxygenless Canfield Ocean may be underway again on Earth today, triggered by human release of fossil carbon fuels, there is unsettling evidence.

The immediate signs are all around us, in media headlines every day: severe droughts, vast wildfires, floods, violent tempests, the melting of glaciers and polar ice caps, the rise in sea levels all show the climate is running amok. Yet these are but the short-term and superficial indicators of the apocalyptic change under way.

Far more ominous, for life on Earth, are early signs that the oceans currents are weakening [ii], the oceans themselves are starting to lose their oxygen [iii] and becoming more acidic [iv]. Their ability to soak up carbon from the atmosphere is in decline. [v] The number of ‘dead zones’ where little or no marine life can survive is proliferating off our coastlines. [vi]

Humans are accelerating the process in a variety of ways, particularly by releasing vast quantities of nutrients in the form of agricultural fertiliser, lost topsoil, industrial waste and sewage into the oceans, as well as through our expanding carbon dioxide and methane emissions.

Like Coleridge’s Ancient Mariner, we have slain the albatross, an emblem of Nature that “caused the breeze to blow”. It hangs, leaden, about our necks, a curse both symbolic and real.

The progression to a lifeless ocean and a stricken land is a slow one, taking millennia, even given the haste with which we are stamping on the fossil fuels accelerator. But once set firmly in motion it cannot be turned aside by any human act. It is irreversible.  

How sad that we should turn the garden of the Earth back into a slagheap fit only for microbes.

How sad we seem to lack even the elementary understanding or moral principle to realise the significance of our crime, and act together to atone for it – before its full enormity is felt.


  • Julian Cribb AM is a Canberra science author and co-founder of the Council for the Human Future. 

[i] Canfield DE, A new model for Proterozoic ocean chemistry. Nature, Dec 1998.

[ii]  Thornally DJR, Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years. Nature, 12 Apr 2018.

[iii] IUCN Ocean Deoxygenation. 2019.

[iv] NOAA. Ocean Acidification. Apr 2020.

[v] UNESCO. UNESCO cautions ocean risks losing its ability to absorb carbon, exacerbating global warming. 27 Apr 2021.

[vi] World Economic Forum. Dead zones in our oceans have increased dramatically since 1950. 18 Jan 2018.

4 thoughts on “Humanity: sailing into a stagnant ocean

  1. Thank you so much for yet another excellent and informative article. It has prompted me to further research the subject of a Canfield Ocean. It would seem that, one way or another, in either the near or distant future, our planet will undergo another such occurrence.

    Liked by 1 person

  2. Pingback: #102 Weekend reads – we have passed the 6th of the nine planetary boundaries - The Digital Conversationalist

  3. Pingback: What can I do to act on climate change? First job is knowledge - The Digital Conversationalist

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