Take a breath! Get your regular intake of oxygen and smoothly expel a whiff of carbon dioxide: The concentration of carbon dioxide in Earth's atmosphere is rising. In turn, the concentration of oxygen drops a tiny bit.
Currently, each year human economic activity converts fossil carbon into 7 Gigatons of carbon dioxide. Burning coal, oil and gas consumes oxygen and exhausts carbon dioxide. The amount of carbon dioxide exhausted each year adds up to about 1% of the carbon stockpiled in the atmosphere. That steady input of carbon keeps anthropogenic global change going.
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| Peaty soil in the Andean highland (Ecuador) Credit: Martin Mergili (imaggeo.egu.eu) |
How dramatically the current play of anthropogenic global change enfolds, that play is nothing compared to the play that had enfolded long time ago when oxygen got released into the environment. Some Billion years ago, the oxygen-producing photosynthesising life battle to master the world.
Let's look at both plays, the ancient and the modern!
Carbon, thumps up!
Most remarkably, since the industrial revolution set off two centuries ago the concentration of carbon dioxide in the atmosphere increased by 40%. Much of the carbon exhausted by human economic activity got neither absorbed in the biosphere or got stored in the deep ocean. The deep ocean is the main reservoir of carbon on Earth that could be recycled rapidly.
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| A black smoker in 3,000 meters depth at the Mid-Atlantic Ridge. Credit: MARUM - Center for Marine Environmental Sciences (imaggeo.egu.eu) |
Respiration and microbial oxidation together are of a very similar strength than photosynthesis. Jointly these processes recycle rapidly the carbon that is available in the atmosphere. Recycling of the carbon stored in the ocean is a bit slower.
The annual anthropogenic input of carbon-dioxide into the atmosphere is several times bigger than the annual imbalance between photosynthesis, respiration and microbial oxidation. This makes the anthropogenic input of carbon into the atmosphere such a strong driver of change.
Oxygen, thumps up !
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| Redox processes causing a pattern of red to greyish green mottles in a Regosol, Ria Formosa, Portugal Credit: Antonio Jordán (imaggeo.egu.eu) |
It is a fascinating play enfolded once photosynthesis evolved. Initially, oxygen increased in the atmosphere. The oxygen build-up in the ocean was delayed. Oxygen concentration increased to about-modern levels only two billion years after oxygen appeared for the first time. Finally, a network of multiple geochemical feedback-loops relate biosphere, oceans, atmosphere and the lithosphere.
Finally, all oxygenated...
Finally, the photosynthesising algae and bacteria ruled the seas. Nearly 4 Billion years in its history, Earth switched into its present oxygenated stage. The play had been settled in favour for life as we know it. The Ediacaran [*] started 600 Million years ago; first complex animals and plants lived in a widely oxygenated ocean. To grow and store energy in their tissues, the plants tap into the ample energy that sunlight provides. Animals get sufficient oxygen supply to consume plant tissue vigorously. The continents were barren land, but that would change rapidly. A long-lasting phase of Earth history came to its end, oxygen and carbon-dioxide are taking over from sulphur, iron, hydrogen and methane.
Since the Ediacaran, the oxygen concentration in the atmosphere varied around present values. Feedback between geochemical cycles and the biosphere cause variations of the oxygen concentration, but keep its excursions limited. Up to recent times the same could be said for the carbon-dioxide concentrations; feedback between geochemical cycles and the biosphere kept excursions of carbon-dioxide concentration limited. Now humans have changed that balance and put on stage: anthropogenic global change. Human economic activity, burning fossil fuels to drive economy of billions of people, kick the feedbacks of carbon fluxes out of current balances.
Ukko El’Hob
[*] from Wikipedia: “The Ediacaran Period (ca. 635-542 Mya) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum). Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a "cap carbonate", because it caps glacial deposits. This bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age.”
This text was inspired by the article “The rise of oxygen in Earth's early ocean and atmosphere” by Timothy W. Lyons, Christopher T. Reinhard and Noah J. Planavsky, which was published in February 2014 in Nature. Many insights are taken from “The global oxygen cycle “ by S.T. Petsch, which was published 2003 by Elsevier in volume 8 of in the “Treatise on Geochemistry” (Editor: William H. Schlesinger. Executive Editors: Heinrich D. Holland and Karl K. Turekian). Any inconsistency, error or slanted statement is responsibility of the author.
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