The far-future ocean: Warm yet oxygen-rich

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The oceans are losing oxygen. Numerous studies based on direct measurements in recent years have shown this. Since water can dissolve less gas as temperatures rise, these results were not surprising. In addition to global warming, factors such as eutrophication of the coastal seas also contribute to the ongoing deoxygenation. Will the oceans become completely oxygen-depleted at some point in the future if global warming continues? Such anoxic phases have actually occurred several times in the Earth's history, combined with major mass extinction events. They were also accompanied by high carbon dioxide concentrations in the atmosphere and high global temperatures.

Today, scientists of the GEOMAR Helmholtz Centre for Ocean Research Kiel published in the international journal Nature Communications on the development of the oxygen content of the oceans up to the year 8000. In their scenario, they assume that a large part of the fossil resources will be burnt, that emissions will continue to rise until the end of the century and then decrease to zero by the year 2300. In the model, the planet heats up by a further 6 degrees, and temperatures remain at this high level until the end of the simulation.

The surprising result concerns the oxygen content of the : After a further decrease over several hundred years, the oxygen inventory of the ocean rises again and even reaches a higher level than before industrialization in just under 4000 years. At first glance, it seems paradoxical that despite the expected further expansion of the already existing oxygen minimum zones in the world's oceans, the model yields an unexpected increase in oxygen as global temperatures rise.

It is known from investigations of the Kiel Collaborative Research Centre 754 that such oxygen-poor areas are death zones for larger organisms such as fish or cephalopods. However, certain bacteria that breathe nitrate instead of oxygen thrive there very well. "They draw their energy from a chemical process we call denitrification. It is an important component of the nitrogen cycle, that results in less oxygen being consumed during respiration of organic material than that produced during photosynthesis" explains Professor Oschlies.

In the new model simulation, the researchers have for the first time consistently coupled the oxygen cycle with the nitrogen cycle in such long-term global simulations. The researchers found that due to the extended oxygen minimum zones, more and more organic material is no longer respired with oxygen but with nitrate through denitrification. After several thousand years, the associated oxygen savings exceed the oxygen loss of the oceans caused by warming. "However, we cannot speak of a recovery, since the extensive oxygen minimum zones near the sea surface would stay. A large part of the additional goes into the deep ocean," says Angela Landolfi, co-author of the study.

However, there is a new problem: the anoxic phases that have occurred in Earth's history during warm climatic conditions are even more difficult to explain with the new findings. There are obviously factors and feedback processes in the of biological, physical and chemical processes in the ocean that are not yet fully understood. "This is why the study is also important for the present. It points to knowledge gaps, such as the interaction of denitrification and nitrogen fixation, that can also be relevant for ongoing ocean changes," says Andreas Oschlies, summarising the significance of the study.


Explore further

Further drivers of ocean deoxygenation identified

More information: Andreas Oschlies et al, Loss of fixed nitrogen causes net oxygen gain in a warmer future ocean, Nature Communications (2019). DOI: 10.1038/s41467-019-10813-w
Journal information: Nature Communications

Citation: The far-future ocean: Warm yet oxygen-rich (2019, June 27) retrieved 20 October 2019 from https://phys.org/news/2019-06-far-future-ocean-oxygen-rich.html
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Jun 28, 2019
This is a confusing article that drags in too many hypotheticals and Blind Science relating to purely speculative 'Global Warming' and that humans even have the capacity...... not just in America or EU, but regulate the chemical makeup of the World's Oceans. Which are made up of H2O..... WATER!

Remove all the Oxygen and you'll just have Hydrogen! .......and look at the ocean. Apparently it's smarter than we are. If the Polar Caps melt.... doesn't that mean it will be 'ICE' (frozen water) created eons? Plus.... I'm assuming it would have much higher 'Oxygen Content'. But my basic dispute is with these scientists assuming they know more from just another of the myriad of Scientific Models absent of any real proof! To me? This is not worth reading like so much of the good stuff Phys.org Presents!

Jun 28, 2019
Ummm, they're not talking about taking the oxygen out of H₂O. Did you not understand that gases dissolve in water? You know, like CO₂ in your soda?

Jun 28, 2019
And what exactly is water? Right... H2O and otherwise it's it's just H2 hydrogen by itself. Now to assume Oxygen is going somewhere.... since everything that was always here.... remains in existence in some form.... where is the Oxygen and what did it change into? The material world is finite. Meaning the Oxygen merely changes form or that it remains in some form. If a Gas then it joins all the other Hydrogen, Nitrogen and yes Oxygen in the atmosphere.

Animals breathe oxygen yes.... but it's exchanged for Nitrogen we (and other animals) expel and is then consumed by plant life. Which in turn expels Oxygen and we continue the cycle of Life.

Global Warming is Man's desperate attempt to explain things he never created or that just happened impossibly randomly like Evolutionist believe. 1. There is no such thing as a Closed Box System. Therefore both the Oceans and the atmosphere are all part of the same thing!

Jun 28, 2019
Why do you fools keep insisting Evolution and Global Warming are both of a Myriad of Theories that have been modeled (like this hunk of misinformed junk) and are but 1000's of man made Models and Theories in existence today and still remain just that. Which like Life itself is in constant flux. Another new theory after taking a picture of a Black Hole and checking out these crazy twin anomalies says they have now found even more black holes and how do you explain how each twin Black Hole is aware of the other's course and movement in the Universe?

Don't tell me String Theory.... because that's just another unproven Theory as this Model is!

Actually if you read articles even here on Phys.org, you'll find that they've discovered a black hole that is older than the Universe. Now what does that mean? That the Big Bang Theory may be wrong after all and Einstein's General Relativity is closer to being proven than not w/ pictures no less of Black Holes! Infinite Universes Theory is Closer!

Jun 28, 2019
No editing tools so here's first a quote; "Earth's history during warm climatic conditions are even more difficult to explain with the new findings". Thus it'll take another 1000's of Years to prove this one too. This is just another Globalist..... Scientific attempt to prove is smarter than the Universe!

I won't be taken in by these Fixed Models and Theories any more than any other theory of model somebody decided was another way to explain the unexplainable. We have Atomic Matter and Sub Atomic Quantum Physics that more resembles life than some DEAD STAR..... or some man made Theory that's still incapable of being proved. Because it will always be a THEORY and never a Scientific Fact..... as they only exist in the Math that Einstein already did in his General Theory of Relativity! ;-P

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