Global ocean de-oxygenation quantified

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Oxygen is an essential necessity of life on land. The same applies for almost all organisms in the ocean. However, the oxygen supply in the oceans is threatened by global warming in two ways: Warmer surface waters take up less oxygen than colder waters. In addition, warmer water stabilizes the stratification of the ocean. This weakens the circulation connecting the surface with the deep ocean and less oxygen is transported into the deep sea. Therefore, many models predict a decrease in global oceanic oxygen inventory of the oceans due to global warming. The first global evaluation of millions of oxygen measurements seems to confirm this trend and points to first impacts of global change.

In the renowned scientific journal Nature the oceanographers Dr. Sunke Schmidtko, Dr. Lothar Stramma and Prof. Dr. Martin Visbeck from GEOMAR Helmholtz Centre for Ocean Research Kiel just published the most comprehensive study on global content in the world's oceans so far. It demonstrates that the ocean's oxygen content has decreased by more than two percent over the last 50 years. "Since large fishes in particular avoid or do not survive in areas with low oxygen content, these changes can have far-reaching biological consequences," says Dr. Schmidtko, the lead-author of the study.

The researchers used all historic oxygen data available around the world for their work, supplemented it with current measurements and refined the interpolation procedures to more accurately reconstruct the development of the oxygen budget over the past 50 years. In some areas previous research had already shown a decrease in oxygen. "To quantify trends for the entire ocean, however, was more difficult since oxygen data from remote regions and the deep ocean is sparse," explains Dr. Schmidtko, "we were able to document the oxygen distribution and its changes for the entire ocean for the first time. These numbers are an essential prerequisite for improving forecasts for the ocean of the future."

The study also shows that, with the exception of a few regions, the decreased throughout the entire ocean during the period investigated. The greatest loss was found in the North Pacific. "While the slight decrease of oxygen in the atmosphere is currently considered non-critical, the oxygen losses in the ocean can have far-reaching consequences because of the uneven distribution. For fisheries and coastal economies this process may have detrimental consequences," emphasizes the co-author Dr. Lothar Stramma.

"However, with measurements alone, we cannot explain all the causes," adds Professor Martin Visbeck, "natural processes occurring on time scales of a few decades may also have contributed to the observed decrease." However, the results of the research are consistent with most model calculations that predict a further decrease in oxygen in the oceans due to higher atmospheric carbon dioxide concentrations and consequently higher global temperatures.

The new study is an important result for the ongoing work in the Collaborative Research Center (SFB) 754 funded by the German Research Foundation (DFG) at the Kiel University and GEOMAR. The SFB 754's aim is to better understand the interaction between climate and biogeochemistry of the tropical . "From the beginning of March onwards, four expeditions aboard the German research vessel METEOR will investigate the tropical oxygen minimum zone in the eastern Pacific off Peru. We hope to obtain further data on regional development which will also help us to better understand the global trends," emphasizes Dr. Stramma, the expedition coordinator for the SFB.


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More information: Sunke Schmidtko et al, Decline in global oceanic oxygen content during the past five decades, Nature (2017). DOI: 10.1038/nature21399
Journal information: Nature

Citation: Global ocean de-oxygenation quantified (2017, February 15) retrieved 25 August 2019 from https://phys.org/news/2017-02-global-ocean-de-oxygenation-quantified.html
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Feb 15, 2017
Well AGW deniers. Add on one more concern to your worry pile. Deniers are such LOSERS. So from the article
the oxygen supply in the oceans is threatened by global warming in two ways: Warmer surface waters take up less oxygen than colder waters. In addition, warmer water stabilizes the stratification of the ocean.
So as the circulation breaks down, less oxygen is works it way down into the deep sea. In addition, the surface waters are becoming more acidic from the CO2+H2O carbonic acid created by the increasing global CO2 levels.

So what will be the result of that deniers and goons?


Feb 15, 2017
"While the slight decrease of oxygen in the atmosphere is currently considered non-critical..."

Yes I looked at graphs representing this. A separate issue from global ocean de-oxygenation, but a data point the co-author Dr. Lothar Stramma thought worth mentioning.

I listened to Dr. Peter Brewer of Monterey Bay Aquarium Institute talk about atmospheric oxygen depletion in response to warming oceans. Something to keep an eye on.


Feb 16, 2017
Well AGW deniers. Add on one more concern to your worry pile. Deniers are such LOSERS. So from the article
the oxygen supply in the oceans is threatened by global warming in two ways: Warmer surface waters take up less oxygen than colder waters. In addition, warmer water stabilizes the stratification of the ocean.
So as the circulation breaks down, less oxygen is works it way down into the deep sea....

So what will be the result of that deniers and goons?


Warming surface waters causing stratification and reduced mixing means that dead plankton sinking to the bottom will be "eaten" by microbes which use up oxygen that isn't replenished from the surface. These strata will expand and lead to a loss of carrying capacity for large life forms in the ocean.

Feb 16, 2017
O monkey antisciencegoracle / factsdoesn'tmatter sock, where are you hiding ? We'd like to have some fun come join us, i promise we got plenty bananas for youuuu :D

Feb 16, 2017
@Davy_Crockett; Thanks. Absolutely correct and you clarified that well. I was thinking of the great ocean conveyor (the gulf stream, .. etc). I just read a story where scientist have noticed a change in it's motions, hinting at a pending shut down (ie deep sea circulation break down). I'll look it up and post the title.


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