Ocean sink for carbon dioxide produced by humans – ScienceDaily

The ocean takes CO₂ in two stages: first, the CO₂ dissolves in the surface water. Then, the staggering circulation of the ocean distributes it: ocean currents and mixing processes carry dissolved CO₂ from the surface to the interior of the ocean, where it accumulates over time.

Carbon sinks in the ocean

This reverse circulation is the driving force of the ocean sink for CO₂. The size of this sink is very important for the atmospheric CO₂ levels: without this sink, the concentration of CO₂ in our atmosphere and the magnitude of anthropogenic climate change would be considerably higher.

Determine how much of the CO produced by humans₂ Ocean absorption has long been a priority for climatologists. An international team of scientists headed by Nicolas Gruber, professor of environmental physics at ETH Zurich, has determined this ocean sink over a period of 13 years. As indicated in the last issue of Science, the researchers found that the ocean had absorbed up to 34 gigatonnes (billion metric tons) of man-made carbon between 1994 and 2007. This figure represents 31% of all anthropogenic CO emissions.₂ issued during this time.

The marine sink is intact

This percentage of CO₂ Ocean occupation has remained relatively stable compared to the previous 200 years, but the absolute amount has increased considerably. This is because as long as the atmospheric concentration of CO₂ rises, the ocean sink strengthens to a greater or lesser extent: the more CO₂ in the atmosphere, the more the oceans absorb, until final saturation.

Until now, this point has not been reached. "During the period under review, the global ocean continued to absorb anthropogenic CO.₂ at a rate corresponding to the increase of atmospheric CO₂ , "Explains Gruber.

These data-driven research results also confirm various previous model-based estimates of ocean sinks for CO production.₂. "This is an important idea, which allows us to believe that our approaches have been correct," Gruber adds. The results also allow researchers to draw conclusions about CO₂ ecosystems on earth, which are more difficult to determine.

Regional differences in the rate of absorption

Although the overall results suggest an intact ocean sink for CO production₂, the researchers also found in the different ocean basins considerable differences with respect to the expected absorption of the increase in CO₂. The North Atlantic, for example, absorbed 20% less CO₂ than expected between 1994 and 2007. "This is probably due to the slowdown of the southern rollover circulation in the North Atlantic in the late 1990s, which is most likely a consequence of climate variability," says Gruber. But this lower sink in the North Atlantic was offset by a considerably greater absorption in the South Atlantic, so that assimilation by the entire Atlantic s & # 39; 39 is developed as expected.

The researchers have documented similar fluctuations in the Southern Ocean, the Pacific and the Indian Ocean. Gruber points out: "We have learned that the marine sink does not only respond to the increase in CO₂. Its high sensitivity to climate variations suggests significant potential for feedback with ongoing climate change. "

Results of two surveys

The results are based on a global survey of CO₂ and other chemical and physical properties in the various oceans, measured from the surface up to depths of up to 6 kilometers. Scientists from 7 countries participated in the coordinated international program that began in 2003. On a global scale, they conducted more than 50 research campaigns until 2013, which were then synthesized into a product of global data.

The researchers used for their analyzes a new statistical method developed by Gruber and his former doctorate. student, Dominic Clement. This method allowed them to distinguish between changes in manufacturing and natural CO emissions.₂ components that make up the changes in the total concentration of dissolved CO₂ in the water. Natural CO₂ refers to the amount of CO₂ that existed in the oceans before industrialization.

Gruber had already participated in a similar study at the turn of the millennium. Using the observations obtained from the very first global CO₂ According to a study conducted between the late 1980s and the mid-1990s, the ocean had absorbed about 118 gigatonnes of carbon from the beginning of industrialization around 1800 until 1994. Its team of current researchers has extended this analysis until 2007, this not only to establish the budget for synthetic carbon dioxide₂ for the period 1994 to 2007, but also to assess the intact state of the carbon sink of the ocean.

Increased CO₂ content acidifies marine habitats

By moderating the rate of global warming, the oceanic well of CO production₂ provides an important service for humanity, but it has a price: the CO₂ dissolved in the ocean acidifies the water. "Our data showed that this acidification extends into the depths of the ocean, especially at depths of over 3,000 m," Gruber said.

This can have serious consequences for many marine organisms. Calcium carbonate dissolves spontaneously in acidified environments, posing a risk to mussels and corals whose shell and skeleton are calcium carbonate. The changing chemical composition of the ocean can also have an impact on physiological processes such as the breathing of fish. Gruber is convinced: "It is essential to document the chemical changes induced in the ocean by human activity, especially to understand the impact of these changes on marine life."

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Material provided by ETH Zurich. Original written by Michael Keller. Note: Content can be changed for style and length.