The ocean is a carbon sink, but for how long?

The ocean plays a major role in the carbon cycle, especially by storing this element in its depths and preventing it from reaching the atmosphere in the form of CO.2it seems that rising temperatures may well spoil things.

period carboncarbon is a set of processes that provide transittransit carbon between the atmosphere, biosphere and geosphere. The ocean plays a special role in this cycle because it is an important carbon sink. This means that this chemical elementchemical element it stabilizes and is kept there for a very long time. In the current context, an alarming increase in the rate of CO is noted2 In Latmosphereatmosphere, this concept of storage (we often even talk about sequestration) is important. Indeed, storing carbon on the ocean floor prevents it from being released too quickly into the atmosphere, mainly as CO2.2. In normal times, this process therefore makes it possible to adjust the ratio gasgas carbon in the atmosphere.

The carbon cycle is broken with the increase in temperature

But scientists have just discovered that the ability to sequester organic carbon will change as ocean temperatures rise. It is done by analyzing the samples sedimentsediment The researchers came to this conclusion published in the Journal of the Seabed Nature. This sediment study actually allowed us to observe the burial of organic carbon over the past 30 million years. weatherweather during this time. It turns out that although organic carbon sequestration is a very active and efficient process over time, it is much more sensitive to climate change than previously thought.

Instead of being sequestered, carbon is released into the atmosphere

The scientists came to this conclusion using a new method to determine the burial rates of organic carbon compared to inorganic carbon. Their results show that during the warm period of the middle Miocene (15 million years ago), the amount of organic carbon buried on the ocean floor was relatively low. This would be due to the increase in temperature of the activity of bacteria that break down organic matter. However, degradation issueissue does not store organic carbon. On the contrary, this process releases a large part of the organic carbon in the form of CO2, thus increasing the greenhouse effect. Very unfortunate consequences for the future…

Thanks to 30 years of data, scientists have been able to see the role of the ocean more clearly. carbon sinkcarbon sink. Nicolas Metzl, researcher at CNRS’s LOCEAN unit and co-author of the study, tells us why the results have been different so far.

Article by Bruno Scala published on July 13, 2011

A study published on the journal’s website Natural Geology, elucidating the role of the North Atlantic Ocean in ocean carbon storage. The study analyzes the evolution of carbon dioxide concentration in the atmosphere and the Atlantic Ocean.

Water traps at the air-ocean interface moleculesmolecules CHO2 atmospheric. to workemissionemission CHO2 in the atmosphere is increasing dramatically due to human activity, this phenomenon – carbon sequestration – is a boon to climate change. due to Global WarmingGlobal WarmingThe dissolution of CO2 and in the ocean, it is less efficient in certain regions, indicating that the ocean is doing a less good job of absorbing carbon. As research by Galen McKinley (University of Wisconsin) shows, this is especially true in the subtropical regions of the Atlantic Ocean.

However, apart from this region, ocean and atmospheric carbon dioxide concentrations have evolved substantially the same over the past 30 years, according to the study. This indicates that the carbon storage activity of the oceans remains stable.

30 years of data

To reach this conclusion, the team of scientists referred to data series covering a period of 30 years. ” For about 5 years, the international community has been organizing itself to prepare a synthesis of CO observations2 oceanic, so they are comparable because the same equipment or the same methods are not always used from one country to another. This synthesis allows for a more accurate assessment of CO variations2 in the ocean Nicolas Metzl of the Pierre Institute explains Simon LaplaceSimon Laplace (LOCEAN/CNRS) and study co-author, interview with Futura-Sciences.

CO if everyone agrees2 atmosphere continues to increase (see graph above), however, researchers were more divided on the evolution of CO.2 oceanic. At the root of this disagreement were different conclusions.

The results show that CO2 it increased faster in the ocean than in the atmosphere, but only for a short period of time, ten or fifteen years. These studies were not wrong, but there is such variability in CO in the ocean2 it is still difficult to separate natural variations from one season to another, or even from one year to another, from those related to climate change, and to extrapolate these results for the next several decades… Geographical variability must also be taken into account. “, Nicholas Metzl continues.

Natural variability and anthropogenic variability

Therefore, the task before the researchers is to distinguish between variability of natural origin and variability of anthropogenic origin. The data used here allow us to remove these natural variations and draw conclusions about global consequences: the concentration of carbon dioxide in the ocean is not increasing faster than in the atmosphere. ” For 30 years, we observe that the activity of carbon sinks in the ocean has not increased in the subtropics, but even decreased. », concludes Nicolas Metzl (see map above).

It also emphasizes the importance of observations and databasedatabase long-term international. ” In addition to the results, one of the main points of this study is the collection of all the data used. One of the goals in the coming years will be to obtain standardized data and optimize the ocean carbon dioxide observation network to assess the role of the ocean not only in the North Atlantic, but especially on a global scale. they better assess the quality of climate models. This is the purpose of the conference to be held in Paris from September 14 to 16, 2011 under the leadership of UNESCO.

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