(ORDO NEWS) — Climate change continues to be of concern to scientists and the general public. One of the key aspects of this problem is the state of the World Ocean, so Australian scientists studied its bottom sediments and were able to assess changes in currents over the past 13 million years.
To study climate change at the global level, many important factors must be taken into account. Among them is such a significant “player” as the World Ocean, which has a colossal volume and covers most of our planet.
The ocean is also a huge reservoir of carbon dioxide, an important greenhouse gas. The authors of the new study are interested in how the circulation of the deep ocean has changed over geological timescales.
They are sure that this must be taken into account in order to predict the dynamics of the temperature of the oceans, as well as the dissolution of carbon dioxide in it.
“Today, the ocean has been able to absorb a quarter of the carbon dioxide created by human activity and more than 90 percent of the excess heat associated with it,” said one of the authors of the new article, Dr. Adriana Dutkiewicz (Adriana Dutkiewicz) from the University of Sydney (Australia).
Carbon dioxide dissolved in ocean water is necessary for plankton living organisms soaring in it for the construction of skeletons and shells.
After death, plankton sinks to the bottom, taking with it the carbon stored during life. Because of this, sedimentary rocks are constantly formed on the ocean floor one of the largest reservoirs of carbon on a global scale.
It is extremely important that the waters of the World Ocean are constantly involved in a huge circulation, forming the so called ocean conveyor. It unites the oceans and, due to the difference in temperature and salinity of the water, sinks deeper in a certain part of its path.
Some scientists believe that continued global warming is causing these deep currents to move faster, while others believe the opposite is true: the ocean conveyor belt is slowing down. The new article aimed to find out which of them is right.
“Satellite data, which is commonly used to build models, only cover a few decades, which makes it difficult to really understand the long term changes in the ocean,” says Dr. Dutkiewicz. “Therefore, we decided to use the geological record preserved at the bottom of the ocean to learn more about such changes.”
Over the past half century, geologists have managed to learn a lot about the sediments on the seabed. Dutkiewicz and her colleague, Professor Dietmar Muller, used data from more than 200 underwater drillings. Thanks to them, scientists assessed the state of bottom sediments in different parts of the oceans.
“The interrupted sedimentation process corresponds to a fast current, while stable sedimentation indicates calmer conditions,” says Prof. Müller. “By combining this information with knowledge about the shape of the ocean floor, geologists were able to learn when and where sedimentation breaks occurred.”
Scientists have compiled a map, according to which, over the past 13 million years, the process of deposition of bottom sediments has been interrupted less and less. This corresponds to a decrease in the average temperature on the planet and the growth of ice sheets on land.
It turns out that all this time the global ocean conveyor belt has been gradually slowing down. However, before that, during a period of sharp warming (when the Earth was three to four degrees warmer than now), the deep waters of the ocean moved much faster.
Summing up his work and taking into account the publications of colleagues, Dutkevitch concludes that the heated ocean not only mixes faster, it is also able to absorb more carbon dioxide. The same acid that, remaining in the atmosphere, would contribute to the greenhouse effect.
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