The color of the bottom of the sea is changing from white to brown by the human being - The Province

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Human activities are dissolving the geological record at the bottom of the ocean, due to rising levels of CO2 and the acidification of sea water, according to a new investigation warns.


Normally the depth of the deep sea is of a white limestone color. It is composed, to a great extent, of the mineral calcite (CaCO3) formed by the skeletons and shells of many planktonic organisms and corals. The seabed plays a crucial role in controlling the degree of ocean acidification. The solution of the calcite neutralizes the acidity of the CO2 and, in the process, prevents the seawater from becoming too acidic.


But these days, at least in certain 'hot spots' like the North Atlantic and the southern oceans, the calcareous bed of the ocean is becoming more dark brown. As a result of human activities, the level of CO2 in the water is so high and the water is so acidic that the calcite simply dissolves.


The research team led by McGill University that published its results this week in a study at PNAS believes that what they are seeing today is just a foretaste in the way that the ocean floor will probably be affected in the future.


Lasting repercussions

Because it takes decades or even centuries for CO2 to sink to the bottom of the ocean, almost all of the CO2 created through human activity is still on the surface. But in the future, it will invade the deep ocean, spread over the ocean floor and causes even more particles to dissolve of calcite on the seabed, "senior author Olivier Sulpis said in a statement. He is working on his doctorate in the Department of Earth and Planetary Sciences at McGill.


"The speed at which CO2 is currently being emitted in the atmosphere is exceptionally high in the history of the Earth, faster than in any other period from at least the extinction of dinosaurs. And at a much faster rate than the natural mechanisms in the ocean can cope with, it raises concerns about ocean acidification levels in the future. "


In future work, researchers plan to see how this dissolution of the deep ocean floor is likely to evolve over the coming centuries, in several possible future scenarios of CO2 emissions. They think it is critical for scientists and those responsible for the formulation of policies to develop precise estimates of how marine ecosystems will be affected, in the long term, by acidification caused by humans.


Simulations in the laboratory

Because it is difficult and expensive to obtain deep-sea measurements, the researchers created a set of micro-seabed microenvironments in the laboratory, which reproduce abyssal bottom currents, seawater temperature and chemistry, as well as seawater compositions. sediments These experiments helped them understand what controls the dissolution of calcite in marine sediments and allowed them to quantify accurately its speed of dissolution based on various variables environmental By comparing pre-industrial and modern seafloor dissolution rates, they were able to extract the anthropogenic fraction from the total dissolution rates.


The velocity estimates for ocean bottom currents came from a high resolution ocean model developed by the University of Michigan physical oceanographer Brian Arbic and a former postdoctoral fellow in his laboratory, David Trossman, who is now a research associate at the University Texas-Austin.


"When David and I developed these simulations, the applications for the dissolution of geological material at the bottom of the oceans were far from our minds. Scientific research can sometimes take unexpected detours and pay unexpected dividends, "said Arbic, an associate professor in the Department of Earth and Environmental Sciences at the University of Michigan.


Trossman adds: "As well as climate change is not just about polar bears, the acidification of the oceans is not just about coral reefs. Our study shows that the effects of human activities have become evident to the seabed in many regions, and the consequent increase in acidification in these regions may affect our ability to understand the history of Earth's climate. "


"This study shows that human activities are dissolving the geological record at the bottom of the ocean," says Arbic. "This is important because the geological record provides evidence of anthropogenic and natural changes."



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