McGill Research: Changes to the seabed are fear for the future | Education

The bottom of the ocean, as we know it, dissolves quickly as a result of human activities. Normally, the bottom of the deep sea is chalky white. It is composed largely of mineral calcite (CaCO3) formed from the skeletons and shells of many planktonic and coral organisms. The seabed plays a crucial role in controlling the degree of ocean acidification. The dissolution of calcite neutralizes the acidity of CO2 and thus prevents the seawater from becoming too acidic. But these days, at least in some hot spots such as the North Atlantic and the Southern Oceans, the chalky bed of the ocean is getting darker brown. Due to human activities, the level of CO2 in the water is so high and the water is so acidic that the calcite is just dissolving.

The McGill-led research team that released its findings this week in a PNAS study believes that what she sees today is only a foretaste of how the ocean floor is likely to be affected in the future.

Lasting effects

"Because it takes decades, if not centuries, for CO2 to sink to the bottom of the ocean, almost all of the CO2 generated by human activities is still on the surface. But in the future, it will invade the ocean depths, extend above the seafloor and cause the dissolution of more calcite particles at the bottom of the sea, "says lead author Olivier Sulpis, who is preparing his PhD at the Department of Earth and the planets of McGill. Sciences. "The rate at which CO2 is currently emitted into the atmosphere is exceptionally high in Earth's history, faster than ever since the extinction of the dinosaurs. And at a much faster rate than the natural mechanisms of the ocean, this raises concerns about the levels of ocean acidification in the future. "

In future work, the researchers plan to examine the likely evolution of this deep-sea dissolution over the next centuries, under various potential CO2 emission scenarios. They believe that it is essential that scientists and policy makers develop accurate estimates of how marine ecosystems will be affected, in the long run, by human-induced acidification.

How the work was done

Because it is difficult and expensive to obtain measurements on the high seas, researchers have created in the laboratory a set of microenvironments resembling a seabed, reproducing abyssal bottom currents, temperature and water chemistry. sea, as well as the composition of the sediments. These experiments helped them understand what controls the dissolution of calcite in marine sediments and allowed them to accurately quantify its dissolution rate according to various environmental variables. By comparing the dissolution rates of the pre-industrial and modern seabed, they were able to extract the anthropogenic fraction of the total dissolution rates.

The ocean bottom current velocity estimates come from a high-resolution ocean model developed by the University of Michigan's Physical Oceanographer, Brian Arbic, and by a former postdoctoral fellow at his laboratory, David Trossman, who is now a research badociate at the University of Texas at Austin. .

"When David and I developed these simulations, the applications to the dissolution of geological materials at the bottom of the oceans were far from our minds, just showing that scientific research can sometimes take unexpected turns and yield unexpected dividends." declared Arbic. , Associate Professor, Department of Earth Sciences and the Environment, University of Michigan.

Trossman adds, "Just as climate change is not just about polar bears, ocean acidification is not just about coral reefs." Our study shows that the effects of human activities have become apparent until the end of the century. sea ​​bottom in many areas and the resulting increased acidification in these areas could affect our ability to understand the history of the Earth's climate. "

"This study shows that human activities dissolve geological records deep in the ocean," says Arbic. "It's important because these archives provide evidence of natural and anthropogenic changes."

Read the study

http://www.pnas.org/content/early/2018/10/23/1804250115

-Mc McGill University

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