Ocean acidification, a worrying by-product of excess carbon dioxide in the atmosphere, is sometimes known as “climate change’s equally evil twin.” Drops in ocean pH are believed to be having a devastating effect on marine life, eroding corals, making it difficult for certain critters to build their shells and threatening the survival of zooplankton. Now, as Caroline Haskins reports for Motherboard, a new study has found that the effect of acidification extends all the way to the bottom of the ocean, where parts of the sea floor may be dissolving.
For millennia, the ocean has had a nifty way of both absorbing excess carbon in the atmosphere and regulating its pH. The bottom of the sea is lined with calcium carbonate, which comes from the shells of zooplankton that have died and sunk to the ocean floor. When carbon dioxide from the atmosphere is absorbed into the ocean, it makes the water more acidic, but a reaction with calcium carbonate neutralizes the carbon and produces bicarbonate. The ocean, in other words, can absorb carbon without “throwing [its] chemistry wildly out of whack,” as Stephanie Pappas writes in Live Science.
In recent decades, however, the large amount of carbon dioxide being pumped into the atmosphere has upset the balance of this finely-tuned system. Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of carbon dioxide, and calcium carbonate on the seafloor is dissolving too quickly in an effort to keep up. As a result, according to a study published recently in PNAS, parts of the seafloor are disintegrating.
The study authors used existing data on water chemistry, seafloor currents and the calcium carbonate content of deep-sea sediments to model the global distribution of sea floor dissolution both before and after the Industrial Revolution. They found that when it comes to most parts of the ocean floor, the pre- and post-Industrial dissolution rates are actually not dramatically different. But there are several “hotspots” where the ocean floor is dissolving at an alarming rate.
Chief among such “hotspots” is the northwest Atlantic, where between 40 and 100 percent of the seafloor has been dissolved “at its most intense locations,” the study authors write. In these areas, the “calcite compensation depth,” or the layer of the ocean that does not have any calcium carbonate, has risen more than 980 feet. Olivier Sulpis, an earth science researcher at McGill University and lead author of the study, tells Haskins that the northwest Atlantic is particularly affected because ocean currents usher large amounts of carbon dioxide there. But smaller hotspots were also found in the Indian Ocean and the Southern Atlantic.
“[The ocean] is doing its job just trying to clean up the mess, but it’s doing it very slowly and we are emitting CO2 very fast, way faster than anything we’ve seen since at least the end of the dinosaurs,” Sulpis tells Brian Kahn of Earther.
Ocean acidification is threatening corals and hard-shelled marine creatures, like mussels and oysters, but scientists still don’t know how it will affect the many other species that make their home at the bottom of the sea. If past acidification events are any indication, the outlook is not very good. Some 252 million years ago, huge volcanic eruptions shot massive amounts of carbon dioxide into the air, causing the rapid acidification of the world’s oceans. More than 90 percent of marine life went extinct during that time.
Some scientists refer to the current geologic period as the “Anthropocene,” a term that refers to the overwhelming impact modern-day humans are having on the environment. The authors of the new study believe that the burn-down of seafloor sediments once rich in carbonate will forever change the geologic record.
“The deep sea … environment,” they write, “has indeed entered the Anthropocene.”