It seems humanity isn’t just content to screw up the surface of the planet. We’re going to do the deep ocean, too.
Findings published this week show that all the carbon dioxide piling up in the ocean’s dark depths is causing the seafloor as we know it to dissolve. The results, published this week in the Proceedings of the National Academy of Sciences, are yet another reminder this era of human history will leave a geological mark long after we’re gone.
There are a variety of ways that CO2 cycles through the Rube Goldberg contraption that is our planet. The ocean is one key component. Eventually, CO2 absorbed at the ocean’s surface makes its way to the depths of the ocean, where calcium carbonate helps convert it into bicarbonate.
This whole system has been working fine for millions of years, but human carbon emissions have started to throw it out of whack. Excess carbon dioxide reaching the deep ocean means that the natural system can’t keep up and the stores of calcium carbonate on the seafloor are dissolving. That also means the water at the bottom of the ocean—like the water at the top—is getting more acidic.
“[The ocean] is doing it’s 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,” said Olivier Sulpis, a PhD student at McGill University who led the research. “It’s an efficient mechanism. The problem is we are putting too much pressure on the mechanism.”
Using lab experiments, data collected from the deep seas, and models of ocean circulation, Sulpis and his colleagues found that there were hot spots where the ocean floor was rapidly dissolving. That includes the northwest Atlantic and Southern Ocean, where the bottom waters are relatively young and laden with carbon dioxide from human activities. At the Atlantic hot spot, there are some parts of the region where human carbon dioxide accounts for all of the dissolution happening on the seafloor. In the Pacific, where bottom waters are centuries-old, humanity has yet to leave an imprint, but the inexorable march of the ocean conveyor belt coupled with rising emissions ensure it will eventually see dissolution rates increase.
“The study appears to be robust and it’s amazing to me that the signal is as strong is as it is,” said Matthew Long, an ocean researcher at the US National Center for Atmospheric Research. “Humanity is a global influence.”
Now this isn’t to say that there’s a climate change-fuelled hole being bored into the ocean. But as CO2 dissolves more and more of the ghostly white calcium carbonate, different sediments will be left over. That means in millions of years, geologists—human, alien or otherwise—will be able to see a clear demarcation line of human activity in ocean sediment cores in addition to all the other junk ending up down there.
“There is not a single place on Earth that cannot feel our activity,” Sulpis. “We don’t know much about the seafloor, but even if we’ve never been there, we can still find plastic, CO2, all kinds of stuff.”
More immediately, it’s not yet clear how the seafloor will be affected by this dissolution. Sulpis said fossils dating to the last time oceans were this full of carbon dioxide can provide some clues as well as impacts we’re seeing closer to the surface from more acidic seas right now. We know, for example, that organisms that build calcium carbonate shells, including corals, are having a hard time. But all the worms and other weird things living in the deep ocean? We just don’t know what rising acidity means for them, which itself is extremely disconcerting.