How the Ocean 'Breathes': Migrating Deep Sea Creatures Suck Oxygen

Oxygen circulates through our oceans, allowing it to "breathe" as levels dip up and down. Now, though, scientists have discovered that deep sea creatures that rise to the surface at night to feed have a major impact on these levels, changing the way we think about the ocean.

Deep sea animals live within the darkness of the ocean. Yet hundreds of feet below the surface, there is little food to be found. That's why these creatures will rise to the surface at night, taking advantage of the natural cover in order to feed on the creatures by moonlight. They then retreat back to the depths, consuming vast amounts of oxygen from what is known as the "oxygen minimum zone."

It's this oxygen consumption that has interested researchers. The sheer number of animals that live at these depths, about 650 feet to 2,000 feet beneath the surface, means that their oxygen consumption could be massive.

"Generally, scientists have thought that microbes and bacteria primarily consume oxygen in the deeper ocean," said Daniele Bianchi, postdoctoral researcher at McGill University, in a news release. "What we're saying here is that animals that migrate during the day are a big source of oxygen depletion. We provide the first global data set to say that."

So how did researchers find how much oxygen was being consumed? They produced a global model of oxygen depletion and diel vertical migrations (DVMs). These migrations are the movements that you can see among deep sea species as they move up and down the water column. More specifically, they mined acoustic oceanic data collected by 389 American and British research cruises between 1990 and 2011. This allowed them to see how many animals ascended and descended and correlate it to the samples they took from various locations.

In the end, they found that the global consumption of the gas is between 10 and 40 percent of the oxygen at these depths. They also found that the deep ocean can just barely replenish this oxygen consumed during these mass migrations. And this balance could be easily upset, especially with the onset of climate change.

"If the ocean oxygen changes, then the depth of these migrations will also change," said Bianchi in a news release. "We can expect potential changes in the interactions between larger guys and little guys. What complicates this story is that if these animals are responsible for a chunk of oxygen depletion in general, then a change in their habits might have a feedback in terms of oxygen levels in other parts of the deeper ocean."

The findings are crucial for better understanding this deep ocean habitat. In addition, it shows the underappreciated role that these animals have in ocean chemistry on a global scale. It also reveals the importance of understanding the changes that could result in the deep sea due to climate change.

The findings are published in the journal Nature Geoscience.