The ocean twilight zone could store vast amounts of carbon captured from the atmosphere – but first we need to build a 4D system to track what's going on down there
Published in Science & Technology News
Deep below the ocean surface, the light fades into a twilight zone where whales and fish migrate and dead algae and zooplankton rain down from above. This is the heart of the ocean’s carbon pump, part of the natural ocean processes that capture about a third of all human-produced carbon dioxide and sink it into the deep sea, where it remains for hundreds of years.
There may be ways to enhance these processes so the ocean pulls more carbon out of the atmosphere to help slow climate change. Yet little is known about the consequences.
Peter de Menocal, a marine paleoclimatologist and director of Woods Hole Oceanographic Institution, discussed ocean carbon dioxide removal at a recent TEDxBoston: Planetary Stewardship event. In this interview, he dives deeper into the risks and benefits of human intervention and describes an ambitious plan to build a vast monitoring network of autonomous sensors in the ocean to help humanity understand the impact.
The ocean is like a big carbonated beverage. Although it doesn’t fizz, it has about 50 times more carbon than the atmosphere. So, for taking carbon out of the atmosphere and storing it someplace where it won’t continue to warm the planet, the ocean is the single biggest place it can go.
Ocean carbon dioxide removal, or ocean CDR, uses the ocean’s natural ability to take up carbon on a large scale and amplifies it.
Carbon gets into the ocean from the atmosphere in two ways.
In the first, air dissolves into the ocean surface. Winds and crashing waves mix it into the upper half-mile or so, and because seawater is slightly alkaline, the carbon dioxide is absorbed into the ocean.
The second involves the biologic pump. The ocean is a living medium – it has algae and fish and whales, and when that organic material is eaten or dies, it gets recycled. It rains down through the ocean and makes its way to the ocean twilight zone, a level around 650 to 3300 feet (roughly 200 to 1,000 meters) deep.
The ocean twilight zone sustains biologic activity in the oceans. It is the “soil” of the ocean where organic carbon and nutrients accumulate and are recycled by microbes. It is also home to the largest animal migration on the planet. Each day trillions of fish and other organisms migrate from the depths to the surface to feed on plankton and one another, and go back down, acting like a large carbon pump that captures carbon from the surface and shunts it down into the deep oceans where it is stored away from the atmosphere.
The single most shocking sentence I have read in my career was in the Intergovernmental Panel on Climate Change’s Sixth Assessment Report, released in 2021. It said that we have delayed action on climate change for so long that removing carbon dioxide from the atmosphere is now necessary for all pathways to keep global warming under 1.5 degrees Celsius (2.7 F). Beyond that, climate change’s impacts become increasingly dangerous and unpredictable.