The Seabed is Breathing. If We Listen, We Can Learn About the Future’s Climate

Breathe.
Inhale. Exhale. Repeat.
And notice how essential your breathing is.

The same is true for the deep sea. Across the ocean floors of the world, sediments open up to oxygen. They inhale. Exhale. Repeat. This breathing, too, is essential — not just for life in the deep, but for life on Earth.

- The deep sea is incredibly important. It provides food and resources. It supports biodiversity. It plays a key role in regulating the Earth’s climate. But it’s also under growing pressure from pollution, human activity, and climate change. We need to understand how to help the oceans continue to support us — and studying the ocean floor’s breathing can teach us a lot, says Wenjie Xiao, a biogeochemist researching microbial activity on the deep seafloor.

The scientific term for this "breathing" is sediment respiration. Even in the darkest and deepest parts of the ocean, microbes live within sediment layers, using oxygen to break down organic matter. These microbes help regulate global cycles of key elements such as nitrogen, manganese, iron, sulfate, and methane.

The oceans hold the largest reservoir of reactive organic carbon on Earth. Some of it gets stored in deep sediments, while some gets broken down by microbes — and released as CO₂.

- CO₂ is a greenhouse gas, and the amount released from the seabed has a major impact on our long-term climate. If we want to understand what’s happening — and make reliable predictions about what the future climate might look like — we need to quantify how much carbon is escaping from the ocean floor, Xiao explains.

Monitoring Ocean’s Breathing

To do that, Xiao suggests to launch an ambitious project to monitor deep seabed respiration. The deep sea is defined as parts of the ocean that lie more than 1,000 meters below the surface.

This idea would involve measuring oxygen dynamics on the deep-sea floor and collecting sediment samples from a range of deep-sea sites, chosen to represent different environments with varying temperature, productivity levels, distance from land, and depth.

- In the sediments, we find biomarkers — molecular fingerprints that record how microbes are living, and even how they once lived. By analyzing biomarkers from warmer periods in Earth’s past, we can see how microbes responded to warming back then — and use that knowledge to predict how they might react to warming in the future.

The Microbes Have Been Writing a Diary for Millions of Years

Xiao compares the deep-sea sediment record to an ocean diary, written by the microbes themselves:

- If we can get this monitoring system up and running, it would be like reading the pages of the ocean’s diary — a diary that’s been written by microbes over millions of years.

Collecting sediment samples is relatively routine on research expeditions. Retrieving oxygen measurements, on the other hand, are more technically challenging. That’s why Xiao proposes a large, coordinated effort to collect enough high-quality oxygen data to build a reference library. Once that’s in place, future studies could take advantage of simpler, faster sampling methods.

We Need to Live More Wisely and Responsibly

- As a scientist, I want to contribute to climate and ocean research. As a human being, I care about helping others understand this beautiful and complex planet — how we’re all part of a larger system, and how that awareness can help us live more wisely and responsibly on Earth, Xiao says. 

The ocean represents around 60% of Earth’s surface. Most of it is still unexplored, but there is a general, scientific consensus that the deep sea harbors a wealth of genetic resources, minerals, raw materials, and pharmacologically promising organisms, waiting to be discovered.

So far, the deep sea has given us ecteinascidin, a compound derived from tunicates that has proven effective against certain cancers. Some deep-sea sponges have shown antimicrobial properties, and a substance from the snail Conus magnus works as a powerful painkiller.