Case Study: How the ocean breathes

Dr Helen Czerski from UCL Mechanical Engineering shares her experience in gathering data and understanding the carbon cycle of the ocean.

Using a ‘bubble camera’ in stormy seas to understand the carbon cycle of the ocean

Scientists have understood for some time that the ocean has a huge store of carbon. The ocean actually absorbs a third of the extra carbon dioxide humans are adding to the atmosphere through burning fossil fuels. This matters, because we urgently need to track how carbon flows between the land, ocean and atmosphere, and governments and policy-makers need better tools to monitor and evaluate carbon reduction strategies.

Yet we still don’t completely understand the physical mechanisms by which carbon dioxide is taken in by the ocean, or how other gases like oxygen are transferred across the surface – essentially the breathing process of the ocean. This knowledge is crucial for the carbon budget of the Earth, especially because of the need to predict how these processes will change in the future as the Earth system adapts to the changes that humans have caused.

In response to this, Dr Helen Czerski from UCL Mechanical Engineering has been working with scientists across the world to gather data and understand the process better. One important pillar of this was a research trip to the North Atlantic, supported by funding from the National Science Foundation (USA), the National Science Foundation (USA) and the Natural Environment Research Council (UK).

Research ships in stormy seas

“There are three big reservoirs of carbon on planet Earth,” Dr Czerski explains. “The atmosphere, the ocean and the land. The ocean is massive, but we tend to ignore it because we can’t see it. The atmosphere is less massive, but we pay a lot of attention to it because we walk around in it.” It’s hard to study the details of invisible dissolved gases moving around in the ocean, but it’s now a priority.

Dr Czerski explains how different parts of the ocean are essentially breathing in and breathing out.

“The ocean is this big engine that's overturning,” she explains. “It's breathing out at the equator, and it's breathing in at the high latitudes, like the North Atlantic.” Although scientists understand this process is happening, we don’t fully understand the mechanisms that control how much gas is coming and going, and how they might be affected as the planet warms up, if storms become more intense, or if other environmental factors change.

Research so far indicates that bubbles in the ocean may speed up the process of ocean breathing, but few people have tried to measure the bubbles themselves. Dr Czerski helped to design a novel high-resolution underwater optical instrument for imaging oceanic bubbles at the sea. This ‘bubble camera’ – the only one of its kind currently in use – was designed specifically to count the number of bubbles just below the ocean’s surface, in very rough conditions. She has taken the camera on research ships, working alongside other scientists looking at different aspects of the ocean’s breathing system.

“To answer the questions we have, you absolutely have to have data from the ocean itself,” Dr Czerski says. “And the only way to get that is to go to sea in a ship. We’re not at a stage where we can send robots, because we don’t know what the robots should be looking at.”

The research ship to the North Atlantic carried scientists across career stages, who measured the waves, the weather, the movement of the gases, physical oceanography and much more. Dr Czerski measured the bubbles with the bubble camera. “It takes photos in quite a specific way,” she explains. “Seafarers have seen stormy seas for centuries, but the interesting bit is just a metre or two below the surface. The surface can be going up and down by 10 metres, so you need to get into that bit where you definitely don't want to go as a person. It's really complicated and difficult to measure, so that's what the camera is for.”

An urgency to understand how the ocean breathes

During the six-week North Atlantic expedition, the team experienced three big storms and a number of smaller ones. Waiting for the storms was important to the project, as there was no existing data in violent conditions. The team needed to understand the difference that varying conditions make to the ocean’s breathing process. Dr Czerski was able to collect “the only direct bubble population data for the highest wind speeds that anyone’s ever taken.” She found that the top metre of the ocean is where the most important action is in terms of the breathing process and the role bubbles play.

However, there is a lot more work to be done to understand all the processes at play. “When you go out into these environments, it's not just about data collection, it's about seeing yourself as part of it,” says Dr Czerski. “It's messy, it's hard, it's dirty and it's physically exhausting. But we need to go into extreme environments to understand our own home.”

Dr Czerski explains that the ocean is the Earth’s buffer for a number of gases, with the atmosphere sitting on top. “The atmosphere is actually a relatively small reservoir of carbon and sitting right underneath it is this great big reservoir of carbon in the ocean,” she says. “Then you get the people trying to come up with ways to push carbon downwards.” One of these ideas includes biological methods such as seagrass, to increase the amount of carbon the ocean can take in. Another is carbon sequestration, where carbon is collected, turned into rocks and placed into the ocean. But there are currently no robust methods to monitor and evaluate whether these methods will work in the long term, and thus there’s no certainty about the long-term consequences.

Dr Czerski says the risk with this is that scientists don’t know enough about the carbon cycle of the ocean yet to know if the carbon will stay there. “People are in a hurry to solve a problem,” she says. “But it’s better to understand where carbon comes from and goes to, to have any chance of predicting what's going to happen in the future ocean.”