Is This Stormy Sea a Climate Friend or Foe?
WHY YOU SHOULD CARE
Because the Southern Ocean will tell us a lot about how much — and how fast — the planet is warming.
By Virat Markandeya
It was aboard the M/V Benguela Stream that Peter Landschützer took a photo of a sunset while crossing the Atlantic Ocean, off the continental shelf. The cargo ship was not only transporting bananas from the Caribbean to the United Kingdom but also serving as a voluntary observation ship where Landschützer, then a doctoral student, could take measurements of the ocean. He had fallen seasick, recovered and, at that moment, literally saw the clouds part.
“When you do marine science, getting a data point is really, really tough,” says Landschützer, 34, a group leader at the Max Planck Institute for Meteorology in Hamburg, Germany, of the photo that often begins his presentations. “This reminds me what it takes to understand the ocean.”
That understanding is becoming an existential question for humanity. Landschützer’s groundbreaking work focuses on the Southern Ocean — the mysterious, remote expanse around Antarctica that helps mitigate climate change by acting as a massive carbon sink. But how much carbon it consumes has been changing and is the subject of considerable scientific debate. The intense Austrian is at the forefront of figuring it all out.
This is, in fact, the only ocean on the globe that has turned from a source of carbon dioxide to a sink of carbon dioxide.
Landschützer has made a name for himself by coming up with a two-step method to create estimates of ocean carbon dioxide fluxes with sparse data points. The European Geosciences Union, while bestowing an early-career scientist award on Landschützer in 2019, called his method a gold standard for measuring the role that oceans play in the global carbon budget.
Since 1870, Earth’s oceans have absorbed a quarter of human-generated carbon dioxide, slowing down climate change. The Southern Ocean accounts for 40 percent of this global carbon sink. This power comes from the Antarctic Circumpolar Current, Landschützer explains, which takes surface waters into intermediate depths while very old and carbon-rich waters are reintroduced back to the surface. “This is, in fact, the only ocean on the globe that has turned from a source of carbon dioxide to a sink of carbon dioxide, from preindustrial times to now,” he adds.
How much of a carbon sink it is, though, has been the source of a flurry of scientific activity. In a 2015 paper published in the journal Science, Landschützer found that after some decline, the Southern Ocean’s carbon-absorbing abilities had been strengthening in recent years — meaning it had become more of a bulwark against climate change. But the carbon uptake was highly variable, and if trends reversed, it would lead to an acceleration in global warming. In particular, the paper showed that the large climate models used by the Intergovernmental Panel on Climate Change were underestimating the multiyear variation in the carbon uptake.
That 2015 paper relied on shipboard measurements that, though considered the most accurate, were sparse — particularly in winter. A 2018 paper using data from profiling floats, which come to the ocean surface and submerge to about 6,000 feet, estimated a considerably lower uptake of CO2 than Landschützer had.
Combining float and shipboard observations revealed that the answer lay somewhere in the middle. A November 2019 paper by Landschützer and others found a change in the estimate of carbon intake, but it was not as large as the indications from two years ago. Researchers are still working to figure out what the most accurate estimate of this carbon sink is — at a time when scientists are trying to account for a rapid acceleration in global warming.
“I would argue that he has really advanced our understanding of air-sea fluxes everywhere, but the Southern Ocean is where he has been particularly helpful,” says Christopher Sabine, a professor of oceanography at the University of Hawaii at Manoa.
Landschützer grew up close to nature in landlocked Austria, near the start of the Alps, with two family dogs. In the summer, he hiked for hours in search of forest mushrooms. He has a minimalist, orderly sensibility. He likes his desk clean and empty save for a computer screen. If there is paper around, it signals to him that work lies unattended.
Landschützer happened to begin his doctorate at an opportune time for availability of ocean data. The Surface Ocean CO2 Atlas, aka SOCAT, debuted in 2011, as he began his studies at the University of East Anglia. Dorothee Bakker, chair of the SOCAT initiative and one of Landschützer’s thesis advisers, says he distinguished himself by creating eye-catching graphs to go along with his research. “He’s clearly a very strong scientist, but he’s also very driven, very dedicated,” Bakker says. “He knows what he wants to do.”
While data has been sparse in the Southern Ocean, particularly for the winter months, new autonomous methods are providing a way to complement shipboard observations. The Drake Passage, one of the few places where such shipboard observations are available, is, after all, only a line in a 7.8 million-square-mile expanse.
Landschützer used machine learning to come to terms with this sparse data. “He wrote the code and then he worked out what he thought was the best method for using a neural network approach,” Bakker says. “So the machine learning, to map carbon dioxide in the surface oceans, that really is his work.”
Aside from the now-widespread floats, there are saildrones, 7-meter-long autonomous vehicles, one of which was able to circumnavigate the Southern Ocean in more than six months. The saildrone carried an instrument developed by the National Oceanic and Atmospheric Association to measure carbon fluxes, much as ships do.
“The new autonomous sensors and new autonomous platforms are really revolutionizing how we see the ocean,” says Sabine. “They don’t really care if it’s rough. They don’t need to go into port.”
When looking at how fast the Earth is warming, the variations in the Southern Ocean’s carbon uptake become important in planning the next five to 10 years, says Landschützer, not some far-off future. “This is what matters to us right now,” he says.
- Virat Markandeya, OZY Author Contact Virat Markandeya