Fjords – the long, narrow marine inlets in places like Scandinavia, New Zealand and Alaska – are the stuff of myths and legends and happen to be among the most beautiful natural features on Earth. They’re also, according to a study published in Nature by a diverse group of researchers, excellent at absorbing excess carbon.
Despite accounting for only .3% of Earth’s surface, fjords manage to soak up 11% of the carbon absorbed by marine sediment – to the tune of 18 metric tons per year. Their ability to retain so much carbon (thereby preventing it from being released into the atmosphere as a greenhouse gas) may be important as the planet warms and glaciers melt, creating more fjords.
“Carbon sequestration is the big buzzword, but we’re still getting a handle on how it works,” said Thomas Bianchi, a University of Florida geochemist on the team that made the discovery. In order to make informed land-use decisions and accurate climate predictions, “finding and understanding these hot spots is critical,” he said.
Fjords are actually uniquely positioned to be major carbon sinks. For starters, they’re often flanked by lush, richly-forested cliffs and banks, which is the ideal location for collecting carbon-rich soil runoffs. Compared to oceans and river deltas, which are typically bordered by sandy beaches or wetlands, and the fjords’ advantage is clear. Their long, deep construction also plays a part – the carbon-rich sediment sinks to low-oxygen zones in the water, where it’s unlikely to be consumed by bacteria and pumped back into the atmosphere as a greenhouse gas.
“It’s amazing that systems that are so small can have such a huge global impact,” Bianchi said. “It sends the message that fjords are not only beautiful, they’re providing a very important service.”
While scientists were aware that fjords had the potential to act as major carbon sinks, most research focused on river deltas due to their larger surface area. However, when averaged by area, fjords buried carbon at a rate double that of the oceans overall.
The study looked at fjords all across the globe, starting with New Zealand. They then compared their results with previous data from the Arctic, sub-Arctic Canada, British Columbia, Norway, Sweden, Scotland, Greenland, Svalbard, Alaska, Chile, and Antarctica. There’s still much to learn – they found that Alaska’s fjords absorb much more carbon than those in other area, but have no idea why.
Part of the difficulty in studying fjords is that they’re difficult to access. Unlike rivers and oceans, which can typically be accessed by car or boat, fjords tend to be isolated – some can only be reached by helicopter. Because they’re formed by receding glaciers, they also happen to occur in places where its cold. It’s obviously difficult, if not impossible, to take sediment samples from a fjord covered in ice. Satellite data, which can easily estimate the surface area of larger marine environments, isn’t much help in mapping a fjord that’s only 2km wide.
The role of fjords in carbon sequestration will only grow larger. As the planet warms, more glaciers will melt, creating more fjords. Their knack for carbon containment will be important in battling future climate change, though researchers caution that even carbon sinks as efficient as fjords are no match for what humans pump into the atmosphere.