Not Just Sea Level Rise: Melting Glaciers Release Vast Amounts of Carbon, Study Finds

What happens when waterways become inundated by glacial organic carbon? It could have short term benefits and very long term harm. Robert Spencer/Florida State University

As the world warms, glaciers around the world are rapidly hemorrhaging ice and threatening catastrophic sea level rise. But melting glaciers also pose another kind of menace: the release of vast amounts of stored organic carbon into waterways.

Florida State University assistant professor Robert Spencer and his colleagues have spent nearly a decade researching this overlooked aspect of glacial melt. In a paper published Monday, the team presented the first-ever estimate of how much carbon is due to be unlocked as the glaciers disappear — and just how little is known about what that might mean for aquatic ecosystems and the fate of surrounding fisheries.

By 2050, roughly 15 teragrams of dissolved organic carbon is due to be released into waterways from melting glaciers, the team estimates. For context, one teragram is a trillion grams, and fifteen teragrams is the equivalent of half the dissolved organic carbon that flows through the Amazon River each year. Put another way, it's a whole lot.

Glacier 2
Robert Spencer Robert Spencer/Florida State University

But what happens when waterways become inundated by glacial organic carbon? Spencer says that scant research means scientists are not entirely sure. But they do know that glacial organic carbon is a very good food source for the carbon-eating organisms at the bottom of the food chain—much better than other types of organic carbon, which usually gets into waterways from forests and wetlands.

"So the microbes at the base of the food web would use this carbon much more readily," says Spencer. "It's like putting a cake in front of them. The effect cascades up the food web, to insect larvae, then fish, then birds, and so on."

This might initially result in a more productive ecosystem. Fisheries may see fish populations go up. But it won't last. Once glaciers disappear or decline to the point where their contribution of carbon is negligible (an outcome Spencer says is now inevitable) the nutrition source will disappear for good. Plus, without glacial freshwater feeding into streams, water temperature will go up, potentially harming habitats for certain fish that need cold water to survive.

"In the short term, we'll see more productivity. But it's a short term boom for a very long term loss. It could be a double edged sword. [When] glaciers decline, they're not coming back," Spencer says. He emphasized that much more research is required to fully understand the relationship between glacial organic carbon and fisheries.

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Robert Spencer/Florida State University

Glaciers across the globe are melting. Already, 40 percent of the glaciers on the Tibetan plateau are projected to disappear by 2050. An ice sheet in West Antarctica is shedding a volume of ice equivalent to Mount Everest every two years. The Mendenhall Glacier, a popular destination for visitors to Southeast Alaska, has retreated roughly 1.3 miles in the last 50 years. When Spencer returns to Alaska each summer, he says he can clearly see how much the glaciers have shrunk since the summer before. "It's an ongoing story of misery," he says, likening the speeding rate of melt to an ice cube on a countertop. It begins to melt slowly. For a while, you still have something that looks like an ice cube. But at a certain point, it begins to melt very fast. Suddenly, you have a puddle.

"You're going to reach a tipping point in the quite near term. We're talking about major loss of glaciers in our lifetime."