Carbon released from glaciers could alter ecosystems

Long considered lifeless, polar ice sheets and mountain glaciers are in fact teeming with microbial life. Over millennia, these bacteria have contributed to the accumulation of billions of tons of organic carbon within the ice, which, when the glaciers retreat and the ice sheets melt, will be fed back into the water cycle. By 2050, the amount of organic carbon released could be equal to the amount carried by the Amazon river in a year, says a recent article in Nature Geosciences, co-authored by Tom Battin, who inaugurated the Stream Biofilm and Ecosystem Laboratory at ENAC earlier this year. The study was led by researchers from the Universities of Alaska and Florida.

Organic carbon plays a central role in aquatic ecosystems, where it feeds the tiny organisms that occupy the lowest rungs of the food ladder. As it enters river, the carbon acts as what the authors refer to as a “subsidy” to aquatic ecosystems. Microorganism populations flourish as they consume this plentiful source of energy, with potential consequences across the food chain. By expiring CO2 in the process, the microorganisms link the hydrological cycle and the carbon cycle.

This notion that melting ice has consequences beyond the global water cycle is relatively new. “When we think of melting glaciers, we usually think of rising sea levels and the hydrological cycle. But over the past years, it has become increasingly clear that they have a important impact on the global carbon cycle as well,” says Battin. Moreover, research suggests that previously ice-locked organic carbon is highly available to microorganisms, which means that it this impact could be almost immediate.

For their study, the researchers compiled existing data on glaciers and ice sheets around the world to take stock of the organic carbon frozen into terrestrial ice masses and make predictions on its fate. By combining measurements of ice-locked carbon in several ice environments with data on the volume of ice stored in the planet’s glaciers and ice sheets, they estimated the total amount of frozen organic carbon on the planet to be roughly 6 petagrams, or 6 billion metric tons. Estimates of current and future ice melt allowed them to make predictions on the dynamics of organic carbon release back into the hydrological cycle.

According to Battin, Switzerland is an ideal real-world laboratory to study the consequences of the release of ice-locked organic carbon into streams and rivers on riverine ecosystems and their biodiversity, and he looks forward to investigating these questions in coming years.