Glacier-fed rivers might help trap greenhouse-gas emissions at the same time global heating threatens their health, suggests a new study.
University of Alberta biology PhD student Kyra St. Pierre and her team published a study Aug. 19 in the Proceedings of the National Academy of Sciences on how glacier-fed lakes and rivers were a surprise new carbon sink.
St. Pierre, who is now at the University of B.C., said she and her team were studying the Lake Hazen watershed on Ellesmere Island when they noticed dissolved CO2 levels in the lake and its rivers were much lower than levels in the air above, implying that they should be sucking up CO2 (as gases naturally flow from high to low concentrations).
That was a surprise, as scientists previously thought rivers were CO2 sources on account of all the stuff living, breathing and rotting in them, St. Pierre said. But glacial areas like Lake Hazen are mostly ice and rock, so they don’t have all that biological material in their water.
Based on changes in CO2 concentrations over distance, carbon isotopes, and the cations in the water, St. Pierre and her team determined that chemical weathering of rocks in this watershed was trapping CO2 faster than it was being absorbed from the air, making the watershed a carbon sink – and potentially a huge one.
“In high melt years, you get up to 40 times greater of a carbon sink than the Amazon rainforest,” she said, based on carbon absorbed per square metre.
St. Pierre said the team believes this may be true for other glacier-fed river systems such as the North Saskatchewan, but it’s tough to say how significant of a sink they might be, as so little research has been done on this aspect of them.
The team also found these sinks wouldn’t last. More global warming means more melt-water, weathering and CO2 trapping, but also less ice to melt. Most glaciers south of the Arctic are already past their peak melt rates, suggesting they’ll become less effective sinks as warming continues.
“It’s a very short-term sink at this point,” St. Pierre said.
Retired U of A water biologist David Schindler, who was not involved with this study, said in an email that its results made sense, as glacier ice formed when the air had less CO2 in it.
“But the message is a sad one,” he continued: atmospheric CO2 levels have been on the rise since 1957 despite this significant sink, and will rise even faster once this glacier ice disappears.
“Climate change is no joke, and measures to reduce it must be the most important item on the political agenda for the next 50 years, if we are not to suffer both expensive and socially disruptive long-term consequences.”
The study is available at bit.ly/2Z8ZffB.