Thawing permafrost in the Arctic Circle is having an unexpected side effect: it’s turning northern lakes and ponds brown.
Permafrost contains massive amounts of carbon, and scientists have predicted in the past that thawing permafrost could release all of that carbon. Now, they’re seeing evidence of just that.
A new study by an international team of scientists from Canada, Finland, Sweden and Denmark looked at 253 freshwater Arctic and subarctic lakes and ponds. They found that as permafrost melts and releases organic carbon, it makes its way to these northern ponds and changes their chemical makeup.
“Land-derived organic carbon is having a growing influence on Arctic and subarctic ponds, which carries over into the food web,” the study authors said. “The browning of these systems leads to oxygen depletion and cooler water at the bottom of the ponds, which can have a major impact on the microbial activity responsible for the production and consumption of greenhouse gases, particularly the production of methane, a powerful greenhouse gas.”
The carbon that is leaching into northern lakes and ponds is good at absorbing sunlight, the researchers said. That in turn makes the water darker and more stratified, which has a profound effect on the plants, animals and other organisms that live within them.
The team of scientists analyzed chemical, biological, optical, and isotopic measurements taken at the more than 200 bodies of water in 14 different circumpolar regions to come to their conclusions. The samples were all taken between 2002 and 2016, and 55 of the ponds were sampled multiple times.
Though there were variations between all of the ponds, the effects of the thawing permafrost could be observed in catchment soil, the scientists said.
The study has been published in the journal Limnology and Oceanography Letters. Core funding was provided by the Canada Research Chairs Program and the Centre for Northern Studies.
By Kyla Cathey, Earth.com staff writer