Rarely made detailed measurements of carbon dioxide and methane under lake ice reveal a story more complex than simple models of gas buildup, with surprising findings for climate change impacts.

Winter is coming, but for limnologists, winter, until recently, has often been ignored when it comes to lake biogeochemistry. Most mid and high latitude lakes are covered seasonally by ice, and what appears to be a quiet and dormant world to the ice skaters and snowmobiles atop is actually a complex world of decomposers and chemistry in the cold water below. These processes are suspected to have an important effect on the net annual budgets of lake carbon emission, but current theories are based on simple assumptions.

Denfeld et al. [2018] made rare measurements of under-ice carbon dioxide and methane concentrations in a small boreal lake in Sweden. Their measurements and mapping of lake carbon after ice off were coupled together to reveal a strong role of winter melt event driving external carbon inputs leading to under-ice carbon build-up. Further, the ratio of methane to carbon dioxide accumulation shifted through the winter.

With climate projections showing warmer winters and less consistent ice cover, the future may make winter lake dynamics an even more prominent component of lake carbon cycling, influencing dynamics regarding lake nutrients and water quality, and also the contribution of freshwaters to the global carbon budget and climate change feedbacks.

Citation: Denfeld, B. A., Klaus, M., Laudon, H., Sponseller, R. A., & Karlsson, J. [2018]. Carbon dioxide and methane dynamics in a small boreal lake during winter and spring melt events. Journal of Geophysical Research: Biogeosciences, 123. https://doi.org/10.1029/2018JG004622

—Ankur Rashmikant Desai, Editor, JGR: Biogeosciences