Climate warms. Permafrost (permanently frozen ground) melts. It forms lakes. Organic matter that was previously frozen is released in the bottom of these lakes. Microbes eat that organic matter. It produces methane. Lakes burp out methane. Methane is a greenhouse gas. (Not only arctic lakes emit methane, temperate and tropical lakes do it as well, through different processes).
The question is: what amount of methane is released by lakes all around the arctic, by what type of lakes.
To answer that question, we have two combined methods:
Bubbles traps (plastic skirts) put on high emitted spots on lakes.
Transects (a sweet word to my ears). We do 2 or 3 by studied lake. We shovel a 1x50m on the lake, then splash it with water to have a good visibility. Then we walk along the transect, identify the type of bubble we see, measure them, and GPS them. Afterwards, to each type of bubble is assigned a mean flux, then the emission values are extrapolated to the whole lake. We also measure ice thickness, water depth, make sediment, gas and water samples..
The goal of the field trip I was in was to have a good idea of lake emissions alomg a North-South transect from Fairbanks to the Kenai Peninsula (South Coast of Alaska, East of Anchorage). We surveyed 13 lakes along this North-South gradient, everytime making transects and samples.