Triangles are 48 training lakes from five geographic regions in Alaska, representing boreal and tundra ecosystems, yedoma and non-yedoma soils, thermokarst, kettle, and anthropogenic lakes resulting from gold or gravel extraction. The regression model for these lakes (backscatter = 1.0*10−3x + 0.019, r2 = 0.91, P < 0.01, n = 48) was inverted (Fig. 1b) to estimate ebullition in individual lakes and regional-scale lake maps. Dotted lines delineate 95% confidence interval. Circles are 16 validation lakes where additional field work was performed in 2016 and 2017 in two geographic regions in Alaska, showing good agreement with the model, but not included in the model.