Using semi-automated bubble traps, bubble survey transects, and point process models to understand ebullition spatial heterogeneity in thermokarst lakes

Ebullition is an important but highly heterogeneous mode of methane emission in lakes. Variability in both its spatial distribution and temporal flux results in large uncertainties in whole-lake emission estimates based on limited field measurements. Analysis of 213,600 short-and long-term flux measurements using submerged bubble traps on 162 ebullition seeps in 24 panarctic lakes confirmed that seep classes, identified according to bubble patterns in winter lake ice, have statistically distinct associated fluxes irrespective of lake or region. To understand the drivers of ebullition's spatial variability we combined point-process modeling with field measurements of 2,679 GPS-marked and classified ebullition seeps in three Alaskan thermokarst (thaw) lakes that varied by region, permafrost type, and seep distribution. Spatial analysis of field data revealed that seeps cluster above thawed permafrost soil mounds in lake bottoms. Soil mounds are the ice wedge polygon centers and thus part of a regular micro-scale landscape pattern across permafrost landscapes, which makes their distribution (including on lake bottoms) also predictable.