Evapotranspiration across plant types and geomorphological units in polygonal arctic tundra

•Microtopographic variations in polygonal tundra explain most spatial variation in ET.•ET from mosses and open water was twice as high as that from lichens and bare ground.•ET from polygon troughs and low-centers was higher than from edges and high-centers.•Polygon degradation may have a strong effect on the spatial pattern of ET.•Seasonal ET was decoupled from carbon fluxes, suggesting high E/ET ratios in early summer.