Fig. 4: Methane concentrations and carbon isotopic compositions of methane in proglacial groundwaters.
From: Groundwater springs formed during glacial retreat are a large source of methane in the high Arctic
a, Histogram of measured methane concentrations in proglacial springs (nM, n = 123). Note: log scale on the x axis. b, Methane concentrations sorted by outcropping geology at the sampling site. Note: log scale on the y axis. (Palaeogene and Neogene: n = 25; Early Cretaceous: n = 45; Middle–Late Jurassic: n = 16; Triassic–Middle Jurassic: n = 27; Carboniferous and Permian: n = 10.) c, Distribution of δ13C–CH4 values of sampled groundwaters with high enough methane concentrations for isotopic analysis (n = 36). In b,c, boxes range from the 25th percentile to the 75th percentile; the line across the box represents the median; the whiskers extend to the maximum and minimum values; circles beyond this range represent outliers.
