Extended Data Fig. 5: Comparison of firn model scenarios.
From: Isotopic constraint on the twentieth-century increase in tropospheric ozone
Shown are results obtained with or without the deepest LOCK-IN data point, and with constant or SCRIPPS-based O2 trend estimates, as well as forward firn model tests of atmospheric model scenarios. Top left, ∆36 data in firn and ice (LOCK-IN in green, GISP2 in red, WAIS Divide in blue, Siple Dome in purple) plotted against mean 18O18O age, compared with atmospheric trends obtained by inverse firn/ice modelling. Shown also are the ±2σ-equivalent uncertainty envelope for the inverse model (long-dashed black lines) and the best-guess trends obtained using: the SCRIPPS-based O2 scenario and excluding the deepest LOCK-IN data point (short-dashed black line); a constant-O2 scenario and excluding the deepest LOCK-IN data point (red line); the SCRIPPS-based O2 scenario and all LOCK-IN data points (dashed grey line); and a constant O2 scenario and all LOCK-IN data points (blue line). Top right, δ18O18Ocor in firn and ice (defined in Methods, ‘Δ36 for firn modelling’; LOCK-IN in green, GISP2 in red, WAIS Divide in blue, Siple Dome in purple) plotted against depth, compared with model results in firn and ice using the SCRIPPS-based O2 scenario. The solid lines show the simulation excluding the deepest LOCK-IN data point and the dashed lines correspond to the simulation with all data points. Bottom left, ∆36 data in firn and ice (same colours as in upper panels) compared with simulated profiles using the forward firn model (LOCK-IN, solid lines; WAIS Divide, long dashed lines; GISP2, short dashed lines; Siple Dome, short–long-dashed lines). Outputs shown correspond to SCRIPPS-based atmospheric concentration trends for O2 and constant values for δ18O and ∆36 (black lines); constant values for O2, δ18O and ∆36 (grey lines; results are nearly the same as the black lines); SCRIPPS-based atmospheric concentration trends for O2 and constant values for δ18O, with the +25% box model scenario for ∆36 (orange lines); the +200% box model scenario for ∆36 (blue lines); and the +300% box model scenario for ∆36 (red lines).
