Extended Data Fig. 6: Results of sensitivity tests on atmospheric trend reconstructions from the inverse firn model.
From: Isotopic constraint on the twentieth-century increase in tropospheric ozone
∆36 data in firn and ice (stars with ±2 s.e.m. uncertainties shown as vertical bars; LOCK-IN in green, GISP2 in red, WAIS Divide in blue, Siple Dome in purple) plotted against mean 18O18O age and compared with modelled atmospheric trends (lines). The solid black line is the preferred scenario, obtained using a SCRIPPS-based O2 concentration trend and excluding the deepest LOCK-IN data point, with its uncertainty envelope shown alongside (dashed black lines). The left panel shows the simulation that includes the deepest LOCK-IN data point (red line), a simulation with the deepest LOCK-IN data point corrected (grey star) from a maximum estimate of 10% surface air contamination (purple line), tests of the sensitivity to the optimal solution (grey lines; see Methods, ‘Sensitivity tests on atmospheric trend reconstructions’), the simulation excluding WAIS Divide data (blue line), and simulations excluding the Siple Dome data (green solid line) or excluding the Siple Dome data and using NEEM-US-data-based diffusivity to simulate WAIS Divide firn (green dashed line). The dashed grey line shows that a straight trend with a weak slope can remain in the uncertainty envelope. The right panel shows tests of LOCK-IN firn physics parameters (green; see Methods, ‘Sensitivity tests on atmospheric trend reconstructions’) and tests of LOCK-IN diffusivity constrained with field data only (blue), all nearly superimposed to the preferred trend.
