Extended Data Fig. 1: Loss of seasonal cycle amplitude shown in the spectral domain.
From: Limitations of ice cores in reconstructing temperature seasonality
Power spectral density of reanalysis daily surface air temperature at the coring site6, the WDC δD data covering the same time-period7 and as an example for the deeper ice record, the diffusion corrected and raw J23 WDC δD data of a time-window of the same length 5ka BP (as in J23, Fig. 1a). Shading indicates 90% confidence intervals. The ratio of the variance in the frequency band around the annual cycle (1/1.2-1.2) yr−1 (vertical dashed lines) is 0.222 (1979-2005) and 0.212 (5ka BP diffusion corrected) showing that only about 20% of the amplitude is preserved. The results are not sensitive to the choice of the time-window.
