Fig. 4
From: Reduced marine phytoplankton sulphur emissions in the Southern Ocean during the past seven glacials
Relationship between residual nssSO42− flux and δ18O at Dome Fuji (DF). a Residual nssSO42− flux, considering only the terrestrial CaSO4 contribution, plotted against δ18O14,15. b Residual nssSO42− flux considering the contributions of CaSO4, MgSO4, Ca(NO3)2, and Mg(NO3)2 plotted against δ18O14,15. Residual nssSO42− flux and δ18O are averages over 1000 years. Before averaging, the δ18O depths that differ from the ion data depths have been interpolated to match. Straight lines in a and b display results of linear regressions. Correlation coefficients (r) were calculated with sample size (n) = 681 and for significance level (α) = 0.05. c Normalized power spectra of residual nssSO42− flux and δ18O at DF. The residual nssSO42− flux was calculated in the same manner as b. Power spectra were calculated with the Blackman-Tukey method (30% lag) using the Analyseries software package55 (see Methods). To use the software, the raw data were resampled to a 200-yr interval using linear interpolation
