FIP ratios per year from 2001 to 2010. The columns show the FIP ratios for Fe, Mg, and Si. Each row corresponds to the same year. In each panel, a 2D histogram of all 12 min observations of FIP ratios vs the from the respective year are shown. Each vertical slice is normalized to its maximum. The number of contained data points is given in the inset of each panel. The dashed horizontal line indicates a FIP ratio of one. The gray solid line marks the median of the FIP ratio in each respective O charge state ratio bin.