Derived from the lipid fraction of 2G-GDGTs purified using the published protocol of preparative HPLC (Biddle et al., 2006; open symbols) or the orthogonal method developed in this study (solid symbols). Except for a few single measurements, most results are the means and standard errors of duplicate or triplicate analyses. The shaded bars (in gray color or as slashes) mark the isotopic values of the time-zero samples.-999.999 = below detection limit-888.888 = not determined-777.777 = not applicable