Polar sea ice variability - Arctic Our ability to quantitatively reconstruct Arctic paleo-sea-ice distributions has been greatly improved by a novel biomarker approach [...] 25 , brassicasterol, and PIP 25 , derived from a recent study of Arctic Ocean surface sediments (Fig. 2; Xiao et al., 2015 ). During the last years, a large number of IP 25 /PIP 25 studies have been [...] the IP 25 approach as key proxy for the reconstruction of past Arctic Ocean sea-ice conditions, however, more ground-truth data related to the synthesis, diagenesis, and preservation of this biomarker