Our ability to quantitatively reconstruct Arctic paleo-sea-ice distributions has been greatly improved by a novel biomarker approach which is based on the determination of a highly-branched isoprenoid (HBI) with 25 carbon atoms (C₂₅ HBI monoene = "IP₂₅"), a biomarker only biosynthesized by diatoms living in the Arctic ice (Belt et al., 2007). There is, however, one ambiguity in the interpretation of IP₂₅ data: IP₂₅ is absent under a permanent ice cover limiting light penetration and, thus, sea-ice algal growth, i.e., IP₂₅ = 0 as it also would be under totally ice-free conditions (Fig. 1). Here, Müller et al. (2009, 2011) succeeded in overcoming this difficulty of interpretating IP₂₅ data by combining the environmental (sea surface) information carried by the sea-ice proxy IP₂₅ and open-water phytoplankton biomarkers in a phytoplankton-IP₂₅ index, the so-called “PIP₂₅ Index“ (Fig. 1).  The advantage of this approach is obvious when comparing distribution maps of IP₂₅, brassicasterol, and PIP₂₅, derived from a recent study of Arctic Ocean surface sediments (Fig. 2; Xiao et al., 2015). During the last years, a large number of IP₂₅/PIP₂₅ studies have been carried out to reconstruct the late Quaternary Arctic sea-ice history (see reviews Stein et al., 2012; Belt and Müller, 2013; example Fig. 3). More recently, it has been demonstrated that IP₂₅ is even preserved in Pliocene sediments (Stein and Fahl, 2013; Knies et al., 2014). Furthermore, a study of surface sediments in combination with numerical modelling results of the sea ice distribution showed that both methods successfully reproduce the degree and spatial distribution of the average ice coverage in the Fram Strait and Nordic Seas (Müller et al., 2011; Spielhagen et al., 2015).

At the AWI (partly in cooperation with Bergen University), several ongoing PhD projects are dealing with the reconstruction of the Arctic sea-ice history on different time scales (i.e., Pliocene, MIS 6 to 1, MIS 3 to 1, and Deglacial-Holocene) and different regions, using this biomarker approach (Fig. SeaIce4). In order to fully establish the IP₂₅ 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, are still needed. In this context, our study of IP₂₅ and other biomarkers also includes investigations of material from sea ice and sediment traps. 

AWI: R. Stein K. Fahl  J. Müller W. Luttmer

PhD students (AWI): T. Hörner A. Kremer H. Kolling

PhD students (Uni Bergen & AWI): C. Clotten, H. Sadatzki