What do IP25 and related biomarkers really reveal about sea ice change?

Significant changes to Arctic and Antarctic sea ice in recent decades has prompted the development and application of novel approaches to the reconstruction of past sea ice conditions over much longer timeframes. One such approach is based on the variable distribution of certain source-specific highly branched isoprenoid (HBI) lipid biomarkers in well-dated marine sediment records. Thus, IP25 and IPSO25 have emerged as useful proxy measures of seasonal sea ice in the Arctic and Antarctic, respectively. An overview of the salient features of IP25, IPSO25 and related biomarkers is presented, together with aspects that are currently less well-understood and potentially provide direction for future research. (C) 2018 Elsevier Ltd. All rights reserved.