HBIs and Sterols in Surface Sediments Across the East Siberian Sea: Implications for Palaeo Sea-Ice Reconstructions

Highly branched isoprenoids (HBIs) in marine sediments have emerged as promising semi-quantitative proxies to reconstruct seasonal sea ice in polar oceans. In this work, we examine the distribution of sympagic HBIs (IP25 and HBI-II), pelagic phytoplankton biomarkers (brassicasterol, dinosterol and HBI-III) as well as terrestrial sterols (campesterol and beta-sitosterol) in the surface sediments of the East Siberian Sea (ESS) to test their reliability as sea-ice proxies under continental run-off influence. Our data suggest that dinosterol performs better than brassicasterol to assess sea ice across the ESS shelf, yet the correlation between PDIP25 and spring sea ice is relatively weak but improves when removing sites with salinity <25. Strongest relationship is found between PIIIIP25 and summer sea ice in regions remote from riverine influence. Overall, our results show that semi-quantitative estimates of sea ice based on biomarkers can be problematic in Arctic Ocean margins because of biases induced by continental run-off on biological productivity and sea-ice production.