Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution

• Published in: Nature Communications
• Main Authors: Wang, Karen Jiaxi, Huang, Yongsong, Majaneva, Markus, Belt, Simon T., Liao, Sian, Novak, Joseph, Kartzinel, Tyler R., Herbert, Timothy D., Richter, Nora, Cabedo-Sanz, Patricia
• Format: Text
• Language: English
• Published: Nature Publishing Group UK 2021
• Subjects: Article; Greenland; Svalbard; Sea ice
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782803/; http://www.ncbi.nlm.nih.gov/pubmed/33397905; https://doi.org/10.1038/s41467-020-20187-z

Alkenones are biomarkers produced solely by algae in the order Isochrysidales that have been used to reconstruct sea surface temperature (SST) since the 1980s. However, alkenone-based SST reconstructions in the northern high latitude oceans show significant bias towards warmer temperatures in core-tops, diverge from other SST proxies in down core records, and are often accompanied by anomalously high relative abundance of the C(37) tetra-unsaturated methyl alkenone (%C(37:4)). Elevated %C(37:4) is widely interpreted as an indicator of low sea surface salinity from polar water masses, but its biological source has thus far remained elusive. Here we identify a lineage of Isochrysidales that is responsible for elevated C(37:4) methyl alkenone in the northern high latitude oceans through next-generation sequencing and lab-culture experiments. This Isochrysidales lineage co-occurs widely with sea ice in marine environments and is distinct from other known marine alkenone-producers, namely Emiliania huxleyi and Gephyrocapsa oceanica. More importantly, the %C(37:4) in seawater filtered particulate organic matter and surface sediments is significantly correlated with annual mean sea ice concentrations. In sediment cores from the Svalbard region, the %C(37:4) concentration aligns with the Greenland temperature record and other qualitative regional sea ice records spanning the past 14 kyrs, reflecting sea ice concentrations quantitatively. Our findings imply that %C(37:4) is a powerful proxy for reconstructing sea ice conditions in the high latitude oceans on thousand- and, potentially, on million-year timescales.