Diatom distributions delineated by lipid, genomic and microscopic observations: the imprint of past summer sea ice extent

In 2014 the RVIB Nathaniel B. Palmer was used to undertake a US-led voyage focused on a geological and oceanographic survey of the George V and Sabrina coastlines with respect to the history of the East Antarctic glacial ice drainage basins (NBP14-02). During this voyage biological survey work was undertaken to broaden methodological applications of the phytoplankton community beyond microscopic observations in an attempt to help with providing ground-truth data for both modern biological distributions and palaeo-oceanographic interpretations. Surface water, sampled and concentrated from the ship’s intake line, was filtered for algal lipid (isoprenoid) and genomic analysis. Preliminary results from all three applications are presented and considered across the sampling locations ranging from the permanently open ocean zone (POOZ) with no seasonal sea-ice cover, the near-shore summer sea ice zone (SIZ), where sea ice remains long into the summer melt season, and the marginal ice zone (MIZ), located between the POOZ and the SIZ, and with a highly variable latitudinal sea ice edge throughout the season.

Highly branched isoprenoids and fatty acids were identified in the surface waters with concentrations varying in some cases distinctly across the survey transect in relation to winter and summer sea ice extents of the preceding season. Microscopic and genomic analyses of the diatom (18S rDNA) communities indicate that similarly variable community distributions occur in tandem to the lipid analyses. This on-going research under-pins the hypothesis that specific diatoms are suspected of producing different lipids (specifically trienes and dienes), associated with diatoms growing in/under sea ice or associated with diatoms growing in Antarctic waters when sea ice clears. The implications of ground-truthing the diatom to lipid associations in this study will mean that HBI biomarkers will be the first reliable proxy for Antarctic summer sea-ice coverage going back 1,000s to 1,000,000s of years.