Development of source specific diatom lipids biomarkers as Antarctic Sea Ice proxies

• Main Authors: Smik, L, Belt, ST, Brown, TA, Lieser, JL, Armand, LK, Leventer, A, Allen, CS
• Format: Conference Object
• Language: English
• Published: Copernicus GmbH 2016
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Physical Geography and Environmental Geoscience not elsewhere classified; Antarctic; Arctic; Southern Ocean; Antarc*; Antarctica; Sea ice
• Online Access: http://ecite.utas.edu.au/110165

C25 highly branched isoprenoid (HBI) are lipid biomarkers biosynthesised by a relatively small number of diatomgenera, but are, nonetheless, common constituents of global marine sediments. The occurrence and variableabundance of certain C25 highly branched isoprenoid (HBI) biomarkers in Antarctic marine sediments haspreviously been proposed as a proxy measure of paleo sea-ice extent in the Southern Ocean and a small numberof paleo sea-ice reconstructions based on the variable abundances of these HBIs have appeared in recent years.However, the development of HBIs as proxies for Antarctic sea ice is much less advanced than that for IP25(another HBI) in the Arctic and has been based on relatively small number of analyses in sea ice, water columnand sediment samples. To provide further insights into the use of these HBIs as proxies for Antarctic sea ice, we here describe anassessment of their distributions in surface water, surface sediment and sea ice samples collected from a numberof Antarctic locations experiencing contrasting sea ice conditions in recent years. Our study shows that distributions of a di-unsaturated HBI (diene II) and tri-unsaturated HBI (triene III) insurface water samples were found to be extremely sensitive to the local sea-ice conditions, with diene II detectedfor sampling sites that experienced seasonal sea ice and highest concentrations found in coastal locations withlonger-lasting ice cover and a recurrent polynya. In contrast, triene III was observed in all of the samples analysed,but with highest concentrations within the region of the retreating sea ice edge, an observation consistent withsignificant environmental control over the biosynthesis of diene II and triene III by sea ice diatoms and open waterphytoplankton, respectively. However, additional local factors, such as those associated with polynya formation,may also exert some control over the distribution of triene III and the relative concentrations of diene II andtriene III, in particular. This may have important implications for the use of these biomarkers for paleo sea icereconstructions. Sedimentary distribution showed significant variation in abundances of diene II and triene III between differentregions of Antarctica, but also on a more local scale, potentially reflecting a high degree of sensitivity towardsindividual sea ice dynamics that favour the individual species responsible for their biosynthesis. However, highestconcentrations of diene II were generally observed in near coastal locations, consistent with the identification ofelevated abundances of this HBI in first year or land fast ice in these settings. The identification of the sea icediatom source of diene II will likely be significant in interpretations of the occurrence of this biomarker in paleosea ice records.