Journal
ORGANIC GEOCHEMISTRY
Volume 95, Issue -, Pages 71-80Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.orggeochem.2016.02.011
Keywords
Antarctic; Sea ice; Proxy; Highly branched isoprenoid; HBI alkenes; Diatom
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Funding
- Australian Government's Cooperative Research Centre program through the Antarctic Climate & Ecosystem CRC (ACE CRC)
- Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership [SR140300001]
- Department of Biological Sciences in the Faculty of Science and Engineering at Macquarie University
- NSF [1143836]
- University of Plymouth
- Directorate For Geosciences
- Office of Polar Programs (OPP) [1143836] Funding Source: National Science Foundation
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The occurrence and variable abundance of certain di- and tri-unsaturated C-25 highly branched isoprenoid (HBI) biomarkers in Antarctic marine sediments has previously been proposed as a possible proxy measure of paleo sea-ice extent in the Southern Ocean. In the current study, we obtained 47 near-surface (ca. 0-10 m) water samples taken from locations in East Antarctica with different sea ice settings and analysed them for their HBI, sterol and fatty acid content. Sampling locations ranged 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. A di-unsaturated C-25 HBI (diene II) was only identified in surface waters from the MIZ and the SIZ, consistent with a sea-ice diatom origin for this biomarker. In contrast, a tri-unsaturated C-25 HBI (triene III) was detected in all samples from the POOZ, the MIZ and the SIZ, and with a stable isotopic composition (delta C-13 = -35 +/- 1.5%) consistent with a phytoplankton source. The highest concentrations of diene II and triene III were in samples from the SIZ and the MIZ, respectively, thus providing further insights into the sea-ice conditions likely favourable for their production and how their relative abundances (the II/III ratio) in underlying sediments might be better interpreted for paleo sea-ice reconstruction. In this respect, relatively high II/III might be a good indicator of extended (into summer) seasonal sea-ice cover, while lower II/III may provide a better indicator of the MIZ. However, the observation of highly variable II/III within the polynya setting of the SIZ may also have significant impacts on sedimentary values. Distributions of diatom sterols and fatty acids were also variable between the three sampling zones, but these were not as distinctive as those observed for the HBIs. (C) 2016 Elsevier Ltd. All rights reserved.
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