Evaluation of lipid biomarkers as proxies for sea ice and ocean temperatures along the Antarctic continental margin
2021
Abstract. The importance of Antarctic sea ice and Southern Ocean warming has come into
the focus of polar research during the last couple of decades. Especially
around West Antarctica, where warm water masses approach the continent and
where sea ice has declined, the distribution and evolution of sea ice play a
critical role in the stability of nearby ice shelves. Organic geochemical
analyses of marine seafloor surface sediments from the Antarctic continental
margin allow an evaluation of the applicability of biomarker-based sea-ice
and ocean temperature reconstructions in these climate-sensitive areas.
We analysed highly branched isoprenoids (HBIs), such as the sea-ice proxy
IPSO 25 and phytoplankton-derived HBI-trienes, as well as phytosterols and
isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), which are
established tools for the assessment of primary productivity and ocean
temperatures respectively. The combination of IPSO 25 with a
phytoplankton marker (i.e. the PIPSO 25 index) permits semi-quantitative
sea-ice reconstructions and avoids misleading over- or underestimations of
sea-ice cover. Comparisons of the PIPSO 25 -based sea-ice distribution
patterns and TEX 86 L - and RI-OH ′ -derived ocean temperatures with (1) sea-ice concentrations obtained from satellite observations and (2)
instrument measurements of sea surface and subsurface temperatures
corroborate the general capability of these proxies to determine oceanic key
variables properly. This is further supported by model data. We also
highlight specific aspects and limitations that need to be taken into
account for the interpretation of such biomarker data and discuss the
potential of IPSO 25 as an indicator for the former occurrence of
platelet ice and/or the export of ice-shelf water.
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