Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25

Abstract

The presence of a di-unsaturated highly branched isoprenoid (HBI) lipid biomarker (diene II) in Southern Ocean sediments has previously been proposed as a proxy measure of palaeo Antarctic sea ice. Here we show that a source of diene II is the sympagic diatom Berkeleya adeliensis Medlin. Furthermore, the propensity for B. adeliensis to flourish in platelet ice is reflected by an offshore downward gradient in diene II concentration in >100 surface sediments from Antarctic coastal and near-coastal environments. Since platelet ice formation is strongly associated with super-cooled freshwater inflow, we further hypothesize that sedimentary diene II provides a potentially sensitive proxy indicator of landfast sea ice influenced by meltwater discharge from nearby glaciers and ice shelves, and re-examination of some previous diene II downcore records supports this hypothesis. The term IPSO25—Ice Proxy for the Southern Ocean with 25 carbon atoms—is proposed as a proxy name for diene II.

Highly branched isoprenoids for Southern Ocean semi-quantitative sea ice reconstructions: a pilot study from the Western Antarctic Peninsula

“…The d 13 C values of IPSO25 are between -10.3‰ and -14.7‰ which is the commonly observed range for IPSO25 in surface sediments and sea ice derived organic matter (Massé et al, 2011, Belt et al, 2016, and contrasts the low…”

“…Uncertainties in the sourcespecificity of brassicasterol (Belt et al, 2013), however, require caution when pairing this sterol with a sea ice biomarker lipid for sea ice reconstructions. While the applicability of HBIs (and sterols) to reconstruct past sea ice conditions has been thoroughly investigated in the Arctic Ocean (Belt, 2018;Xiao et al, 2015), only two studies document the distribution of HBIs in Southern Ocean surface sediments (Belt et al, 2016;Massé et al, 2011). The circum-Antarctic data set published by Belt et al (2016), however, does not report HBI triene abundances.…”

Fatty acid carbon isotopes: a new indicator of marine Antarctic paleoproductivity?

“…While this would lend support to the hypothesis that diatoms are not the main producers of these compounds, the differing effects of diagenesis on the preservation of diatoms and lipids could also explain some of the differences in observed concentrations, particularly in the upper part of the core. The known producer of the HBI diene, Berkeleya adeliensis, for example, was not recorded within the core, likely due to their lightly silicified frustules which are more susceptible to dissolution (Belt et al, 2016). Therefore, despite the lack of a correlation between diatom abundances and FA concentrations, we cannot entirely rule out the possibility of a minor contribution of FAs by diatoms.…”

“…In Antarctic marine sediments HBIs have been used as a tool for reconstructing sea ice (Belt et al, 2016(Belt et al, , 2017. Smik et al (2016) compared the concentrations of HBIs in sediment samples offshore East Antarctica from the permanently open-ocean zone (POOZ), the marginal ice zone (MIZ) and the summer sea-ice zone (SIZ).…”

“…The HBI diene biomarker (or IPSO25 for Ice Proxy Southern Ocean with 25 Carbons) is mainly biosynthesised by Berkeleya adeliensis (Belt et al, 2016), a diatom which resides and blooms within the sea ice matrix, and thus can be used as a proxy for fast ice attached to the coast. In contrast, the presence of the HBI triene mostly in the MIZ is suggestive of a predominantly pelagic phytoplankton source (e.g.…”