TY - JOUR
T1 - Abiotic degradation of highly branched isoprenoid alkenes and other lipids in the water column off East Antarctica
AU - Rontani, Jean François
AU - Smik, Lukas
AU - Belt, Simon T.
AU - Vaultier, Frédéric
AU - Armbrecht, Linda
AU - Leventer, Amy
AU - Armand, Leanne K.
N1 - Publisher Copyright:
© 2019
PY - 2019/3/20
Y1 - 2019/3/20
N2 - In some previous studies, the ratio between a di-unsaturated highly branched isoprenoid (HBI) lipid termed IPSO 25 and a structurally related tri-unsaturated counterpart (HBI III) (viz. IPSO 25 /HBI III) has been used as a proxy measure of variable sea ice cover in the Antarctic owing to their production by certain sea ice algae and open water diatoms, respectively. To investigate this further, we quantified selected lipids and their photo- and autoxidation products in samples of suspended particulate matter (SPM) collected at different water depths in the polynya region west of the Dalton Iceberg Tongue (East Antarctica). The results obtained confirm the high efficiency of photo- and autoxidation processes in diatoms from the region. The systematic increase of the ratio IPSO 25 /HBI III with water depth in the current samples appeared to be dependent on the sampling site and was due to both (i) a relatively higher contribution of ice algae to the deeper samples resulting from their increased aggregation and therefore higher sinking rate, or (ii) a stronger abiotic degradation of HBI III during settling through the water column. Analyses of samples taken from the water-sediment interface and some underlying near-surface sediments revealed a further increase of the ratio IPSO 25 /HBI III, indicative of further differential oxidation of the more unsaturated HBI. Unfortunately, specific oxidation products of HBI III could not be detected in the strongly oxidized SPM and sediment samples, likely due to their lability towards further oxidation. In contrast, oxidation products of HBI III were detected in weakly oxidized samples of phytoplanktonic cells collected from Commonwealth Bay (also East Antarctica), thus providing more direct evidence for the involvement of photo- and/or autoxidation of HBI III in the region. This oxidative alteration of the ratio IPSO 25 /HBI III between their source and sedimentary environments might need to be considered more carefully when using this parameter for palaeo sea ice reconstruction purposes in the Antarctic.
AB - In some previous studies, the ratio between a di-unsaturated highly branched isoprenoid (HBI) lipid termed IPSO 25 and a structurally related tri-unsaturated counterpart (HBI III) (viz. IPSO 25 /HBI III) has been used as a proxy measure of variable sea ice cover in the Antarctic owing to their production by certain sea ice algae and open water diatoms, respectively. To investigate this further, we quantified selected lipids and their photo- and autoxidation products in samples of suspended particulate matter (SPM) collected at different water depths in the polynya region west of the Dalton Iceberg Tongue (East Antarctica). The results obtained confirm the high efficiency of photo- and autoxidation processes in diatoms from the region. The systematic increase of the ratio IPSO 25 /HBI III with water depth in the current samples appeared to be dependent on the sampling site and was due to both (i) a relatively higher contribution of ice algae to the deeper samples resulting from their increased aggregation and therefore higher sinking rate, or (ii) a stronger abiotic degradation of HBI III during settling through the water column. Analyses of samples taken from the water-sediment interface and some underlying near-surface sediments revealed a further increase of the ratio IPSO 25 /HBI III, indicative of further differential oxidation of the more unsaturated HBI. Unfortunately, specific oxidation products of HBI III could not be detected in the strongly oxidized SPM and sediment samples, likely due to their lability towards further oxidation. In contrast, oxidation products of HBI III were detected in weakly oxidized samples of phytoplanktonic cells collected from Commonwealth Bay (also East Antarctica), thus providing more direct evidence for the involvement of photo- and/or autoxidation of HBI III in the region. This oxidative alteration of the ratio IPSO 25 /HBI III between their source and sedimentary environments might need to be considered more carefully when using this parameter for palaeo sea ice reconstruction purposes in the Antarctic.
KW - Alteration of IPSO /HBI III ratio
KW - East Antarctica
KW - Lipids
KW - Near-surface sediments
KW - Paleoceanographic implications
KW - Photo- and autoxidation
KW - Suspended particulate matter
UR - http://www.scopus.com/inward/record.url?scp=85062212244&partnerID=8YFLogxK
U2 - 10.1016/j.marchem.2019.02.004
DO - 10.1016/j.marchem.2019.02.004
M3 - Article
SN - 0304-4203
VL - 210
SP - 34
EP - 47
JO - Marine Chemistry
JF - Marine Chemistry
ER -