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. (2011). Highly branched isoprenoids as proxies for variable sea ice conditions in the Southern Ocean. Antarct. Sci., .
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. (2019). Abiotic degradation of highly branched isoprenoid alkenes and other lipids in the water column off East Antarctica (Vol. 210).
Abstract: In some previous studies, the ratio between a di-unsaturated highly branched isoprenoid (HBI) lipid termed IPSO25 and a structurally related tri-unsaturated counterpart (HBI III) (viz. IPSO25/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 IPSO25/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 IPSO25/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 IPSO25/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.
Keywords: Alteration of IPSO/HBI III ratio East Antarctica Lipids Near-surface sediments Paleoceanographic implications Photo- and autoxidation Suspended particulate matter
Programme: 1010
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. (2015). High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice (Vol. 120).
Abstract: We report concentration and nitrogen and oxygen isotopic measurements of nitrate, total dissolved nitrogen, and particulate nitrogen from Antarctic landfast sea ice, covering almost the complete seasonal cycle of sea ice growth and decay (from April to November). When sea ice forms in autumn, ice algae growth depletes nitrate and accumulates organic N within the ice. Subsequent low biological activity in winter imposes minor variations in the partitioning of fixed N. In early spring, the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed N within sea ice, up to 20 times higher than in the underlying seawater. At this time, remineralization and nitrification also accelerate, yielding nitrate concentrations up to 5 times higher than in seawater. Nitrate ?15N and ?18O are both elevated, indicating a near-balance between nitrification and nitrate assimilation. These findings require high microbially mediated turnover rates for the large fixed N pools, including nitrate. When sea ice warms in the spring, ice algae grow through the full thickness of the ice. The warming stratifies the brine network, which limits the exchange with seawater, causing the once-elevated nitrate pool to be nearly completely depleted. The nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment, affecting its N cycling (e.g., allowing for nitrification) and impacting algal physiology (e.g., as reflected in the N and O isotope effects of nitrate assimilation).
Keywords: Antarctic isotopes nitrogen nutrients sea ice
Programme: 1010
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. (2015). Trace elements in Antarctic fish species and the influence of foraging habitats and dietary habits on mercury levels (Vol. 538).
Keywords: Heavy metals Nototheniidae Southern Ocean Stable isotopes
Programme: 1010
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. (2014). Autoxidative and photooxidative reactivity of highly branched isoprenoid (HBI) alkenes (Vol. 49).
Abstract: Autoxidation of several mono-, di-, tri- and tetra-unsaturated highly branched isoprenoid (HBI) alkenes was induced in organic solvents using a radical initiator and enhancer, and their degradation rates were compared to those of classical phytoplanktonic lipids (mono-unsaturated fatty acids, sterols and chlorophyll phytyl side-chain). Autoxidation of two HBI trienes was also investigated in senescent and highly photodegraded diatom cells, collected in the Antarctic, using Fe2+ ions as radical inducers. Autoxidation rates of HBI alkenes were found to increase with the number of tri-substituted double bonds, as expected. Further, HBI trienes possessing one bis-allylic position (where hydrogen abstraction is highly favoured) were found to be particularly reactive towards autoxidation and degraded at similar rates compared to polyunsaturated fatty acids in diatom cells. By comparison of the autoxidation products of the most reactive tri-unsaturated HBI with the corresponding photooxidation products, some specific tracers of these two types of abiotic degradation processes were identified. The lack of reactivity of the mono-unsaturated HBI IP25 and a structurally similar di-unsaturated HBI towards autoxidative degradation supports the good preservation of these biomarkers in marine sediments.
Programme: 1010
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. (2014). Contribution of sea ice organic matter in the diet of Antarctic fishes: a diatom-specific highly branched isoprenoid approach (Vol. 37).
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Morin, S., Savarino, J., Bekki, S., Gong, S. and Bottenheim, J. W. (2007). Signature of Arctic surface ozone depletion events in the isotope anomaly (δ17O) of atmospheric nitrate. Atmospheric chemistry and physics, 7, 1451–1469.
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De Angelis, M., J.R. Petit, J. Savarino, R. Souchez, and M.H. Thiemens. (2004). Contributions of an ancient evaporitic-type reservoir to subglacial Lake Vostok chemistry. Earth Planet. Sci. Lett., 222, 751–765.
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McCabe, J.R.; Thiemens, M.H.; Savarino, J. (2007). A record of ozone variability in South Pole Antarctic snow: Role of nitrate oxygen isotopes. J. Geophys. Res., 112.
Keywords: nitrate; isotopes; ozone; 1041 Geochemistry: Stable isotope geochemistry; 0305 Atmospheric Composition and Structure: Aerosols and particles; 3344 Atmospheric Processes: Paleoclimatology; 1610 Global Change: Atmosphere; 0776 Cryosphere: Glaciology
Programme: 1011
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Grannas et al. (2008). An overview of snow photochemistry: evidence, mechanisms and impacts. Atmospheric chemistry and physics, 7. Retrieved July 1, 2024, from http://www.google.fr/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fwww.atmos-chem-phys.org%2F7%2F4329%2F2007%2Facp-7-4329-2007.pdf&ei=TC3nSZihIYSLsAbenqCpBw&usg=AFQjCNFwaE5Rq_f-LkHGjZxltXcKaVxaDA&sig2=qdMuZAVEnaWHS0LezrAMYw
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