34 research outputs found

    Biotic and abiotic degradation of the sea ice diatom biomarker IP 25 and selected algal sterols in near-surface Arctic sediments

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    International audienceThe organic geochemical IP 25 (Ice Proxy with 25 carbon atoms) has been used as a proxy for Arctic sea ice in recent years. To date, however, the role of degradation of IP 25 in Arctic marine sediments and the impact that this may have on palaeo sea ice reconstruction based on this biomarker have not been investigated in any detail. Here, we show that IP 25 may be susceptible to autoxidation in near-surface oxic sediments. To arrive at these conclusions, we first subjected a purified sample of IP 25 to autoxidation in the laboratory and characterised the oxidation products using high resolution gas chromatography-mass spectrometric methods. Most of these IP 25 oxidation products were also detected in near-surface sediments collected from Barrow Strait in the Canadian Arctic, although their proposed secondary oxidation and the relatively lower abundances of IP 25 in other sediments probably explain why we were not able to detect them in material from other parts of the region. A rapid decrease in IP 25 concentration in some near-surface Arctic marine sediments, including examples presented here, may potentially be attributed to at least partial degradation, especially for sediment cores containing relatively thick oxic layers representing decades or centuries of deposition. An increase in the ratio of two common phytoplanktonic ster-ols-epi-brassicasterol and 24-methylenecholesterol-provides further evidence for such autoxidation reactions given the known enhanced reactivity of the latter to such processes reported previously. In addition, we provide some evidence that biodegradation processes also act on IP 25 in Arctic sediments. The oxidation products identified in the present study will need to be quantified more precisely in down-core records in the future before the effects of degradation processes on IP 25-based palaeo sea ice reconstruction can be fully understood. In the meantime, a brief overview of some previous investigations of IP 25 in relatively shallow Arctic marine sediments suggests that overlying climate conditions were likely dominant over degradation processes, as evidenced from often increasing IP 25 concentration downcore, together with positive relationships to known sea ice conditions

    Identification of di- and triterpenoid lipid tracers confirms the significant role of autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic

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    publisher: Elsevier articletitle: Identification of di- and triterpenoid lipid tracers confirms the significant role of autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic journaltitle: Organic Geochemistry articlelink: http://dx.doi.org/10.1016/j.orggeochem.2017.03.011 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved

    Content in fatty acids and carotenoids in phytoplankton blooms during the seasonal sea ice retreat in Hudson Bay complex, Canada.

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    The Hudson Bay complex (HBC) is home to numerous indigenous communities that traditionally have relied heavily on its marine resources. The nutritional quality and stocks of the entire HBC food web depend in large part on the phytoplankton production of bioactive molecules (long chain polyunsaturated fatty acids and carotenoids) and their transfer through trophic levels. The purpose of this study was thus to determine which molecules were produced during spring phytoplankton blooms, as well as the environmental factors driving this production. We investigated 21 stations in 5 sub-regions of the HBC. At the time of sampling, the sub-regions studied had different environmental settings (e.g., ice cover, nutrients, seawater salinity and temperature) conditioning their bloom stages. Pre- and post-bloom stages were associated with relatively low concentrations of bioactive molecules (either fatty acids or carotenoids). In contrast, the highest concentrations of bioactive molecules (dominated by eicosapentaenoic acid and fucoxanthin) were associated with the diatom bloom that typically occurs at the ice edge when silicates remain available. Interestingly, the large riverine inputs in eastern Hudson Bay led to a change in protist composition (larger contribution of Dinophyceae), resulting in lower while more diverse content of bioactive molecules, whether fatty acids (e.g., aa-linolenic acid) or carotenoids (e.g., peridinin). As greater stratification of the HBC is expected in the future, we suggest that a mixotrophic/heterotrophic flagellate-based food web would become more prevalent, resulting in a smaller supply of bioactive molecules for the food web

    Monitoring abiotic degradation in sinking versus suspended Arctic sea ice algae during a spring ice melt using specific lipid oxidation tracers

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    publisher: Elsevier articletitle: Monitoring abiotic degradation in sinking versus suspended Arctic sea ice algae during a spring ice melt using specific lipid oxidation tracers journaltitle: Organic Geochemistry articlelink: http://dx.doi.org/10.1016/j.orggeochem.2016.05.016 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved

    Monitoring photo-oxidative and salinity-induced bacterial stress in the Canadian Arctic using specific lipid tracers

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    Publisher policy: author can archive post-print on open access repository after an embargo period of 18 months.Publisher's version/PDF cannot be used. Must link to publisher version with DOI. Author's post-print must be released with a Creative Commons Attribution Non-Commercial No Derivatives License

    The Choice of Ignorance: The Debate on Ethnic and Racial Statistics in France

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    A researcher or a journalist trying to compare the situation of ethnic and racial minorities in the United States and in France immediately confronts a crippling obstacle. The concept of ‘ethnic and racial minority’ as such is not used in France. This is not simply a matter of vocabulary –something the French typically like to argue about; the problem rather lies in the very incomparability of populations that one is talking about. Many of the categories that do exist in political discourse and public debate can of course be found in statistics. But there are no data describing the situation of minorities in France that could be compared with those produced in the United States. This state of affairs in French statistics – gathering has been the subject of major criticism for some 20 years now; it has gotten to the point that it has triggered a controversy of rare violence between those that would like to see statistics take into account the diversity of the population and those who denounce the danger that such statistics might pose of ethnicizing or racializing society. The media focus on the contentiousness of this debate has been such as to sometimes lose sight of the very existence of discrimination and the flaws of the Republican model that are at the root of the controversy in the first place
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