Abstract The organic geochemical IP25 (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 IP25 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 IP25 may be susceptible to autoxidation in near-surface oxic sediments. To arrive at these conclusions, we first subjected a purified sample of IP25 to autoxidation in the laboratory and characterised the oxidation products using high resolution gas chromatography–mass spectrometric methods. Most of these IP25 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 IP25 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 IP25 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 sterols – 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 IP25 in Arctic sediments. The oxidation products identified in the present study will need to be quantified more precisely in downcore records in the future before the effects of degradation processes on IP25-based palaeo sea ice reconstruction can be fully understood. In the meantime, a brief overview of some previous investigations of IP25 in relatively shallow Arctic marine sediments suggests that overlying climate conditions were likely dominant over degradation processes, as evidenced from often increasing IP25 concentration downcore, together with positive relationships to known sea ice conditions.

中文翻译：

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近地表北极沉积物中海冰硅藻生物标志物 IP 25 和选定藻甾醇的生物和非生物降解

摘要 近年来，有机地球化学 IP25（具有 25 个碳原子的冰代理）已被用作北极海冰的代理。然而，迄今为止，尚未详细研究 IP25 在北极海洋沉积物中降解的作用以及这可能对基于该生物标志物的古海冰重建产生的影响。在这里，我们表明 IP25 可能容易在近地表含氧沉积物中自动氧化。为了得出这些结论，我们首先在实验室中对纯化的 IP25 样品进行自动氧化，并使用高分辨率气相色谱-质谱法对氧化产物进行表征。大多数这些 IP25 氧化产物也在从加拿大北极巴罗海峡收集的近地表沉积物中检测到，尽管他们提出的二次氧化和其他沉积物中 IP25 相对较低的丰度可能解释了为什么我们无法在该地区其他部分的材料中检测到它们。一些近地表北极海洋沉积物中 IP25 浓度的快速下降，包括此处介绍的例子，可能至少是部分退化的原因，特别是对于含有代表数十年或数百年沉积的相对较厚的含氧层的沉积物核心。两种常见的浮游植物甾醇（表油菜甾醇和 24-亚甲基胆固醇）的比例增加为此类自氧化反应提供了进一步的证据，因为后者对先前报道的此类过程的反应性增强。此外，我们提供了一些证据，表明生物降解过程也会影响北极沉积物中的 IP25。在完全了解降解过程对基于 IP25 的古海冰重建的影响之前，本研究中确定的氧化产物将需要在未来的下核记录中更精确地量化。与此同时，对先前在相对较浅的北极海洋沉积物中 IP25 的一些调查的简要概述表明，上覆的气候条件可能在退化过程中起主导作用，这从经常增加的 IP25 浓度下降证明，以及与已知海冰条件的积极关系。在完全了解降解过程对基于 IP25 的古海冰重建的影响之前，本研究中确定的氧化产物将需要在未来的下核记录中更精确地量化。与此同时，对先前在相对较浅的北极海洋沉积物中 IP25 的一些调查的简要概述表明，上覆的气候条件可能在退化过程中起主导作用，这可以从经常增加的 IP25 浓度下降证明，以及与已知海冰条件的积极关系。在完全了解降解过程对基于 IP25 的古海冰重建的影响之前，本研究中确定的氧化产物将需要在未来的下核记录中更精确地量化。与此同时，对先前在相对较浅的北极海洋沉积物中 IP25 的一些调查的简要概述表明，上覆的气候条件可能在退化过程中起主导作用，这可以从经常增加的 IP25 浓度下降证明，以及与已知海冰条件的积极关系。