Organic-geochemical bulk parameters and specific biomarkers of three sediment core from the Laptev Sea

In order to examine the variation in marine and terrigenous sources of the organic matter during the last 15,000 Cal. yr BP, hydrogen index values, C/N ratios, and specific biomolecules (short- and long-chain n-alkanes, short-chain fatty acids, sterols, alkenones, and pigments) were determined in three sediment cores from the Laptev Sea continental margin. The results show that the interpretation of the biomarker data is much more complicated and less definitive in comparison to similar data sets from low-latitude open-ocean environments. This is mainly caused by the complexity of the Arctic Ocean system, which is characterized by a high seasonality of sea-ice cover and primary productivity, sea-ice sediment transport and a high fluvial supply of freshwater (aquatic) organic matter. A combination of organic geochemical, organic petrographic and micropaleontological data may yield to a more precise identification of organic-carbon sources for these complex systems. On the Laptev Sea shelf (cores KD9502-14 and PS2725-5), terrigenous organic-carbon input controlled by river discharge seems to be predominant during the last about 10,000 Cal. yr BP. Maximum supply of terrigenous organic carbon was reached in the Early Holocene (i.e., about 9000-10,000 Cal. yr BP). Further offshore at the upper continental slope (core PS2458-4), a major change in organic-composition occurred near 10,000 Cal. yr BP. During this period hydrogen indices as well as the amounts of short-chain n-alkanes, short-chain fatty acids, dinosterol and brassicasterol significantly increased, indicating increased relative proportions of marine organic matter preserved in the later time interval.

为探究过去15000校准年前（Cal. yr BP）期间有机质的海洋与陆源来源演变特征，本研究对拉普捷夫海（Laptev Sea）大陆边缘的3个沉积岩芯开展了地球化学分析，测定了氢指数（hydrogen index）、C/N比值以及特定生物标志物：短链与长链正构烷烃（n-alkanes）、短链脂肪酸（fatty acids）、甾醇（sterols）、烯酮类（alkenones）与色素类物质。
研究结果显示，相较于低纬度开阔大洋环境的同类数据集，本研究的生物标志物数据解译过程更为复杂，确定性显著更低。这一现象主要源于北冰洋系统的复杂性：该系统以海冰覆盖与初级生产力的强季节性、海冰输运沉积物，以及河流输入的淡水（水生）有机质通量极高为典型特征。
联合运用有机地球化学（organic geochemistry）、有机岩石学（organic petrographic）与微古生物学（micropaleontological）分析手段，或可更精准地识别这类复杂系统中的有机碳来源。
在拉普捷夫海陆架的KD9502-14与PS2725-5两个岩芯中，过去约10000校准年前以来，受河流径流调控的陆源有机碳输入占据主导地位。陆源有机碳的供给峰值出现在全新世（Holocene）早期，即约9000~10000校准年前。
而在更远海域的上陆坡（PS2458-4岩芯），有机组成在约10000校准年前附近发生了重大转变。该时期氢指数以及短链正构烷烃、短链脂肪酸、甲藻甾醇（dinosterol）与菜籽甾醇（brassicasterol）的含量显著升高，表明后期沉积序列中保存的海洋有机质相对占比有所提升。