Pollen record and age determination of a sediment core from the Kara Sea

AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon.
A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.

经AMS-¹⁴C测年的鄂毕河、叶尼塞河河口及毗邻喀拉海近岸海域的沉积物岩芯，本研究对其展开调查以明确硅质碎屑与有机碳的通量特征，及其与古环境变化的关联。全新世期间沉积物通量的变化，与冰后期海平面上升、河流径流量变化及海岸侵蚀输入物的改变密切相关。与之相对，全新世中晚期绝大多数陆源沉积物沉积于河口及河口紧邻海域；而约9 Cal. kyrs. BP之前的早全新世时期，大量沉积物则堆积于更北侧的喀拉海陆架之上。彼时的沉积物最大堆积速率，与当时较低的海平面、加剧的海岸侵蚀，以及因普托拉纳地块山地冰消作用末期阶段导致的河流径流量增加密切相关。由磁化率峰值所指示的叶尼塞源物质供给增加，大概率以气候相关的脉冲式事件形式出现，其峰值分别出现在距今约11、10和9 Cal. kyrs. BP时段。随着海平面上升，全新世主要沉积中心向南方迁移。基于氢指数（hydrogen index）与正构烷烃（n-alkanes）的分析结果，研究区有机质主要为陆源成因。早全新世沉积物的最大堆积速率可达1.5至6 g/cm²/年以上，这表明彼时物源区气候更为湿润，植被覆盖度有所提升。总体而言，河口及喀拉海近岸海域的有机碳堆积速率较高，是陆源有机碳的重要沉积汇。
来自叶尼塞河北部河口的一则经AMS-¹⁴C测年的沉积物岩芯中，全新世磁化率（magnetic susceptibility, MS）变化的高分辨率记录，可指示百年至千年尺度上北极气候变化与河流径流量的自然波动。磁化率的短期峰值大概率与气候变暖、降水增强、风化/侵蚀作用加剧以及河流径流量提升相关，其出现周期约为300至700年。