Age determination of three sediment cores from the Eurasian continental margin

Sediment cores located along the Eurasian continental margin (Arctic Ocean) have been studied to reconstruct the environmental changes in terms of waxing and waning of the Barents/Kara Sea ice-sheets, Atlantic water inflow, and sea-ice distribution over the last 150 kyr. The stratigraphy of the cores is based on stable oxygen isotopes, AMS 14C, and paleomagnetic data. We studied variations in marine and terrigenous input by a multiproxy approach, involving direct comparison of sedimentological and organo-geochemical data. Extensive episodes of northern Barents Sea ice-sheet growth during marine isotope stages (MIS) 6 and 2 have been supported by, at least, subsurface Atlantic water inflow, moisture-bearing storms, low summer insolation, and minimal calving of ice. Ice advance during MIS 4 was probably restricted to the shallow shelf. Between MIS 4 and MIS 2, large ice-sheet fluctuations correspond to contemporary Laurentide surging events and indicate short-term climatic changes in the Arctic Ocean as has been recorded in lower latitudes. In contrast, in low precipitation areas in eastern Eurasia, glacial activity was rather limited. Only distinct ice-rafted debris (IRD) input during Termination II and early MIS 3 reflects severe glaciations on the northern Severnaya Semlya margin during MIS 6 and MIS 4. We conclude that (1) oscillations of ice-sheets are less frequent along the eastern Eurasian margin than in areas with continuous moisture supply like the western Eurasian margins and that (2) major fluctuations of the Kara Sea ice-sheet during the last 150 kyr apparently followed the major interglacial/glacial MIS 5/4 and MIS 7/6 transitions rather than the precession (23 kyr) and the tilt (41 kyr) cyclicity of the Earth's orbit as observed for the Scandinavian (SIS) and the Svalbard ice-sheets, respectively [Mangerud, J., Jansen, E., Landvik, J.Y., 1996. Late Cenozoic history of the Scandinavian and Barents Sea ice-sheets. In: Solheim, A., Riis, F., Elverhøi, A., Faleide, J.J., Jensen, L.N., Cloetingh, S. (Eds.), Impact of Glaciations on Basin Evolution: Data and Models from the Norwegian Margins and Adjacent Basins. Global and Planetary Chance, Special Issue 12, pp. 11-26.]. Surface and/or subsurface Atlantic water masses coupled with seasonally ice-free conditions penetrated continuously to at least the Franz Victoria Trough during the last 150 kyr. However, sustained periods of open water were largely restricted to substages 5.5, 5.1, and the Holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter (MOM). Signals of periodic open-water conditions along the northern margin of Severnaya Semlya are of less importance. Higher production of foraminifera, probably due to Atlantic water inflow occurred between 38 and 12 14C kyr and corresponds to periodic Atlantic water advection penetrating into the Arctic Ocean. However, marine organic proxies indicate a continuous decrease of surface-water productivity from the western to the eastern Eurasian continental margin due to a more extensive sea-ice cover over the last 150 kyr.

针对北冰洋欧亚大陆边缘分布的沉积岩芯开展研究，旨在重建过去15万年以来巴伦支海/喀拉海冰盖消长、大西洋水流入侵以及海冰分布相关的环境演变历史。岩芯地层学研究基于稳定氧同位素、加速器质谱¹⁴C（Accelerator Mass Spectrometry ¹⁴C, AMS ¹⁴C）与古地磁数据。本研究采用多代用指标方法，通过沉积学与有机地球化学数据的直接对比，分析了海洋输入与陆源输入的变化特征。

已有证据表明，海洋同位素阶段（Marine Isotope Stages, MIS）6与2时期，巴伦支海北部冰盖曾广泛发育，这一过程至少与次表层大西洋水入侵、携水汽风暴、夏季太阳辐射量偏低以及冰体崩解程度极低密切相关。MIS 4时期的冰体扩张可能仅局限于浅海陆架范围。在MIS 4至MIS 2之间，大规模冰盖波动与同期劳伦冰盖涌升事件相对应，这表明北冰洋存在短期气候变化，且该信号在低纬度地区亦有记录。

与之形成鲜明对比的是，欧亚大陆东部低降水区域的冰川活动相对有限。仅在终止期II与MIS 3早期出现的显著冰筏碎屑（Ice-Rafted Debris, IRD）输入事件，才反映出MIS 6与MIS 4时期北地群岛边缘发生的强烈冰川作用。

本研究得出两点核心结论：（1）欧亚大陆东部边缘的冰盖振荡频率低于欧亚大陆西部这类持续有水汽补给的区域；（2）过去15万年以来喀拉海冰盖的大规模波动，明显遵循主要间冰期/冰期的MIS 5/4与MIS 7/6转换周期，而非斯堪的纳维亚冰盖（Scandinavian Ice Sheet, SIS）与斯瓦尔巴冰盖所记录的地球轨道岁差（23千年）与倾斜（41千年）周期[引自Mangerud J、Jansen E、Landvik JY于1996年发表的《斯堪的纳维亚与巴伦支海冰盖的晚新生代演化历史》，收录于Solheim A、Riis F、Elverhøi A、Faleide JJ、Jensen LN、Cloetingh S主编的《冰川作用对盆地演化的影响：挪威大陆边缘及邻近盆地的数据与模型》，《全球与行星变化》特刊第12期，第11-26页]。

在过去15万年以来，表层及/或次表层大西洋水团与季节性无冰环境持续侵入，至少可达弗朗茨维多利亚海槽区域。然而，持续的开阔水环境主要局限于MIS 5.5亚期、MIS 5.1亚期以及全新世，这一点可通过显著的碳酸盐溶蚀作用与更高的海洋有机质（Marine Organic Matter, MOM）堆积量得到佐证。北地群岛北部边缘出现的周期性开阔水环境信号，其重要性相对较低。

在距今38至12个¹⁴C千年之间，有孔虫生产力出现升高，这大概率与大西洋水入侵有关，该时期对应着周期性大西洋水团平流侵入北冰洋的过程。不过，海洋有机质代用指标显示，由于过去15万年以来海冰覆盖范围更广，欧亚大陆大陆边缘从西向东的表层水体生产力呈持续下降趋势。