重建晚第四纪冰期-间冰期西北冰洋筏冰输运和表层洋流演变历史

The modern large scale surface circulation in the Arctic Ocean is composed of the Transpolar Drift (TPD) from the Siberian shelves to the Fram Strait in the Eastern Arctic Ocean, and the Beaufort Gyre (BG) in the Western Arctic Ocean. Their pathways, location and intensity greatly influence the distribution and transportation of sea-ice and icebergs, the water mass structure, the fresh water budget, as well as surface ocean productivity and carbon cycle in the Arctic Ocean. At present, the confluence of the TPD and the BG is in the vicinity of the Mendeleev Ridge. While during the last glacial, limited geological evidences and model simulations suggest different pathways of the Arctic surface circulation. The BG might have merged into a direct trans-Arctic path towards the Fram Strait. Moreover, the development of ice shelves extending from the continental ice sheets to the Arctic Ocean, alters the surface water pathways and sedimentation pattern at regional basis. An accurate knowledge of the evolution history of the BG and the TPD during the glacial-interglacial time scales is a key understanding the role of the Arctic Ocean in the global climate system, which is yet not well studied..Mineralogical fingerprints of the Ice Rafted Debris (IRD) and clay mineral composition in sediments bare information about the source regions surrounding the Arctic Ocean. In this project, 5 sediment cores retrieved during the Chinese 3-7 Arctic Research Expeditions (CHINARE 3-7) from the central Arctic Ocean deep basin, will be used to study the IRD mineralogical composition and clay mineral assemblage, grain size distribution, in order to track the ice berg and sea ice transportation pathways during the late Quaternary glacial-interglacial cycles. These information provides important insights to the evolution of surface water circulation in the western Arctic Ocean, and the stability and development of surrounding ice sheet / ice shelf.

现代北冰洋大尺度表层环流由东北冰洋的穿极流和西北冰洋的波弗特环流组成。二者的流向、相对位置和强度对海冰和冰山的输运、北冰洋表层水体结构、淡水平衡、表层海水生产力和碳循环有重要的影响。现代环境下，穿极流和波弗特环流的交汇地在门捷列耶夫脊附近。而在冰期，有限的地质记录和数值模拟显示波弗特环流可能汇入穿极流，流向弗莱姆海峡。冰期时延伸到北冰洋的冰架也改变了区域的表层环流和沉积模式。准确理解冰期-间冰期穿极流和波弗特环流的演化历史，是理解北极在全球气候变化中作用的重要环节，这类研究在国际上还非常有限。沉积物中冰筏碎屑和黏土矿物组成反映了环北冰洋不同源区的信息。通过分析采集自第3-7次中国北极考察，对波弗特环流演化敏感的北冰洋中心海区的5根沉积物柱状样中矿物组成和粒度的变化，本项目旨在追踪晚第四纪历次冰期-间冰期西北冰洋冰山输入和海冰搬运的路径情况，重建表层洋流和和周边冰盖和冰架的稳定性和演变历史。

北冰洋被欧亚和美洲大陆所包围，是全球最小的大洋却有用最宽广的大陆架。其特殊的地理格局使得第四纪以来北极冰盖和冰架大尺度的消长，进而主导了全球气候的变化。前人研究显示北极冰盖在不同区域的发育程度有差异，并进而影响北冰洋洋流。本项目旨在揭示晚第四纪冰期-间冰期旋回中北极冰盖和洋流的演化过程。通过对中国北极考察在美亚北冰洋采集的沉积物岩芯多项指标的分析，本项目深入探讨了北冰洋晚第四纪沉积物地层年代的建立，并在此基础上分析北冰洋沉积物中沉积组分的分布和时间序列变化。具体获得以下重要成果：1. 通过岩性、元素旋回特征、生物地层学信息，建立了约1百万年以来美亚海盆沉积物地层序列，并在此基础上提取出轨道尺度上北极气候和环境变化的信息，指出低纬度气候过程在冰期和间冰期皆对北极有深刻影响；2. 分析了北冰洋冰筏碎屑的组成及其源区，并由此重建了欧亚冰盖和北美劳伦冰盖在中更新世至晚更新世对美亚海盆的筏冰输运历史，识别出欧亚冰盖在深海氧同位素6期（MIS 6）以来较为发育，而在MIS 6之前筏冰主要来自劳伦冰盖；此外，在楚克奇边缘地的记录中发现末次冰消期的一次煤屑沉积时间，推断与劳伦冰盖麦肯锡河流域的消融和排泄有关；3. 通过对粘土矿物、Sr-Nd-Pb同位素等物源指标的分析显示，美亚北冰洋马卡洛夫海盆主要受穿极流影响，在MIS 5以来间歇性受到波弗特环流对北美物源输运的影响；同时，MIS 6/5和4/3冰消期，欧亚冰盖大量的融冰水倾泻入北冰洋，造成北冰洋表层整体逆时针环流，与现代情况和模拟得出的末次冰盛期情况完全不同。