早全新世白令海北部陆坡沉积环境快速变化

理解增暖背景下海洋环境的演化过程是海洋学和气候学一项重要的研究内容。在地质时期，地球经历了多次增暖时段（包括早全新世），这为认识海洋环境演化过程提供了重要参考。早全新世全球气候经历了快速增暖，并伴随着冰原融化和海平面快速上升，对包括白令海在内的高纬边缘海的沉积过程和海洋环境产生显著影响。白令海发育宽阔的大陆架，毗邻北美大陆，接受来自育空河、阿纳德尔河和库斯科维姆河物质的供给。目前我们对白令海如何响应早全新世气候的认识还存在明显不足。本研究对位于白令海北部陆坡LV63-19-3岩心沉积物中陆源碎屑组份进行了高分辨率调查，结合沉积年龄模型，研究了早中全新世（距今11.7～5.5 ka）白令海北部陆坡陆源沉积演化过程。研究结果显示，在距今11.5～11 ka，白令海北部陆坡沉积速率高达392.9 cm/ka，在距今约9.7 ka以后降至17.2 cm/ka。在距今11～10.7 ka，发现一层厚约40 cm的暗色纹层状沉积层。在高沉积速率时段，沉积物平均粒径较细，距今9 ka以来平均粒径逐渐增大。主微量元素分析结果表明，陆源碎屑沉积物母岩性质以长英质沉积物为主，并存在少量火山碎屑源贡献。白令海北部陆坡高沉积速率事件对应于冰原融水脉冲（MWP）-1B事件（距今11.4～11.1 ka），并导致白令海陆坡硅质生产力勃发。在距今11～10.7 ka研究区春夏季海冰覆盖增加抑制表层水体氧供给，夏、秋季持续冰川融水和高表层生产力进一步加剧了水体层化和海洋内部消耗，共同促进了纹层状沉积层的形成。距今9 ka以来白令海季节性海冰活动增强，但是陆源碎屑物质质量累积速率则逐渐减小，表明随着海平面上升，供给到研究区的陆源物质减少。我们认为早全新世白令海北部陆坡沉积环境快速变化是海平面、冰融水脉冲事件和季节性海冰活动共同作用的结果，实际上受高纬日射量、北美大陆冰原融化和全球气候变化控制。

Rapid changes in sedimentary environment on the northern slope of the Bering Sea during the early Holocene

It has been an important research topic in oceanography and climatology to understand the evolution of marine environment in the context of anathroprogenic warming. In the geological past, the Earth has experienced several warming periods (including the early Holocene), which provide natural analogs for future climate. The global climate experienced rapid warming during the early Holocene, accompanied by ice sheet melting and rapid sea level rise, which have significantly impacted sedimentary processes and marine environment in high-latitude marginal seas, including the Bering Sea. The Bering Sea consists of a broad continental shelf, adjacent to the North American continent, and receives material supplies from the Yukon River, Anadyr River and Kuskokwim River. There are still significant gaps in our understanding of how the Bering Sea responds to the early Holocene climate. In this study, high-resolution analysis of major and minor elements in bulk sediments of Core LV63-19-3 retrieved from the northern slope of the Bering Sea, in combination with a well-constrained sedimentary age model to investigate the sedimentary environment changes on the northern Bering Sea slope during the early to middle Holocene (11.7–5.5 ka BP). The results show that the sedimentation rate on the northern continental slope of Bering Sea was as high as 392.9 cm/ka during 11.5–11 ka BP, and decreased rapidly to 17.2 cm/ka after 9.7 ka BP. At 11–10.7 ka BP, a dark laminated sediment layer about of 40 cm thick was found. In the period of high sedimentation rate, the average grain size of sediments was finer, and increased gradually after 9 kaBP. Both major and minor element concentrations indicate that the lithological properties of terrigenous clastic sediments were mainly felsic sediments with a small amount of pyroclastic contributions. The high sediment rate corresponds to the Meltwater Pulse-1B event (11.4–11.1 ka BP) and resulted in a blooming of siliceous productivity on the Bering Sea continental slope. In the study area from 11 ka BP to 10.7 ka BP, the increase in seasonal sea ice coverage inhibited the oxygen supply from the atmosphere to surface water and subsequent transport to the bottom water, while the glacial meltwater and the persistent high productivity in summer and autumn further exacerbated the surface water stratification and ocean interior oxygen consumption on the continental slope of the Bering Sea, both of which together triggered the formation of laminated sediment. After 9 ka BP, the seasonal sea ice activity in the Bering Sea increased gradually, but the mass accumulation rate of terrigenous detrital materials decreased, indicateing a decrease in the supply of terrigenous materials to the study area along with sea level rise. We suggest that the rapid shift in early Holocene sedimentary environment on the northern Bering Sea continental slope is the result of a combination of sea level, Meltwater Pulse 1B event and seasonal sea ice activity, which is actually controlled by high-latitude solar insolation, North American ice sheet melting, and global climate.