北冰洋阿尔法脊晚第四纪沉积有机质的来源变化及其古环境意义

为探讨晚第四纪有机碳埋藏情况变化与海冰覆盖和环流等变化之间的关系,分析了北冰洋阿尔法脊08B85-D孔沉积物的Mn和Ca含量、粒度组成、有机碳含量和有机碳δ13C组成。结果表明有机碳含量并不具备冰期-间冰期旋回性,有机碳来源具有4种不同模式,海冰覆盖程度和波弗特环流的强度共同决定了阿尔法脊处有机碳来源的构成,在MIS7内若干时段海冰覆盖极少,极盛的波弗特环流可将陆源有机质直接输送至阿尔法脊处,使沉积有机质中陆地来源占主导,形成了具有地层对比意义的独特信号。在MIS6-MIS1,08B85-D孔有机碳始终以海洋源贡献占主导,与海冰覆盖程度维持在较高水平,限制了陆源有机碳的输送有关,特别是在MIS6和MIS4-MIS3时,海冰很盛,波弗特环流有可能消亡。

CHANGING SOURCES OF ORGANIC CARBON IN LATE QUATERNARY SEDIMENTS FROM THE ALPHA RIDGE (ARCTIC OCEAN),AND ITS PALEOENVIRONMENTAL IMPLICATIONS

Links between organic carbon preservation, sea ice condition and oceanic current distribution in the Arctic Ocean are reported through analysis of Mn and Ca content, grain-size composition, content and isotopic composition of organic carbon in sediments from core 08B85-D collected at Alpha Ridge, Arctic Ocean. Glacial-interglacial cycles in sedimentary layers of organic carbon content are not apparent. Four sources of organic carbon are identified, with concentration in sediments controlled primarily by sea ice density and the strength of Beaufort Gyre. During several periods in MIS7, sea ice density in the western Arctic appears to have been low and the Beaufort Gyre particularly active, resulting in transportation of terrestrial-sourced organic carbon to the Alpha Ridge. To the contrary, in that time between MIS6 and MIS1 (especially MIS6 and MIS4–MIS3), the contribution of oceanic organic carbon to sediments exceeds that of the terrestrial carbon, during a time dense sea ice likely restricted transport of terrestrial organic carbon by limiting the Beaufort Gyre.