Diatom biostratigraphy and sea ice concentration reconstruction from core DA06-139G, Vaigat Strait in Disko Bugt, West Greenland

A diatom-based sea-ice concentration (SIC) transfer function is developed using 72 surface samples from west of Greenland and around Iceland, and through comparison with the associated modern SIC. Canonical correspondence analysis on surface sediment diatoms and monthly average of SIC reveals that April SIC is the most important environmental factor controlling the distribution of diatoms in the area, and permits the development of a diatom-based SIC transfer function. The consistency between reconstructed SIC based on diatoms from West Greenland and the instrumental and documentary data during the last ~75 years demonstrates that the diatom-based SIC reconstruction is reliable for studying the palaeoceanography off West Greenland. Relatively warm conditions with strong influence of the Irminger Current (IC) are indicated for the early part of the record (~5000-3860 cal. yr BP), corresponding in time to the latest part of the Holocene Thermal Maximum. The April SIC oscillated around the mean value between 3860 and 1510 cal. yr BP and was above mean afterwards, particularly during the time interval 1510-1120 cal. yr BP and after 650 cal. yr BP, indicating more extensive sea-ice cover in Disko Bugt. A high degree of consistency between the reconstructed April SIC and changes in the diatom species suggests that the sea-ice condition in Disko Bugt is strongly influenced by variations in the relative strength of two components of the West Greenland Current, i.e. the cold East Greenland Current and the relatively warm IC.本研究基于格陵兰西部及冰岛周边海域的72个表层样品，构建了基于硅藻的海冰浓度（sea-ice concentration, SIC）传递函数，并将其与对应的现代海冰浓度数据进行比对。通过对表层沉积物硅藻与海冰浓度月平均值开展典范对应分析，发现4月海冰浓度是控制该区域硅藻分布的最关键环境因子，据此得以建立硅藻-海冰浓度传递函数。基于西格陵兰海域硅藻重建的海冰浓度序列，与近约75年以来的仪器观测及文献记录数据高度吻合，证实了基于硅藻的海冰浓度重建方法可可靠应用于西格陵兰海域的近海古海洋学研究。研究记录的早期阶段（约5000~3860校准年BP（cal. yr BP））呈现相对温暖的气候环境，且受伊尔明格海流（Irminger Current, IC）的显著影响，该时段对应全新世热盛期的最晚阶段。在3860~1510校准年BP期间，4月海冰浓度围绕均值波动；1510~1120校准年BP及650校准年BP之后，海冰浓度高于均值，表明迪斯科湾的海冰覆盖范围更广。重建的4月海冰浓度序列与硅藻物种组成变化高度一致，说明迪斯科湾的海冰条件主要受西格陵兰海流两个分支相对强度变化的调控：即寒冷的东格陵兰海流与相对温暖的伊尔明格海流。