Sedimentary processes and environmental changes in the longest fjord, Wijdefjorden, in the Northern Spitsbergen since the last deglaciation: Preliminary results of the “end-member analysis”

초록

Svalbard archipelago is currently facing environmental changes due to rapid global warming. In this context, the West Spitsbergen has been the focus of particular concern, because of the prevailing influence of the West Spitsbergen Current, which carries warm Atlantic waters into the Arctic ocean, influencing climates and climate-related environmental changes at northern high latitudes since the last deglaciation. Compared to the West Spitsbergen, however, the Northern Spitsbergen has been rarely investigated, albeit potentially connected to climate-related changes. The Widjefjorden, an elongated fjord with ca. 100 km long facing the tidewaters in fjord head to offshore facing the Eastern Arctic Ocean in the Northern Spitsbergen, is considered a proper site to study climate-induced sedimentary changes since the last deglaciation. In this study, we investigated sedimentary environmental changes such as glacial retreat, iceberg discharge, sea-ice extent, and bottom-current speed during the last deglaciation using end-member analysis (EMA) of grain-size data analyzed in four sediment cores from the Wijdefjorden. Five end-members (EMs 1-5) were defined based on the characteristics of grain-size distribution curves such as mode and skewness. EM1 and EM2 exhibit the predominance of the fine modes (4.3??9.3 μm), together with color and lamination in the sediment, suggesting suspension settling from meltwater plume. EM3 and EM4 are characterized by coarser modes (15??49 μm) and coarse-skewed grain-size distributions. These coarser modes are likely related to winnowing by bottom-currents or underflows. EM5 is polymodal and very poorly sorted, including grains larger than 150 μm. Based on comparison with ice-rafted debris (IRD, > 150 μm) count data and the abundant sand-size grains, we interpret that EM5 represents diamicton or IRD transported by the iceberg and/or sea-ice. The temporal changes in the proportions of EMs allow us to better understand complex climate-r