Ice-rafting patterns on the western Svalbard slope 74-0 ka: interplay between ice-sheet activity, climate and ocean circulation

摘要

The distribution of ice-rafted detritus (IRD) is studied in three cores from the western Svalbard slope (1130-1880 m water depth, 76-78 degrees N) covering the period 74-0 ka. The aim was to provide new insight into the dynamics of the Svalbard-Barents Sea Ice Sheet during Marine Isotope Stages (MIS) 4-1 to get a better understanding of ice-sheet interactions with changes in ocean circulation and climate on orbital and millennial (Dansgaard-Oeschger events of stadial-interstadial) time scales. The results show that concentration, flux, composition and grain-size of IRD vary with climate and ocean temperature on both orbital and millennial time scales. The IRD consists mainly of fragments of siltstones and mono-crystalline transparent quartz (referred to as 'quartz'). IRD dominated by siltstones has a local Svalbard-Barents Sea source, while IRD dominated by quartz is from distant sources. Local siltstone-rich IRD predominates in warmer climatic phases (interstadials), while the proportion of allochthonous quartz-rich IRD increases in cold phases (glacials and stadials/Heinrich events). During the Last Glacial Maximum and early deglaciation at 24-16.1 ka, the quartz content reached up to 90%. In warm climate, local iceberg calving apparently increased and the warmer ocean surface caused faster melting. During the glacial maxima (MIS 4 and MIS 2) and during cold stadials and Heinrich events, the local ice-sheets must have been relatively stable with low ablation. During ice retreat phases of the MIS 4/3 and MIS 2/1 transitions, maxima in IRD deposition were dominated by local coarse-grained IRD. These maxima correlate with episodes of climate warming, indicating a rapid, stepwise retreat of the Svalbard-Barents Sea Ice Sheet in phase with millennial-scale climate oscillations.