Relationship between magnetic susceptibility and sediment grain size since the last glacial period in the Southern Ocean off the northern Antarctic Peninsula - Linkages between the cryosphere and atmospheric circulation

摘要

Magnetic susceptibility (MS) values in Scotia Sea sediments showed strong correlations to ice core non-sea salt Ca2+ concentration (dust input), which emphasizes the role of atmospheric circulation in the Southern Ocean. As a result, the correlation between these values was suggested as a powerful tool for age reconstruction of marine sediments in the Southern Ocean. However, controls on MS variation in Scotia Sea sediments are not clear. In this study, we documented records of grain size, MS values (10(-6) CGS/g) of bulk sediments, and MS values of sand-sized (63 mu m), coarse silt-sized (16-63 mu m), and fine sediment fractions (16 mu m) at sediment cores from the Southern Ocean off the northern Antarctic Peninsula (the south Scotia Sea and the northern Powell Basin) to reveal which size fraction is responsible for increased MS values during the glacial period and how this size fraction is transported to the Southern Ocean deep-sea. The MS values of all cores GCO2-SS02, GC03-C2, GC03-C4, and GC04-G03 increased along with increased sand- and coarse silt-sized fractions and decreased fine sediment fraction. Although The MS values of all size fractions increased during the glacial period, the increased glacial MS values are more related to fine sand- to coarse silt-sized fractions than they are to the fine sediment fraction. The fine sand- to coarse silt-sized sediments with the highest MS values during the glacial period show (semi-)normal distribution patterns, indicating that they are transported by the same mechanism. The sediments are considered to be transported as ice rafted debris (IRD) during the glacial period. Based on our record, the strong correlation between marine core MS values and ice core dust record thus suggests a strong linkage between the cryosphere (iceberg calving activity) and atmospheric circulation (dust) in the Southern Ocean off the northern Antarctic Peninsula.